A FREQUENCY RECONFIGURABLE MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) ANTENNA SYSTEM FOR WIRELESS COMMUNICATION

Abstract

Disclosed herein a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics, wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands.

Specification

Description:A FREQUENCY RECONFIGURABLE MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) ANTENNA SYSTEM FOR WIRELESS COMMUNICATION
Field of the Invention
The present invention relates to electronics and communication engineering, generally to radio frequency (RF) circuit design and microwave engineering. The invention relates to RF switchable/reconfigurable multiple-input multiple-output (MIMO) antenna system for 4G and 5G wireless communication engineering.
Background of the Invention
The advancement of modern wireless communication technologies, particularly the transition from 4G to 5G, has created the need for antennas capable of operating across multiple frequency bands to support various applications. Traditional monopole antennas typically operate within a single resonant frequency band, which significantly restricts their versatility and usability in multi-band scenarios. This limitation has driven the development of reconfigurable antennas that can dynamically switch between different frequency bands or operational modes. Such antennas utilize reconfigurable or switching elements-both active and passive-like PIN diodes, varactor diodes, MEMS switches, and ferrite materials to modify their operational parameters, such as frequency, radiation pattern, and polarization. Despite significant research and development in this area, existing solutions have not fully addressed the need for a multi-band MIMO antenna that can support both current 4G LTE-46 bands and emerging 5G sub-6 GHz n78 bands in multiple reconfigurable modes.
A novel approach is the use of fractal geometries in antenna design, which leverages the self-similar and space-filling properties of fractal structures to enhance impedance matching, reduce antenna size, and increase operational bandwidth. Common fractal structures employed in antenna design include the Sierpinski gasket, Minkowski Island, and Cantor set, among others. In this context, the Hilbert and Koch fractal structures are particularly promising, as they offer space-filling capabilities that can maximize the effective length or perimeter of the antenna's radiator elements within a compact surface area. By incorporating these fractal structures, a more efficient and compact antenna can be designed to meet the demands of modern multi-band wireless communication systems.
However, current reconfigurable antenna designs face multiple technical challenges that limit their effectiveness. One significant issue is the size and complexity of existing reconfigurable MIMO antennas. For example, many designs require a large number of switching elements, such as PIN diodes, or additional components like bandpass filters to achieve frequency tunability across multiple bands. These requirements often result in antennas with larger dimensions, higher insertion losses, and more complex fabrication processes. Additionally, certain designs have limited isolation between antenna elements, which can result in significant mutual coupling and degraded communication performance, especially in densely populated frequency bands.
The limited number of operational modes that current reconfigurable antennas offer is another challenge. Many designs support only two or three frequency bands or modes, which restricts their adaptability in dynamic communication environments where multiple frequency bands may be used simultaneously. Moreover, the performance of existing antennas in terms of key MIMO parameters-such as Envelope Correlation Coefficient (ECC), Diversity Gain (DG), and Channel Capacity-often falls short of the ideal requirements for 4G and 5G communication. High ECC values, lower DG, and reduced channel capacity negatively impacts the reliability and data throughput of wireless communication systems.
To address these gaps, the development of a novel fractal-based switchable/reconfigurable 4×4 MIMO antenna is proposed, which supports dual-band operation in the 4G LTE-46 band (5.15-5.93 GHz) and the 5G n78 band (3.15-3.74 GHz) as well as a dual-frequency mode (3.05-3.76 GHz and 5.24-6.53 GHz). This innovative antenna leverages Hilbert and Koch fractal geometries to optimize the radiator elements, resulting in a compact design that maintains high performance across multiple frequency bands. The use of just two PIN diodes (SMP 1320-079LF) for switching significantly simplifies the design and reduces the antenna's overall size. The antenna's reconfigurability allows it to seamlessly switch between three different operational modes, catering to both single-band and dual-band requirements. The inclusion of fractal structures further enhances impedance matching, increases bandwidth, and improves gain across the operational modes.
The proposed HKFS-MIMO antenna is designed to overcome mutual coupling issues, offering an isolation of less than -15.4 dB between the four antenna ports for all operating modes. Its ECC remains below 0.04, and the DG exceeds 9.97 dB, which ensures that the antenna provides highly reliable communication with minimized fading effects. The measured peak gain ranges from 2.33 dBi to 7.31 dBi across different modes, demonstrating better performance compared to existing antennas that typically show lower gain values or require more complex configurations for multi-band operation.
Moreover, existing literature reveals certain drawbacks in prior designs. Many antennas employ disconnected ground planes or additional components like bandpass filters to achieve reconfigurability, resulting in larger physical dimensions or higher insertion losses. Some designs achieve reconfigurability through varactor diodes, which can complicate the tuning process and introduce limitations due to their variable capacitance range. These antennas often fail to represent critical MIMO diversity parameters, such as Mean Effective Gain (MEG) or Channel Capacity, which are essential for evaluating communication quality in 4G and 5G applications.
