A compact dual-port circularly polarized (CP) multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) for 28 GHz applications is presented. A single cross-shaped dielectric resonator is excited by two orthogonal microstrip feeds, supporting hybrid orthogonal modes that enable CP radiation at both ports without requiring perturbation cuts, parasitic elements, or decoupling structures. The fabricated prototype exhibits a measured 10 dB impedance bandwidth and 3 dB axial ratio bandwidth that fully cover the Federal Communications Commission (FCC)-allocated 28 GHz band (27.5–28.35 GHz). Port isolation remains better than 15 dB, and the antenna exhibits a peak gain of approximately 7.6 dBi with radiation efficiency exceeding 93%, within a compact 40 × 47 mm2 footprint. MIMO performance is verified through envelope correlation coefficient (ECC), diversity gain (DG), and total active reflection coefficient (TARC). The results demonstrate that the proposed single-resonator dual-port CP DRA provides an efficient and integration-friendly solution for compact mmWave MIMO applications in next-generation 5G/6G terminals.

In this letter, a circularly polarized (CP) 4 × 4 array antenna generating a fan-beam radiation pattern is presented, along with its application as the primary pattern of an offset reflector antenna. A sequentially rotated feed network is incorporated into the proposed antenna, enabling a wide axial ratio (AR) bandwidth of 1.9 GHz centered at 8.2 GHz. The proposed array antenna generates about 27.5° and 14.5° of half-power beamwidth (HPBW) in ϕ=0° and ϕ=90° planes, respectively. The fabricated antenna shows good agreement with the simulated results in terms of impedance bandwidth, gain, and radiation characteristics. Furthermore, the offset reflector antenna fed by the proposed CP array is evaluated, resulting in a gain enhancement of approximately 17 dB and a fan-beam radiation characteristic with half-power beamwidths of 3.95° and 2.15°, with an axial ratio bandwidth of 1 GHz.

This paper proposes a circularly polarized (CP) metasurface antenna array integrating absorbers with polarization conversion metasurfaces (PCMs). By synergistically deploying PCM units and absorber units, the antenna array combines the scattering control properties of PCM units with the electromagnetic energy absorption characteristics of absorber units and ultimately achieves broadband radar cross section (RCS) reduction. Simulation results indicate that the array exhibits an impedance bandwidth of 12% (11.8-13.3 GHz), a 3 dB axial ratio (AR) bandwidth of 12.9% (11.78-13.4 GHz), and a 3 dB gain bandwidth of 9.7% (11.64-13 GHz). Within the wideband range of 10.2-20.9 GHz (68.8%), the array achieves 10 dB RCS reduction both out-of-band and in-band, with a maximum reduction of 33.2 dB. A prototype of the antenna array was fabricated and tested, with measured results showing good agreement with simulations, validating the design effectiveness.

This paper proposes a compact, low-profile slot antenna integrated with a metasurface (MS) layer to realize wideband circular polarization and maintain a consistently high gain for IoT applications. The antenna element uses a C-shaped slot in the ground plane, excited by a microstrip feed to generate the circularly polarized waves. The metasurface layer incorporates mushroom-shaped outer cells and centrally placed slanted-slot elements to broaden the axial-ratio (AR) bandwidth and to maintain a consistently high gain. The metasurface consists of twelve adjacent cells arranged in a mushroom-shaped configuration, with a 45° slanted rectangular slots on four central cells. The simulated and measured results demonstrate strong agreement; the impedance-matching bandwidth is 26.7%, and the axial-ratio bandwidth is 15.7% at a central frequency of 6.8 GHz. Finally, the antenna consistently demonstrates a measurement gain exceeding 8 dBic across the AR bandwidth, with a peak measured gain of 9.6 dBic.

