Broadband Circularly Polarized Antenna System with Reconfigurable Filtering and Enhanced Gain for High-Frequency Applications

Abstract

ABSTRACT Broadband Circularly Polarized Antenna System with Reconfigurable Filtering and Enhanced Gain for High-Frequency Applications A broadband circularly polarized antenna system with reconfigurable filtering and enhanced gain is disclosed for high-frequency applications. The antenna structure includes a patch with integrated left-handed metamaterials, achieving wideband circular polarization and improved gain. This antenna is equipped with a reconfigurable filter surrounding the feed line to enable selective bandpass and suppression across a frequency range of 2.69 GHz to 22.9 GHz. The patch design includes specific slots and grooves, as well as an electromagnetic bandgap structure, enhancing impedance matching, bandwidth, and gain. A step-feeding mechanism and partial ground contribute to a compact size, achieving a 63% size reduction while maintaining high performance. The left-handed metamaterials introduce discontinuities, improving gain and polarization control. Fig.1 is the most illustrative figure.

Specification

Description:FIELD OF THE INVENTION
This invention generally relates to the field of radio frequency (RF) and microwave technology, particularly relates to antenna design and performance optimization for wide-bandwidth, high-gain, and compact form factors.

BACKGROUND OF THE INVENTION
Because of the development of new technology, the telecommunications industry is expanding quickly these days. To solve this, it is essential to maximize the performance of the antennae used at each wireless connection point. To reduce the amount of space needed, a compact, high-gain antenna is necessary. To prevent unwanted distribution, receiving, and disturbance, the antenna must have filtering properties. With a CP antenna, signal quality is enhanced, and loss is decreased.

A dual-band circularly polarized antenna composed of flexible liquid crystal polymer is proposed in the literature for ON-smartphone UWB locating field. It uses sequential phase feeding network and a slotted radiator with quad L-feeders in order to accomplish CP with size miniaturization. But the complexity of the antenna and the cost of manufacture are higher. The work in used cross dipoles, 4 parasitic radiators, traveling-wave loop and multiple metallic layers to realize CP across its wideband. A dielectric horn with a spherical-axicon dielectric lens is used to boost an antenna's gain over the 3-12.4 GHz bandwidth. To produce circular polarization, nonuniform metamaterial cells were employed in conjunction with ground slots and a feeding probe that resembled a hook. This antenna has a low profile of 0.06λo. A metamaterial-based polarizer positioned atop a rectangular waveguide's aperture was used to produce the antenna described in reference. The unit cell size of the many metamaterial layers that make up the suggested polarizer varies. With an AR bandwidth from 9.25-12.5 GHz, this antenna offers a broad impedance bandwidth from 7.08 to 13.5 GHz. The antenna that was suggested in exiting literature combined with a metasurface consisting of core and impedance matching layers to enhance the X band fan-beam radiation. Because of the use of many layers, an antenna's height is increased to 0.24λo. A novel U-shaped tiny negative index metamaterial structure was designed and combined with an antenna in order to enhance the gain and bandwidth of an airplane collision avoidance system (ACAS) antenna utilizing metamaterial, as discussed in an article. However, with a single antenna element and a BW of 27.2MHz, the maximum gain that was achieved was only 2.09dB. Split ring resonators are used in the metamaterials to exhibit negative refractive index, effective permittivity, and effective permeability, respectively, over a bandwidth of 0 to 6GHz and at dual frequencies (3.32 and 9.24 THz). A modified annular ring-shaped radiator and an altered step-graded notches loaded partial ground plane with a bandwidth of 5 GHz to 17.9 GHz make up the design presented in another literature.

The rapid growth of telecommunications and radar systems has increased the demand for high-performance antennae that maximize signal quality, bandwidth, and gain while maintaining a compact size. Additionally, reducing interference and achieving effective filtering within antenna systems is vital to support a wide range of operational frequencies without undesirable signal losses. Existing antenna solutions often struggle with complexities that limit scalability or production efficiency, particularly in applications requiring circular polarization and robust impedance matching.

OBJECTS OF THE INVENTION
It is the primary object of the invention to provide an antenna system with broad operational bandwidth, facilitating high-frequency applications.

It is another object of the invention to achieve compact size and high gain for efficient utilization in space-limited environments.

It is another object of the invention to offer reconfigurable filtering capabilities to mitigate interference across the antenna's bandwidth.

It is yet another object to integrate metamaterials to enhance gain and polarization performance.