It is, therefore, desirable to develop an improved HKFS-MIMO antenna that addresses the above limitations, overcomes existing challenges and obviates complexity associated with the prior arts.
Summary of the Invention
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter. Nor is this summary intended to be used to limit the claimed subject matter's scope.
Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, embodiments may be directed to various feature combinations and sub-combinations described in the detailed description.
In the present invention, the HKFS-MIMO antenna addresses the limitations of the prior arts by providing a compact and efficient design that supports high data rates (channel capacity up to 21.73 bits/sec/Hz) and low latency without the need for complex tuning mechanisms or additional components. The use of two PIN diodes allows the antenna to achieve reconfigurability in three modes with simplified switching, thus reducing fabrication complexity while ensuring high isolation and low mutual coupling. Additionally, the antenna's ability to resonate simultaneously across 4G and 5G frequency bands enhances its adaptability for multi-band wireless communication, making it suitable for various applications such as portable cognitive radio and modern MIMO systems.
The HKFS-MIMO antenna provides a significant improvement over existing reconfigurable MIMO antenna designs, addressing key technical challenges related to size, complexity, isolation, and multi-band performance. Its innovative use of Hilbert and Koch fractal geometries, coupled with a simple yet effective switching mechanism, ensures that the antenna meets the demanding requirements of contemporary 4G and 5G wireless communication systems while providing a high degree of flexibility and reliability.
It is one of the objectives of the present invention to provide a frequency reconfigurable antenna that can operate for the current 4G LTE-46 band (5.15 GHz to 5.90 GHz) and the emerging 5G sub-6 GHz n78 band (3.30 GHz to 3.80 GHz) wireless communication applications.
It is one of the objectives of the present invention to provide an antenna having the unique ability to switch between the above two-frequency bands and work for both bands simultaneously, including three switching/ reconfigurable modes, mode-1 (4G LTE-46 band), mode-2 (5G sub-6 GHz n78-band), and mode-3 (4G LTE-46 band and 5G sub-6 GHz n78-bands simultaneously).
It is one of the objectives of the present invention to provide a 4×4 MIMO antenna system that utilizes the investigated fractal-based switching/ reconfigurable antenna to implement, wherein the investigated fractal-based 4×4 MIMO antenna achieves a high isolation of more than 15 dB between the four ports of the MIMO antenna system, a good average peak gain of more than 2.0 dBi in all operating bands, a high data rate, and a high channel capacity.
As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art that the present disclosure has broad utility and application. As should be understood, any embodiment may incorporate only one or a plurality of the above-disclosed aspects of the disclosure and may further incorporate only one or a plurality of the above-disclosed features. Furthermore, any embodiment discussed and identified as being "preferred" is considered to be part of a best mode contemplated for carrying out the embodiments of the present disclosure. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present disclosure.
Accordingly, while embodiments are described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present disclosure and are made merely for the purposes of providing a full and enabling disclosure. The detailed disclosure herein of one or more embodiments is not intended, nor is to be construed, to limit the scope of patent protection afforded in any claim of a patent issuing here from, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself.
Additionally, it is important to note that each term used herein refers to that which an ordinary artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein-as understood by the ordinary artisan based on the contextual use of such term-differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the ordinary artisan should prevail.
Furthermore, it is important to note that, as used herein, "a" and "an" each generally denotes "at least one," but does not exclude a plurality unless the contextual use dictates otherwise. When used herein to join a list of items, "or" , "/" denotes "at least one of the items," but does not exclude a plurality of items of the list. Finally, when used herein to join a list of items, "and" denotes "all of the items of the list."
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the fractal-based geometries of the radiating elements comprise a combination of Hilbert and Koch fractal structures.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the switching mechanism includes at least two PIN diodes configured to selectively activate the radiating elements.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the PIN diodes are activated and deactivated by a biasing voltage applied via the biasing circuit.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the modes of operation include:
a first mode where one fractal-based radiating element is active, operating in a first frequency band;
a second mode where a second fractal-based radiating element is active, operating in a second frequency band; and
a third mode where both radiating elements are active, operating across the first and second frequency bands simultaneously.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics, wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the modes of operation include:
a first mode where one fractal-based radiating element is active, operating in a first frequency band;
a second mode where a second fractal-based radiating element is active, operating in a second frequency band; and
a third mode where both radiating elements are active, operating across the first and second frequency bands simultaneously,
wherein the first frequency band corresponds to the 4G LTE-46 band (5.15 GHz to 5.90 GHz), and the second frequency band corresponds to the 5G sub-6 GHz n78 band (3.30 GHz to 3.80 GHz).