Wireless power transmission (WPT) is poised to revolutionize the future of wireless applications and sensing networks. High-gain antennas are essential for extending WPT coverage, but the unpredictable orientation of wireless devices remains a major challenge. To address this, this paper proposes a dielectric resonator antenna (DRA) with a new cone version (cupped-cone shape) to achieve high gain and a wideband circular polarization, ensuring consistent energy transfer regardless of device orientation. The proposed design enhances bandwidth by supporting multiple resonant modes. Combining two geometric shapes provides greater flexibility for fine-tuning and optimizing the DRA. The proposed DRA is excited using an innovative feeding mechanism with two elliptical slots and a modified microstrip feeding to produce wideband circular polarization, achieving large impedance and axial ratio bandwidths. The design is fabricated from polylactic acid using 3D printing technology, making it lightweight and cost-effective. Measurements show the antenna operates in the WPT band, covering the industrial, scientific, and medical (ISM) frequency of 5.8GHz with a 64% impedance bandwidth, 3-dB axial ratio bandwidth of approximately 31%, and a high gain of about 11.1 dBic by effectively utilizing a higher-order mode while maintaining the bandwidth.

This paper presents a dual four-port circularly polarized (CP) MIMO antenna based on substrate integrated waveguide (SIW) technology for sub-6 GHz applications. The design consists of two identical four-port SIW-based CP-MIMO antennas arranged in a mirror-symmetric configuration with an air gap of 15 mm. Each antenna employs four symmetrically arranged cross-shaped SIW patches excited by coaxial probes. Bidirectional radiation is achieved by applying a 180° phase difference between corresponding ports of the mirror symmetric configuration, referred to as the Backward-Radiating Unit (BRU) and the Forward-Radiating Unit (FRU). The bidirectional radiation mechanism is supported by array-factor-based theoretical modelling, which explains the constructive and destructive interference under phase-controlled excitation. To ensure high isolation and stable polarization performance, the antenna design incorporates defected ground structures, inter-element decoupling strips, and vertical metallic vias. Simulations indicate an operating band from 5.1 to 5.4 GHz. Measurements show a −10 dB bandwidth from 5.25 to 5.55 GHz, with the frequency shift attributed to fabrication tolerances and measurement uncertainties. The antenna achieves inter-port isolation better than −15 dB. A 3 dB axial-ratio bandwidth is maintained across the operating band. Measured axial-ratio values remain below 3 dB from 5.25 to 5.55 GHz, while simulations predict a corresponding range from 5.1 to 5.4 GHz. The proposed configuration achieves a peak gain exceeding 4 dBi and maintains an envelope correlation coefficient below 0.05. These results confirm its suitability for CP-MIMO systems with controlled spatial coverage. With a physical size of 0.733λ0 × 0.733λ0 per array, the proposed antenna is well-suited for vehicular and space-constrained wireless systems requiring bidirectional CP-MIMO coverage.

Abstract This paper presents a circularly polarized (CP) antenna employing both uniform and non-uniform metasurfaces to achieve wideband characteristics. The proposed antenna consists of a dual-feed CP antenna as the source element, a 4 $\times$ 4 metasurface lattice as the superstrate, and a sequential feed network. Initially, the performance of the antenna is analyzed using a uniform metasurface. Subsequently, by adjusting the size of the inner unit cells, the uniform metasurface is transformed into a non-uniform configuration. The proposed design with a uniform metasurface achieves a $-$ 10 dB impedance bandwidth ranging from 5.21 to 6.47 GHz (21.57%) and a 3-dB axial ratio bandwidth from 3.96 to 6.67 GHz (50.9%). The use of a non-uniform metasurface significantly improves the overall antenna performance, achieving a $-$ 10 dB impedance bandwidth and 3-dB AR bandwidth of 4.98 to 7.45 GHz (40%) and 2 to 7.26 GHz (113%), respectively. The optimized design with a non-uniform metasurface is fabricated and tested. Overall size of the antenna is 40 $\times$ 40 $\times$ 3.4 mm $^3$ (0.72 $\times$ 0.72 $\times$ 0.062 $\lambda_{0}^3$ ), where $\lambda_{0}$ represents effective wavelength at an operating frequency of 5.5 GHz. The simulated and measured results of the proposed antenna are found to be in good agreement.