SUMMARY OF THE INVENTION
To meet the objects of the invention, it is disclosed here an antenna system providing broadband circular polarization, comprises: a radiating patch; a feed line structure coupled to the radiating patch; a ground plane; a step-feed mechanism; and multiple tunable filters within the feed line structure; wherein the radiating patch is integrated with left-handed metamaterials positioned to enable circular polarization across an extended frequency range, the feed line structure is configured with a microstrip-based reconfigurable filter, wherein the filter allows selective bandpass and frequency suppression across a bandwidth of 2.69 GHz to 22.9 GHz, the ground plane comprising an electromagnetic bandgap (EBG) structure and a longitudinal slit, structured to improve impedance matching and broaden operational bandwidth, the step-feed mechanism is coupled with partial ground wherein the combination contributing to a reduction in antenna dimensions and facilitating impedance matching across the bandwidth, and the tunable filters is configured to operate in low-pass, band-pass, and high-pass states through controlled pin diodes, thereby modulating the antenna's operational bandwidth and interference rejection capability.

Further disclosed here a method for fabricating the antenna system, comprising steps of: forming the radiating patch on a substrate; integrating left-handed metamaterials with the patch; configuring a microstrip-based reconfigurable filter surrounding the feed line; establishing a partial ground plane with an electromagnetic bandgap and a longitudinal slit; connecting a step-feed mechanism to the partial ground; and assembling the pin diode-tunable filter system to achieve variable low-pass, band-pass, and high-pass filtering states.

BRIEF DESCRIPTION OF THE FIGURES
Fig.1 illustrates the Antenna layout: (a) Top, (b) Bottom, and (c) E.B.G.
Fig.2 LHM's design arrangement: (a) unit cell, and (b) circuit equivalent.
Fig.3 shows Left hand metamaterial characteristics: (a) Permeability, (b) Permittivity, and (c) Refractive index.
Fig.4 shows the (a) Antenna axial ratio and (b) gain.
Fig.5 shows Antenna's (a) Reconfiguration filter (b) Low-pass state, (c) Band-pass state, and (d) High-pass state.
Fig.6 shows the antenna (a) Fabricated layout with measuring arrangement, and (b) S11 comparison; measured vs. simulated results.
Fig.7 shows measured vs. simulated results of radiation concentrations; Farfield radiation in 14GHz (a) zoy-plane, and (b) xoy-plane.
Fig.8 shows measured vs. simulated results of radiation concentrations; Farfield radiation in 19GHz (a) zoy-plane (b) xoy-plane.

DETAILED DESCRIPTION OF THE INVENTION
This invention discloses a broadband, circularly polarized antenna system incorporating left-handed metamaterials (LHM) and a reconfigurable filter structure. The antenna system includes a patch integrated with metamaterials that enable circular polarization over a broad frequency range. Structural modifications, such as specific slots and grooves, provide impedance matching, expand the bandwidth, and optimize gain. Additionally, a tunable filtering configuration enables selective band pass and suppression properties, enhancing operational versatility across various frequencies.