wherein the substrate has a dielectric permittivity of approximately 2.2, a thickness of about 1.57 mm, and a loss tangent of 0.0009.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the ground plane is a partial ground plane positioned at the bottom surface of the substrate.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the biasing circuit includes a chip inductor functioning as an RF choke and a chip capacitor integrated into the feedline to prevent the flow of direct current into the antenna source.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the fractal-based geometries of the radiating elements comprise a combination of Hilbert and Koch fractal structures, wherein the PIN diodes exhibit different parasitic properties in the ON and OFF states, with a specified series resistance and inductance in the ON state and a combination of inductance, capacitance, and high resistance in the OFF state.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the MIMO antenna system comprises a 4×4 configuration with at least four antenna elements, achieving a minimum isolation of 15 dB between antenna ports.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the MIMO antenna system comprises a 4×4 configuration with at least four antenna elements, achieving a minimum isolation of 15 dB between antenna ports, wherein the antenna elements are arranged orthogonally with respect to each other.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the MIMO antenna system comprises a 4×4 configuration with at least four antenna elements, achieving a minimum isolation of 15 dB between antenna ports, wherein the antenna system's peak gain varies across the modes of operation, with different gains for each mode corresponding to the frequency bands in use.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the envelope correlation coefficient (ECC) between the antenna elements is less than 0.04 across the operating frequency bands.
In accordance with one embodiment of the present invention, there is provided a frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries, a feedline coupled to the radiating elements to enable signal transmission and reception, a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands, a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements, and a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands, wherein the MIMO antenna system comprises a 4×4 configuration with at least four antenna elements, achieving a minimum isolation of 15 dB between antenna ports, wherein the ground plane is either disconnected or interconnected between antenna elements, with the interconnected configuration comprising metal plates to achieve enhanced isolation performance.
Brief Description of the Drawings
Figure 1(a) shows proposed HKFS antenna for both 4G and 5G Sub-6 GHz frequency bands operation and Figure 1(b) shows PIN diode's spice model.
Figure 2 shows investigated HKFS antenna's simulated (2a) S-parameter versus frequency plot (2b) peak gain (dB) and input impedance (Mag.) versus frequency plot.
Fig. 3: Parametric study of the investigated HKFS antenna for (a) mode-1 and mode-2 (b) mode-3 for Hilbert fractal shaped width W_6 variations, and (c) mode-1 and mode-2 (d) mode-3 for Koch fractal shaped width W_5 variations.
Fig. 4: Investigated four-port HKFS-MIMO antenna arrangement (a) case I: without connected ground (b) case II: with connected ground plane (L_a=82, L_B=40.5,L_C=26.5,t=0.3,M= 37.47,all dimensions are in mm).
Fig. 5: Simulated S-parameter versus frequency plot of proposed HKFS-MIMO antenna for case I (a) mode-1 (b) mode-2 (c) mode-3 and (d) Peak Gain (dBi) vs. frequency plot for all three modes of frequency reconfigurability.
Fig. 6: Simulated S-parameter versus frequency plot of HKFS-MIMO antenna for case II (a) 〖|S〗_11 | dB for three modes of operation (b) 〖|S〗_21 | dB, 〖|S〗_31 | dB and 〖|S〗_41 | dB for three modes of operation.
Fig. 7: Fabricated prototype of proposed reconfigurable 4×4 HKFS-MIMO antenna for 4G/5G frequency band of operations (a) top view (b) bottom view.
Fig. 8: A comparative simulated and measured 〖|S〗_11 | dB, 〖|S〗_21 | dB, 〖|S〗_31 | dB, 〖|S〗_41 | dB plots for the isolation between the ports of the proposed 4×4 HKFS-MIMO antenna for different modes of operation.
Detailed Description of the Invention
The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While many embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims. The present disclosure contains headers. It should be understood that these headers are used as references and are not to be construed as limiting upon the subjected matter disclosed under the header.
In the present invention, a frequency-reconfigurable antenna, structured with Hilbert and Koch fractal structure (HKFS), is developed using the RT/Duriod 5880 substrate, as shown in Fig. 1(a), where the reconfigurability is achieved by incorporating the two pin diodes and making them ON and OFF with the help of DC supply voltage. The design and optimization of the reconfigurable antenna are performed using the commercially available full-wave electromagnetic simulator, HFSS. The chosen substrate has a dielectric permittivity (ϵ_r) of 2.2, a thickness of 1.57 mm, and a loss tangent of 0.0009. The antenna's two radiating patches are of Koch fractal geometry shape and Hilbert fractal geometry shape, placed on the top-left and top-bottom sides of the antenna's geometry, respectively, and these are positioned at a distance of 1.8 mm from the 50 Ω transmission feedline. An 11 mm × 29 mm partial ground plane is further incorporated at the substrate's bottom surface, as shown in Fig. 1(a). The antenna radiating Hilbert and Koch fractal shapes is coupled to the feedline using PIN diodes (model no. SMP1320-079LF) [2]. The two PIN diodes (D1 and D2) function as switches to regulate the activation and deactivation of the two fractal-shaped radiating patches of the antenna, namely the Hilbert fractals and Koch fractal radiating patches. The spice model of the PIN diode shown in Fig. 1(b) using an RLC circuit is used to model the PIN diode in the HFSS simulation software.
