This paper proposes a Ka-band broadband circularly polarized (CP) antenna array with high cross-polarization discrimination (XPD). The design employs a four-layer stacked dielectric substrate structure, utilizing a 2×2 sequentially rotated (SR) array of substrate integrated cavity (SIC) magnetoelectric dipole elements as the core radiator. A double-layer substrate integrated waveguide (SIW) SR feeding network achieves precise 90[Formula: see text] phase delay at the center frequency, enabling the array to attain 30.33% impedance bandwidth over 23.45-32.02 GHz and 35.52% axial ratio (AR) bandwidth across 22.48-32.19 GHz. A [Formula: see text] multi-layer square-loop array decoupling surface (ADS) is integrated on the topmost dielectric layer of the antenna array. By optimizing the geometry, dimensions of the square loops, and the substrate thickness, this structure generates reflected waves with specific amplitude and phase characteristics, effectively canceling out the coupling waves propagating between the antenna elements. This design significantly suppresses the mutual coupling among the radiating elements, resulting in a XPD better than [Formula: see text] across the operating band. It thereby substantially mitigates the mutual coupling issue commonly encountered in millimeter-wave antenna arrays. Furthermore, the ADS structure enhances gain performance, yielding a peak gain of 12.47 dBic with gain variations below 3 dB throughout 25.95-33.14 GHz. The fabricated array measures [Formula: see text]. The proposed CP antenna array demonstrates significant potential for application in 5G millimeter-wave communication systems.

ABSTRACT In this paper, we present the design of a planar endfire circularly polarized (CP) antenna utilizing a periodic structure. The CP antenna is constructed on substrate integrated waveguide (SIW) that incorporates a periodic double‐sided rectangular slot structure, culminating in a Vivaldi antenna at the end. The rectangular slot array generates vertically polarized (VP) electric field components for the far‐field, while the Vivaldi antenna contributes horizontally polarized (HP) electric field components. By adjusting the distance between these two components, we achieve a phase difference of 90° between the two polarization components. This results in a planar endfire CP antenna that operates within the frequency range of 23.8 to 25.8 GHz, with an axial ratio of less than 3 dB. The antenna achieves a maximum gain of 11.73 dBi. The combination of high gain at small aperture translates to superior aperture utilization and easy edge/board integration, supporting compact endfire arrays, terminal‐side AoA links and 24‐GHz ISM sensing. Compared with recent planar endfire CP designs, the proposed radiator delivers comparable bandwidth but higher gain with smaller width, using a simple, low‐loss, and manufacturing‐friendly single‐layer PCB implementation.

Abstract A broadband circularly polarized (CP) antenna which exhibits excellent radar cross section (RCS) reduction is designed using polarized conversion metasurface (PCM). The PCM has a near-perfect polarization conversion ratio exceeding 99% from 16.84 to 32.64 GHz. Then the broadband low-RCS CP antenna operating in the Ku-band consists of a two layers antenna loaded with PCM. Its impendence bandwidth is 39.25% (12.04–17.92 GHz), and a corresponding 3 dB axial bandwidth is 20.50% (13.79–16.94 GHz). There is good agreement between measured and simulated results. Meanwhile, the PCM ensures sufficient concealment for the antenna across a wideband and wide-angle range. The monostatic RCS reduction exceeds 8.82 dB for θ -polarized incidence from 13.40 to 37.79 GHz, and for ϕ -polarized incidence, the reduction is better than 8.94 dB. This work presents an effective strategy for satellite communication, antenna stealth, and stealth platforms.

ABSTRACT A compact, low‐profile circularly polarized (CP) antenna element is proposed using a two‐layer printed circuit board (PCB) configuration. The radiator on the top of the first PCB is a rectangular loop inside with four sector‐shaped patches, excited by a cross‐slot of the ground on the top of the second PCB. The cross‐slot is fed with a Γ‐shaped microstrip line on the bottom of the second PCB. Based on this designed method, two CP modes are formed. The measured results show that it has a −10 dB impedance bandwidth (IBW) of 3.23–3.84 GHz (17.26%) and a 3 dB axial‐ratio bandwidth (ARBW) of 3.33–3.71 GHz (10.80%), a realized gain of 7.70 ± 0.10 dBi and an average radiation efficiency of 72.56% over ARBW. Furthermore, a 2 × 2 antenna array is constructed using the proposed element and a four‐way toroidal power divider network. The array is fabricated and measured with a −15 dB IBW of 3.20–3.94 GHz (20.73%), an ARBW of 3.16–3.96 GHz (22.47%), and a realized gain of 12.05 ± 0.19 dBi over 3.3–3.8 GHz band. Therefore, the left‐handed CP array demonstrates that it can be a promising candidate for the 5G n78 systems.