This antenna has a wide range of applications, including 5G, automotive, and broad band radars. By properly engraving the patch and adding a stub to the feed line, super wide Band (SWB) is achieved. Rectangular grooves and the electromagnetic bandgap (EBG) have been added to the ground surface in the meantime to expand the functional bandwidth, which spans the 2.69GHz to 22.9GHz frequency range. When step feeding is combined with partial ground, a 63% size reduction is obtained. Using left-handed metamaterial (LHM) underneath the patch that radiates and reducing the borders of the radiating patch results in circular polarization (CP) and an increase in gain. By surrounding the feed line with a microstrip filter, the recommended operational bandwidth can be altered as necessary, enabling bandwidth modifications. The plated through hole (PTH) hole that is placed into the patch renders an axial ratio (AR) bandwidth (BW) that spans 4.85GHz to 20.85GHz. The disclosed antenna's perpendicular cut in the step-down feed improves impedance matching throughout an extensive range of operation.
Fig. 1 depicts a miniaturized antenna with broadband capabilities. The disclosed antenna was constructed using FR4 material with dimensions of 40 mm in length, 10 mm in width, and 0.8 mm in breadth. A step-type slot with uniform vertical and horizontal dimensions of C1=2mm and C2=2mm divides the patch in two at its center to achieve wideband. In addition to raising CP, LHM is added at ground level, just behind the patch. By creating a downward slot at the fractional ground with measurements like SG = 17 mm and WG = 1.5 mm, the CP is achieved over the majority of the active bandwidth. A rectangle-shaped slot has been cut to increase the effective bandwidth, and an inset feeder has been used for improved impedance match. The feed contains twin rectangle portions of varying sizes, SL1 = 17 mm, SL2 = 8 mm, SW1 = 1.2 mm, and SW2 = 0.8 mm. The left-handed metamaterial is positioned exactly behind the top radiator based on the current distribution, which limits the interaction amongst the top and bottom layers with the exterior current. The bandwidth is increased by 1GHz by double electromagnetic bandgap apertures with sizes of K1=1.5mm, K2=0.6mm, K3=0.75mm, and K4=0.7mm on either side of the longitudinal slit in the ground. The longitudinal slit of dimension CG=19mm and CGW=1.6mm has been carved in the central position of the bottom plane in order to expand the bandwidth through 2.7 to 19 GHz. By providing an additional 1.5GHz of bandwidth, a longitude slit at the center of the ground prevents undesirable changes toward the inferior part of the useful BW. The antenna offers bandwidth modulation through lowpass and highpass filtration based on microstrip lines that operate in tandem with the feed. The AR BW can be lowered to less than two dB throughout the antenna's operating bandwidth by excavating a metal via close to the patch's step slot. To provide radiation zero at the broad end of the operable bandwidth, an inverted open ended rectangle ring trench is carved into the patch closer to the embedded feed. For reaching power nulls around the active bandwidth, two perpendicular slits are etched along the diagonals of the patch. The final measurements are P1=4mm, P2=2mm. PL=13mm, N1=7mm, N2=1mm, SL=5mm, LG=20.7mm, GX=5mm, WG=1.5mm, ML=14mm, LF=2.35mm, WF=0.8mm, FY=1.2mm, WF1=0.5mm, FX=1.5mm, LF1=2.35mm.

The left-handed metamaterial's design arrangement is displayed in Fig. 2. The substrate of metamaterial is FR4 dielectric material, which has a thickness of 0.8 mm. LHM properties are produced by a central inductor when the capacitor and inductor are arranged in parallel. Fig. 3(b) displays the comparable equivalent network of the disclosed LHM. This circuit's equivalent frequency is 3.2GHz, and its passive parts-such as the inductor, capacitor, and resistor-have values of 9.4nH, 0.2 pF, and 50 ohm, respectfully. At 3.2GHz, the left-handed modelling generates negative permittivity; hence, the associated circuit's response is consistent with the simulation of the design. The LHM characteristics of this particular cell, such as negative permittivity, negative permeability, and a negative refractive index (RI), are depicted by the characteristic curve in Fig. 3. The physical dimensions are H=13mm, W=11mm, GY=0.4mm, GX=1.1mm, U=4mm, Q=5mm, and R=8mm. RLC resonance geometries are displayed by equipping antennae with LHM frameworks, which also enable manipulation of radiation within the antenna. Together with this sub-wavelength shape, antenna size reduction is accomplished. Additionally, CP is realized through the modification of radio waves which is verified with the axial ratio plot of Fig. 4 (a) whose value less than 2 for the bandwidth of interest. The LHM is situated behind the radiant patch, which is a part of the ground layer. The antenna design radiates more power and consumes less energy. These additional discontinuities provided by LHM maximizes the gain to 5.28dBi as shown by Fig. 4 (b).

The filtering mechanism provides multiple narrow bands throughout the wide operational range of 2.69GHz to 22.98GHz to avoid unnecessary interference. An incorporated tunable filter comprised of highpass and lowpass filters are surrounding the feeding structure, as shown in Figure 5 (a). Two closely spaced double L-shaped resonating constructions comprise the low-pass filter, which is connected to a feeding line by means of a pin-diode (P1). The bisected T shape acting as high pass filter with diode P3 in its slit is merged to the feed by diode P2. When pindiode P1 is activated alone, there forms a lower band with the center frequency of 2.69GHz as illustrated in Fig. 5 (b). While making all P1, P2, P3 being active brings midband resonance at 11.2GHz as depicted in Fig. 5 (c). As presented in Fig. 5 (d), on exciting P2 and P3 pindiodes gives high pass properties with its operating range prevails between 14GHz to 23GHz.