Further, a biasing circuit is designed to control the PIN diodes (D1 and D2) between
ON and OFF states, and to restrict the flow of the DC current towards the AC source and vice versa. A biasing voltage of 5 V was utilized to activate the diode, while a voltage of 0 V is used to deactivate it. A 100 nH chip inductor that acts as an RF blocking choke is included in the biasing circuit layout and connects in series with the DC transistor voltage source. Furthermore, a 10 pF chip capacitor is integrated into the feedline by creating a slot with a width of 0.2 mm, to limit the passage of DC current into the antenna source. As illustrated in Fig. 1(b), as per the available data sheet of the PIN diode, SMP1320-079LF, the PIN diode displays a parasitic inductance of L_f=0.7 nH and a resistance of R_f=0.75 Ω caused by packaging when it is in the ON state. In the OFF state, however, there is a parasitic inductance of L_f=0.7 nH in series with a parallel combination of induced capacitance, C_p=0.23 pF, and high resistance, R_f=5KΩ. In the feedline of the HKFS antenna, a small open circuit stub of length, L_8+L_11 and width, W_4 is utilized to enhance the impedance matching between the feedline and the Hilbert fractal-shaped radiating patch. Table 1 summarizes the optimized dimensions of the investigated HKFS antenna shown in Fig. 1(a).
Table 1 Various optimized physical dimensions of the investigated HKFS antenna.
Par. L W L_1 W_1 L_2 W_2 L_3 W_3 L_4
Value 24 29 16 4.80 10.9 14.1 9.50 0.20 6.0
Par. W_4 L_5 W_5 L_6 W_6 L_7 W_7 L_8 W_8
Value 0.4 4.20 0.8 6.0 1.8 4.6 1.0 7.4 1.6
Par. L_9 W_9 L_10 W_10 L_11 L_12 L_13 L_14
Value 3.7 11 4.58 0.8 0.6 5.6 1.4 12.3
All dimensions are in mm., Par.: Parameters
The investigated HKFS antenna dimensions are optimized and studied to achieve the maximum performance for the desired frequency range of interest, 5G sub-6 GHz n78 band and LTE 46 band with reconfigurable characteristics. The optimized results of investigated HKFS antenna operates in three different modes based on the supplied biasing voltage to the PIN diodes, which control the ON and OFF states of the Hilbert and Koch fractal shaped radiators in the EM simulator. The investigated HKFS antenna's simulated S-parameter versus frequency plot and peak gain (dBi) and input impedance (Mag.) versus frequency plot are shown in Fig. 2(a) and Fig 2(b), respectively.
From Fig. 2(a) and Fig. 2(b), it can be observed that in mode-1, the Hilbert-shaped fractal radiator is activated when the PIN diode D1 is OFF and D2 is ON, the antenna operates within the 4G LTE-46 frequency band extending between 5.15 GHz to 5.90 GHz, where |S_11 | dB is less than -10 dB. As shown in Fig. 2(b), the antenna's peak gain ranges between 5.0 dBi to 5.16 dBi, with an average gain of 5.18 dBi and the input impedance ranging from 75.53 Ω to 41.20 Ω for mode-1. In mode-2, PIN diode D1 is in the ON state while diode D2 is in the OFF state. The Koch-shaped fractal radiator is turned ON, and the antenna operates in the 5G n78 band, particularly from 3.10 GHz to 3.83 GHz for |S_11 |dB<-10 dB. It has a peak gain that varies between 2.36 dBi to 2.42 dBi, with an average gain of 2.12 dBi and input impedance ranges from 58.16 Ω to 25.29 Ω, as observed from Fig. 2(b) for mode-2. When both PIN diodes are turned ON in mode-3, the antenna activates both the Hilbert and Koch fractal-shaped radiators. It can be seen from Fig. 2(a) that for mode-3, the HKFS antenna operates in the dual frequency bands, from 3.10 GHz to 3.61 GHz (band-1 of mode-3) and 5.30 GHz to 6.58 GHz (band-2 of mode-3) for |S_11 |dB<-10dB, supporting both 5G n78 and 4G LTE-46 bands. The antenna achieves a peak gain ranging from 1.70 dBi to 2.15 dBi (band-1 of mode-3) and 4.90 dBi to 5.91 dBi (band-2 of mode-3), with an average peak gain of 1.81 dBi and 5.29 dBi, respectively, and the input impedance ranging from 56.54 Ω to 23.63 Ω and 68.20 Ω to 45.06 Ω, as shown in Fig. 2(b) for mode-3. It can be inferred from Fig. 2(b) that the antenna under investigation exhibits superior average peak gain performance, and that its input impedance (Meg.) is around 50 Ω for better impedance matching condition for all three frequency reconfigurable modes of HKFS antenna.