Achieving low radar cross section (RCS) and circular polarization (CP) is crucial for antenna designs in satellite and navigation applications. Conventional approaches often involve additional metasurface (MS) layers, modifications to the radiating patch, or separate feeding networks, which increase structural complexity, reduce aperture efficiency, and compromise radiation performance. This paper proposes a novel design for a low RCS circularly polarized antenna (CPA) using a polarization conversion metasurface (PCM) that integrates both RCS reduction and CP generation within a single compact structure. The proposed multifunctional MS serves as both a linear polarization converter and a CPA. This integration minimizes structural complexity while ensuring high radiation efficiency and effective RCS reduction. A novel feeding network is incorporated into the MS to precisely control the phase difference between orthogonal excitations. Dual input feeds are positioned along the x- and y-axes to generate the transverse magnetic (TM010) and TM001 modes, respectively. A controlled 90° time-phase difference is achieved by applying phase ϕ to the x-axis feed and ϕ + 90° to the y-axis feed. This precise phase alignment ensures optimal CP generation while maintaining a compact and structurally efficient design. The antenna operates with a CP bandwidth of 5.52-5.78 GHz and a peak boresight gain of 13.5 dBi. The proposed antenna design is verified through both simulation and experimental measurements, showing significant improvements in CP performance, RCS reduction, and radiation efficiency. These results confirm that the antenna is highly suitable for next-generation satellite and navigation systems.

ABSTRACT In this article, the radiation properties of the asymmetric double spiral shape, used as a calendar in an ancient analog computer, are investigated. This ancient device was discovered in a shipwreck, dated in the second quarter of the first century B.C. by the island of Antikythera in Greece. The equations describing this shape are provided and its antenna characteristics such as input impedance, radiation pattern and gain are examined theoretically and experimentally. It is determined that this asymmetric double spiral is a broadband circular polarization antenna.

Full W-Band Circularly Polarized Antenna With Waveguide Polarizer Based on Evanescent and Propagation Modes

ABSTRACTIn this paper, a high‐gain multiband antenna with circular polarization in a single‐layer design is developed for the 5G, WiMAX, and WLAN bands. The proposed antenna incorporates novel L‐shaped elements strategically placed to improve its performance. These elements change the current distribution within the proposed design and allow operation in multiple TM modes over different frequencies. A theoretical analysis is also presented to calculate the TM modes at each resonant frequency to gain a better understanding of the antenna's performance. An equivalent circuit of the proposed antenna is developed to accurately verify the operating bands. The results show that the antenna supports multiple resonant modes, including TM11, TM02, TM31, and TM21, enabling high gains of 8.5, 7, 11.5, and 7.5 dBi at 3.5, 4.6, 5.2, and 5.8 GHz, respectively, while maintaining circular polarization across all frequency bands. Compared to a conventional patch antenna, the proposed design shows an improvement in maximum gain of 4.5 dBi, an increase in radiation efficiency of up to 6%, and improvements in both multiband capabilities and circular polarization. The current distributions and E‐field within the proposed antenna confirm the expected TM modes and agree well with the theoretical calculations. The proposed antenna was designed with CST software, verified with HFSS, analyzed with an equivalent circuit in ADS, and then fabricated and measured to confirm its reliability. Unlike multilayer designs, the proposed antenna provides higher gain with more than 50% reduction in printed layers and no air gaps, resulting in a significant reduction in fabrication complexity and cost. Its multiband capability, high efficiency, and low‐cost fabrication make it a strong candidate for modern wireless systems.