Abstract A compact, low-profile, and flexible circularly polarized antenna is proposed for off-body 5G wearable applications, featuring a unique folded key-shaped parasitic strip integrated on a Cordura textile substrate. The design excites two orthogonal modes using an asymmetrical feed line, folded stub, and slotted partial ground to achieve circular polarization with a 3 dB axial ratio bandwidth of 21.42% (3.8–4.7 GHz), effectively covering 5G NR bands n77 (3.3–4.2 GHz), n78 (3.3–3.8 GHz), and partial n79 (4.4–5 GHz). The antenna exhibits a measured impedance bandwidth of 66.98% from 2.8 to 5 GHz and a peak gain of 5.2 dBic, while maintaining a compact footprint of 0.28λ₀ × 0.14λ₀ at 2.8 GHz. Fabricated on a flexible textile with excellent mechanical and electromagnetic properties, the prototype demonstrates strong agreement between simulation and measurement, ensuring stable performance under conformal conditions. This design enables high-speed data transfer, robust off-body connectivity, and accurate real-time monitoring, making it highly suited for next-generation wearable 5G systems with strict constraints on size, gain, and SAR compliance.

A compact wideband high data rate implantable antenna is designed for cortical visual prosthesis devices. In order to achieve high data rate, a metamaterial array with negative permeability is formed by loading complementary open resonant rings to reduce the resonant frequency of the antenna and produce circular polarization characteristics. By introducing a meandering structure around the radiation unit, the current path on the antenna surface can be increased, further optimizing the impedance matching. Adding four U-shaped open slots on the ground plane can increase two adjacent resonant points, reducing the antenna size while increasing the impedance bandwidth. The antenna size is reduced to 8 × 8 × 0.635mm³. A complete antenna model is established, and the biocompatibility, radiation characteristics and safety of the antenna are evaluated. The performance of the antenna is tested in a saline solution simulating the characteristics of cerebrospinal fluid. The measured impedance bandwidth is 26.5%, the axial ratio bandwidth is 22.3%, the gain is -20.9 dBi, and the effective communication distance is 4.1m. The designed antenna has wide working frequency band, small size, good electromagnetic compatibility and high data rate communication ability, and is the optimal design scheme for cortical visual prosthesis.

This paper presents a compact, wideband, high-gain circularly polarized (CP) hemispherical dielectric resonator antenna (HDRA) designed for millimeter-wave 5G applications. The proposed antenna employs a linearly polarized (LP) HDRA excited through an annular slot coupled to a 50-Ω microstrip feed, enabling efficient radiation at millimeter-wave frequencies. Wide impedance bandwidth from 20 to 28 GHz is achieved by overlapping multiple adjacent resonant modes of the HDRA. Circular polarization is realized by introducing a frequency-selective surface (FSS) superstrate positioned at an optimized distance above the antenna. To further enhance the axial-ratio bandwidth and gain, a 2 × 2 HDRA array with a sequential-phase feeding network and an additional dielectric superstrate is implemented. The antenna is fabricated and experimentally validated. Measured results demonstrate an impedance bandwidth of 33.3% (20–28 GHz), a peak realized gain of 11.8 dBi, and a 3-dB axial-ratio bandwidth of 31% (20.5–28 GHz). The proposed design offers a compact and efficient solution for millimeter-wave 5G and IoT applications.