To maximize the performance of the proposed HKFS antenna, as illustrated in Fig. 1, a detailed parametric optimization was carried out for each dimension mentioned in Table 1. The design and parametric study of the proposed HKFS antenna were carried out using the full-wave commercially available electromagnetic simulator, HFSS. The parametric study of the proposed HKFS antenna is performed by varying a single physical dimension at a time over a certain range and keeping the rest of the physical parameter's values of the HKFS antenna constant. On the basis of reflection coefficient value, required band of operation, and bandwidth, the optimized value of the varied physical parameter is chosen. These optimization steps were adopted in the optimization of all remaining physical dimensions of the proposed HKFS antenna. For illustration purposes, the detailed parametric study for the two parameters, namely, HKFS antenna's W_6 and W_5 are presented over here. Fig. 3(a) and Fig. 3(b) show the S-parameters versus frequency curves for different modes of operations of the HKFS antenna for the variation of the parameter W_6, whereas Fig. 3(c) and Fig. 3(d) show the S-parameters versus frequency curves for different modes of operations of the HKFS antenna for the variation of the physical parameter W_5. The Hilbert radiator's width, W_6 is varied between 1.0 mm and 2.6 mm with an increment of 0.4 mm. From Fig. 3(a) and Fig. 3(b), it can be observed that by varying the width W_6, for mode 1, the desired frequency range for the 4G LTE-46 band (5.15 GHz to 5.90 GHz) is not impacted substantially; however, a low reflection coefficient of less than -20 dB over a certain frequency band was achieved for W_6 equal to 1.8 mm,2.2 mm and 2.6 mm. So, considering the performance of the HKFS antenna for mode-1, the Hilbert radiator's width, W_6 may be chosen in any of the dimensions out of 1.8 mm,2.2 mm and 2.6 mm. But, when the investigated HKFS antenna is reconfigured to mode-3 (Fig. 3(b)), the value of W_6=1.8 mm is chosen as the optimized dimension due to the least value of the reflection coefficient of -24.6 dB, at the higher resonance frequency. In a similar way, keeping the optimized dimension W_6=1.8 mm fixed, the Koch radiator's width, W_5 is varied between 0.4 mm and 1.2 mm with an increment of 0.2 mm, as shown in Fig. 3(c) for mod-1 and mode-2 and Fig. 3(d) for mode-3. It can be observed from mode-2 of Fig. 3(c) that as the Koch radiator's width, W_5 increases, the mode-1 cutoff frequency remains almost stable around 3.1 GHz, whereas an apparent shift in the upper cutoff frequency of mode-2 is observed. From Fig. 3(c) it is concluded that for the width W_5=0.8 mm and 1.0 mm, the desired frequency range of the HKFS antenna for 5G sub-6GHz n78 band, which spans from 3.3 GHz to 3.80 GHz, can easily be accommodated in mode-2. So, considering the performance of the HKFS antenna for mode-2, the Koch radiator's width, W_5 may be chosen in any of the dimensions out of 0.8 mm and 1.0 mm. But it is further determined from Fig. 3(c) that at mode-1, for W_5=1.0 mm, there is a shift in the cutoff frequency band ranging from 5.23 GHz to 5.92 GHz, which deviates from our desired frequency range from 5.15 GHz to 5.90 GHz for 4G LTE-46 band. So, the value of the Koch radiator's width, W_5 is not considered as 1.0 mm. Furthermore, from Fig. 3(d), it is found that for mode-3, Koch radiator's width, W_5=1.0 mm shows the comparable results in the lower operating band and better results in the higher operating band in terms of reflection coefficient when compared with W_5=0.8 mm in mode-2. But compromising the results of mode-3 with mode-2 to choose the operating frequency band from 3.10 GHz to 3.83 GHz, the value of W_5=0.8 mm is chosen as the final optimized dimension of the HKFS antenna.
Further, a 4×4 frequency reconfigurable HKFS-MIMO antenna is designed based on an HKFS reconfigurable antenna. MIMO technology has gained considerable popularity in wireless communication applications due to its ability to utilize multipath to enhance communication range and link quality without requiring additional frequency spectrum or signal power. Therefore, the utilization of MIMO technology shows great potential for addressing the issue of multipath fading in modern communication applications. This section discusses an orthogonally arranged four port fractals-based 4×4 HKFS-MIMO antenna, shown in Fig. 4. The proposed HKFS-MIMO antenna design shown in Fig. 4 is shown for two different cases (case I and case II). Fig. 4(a) case I presents an HKFS-MIMO antenna with a disconnected ground plane of the antenna element, and Fig. 4(b) case II presents an HKFS-MIMO antenna with a connected ground plane in between the antenna elements. In this report, the two cases of the proposed 4×4 HKFS-MIMO antenna, case I for the antenna elements' disconnected ground and case II for the antenna elements' connected ground, are discussed because there are individual arguments between the authors for connected ground planes in MIMO antennas and non-connected ground planes in MIMO antennas.