Low Profile Circularly Polarized Antennas for Modern Wireless Applications: A Review

A Compact Quasi-Magnetic-Electric Circularly Polarized Antenna With Reconfigurable Patterns

This paper presents an artificial magnetic conductor (AMC)-based crossed dipole antenna (CDA) for right-hand circular polarization (RHCP) and broadside radiation at 2.45 GHz. The proposed antenna comprises a pair of semi-circular planar dipole arms where orthogonal arms are connected using quarter-wavelength rings on both sides of the substrate. The antenna is excited using a single probe feed, and quarter-wave rings maintain a 90° phase shift between orthogonal arms for circular polarization. The AMC surface having square patches is amalgamated with a proposed CDAto realize broadside radiation with higher gain, smaller antenna and low profile compared to a cavity-backed CDA. The proposed AMC-based CDA with a size of 1.06λo × 1.06λo × 0.09λo achieves an impedance bandwidth of 40.7% (2.09-3.16) GHz, an axial ratio bandwidth of 9.21% (2.38-2.61) GHz and broadside gain higher than 7.0 dBic over CP band. The designed antenna is suitable for 2.45 GHz ISM band and S-band satellite applications.

An Ultrawideband Omnidirectional Circularly Polarized Antenna Enabled by Metasurface Integrating Dielectric Polarizer

ABSTRACTWith the rapid development of modern wireless communication technology, antennas, as a core component of the wireless communication system, have become a research focus. The axial ratio (AR) of an antenna is particularly critical to its overall performance. Increasing AR bandwidth can ensure circular polarization performance, enhance system compatibility, and improve anti‐interference capabilities. This paper presents a design of a circularly polarized patch antenna based on metasurface technology. By incorporating a transmission‐type polarization conversion metasurface, copper plates embedded vertically in the ground plane, and n‐shaped parasitic patches, significant improvements in antenna performance are achieved. The tests show that the antenna achieves a 43.4% S11 bandwidth within the frequency range of 4.94–7.68 GHz, and a 31.4% 3 dB AR bandwidth within the range of 4.83–6.43 GHz, demonstrating excellent performance. This study provides new technical support and design ideas for the field of wireless communication.

In this paper, a printed hybrid-mode antenna for dual-band circular polarization (CP) is proposed. In the proposed antenna, one T-shaped element is fed by a coplanar waveguide and one L-shaped element is loaded to the ground plane. The relationship between the antenna’s geometric parameters and the circular polarization characteristic (axial ratio) is examined through electric current distribution and radiation field components. In addition, the antenna’s resonant modes are investigated through characteristic mode analysis (CMA). Through parametric studies, the range of two frequency ratios is explored, revealing that the antenna operates as a dual-band single-sense CP antenna, even in ranges where the two frequency ratios (the ratio of high frequency to low frequency) are smaller compared to antennas in other studies. The proposed antenna has a frequency ratio of less than 1.5 between the two frequencies and can be flexibly designed. The proposed antenna is designed for the 2.5 GHz band and 3.5 GHz band. The measured bandwidths of 10 dB impedance with a 3 dB axial ratio are 2.35–2.52 GHz and 3.36–3.71 GHz, respectively.

Abstract In this paper, a dual-band circularly polarized (CP) transmitarray (TA) antenna based on metasurfaces (MSs) is proposed. This TA can realize wide-angle beam-scanning for left-handed circular polarization (LHCP) in K-band and right-handed circular polarization (RHCP) in Ka-band. The receiver (Rx)-transmitter (Tx) structure is utilized for MS elements, enabling polarization conversion from incident y-polarized (y-pol) waves to LHCP in the lower frequency (LF) and x-polarized (x-pol) waves to RHCP in the higher frequency (HF). Phase compensation for both frequencies can be obtained through the rotation of the LF and HF Tx patches, respectively. After optimizing the arrangement of elements using the multibeam phase matching method (PMM) and genetic algorithm (GA), the array achieves beam-scanning under the movement of LF and HF horns. Then, this TA is simulated, manufactured and measured to verify the performance. The measured results are in excellent agreement with the simulated results, which demonstrate that it can realize beam-scanning of 90° (−45° to +45°) for LHCP at 25.5 GHz and 60° (−30° to +30°) for RHCP at 33.5 GHz, with gain roll-offs of only 2.09 dB and 1.66 dB. Besides, beam squints are only 1.4° and 1.2°, respectively. Maximum gains during the scanning process in the LF and HF bands are 25.86 and 25.29 dBic. Compared to similar antennas, this TA achieves wide-angle LHCP/RHCP beam-scanning in K-/Ka-bands. It also enhances accuracy for beam-scanning, features low gain roll-offs and relatively high gains. The proposed CP antenna is well-suited for satellite communication systems, especially those demanding capabilities of accurate beam-scanning across dual-bands.