Fig. 6 (a) shows a built-up representation of the disclosed UWB antennae. This antenna can be able to either work in super wide band (SWB), higher and lower extremities of SWB or at the mid band when tuned properly. Adding LHM below the patch makes it easier to achieve CP and increases gain. In relation to the lower resonance, the antenna's dimensions are decreased to 0.4λo x 0.1λo. The created antenna's S11 is measured using a VNA, and the results of the simulation are compared with tested in Fig. 6 (b). The test and modeled results differ somewhat, which can be attributed to production errors and an unequal dielectric constant throughout the dielectric surface. The important factor for the antenna is its bandwidth of 20.3GHz.

The radiation concentrations in the anechoic chamber have been computed using this generated antenna on the opposite side that collects signals and the horn acting as the transmission antenna, as seen in Figs. 7 and 8. In the yoz and yox planes, the observed radiation attributes and the predicted radiation attributes at 14GHz and 19GHz were almost the same. The slight variations in the material's characteristics and dimensions, fabrication, soldering and measurement errors, are some of the factors that can cause the discrepancy between simulation and experiment results.
This antenna finds application in the field of radar which operates over a wide band of frequencies, 5G systems, and in the automotive sector.
 
, Claims:We Claim:

1. An antenna system providing broadband circular polarization, comprises:
a radiating patch;
a feed line structure coupled to the radiating patch;
a ground plane;
a step-feed mechanism; and
multiple tunable filters within the feed line structure;
wherein the radiating patch is integrated with left-handed metamaterials positioned to enable circular polarization across an extended frequency range, the feed line structure is configured with a microstrip-based reconfigurable filter, wherein the filter allows selective bandpass and frequency suppression across a bandwidth of 2.69 GHz to 22.9 GHz, the ground plane comprising an electromagnetic bandgap (EBG) structure and a longitudinal slit, structured to improve impedance matching and broaden operational bandwidth, the step-feed mechanism is coupled with partial ground wherein the combination contributing to a reduction in antenna dimensions and facilitating impedance matching across the bandwidth, and the tunable filters is configured to operate in low-pass, band-pass, and high-pass states through controlled pin diodes, thereby modulating the antenna's operational bandwidth and interference rejection capability.

2. The antenna system as claimed in claim 1, wherein the radiating patch includes a central step-slot of uniform vertical and horizontal dimensions, segmented into two sections to enable broad bandwidth and enhanced circular polarization.

3. The antenna system as claimed in claim 1, wherein the left-handed metamaterials exhibit negative permittivity, negative permeability, and negative refractive index properties, positioned beneath the radiating patch to enhance gain and stabilize polarization over the bandwidth.

4. The antenna system as claimed in claim 1, wherein the longitudinal slit within the ground plane extends along a central axis of the bottom plane, thereby expanding the antenna's operational bandwidth by suppressing undesired responses at lower bandwidth limits.

5. The antenna system as claimed in claim 1, wherein the electromagnetic bandgap (EBG) apertures are placed symmetrically adjacent to the longitudinal slit to provide an additional 1 GHz enhancement to the antenna's bandwidth.

6. The antenna system as claimed in claim 1, wherein the reconfigurable filter comprises a low-pass filter with double L-shaped resonators connected to the feed line by a first pin diode, and a high-pass filter with a bisected T-shaped resonator integrated with a second and third pin diode in its slit, allowing selectable operation in low-pass, band-pass, or high-pass modes based on diode activation.

7. The antenna system as claimed in claim 1, wherein the patch structure includes a microstrip-based feed with rectangular segments of varying dimensions, positioned to optimize impedance matching and enhance signal coupling within the operational bandwidth.

8. The antenna system as claimed in claim 1, wherein additional discontinuities within the left-handed metamaterials create resonance variations that increase gain, with an axial ratio bandwidth achieving less than 2 dB across the operational range.

9. The antenna system as claimed in claim 1, wherein a perpendicular metal via is positioned adjacent to the step slot of the patch to further reduce the axial ratio bandwidth and enhance circular polarization control over the specified frequency range.

10. A method for fabricating the antenna system as claimed in claim 1, comprising steps of:
forming the radiating patch on a substrate;
integrating left-handed metamaterials with the patch;
configuring a microstrip-based reconfigurable filter surrounding the feed line;
establishing a partial ground plane with an electromagnetic bandgap and a longitudinal slit;
connecting a step-feed mechanism to the partial ground; and
assembling the pin diode-tunable filter system to achieve variable low-pass, band-pass, and high-pass filtering states.

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