The simulated S-parameters and peak gain performance of the 4×4 HKFS-MIMO antenna for case I (Fig. 4(a)) for all three modes of operation are depicted in Fig. 5. The simulated results of the frequency reconfigurable HKFS-MIMO antenna with discreet ground plane (Fig. 4, case I) have -10 dB impedance bandwidth, ranging from 5.13 GHz to 5.91 GHz for mode-1, 3.08 GHz to 3.72 GHz for mode-2, and dual operating bands for mode-3 from 3.00 GHz to 3.75 GHz (band-1 of mode-3) and 5.32 GHz to 6.68 GHz (band-2 of mode-3), as shown in the 〖|S〗_11| dB plots of Fig. 5(a) to Fig. 5(c). Further, the simulated results, 〖|S〗_21| dB, 〖|S〗_31| dB, and 〖|S〗_41| dB of Fig. 5(a), Fig. 5(b), and Fig. 5(c) show that the isolation between any two antenna's ports is greater than 15.7 dB for all three biasing modes of reconfigurability. Thus, the proposed HKFS-MIMO antenna exhibits adequate isolation between its any the two selected ports, which is more than 15.7 dB, and hence meets the requirement for all modes of reconfigurability. Fig. 5(d) depicts the peak gain of the four-port HKFS-MIMO antenna of case I for different reconfigurability modes of operation. The HKFS-MIMO antenna's peak gain for the three modes ranges from 6.86 dBi to 5.87 dBi for mode-1 with an average peak gain of 6.56 dBi, 2.13 dBi to 3.02 dBi for mode-2 with an average peak gain of 2.54 dBi, and from 2.32 dBi to 2.97 dBi (band-1 of mode 3) and 5.56 dBi to 7.20 dBi (band-2 of mode 3) with an average peak gain of 2.57 dBi and 6.18 dBi, respectively, for dual frequency mode-3.
For case II, Fig. 4(b), the HKFS-MIMO antenna ground planes are connected using thin metal plates of width t=0.3 mm and length M=37.47 mm. From the 〖|S〗_11 | dB plots of Fig. 6(a), for all the three modes of operation, it is observed that with interconnected ground planes (case II) of the HKFS-MIMO antenna, the -10 dB impedance bandwidths are from 5.10 GHz to 5.56 GHz for mode-1, from 3.10 GHz to 3.49 GHz for mode-2, and from 2.97 GHz to 3.52 GHz for band-1 of mode 3 and 5.49 GHz to 6.55 GHz for band-2 of mode 3. Further, from the 〖|S〗_11 | dB, 〖|S〗_21 | dB, and 〖|S〗_31 | dB plots of Fig. 6(b), for all the three modes of operation, it is observed that with interconnected ground planes (case II) of the HKFS-MIMO antenna, an isolation of more than 11.43 dB is achieved. From the analysis of both cases, for disconnected ground planes (case I) and interconnected ground planes (case II) of the HKFS-MIMO antenna, it is observed that the -10 dB impedance bandwidths and isolation between the ports of the HKFS-MIMO decrease for case II for all three different frequency modes of reconfigurability. Therefore, the disconnected ground plane (case I, Fig. 4(a)) is chosen as the final proposed 4×4 HKFS-MIMO antenna for further fabrication, measurement, results analysis, and discussions.
The MIMO antenna diversity employs multiple antenna elements to transmit or receive signals that exhibit distinct fading characteristics. Nevertheless, the installation of multiple antenna elements in portable devices' limited space will unavoidably result in a significant degradation of antenna performance, leading to decreased isolation between the antenna elements. One of the primary obstacles to implementing MIMO technology in portable devices is developing a compact MIMO antenna with maximum isolation. Different parameter characteristics of the investigated fractal-based MIMO antenna for the 4G and 5G frequency bands are analyze and discussed. An envelope correlation coefficient (ECC), which ensures that there is minimal interference or coupling between the individual antenna elements, is less than 0.04 for the investigated HKFS-MIMO antenna (ECC should be below 0.5). To ensure the wireless communication system's high reliability, the MIMO antenna must have a high diversity gain, ideally reaching as close to 10 dB as possible. The achieved diversity gain (DG) of the investigated HKFS-MIMO antenna is above 9.97 dB across the entire operating band in all three modes of operation. The Total Active Reflection Coefficient (TARC) is another parameter used to compute the performance matrix of a MIMO antenna. It is expressed as the ratio of the total incident power to the total radiated power of the MIMO antenna system, which is less than -17.1 dB for mode-1, less than -10.02 dB for mode-2, and -10.01 dB for band 1 of mode-3 and -18.23 dB for band 2 of mode-3 of the proposed HKFS-MIMO antenna operation.