This research paper introduces a novel compact Circularly Polarized (CP) antenna tailored for 5G Wireless Local Area Network (WLAN) and X-band applications. The antenna design includes a circular patch, minimized ground, and a superstrate. Four V-shaped slits are embedded along the boundary of the circular patch, strategically positioned to generate circular polarization operating across multiple frequency bands. The antenna resonates in the ranges between 4.9 GHz and 5.6 GHz, 7.74 GHz and 8 GHz, and 10.9 GHz and 11.2 GHz. The design's effectiveness is verified through a compact antenna with dimensions of 0.636 λ0 × 0.636 λ0 × 0.21 λ0. The results demonstrate 10-dB impedance bandwidths of 13.2%, 3.16%, and 2.7% for 4.9-5.6 GHz, 7.74-8 GHz, and 10.9-11.2 GHz, respectively. In addition, the findings revealed gains of 8 dBi, 6.89 dBi, and 8 dBi at resonant frequencies of 5.3 GHz, 7.9 GHz, and 11.1 GHz, respectively. With a radiation efficiency exceeding 97% across all resonant frequencies, the addition of a superstrate enhances gain by 3 dBi. Comparison between measured and simulated results confirms the accuracy of the proposed design. The triple-band CP compact antenna, augmented by a superstrate, showcases promising characteristics for 5G WLAN and X-band applications.

A Lightweight Flexible Wearable Circularly Polarized Antenna for Navigation and Positioning in IoT Applications

Wearable Broadband Circularly Polarized Antenna With Characteristic Mode Analysis for Wireless Body Area Network Applications

Abstract This article presents a broadband gain‐enhanced circularly polarized (CP) microstrip patch antenna based on metasurface (MS). A truncated corner square patch with a cross‐shaped slot has been employed as the host antenna, configured on a 1.6 mm thick FR‐4 substrate backed by a copper ground plane. The MS layer consisting of a 4 × 4 square array has been designed on another 1.6 mm thick FR‐4 substrate with identical outer dimensions acting as a superstrate layer. The proposed antenna exhibits a −10‐dB reflection coefficient bandwidth spanning from 4.37 to 7.03 GHz (46.67%), along with a 3‐dB axial ratio (AR) bandwidth from 5.13 to 5.78 GHz (12%). At 5.3 GHz, the antenna exhibits a maximum realized gain of 6.8 dBic. Furthermore, polarization of the antenna is characterized as left‐handed circularly polarized. To verify the impedance response, an equivalent circuit model of the antenna has been developed step‐by‐step followed by fabrication of the prototype. The measured results show high degree of similarity with the simulated responses. Being low profile (0.56λo × 0.56λo × 0.028λo at 5.3 GHz), the proposed CP antenna can be utilized for applications of WLAN, Wi‐Fi wireless computer networks etc.

Microstrip patch antennas (MPAs) are widely used in satellite communication due to their low profile, compact size, and ease of fabrication. This paper presents a design of an X-band microstrip patch antenna using an electromagnetic band gap (EBG) structure for CubeSat applications. The X-band is preferred for CubeSat missions in high-speed communication, long distance or deep space because it allows communication at higher data rates, and the antenna is smaller than those used for lower frequency bands. In our study, the EBG elements are analyzed, modified and optimized so that the antenna can fit a 10 cm × 10 cm surface area of a standard 3U CubeSat structure while providing a significant high gain and circular polarization (CP). A noticeable point of this research is that the simplicity of the antenna and the EBG structure are being maintained by just using a simple single-probe feed to achieve a total antenna efficiency exceeding 90%, and the measured gain of around 11.7 dBi at the desired frequency of 8.483 GHz. Furthermore, the measured axial ratio (AR) is around 1.4 dB at 8.483 GHz, which satisfied the lower-than-3 dB requirement for CP antennas in general. The simulation, analysis and measured results are discussed in detail.