A compact single asymmetric coplanar waveguide feed (ACPW‐fed) dual circularly polarized microstrip antenna that operates at 1.8, 3.9, and 5.2 GHz in the entire operating frequency band 600 MHz–6 GHz for the radar detection of the improvised explosive devices (IEDs) carried by a person is introduced. The proposed novel quasi‐omnidirectional antenna consists of single sided rectangular ring microstrip patch antenna. L‐shaped slots are etched at the two opposite corners of the rectangular ring, introducing new resonance and circular polarization waves at the mid and upper bands, respectively. The achieved dual half‐rectangular ring patch antenna (DHRR‐patch) is loaded with strips of various shapes delicately placed at the center of the radiator, providing new resonance at the upper band and the improvement of the CP features. The matching technique designed based on CPW 50 Ω microstrip transmission line combined with the dual broad band matching techniques through quarter‐wave transformer in conjunction with open stubs and distributed lumped element method constitutes the novelty of the study. Based on quasi‐TEM mn (q‐TEM mn ) mode, ACPW‐fed and CP‐slots are employed to generate CP radiations at the q‐TEM 11 and q‐TEM 21 modes, respectively, while the ground plane width is optimized to enhance axial ratio bandwidth (AR‐BW). Input impedance and radiation pattern calculations of the conventional structure using transmission line and cavity model‐based q‐TEM 01 mode are conducted, respectively. Numerical experiments of the studied monolayer antenna are carried out using Advanced Design System (ADS) Version 2009 environment software employing internal one‐port option to excite the antenna. The prototype of the proposed antenna with a compact dimension (0.27 λ g × 0.38 λ g × 0.02 λ g at 1.8 GHz where λ g is the guided wavelength of the q‐TEM 01 mode) is fabricated on high loss laminate FR4 substrate of volume 43 × 38 × 1.6 (mm 3 ) and relative dielectric constant of 4.4 with simple laboratory‐based traditional printed circuit board (PCB) etching process. Measurement results show a fractional impedance bandwidth (FIBW) of 11.1%, 5.9%, and 7.1%, axial ratio (AR) of 4.6, 2.2, and 0.5 dB, and peak gain of 3.7, 4.7, and 6.1 dBic at 1.8, 4.0, and 5.2 GHz, respectively, demonstrating its suitability for IED detection applications. To verify the efficiency of the proposed model, measured results are compared with the simulated results and good agreement has been established.

Planar Circularly Polarized Endfire Antenna Arrays With Wide Axial Ratio Bandwidth Based on Slotted Substrate Integrated Waveguide

ABSTRACT In this paper, an ultra‐broadband circularly polarized (CP) antenna equipped with quasi‐achromatic‐focused metasurface (MS) is proposed. To enhance the C‐shaped CP antenna's radiation performance, we designed a MS‐based on Pancharatnam‐Berry (PB) phase theory. Positioning the initial C‐shaped CP antenna at the focal point of the designed quasi‐achromatic‐focused MS enabled an antenna loaded with MS achieving CP radiation. This MS antenna system demonstrated a peak gain of 13.77 dBic with an average gain exceeding 10 dBic over the 4.52–12.82 GHz band (relative bandwidth: 95.7%). Concurrently, its 3‐dB axial ratio bandwidth reached 89.1%, covering 4.6–12 GHz. This work provides an efficient method to enhance antenna gain in wideband wireless communication systems.

A Broadband Conical Quadrifilar Helical Antenna With Wide Axial Ratio Bandwidth for Satellite Communications and Navigation

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 An intuitive investigation into the design of a compact planar circularly polarised (CP) metasurface antenna (MA) for futuristic mid-band 6 G Wireless cellular networks has been proposed. The proposed design encompasses a simple, customary, and innovative approach for asserting a symmetrically rotated circularly polarised generator (SRCPG) for producing CP radiated waves, along with a top loading of a periodically meta-unit radiating cell which serves as an actuator for overall steady performance. The SRCPG along with MA meta-cells executes dominant magnetic coupling and serves simultaneously an impedance transformer and an effective radiator inducing wideband resonance with stable radiated CP waves (dominant LHCP). The inherent CP intuitions of periodic meta-cells are explored via modal and surface current investigations to ascertain bandwidth and radiation potential characteristics. A 40 mm × 40 mm fabricated prototype antenna has been validated experimentally to operate from (5.25–8.21) GHz with 44% 10-dB bandwidth, 38.23% 3-dB axial ratio bandwidth from (5.5–8.1) GHz, and realised peak gain of 8.64 dBic. The performance statistics with stable performance demonstrate its potential in mid-band 6 G wireless cellular applications.