Other important parameters, such as Mean Effective Gain (MEG), channel capacity (CC) and Channel Capacity Loss (CCL), are also found to be aligned with a MIMO antenna parametric range. HKFS-MIMO antenna MEG, representing the ratio of mean power received by the diversity antenna divided by the mean power received by an isotropic antenna in a multipath fading environment, must fall within the range of -3 dB to -12 dB. Based on the analysis, the MEG values of all four antenna elements in HKFS-MIMO frequency reconfigurable antenna are between -6.17 dB to -7.04 dB for mode-1, -6.77 dB to -7.54 dB for mode-2 and -6.84 dB to -7.37 dB for band 1 of mode-3 and -6.12 to -6.84 dB for band 2 of mode-3, which fall within the specified limits for all modes of antenna operation. Further, the invented HKFS-MIMO antenna shows the high channel capacity (CC) for all three reconfigurable modes, 21.62 bits/sec/Hz for mode-1, a CC of 21.34 bits/sec/Hz for mode-2, 21.51 bits/sec/Hz (band 1 of mode-3), and 21.73 bits/sec/Hz (band 2 of mode-3). Furthermore, the CCL which estimates the reduction in the maximum realizable data rate in a wireless communication MIMO system, and in accordance with the industrial standard, the CCL for a MIMO antenna system should be less than 0.4 bits/sec/Hz. The calculated CCL value of the proposed HKFS-MIMO antenna remains below 0.25 bits/sec/Hz across the entire operational bandwidth for all three modes. Thus, the investigated 4×4 HKFS-MIMO antenna design can be treated as a potential candidate for the modern wireless communication system for the transition to emerging 5G technology.
For the 4×4 HKFS-MIMO antenna is a switchable/reconfigurable multiple-input multiple-output (MIMO) antenna that can be integrated into portable wireless communication devices to receive and transmit the electromagnetic wave for 4G and 5G frequency bands, wherein the operating frequency (measured) are as follows:
mode-1: 5.15 GHz to 5.93 GHz;
mode- 2: 3.15 GHz to 3.74 GHz;
mode-3: 3.05 GHz to 3.76 GHz (band 1 of mode-3) and 5.24 GHz to 6.53 GHz (band 2 of mode-3)
Peak Gain (measured):
mode-1: 6.49 dBi to 6.30 dBi
mode-2: 2.33 dBi to 3.12 dBi
mode-3: 2.36 dBi to 3.11 dBi (in band 1 of mode-3) and 5.60 dBi to 7.31 dBi (in band 2 of mode-3)
MIMO antennas can be placed into or at the surface of any mobile devices for wireless communication such as: router, automobiles, satellites, robotics, un-manned vehicle etc.

Further, the 4×4 HKFS MIMO antenna is fabricated using the photolithography technique on a double-side copper-clad dielectric RT/Duroid 5880 substrate with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 1.57 mm. The top and bottom views of the fabricated prototype of the proposed reconfigurable 4×4 HKFS-MIMO antenna for 4G/5G frequency band operations are shown in Fig. 7(a) and Fig. 7(b), respectively. The prototype of the antenna was created to evaluate and verify the simulated performance characteristics with the measured performance characteristics of frequency reconfigurability. The measurement of the proposed 4×4 HKFS MIMO antenna is carried out using a Vector Network Analyzer (VNA) from Agilent Technologies, model N5230A, which can measure up to the frequency of 20 GHz. During the measurement, the PIN diodes were activated and deactivated using a DC transistor power source.
A comparative simulated and measured 〖|S〗_11 | dB plot and measured 〖|S〗_21 | dB, 〖|S〗_31 | dB, and 〖|S〗_41 | dB plots for the isolation between the ports of the proposed 4×4 HKFS-MIMO antenna for different modes of operation are shown in Fig. 8(a) and Fig. 8(b), respectively. From Fig. 8(a), it can be seen that the measured operating frequency range of the proposed HKFS-MIMO antenna ranges from 5.15 GHz to 5.93 GHz for mode-1, from 3.15 GHz to 3.74 GHz for mode-2, and for dual frequency mode-3, it ranges from 3.05 GHz to 3.76 GHz (band-1 of mode-3) and from 5.24 GHz to 6.53 GHz (band-2 of mode-3). Further, the measured isolation level between the two ports can be obtained from the 〖|S〗_21 | dB, 〖|S〗_31 | dB, and 〖|S〗_41 | dB plots of Fig. 8(b), which is more than 15.4 dB for all three modes of reconfigurability. Based on these examinations, a considerable correlation has been noted between the EM-simulated and measured results. Table 2 presents the summarized EM-simulated and measured results for the investigated 4×4 HKFS-MIMO antenna.
Table 2: Summarized simulated and measured results of proposed 4×4 HKFS-MIMO antenna for different biasing conditions
Biasing Mode PIN diodes Biasing States Activated Radiating Patch Frequency band Range (GHz) Application
D1 D2 Sim. Meas.
Mode 1 OFF ON Hilbert 5.13-5.91 5.15-5.93 LTE-46/WLAN
Mode 2 ON OFF Koch 3.08-3.72 3.15-3.74 5G NR n78
Mode 3 ON ON Hilbert
and
Koch 3.00-3.75
and
5.32-6.68 3.05-3.76 and
5.24-6.53 5G NR n78 and LTE-46/WLAN

Further, the investigated reconfigurable 4×4 HKFS-MIMO antenna has miniaturized physical dimensions and operates in both the 4G LTE-46 band and the 5G n78 band spectrums. The designed antenna is able to reconfigure for three operating states:
mode-1: for 4G LTE -46 band
mode-2: for 5G n78 band
mode-3: for both 4G LTE 46 band and 5G n78 band
Further, the investigated HKFS MIMO antenna fulfills all the parameters' characteristics of a MIMO antenna (isolation, ECC, DG, CC, TARC, MEG), wherein the 4×4 HKFS-MIMO antenna has a smaller physical size, 82 mm×82 mm, or electrical size, 1.24λ_g×1.24λ_g, where λ_g is the smallest cutoff frequency at 3.05 GHz, 4×4 HKFS-MIMO antenna is suitable to be used for two operating frequencies: the 4G LTE-46 band and the 5G n78 band spectrum, wherein 4×4 HKFS-MIMO antenna has good isolation of more than 15.4 dB between the two antenna elements, wherein 4×4 HKFS-MIMO antenna exhibits a low ECC of less than 0.04 and high a DG of greater than 9.97 dB across the entire operating band for all three modes of reconfigurability, low channel capacity loss (CCL) of less than 0.25 bits/sec/Hz, and high channel capacity (CC) of 21.62 bits/sec/Hz for mode-1, 21.34 bits/sec/Hz for mode 2, and 21.51 bits/sec/Hz, and 21.73 bits/sec/Hz for dual frequency band mode-3.
While the invention is amenable to various modifications and alternative forms, some embodiments have been illustrated by way of example in the drawings and are described in detail above. The intention, however, is not to limit the invention by those examples and the invention is intended to cover all modifications, equivalents, and alternatives to the embodiments described in this specification.
The embodiments in the specification are described in a progressive manner and focus of description in each embodiment is the difference from other embodiments. For same or similar parts of each embodiment, reference may be made to each other.
It will be appreciated by those skilled in the art that the above description was in respect of preferred embodiments and that various alterations and modifications are possible within the broad scope of the appended claims without departing from the spirit of the invention with the necessary modifications. , Claims:We Claim:
1. A frequency reconfigurable multiple-input multiple-output (MIMO) antenna system for wireless communication, comprising:
a substrate with at least two radiating elements, wherein the radiating elements have fractal-based geometries;
a feedline coupled to the radiating elements to enable signal transmission and reception;
a switching mechanism to control the activation of the radiating elements, allowing the antenna system to operate in multiple frequency bands;
a biasing circuit to regulate the switching mechanism, thereby providing reconfigurability of the antenna system to operate in at least three distinct modes, wherein the modes include individual and simultaneous activation of the radiating elements; and
a ground plane to enhance antenna performance characteristics; wherein the antenna system exhibits a high level of isolation between ports and is suitable for use in wireless communication applications across multiple frequency bands.
2. The antenna system as claimed in claim 1, wherein the fractal-based geometries of the radiating elements comprise a combination of Hilbert and Koch fractal structures.
3. The antenna system as claimed in claim 1, wherein the switching mechanism includes at least two PIN diodes configured to selectively activate the radiating elements.
4. The antenna system as claimed in claim 1, wherein the PIN diodes are activated and deactivated by a biasing voltage applied via the biasing circuit.
5. The antenna system as claimed in claim 1, wherein the modes of operation include:
a first mode where one fractal-based radiating element is active, operating in a first frequency band;
a second mode where a second fractal-based radiating element is active, operating in a second frequency band; and
a third mode where both radiating elements are active, operating across the first and second frequency bands simultaneously.
6. The antenna system as claimed in claim 4, wherein the first frequency band corresponds to the 4G LTE-46 band (5.15 GHz to 5.90 GHz), and the second frequency band corresponds to the 5G sub-6 GHz n78 band (3.30 GHz to 3.80 GHz).
7. The antenna system of claim 1, wherein the substrate has a dielectric permittivity of approximately 2.2, a thickness of about 1.57 mm, and a loss tangent of 0.0009.
8. The antenna system as claimed in claim 1, wherein the ground plane is a partial ground plane positioned at the bottom surface of the substrate.
9. The antenna system as claimed in claim 1, wherein the biasing circuit includes a chip inductor functioning as an RF choke and a chip capacitor integrated into the feedline to prevent the flow of direct current into the antenna source.
10. The antenna system as claimed in claim 2, wherein the PIN diodes exhibit different parasitic properties in the ON and OFF states, with a specified series resistance and inductance in the ON state and a combination of inductance, capacitance, and high resistance in the OFF state.
11. The antenna system as claimed in claim 1, wherein the MIMO antenna system comprises a 4×4 configuration with at least four antenna elements, achieving a minimum isolation of 15 dB between antenna ports.
12. The antenna system as claimed in claim 10, wherein the antenna elements are arranged orthogonally with respect to each other.
13. The antenna system as claimed in claim 10, wherein the antenna system's peak gain varies across the modes of operation, with different gains for each mode corresponding to the frequency bands in use.
14. The antenna system as claimed in claim 1, wherein the envelope correlation coefficient (ECC) between the antenna elements is less than 0.04 across the operating frequency bands.
15. The antenna system as claimed in claim 10, wherein the ground plane is either disconnected or interconnected between antenna elements, with the interconnected configuration comprising metal plates to achieve enhanced isolation performance.

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