This paper presents a compact, dual-band, dual-polarization button antenna for Wireless Body Area Networks (WBANs) that operates in the 2.45 GHz and 5.8 GHz Industrial, Scientific, and Medical (ISM) bands. The antenna is engineered in the lower band from 2.33 to 2.8 GHz (18.3% fractional bandwidth) as a linearly polarized, top-loaded monopole, which provides an omnidirectional radiation pattern for on-body communication. In contrast, it functions as a cross-dipole in the higher band, achieving a fractional bandwidth of 66.4% (4.8–9.57 GHz) and a 3 dB axial ratio (AR) bandwidth of 57.4%, producing a broadside radiation with circular polarization for off-body communications. Prototype measurements in both free-space and on-body settings confirm the antenna’s robust performance, successfully validating its dual-band operation, dual-polarization characteristics. Furthermore, Specific Absorption Rate (SAR) simulations conducted on a human model demonstrate that the values are significantly below the established safety limits, confirming the antenna’s suitability for practical wearable applications.

ABSTRACT This paper describes the design and implementation of a dual‐layer frequency selective surface (FSS) based dual‐band high‐gain circularly polarized (CP) meander‐shaped monopole antenna for the applications of Wi‐Fi and C‐band. To achieve the final configuration, the design process involves several steps: designing the meander‐shaped antenna, modeling the FSS, circuit analysis, and practical realization. The antenna prototype (electrical dimension: 0.333 λ₀ × 0.266 λ₀, λ₀ at 2 GHz and physical dimension of 50 × 40 mm 2 ) comprises a meander‐shaped strip and a 3 × 3 matrix dual layer periodic FSS embedded under the antenna structure without disturbing the impedance bandwidth. The low‐cost FR4 dielectric substrate is used to design both the antenna and FSS layer. Initially, only the antenna part was designed, which yielded −10 dB impedance bandwidths (IBWs) and 3‐dB axial ratio bandwidths (ARBWs) of 1160 and 600 MHz in the lower band, and 560 and 700 MHz in the upper band, respectively. Without an FSS structure, the peak gains of the antenna are 3.6 dBi (lower band) and 3.8 dBi (upper band). The proposed FSS‐based antenna is fabricated and measured in the microwave test bench. The measured results show 3‐dB ARBWs of 350 MHz (2.35–2.7 GHz) and 600 MHz (3.9–4.5 GHz) with LHCP waves. The measured peak gains are 8 dBi in the lower band and 8.5 dBi in the upper band. With small tolerance, the measured results agree with simulations.

This paper presents a single-layer miniaturised wideband transmissive linear-to-circular (LTC) polarisation converter. The unit cell employs symmetrically arranged meandered metallic strips with engineered gaps that govern its resonance behavior. The meandered geometry increases inductance, reduces electrical size, and enhances polarisation conversion efficiency. The metasurface converter achieves wideband LTC conversion for both x- and y-polarised incidences from 5.23 to 12.85GHz, corresponding to an 84.3% fractional bandwidth, with an axial ratio (AR) below 3 dB. It exhibits high angular stability, sustaining performance up to 85° for the transverse electric mode and 60° for the transverse magnetic mode. Within the AR bandwidth, the insertion loss remains low at 1.6-2.69 dB. The metasurface features an ultra-thin profile of 0.0038 λo with compact lateral dimensions of 0.0904 λo × 0.0904 λo, where λo denotes the wavelength at the center frequency (9.04GHz) of the AR bandwidth. Both numerical simulations and experimental measurements validate its effectiveness in delivering wideband, wide-angle stable polarisation conversion with high transmission efficiency.

This paper presents a compact magneto-electric dipole (MED) antenna optimized for wideband circularly polarized (CP) radiation for 5G applications. It incorporates a staircase-shaped electric dipole with trimmed corners to excite orthogonal modes for enhanced CP performance. The proposed single-layer MED antenna achieves a wide-impedance bandwidth ( dB, – GHz) and CP bandwidth ( dB, – GHz) with a compact footprint of . There is a symmetrical radiation pattern with a co-to-cross polarization ratio dB and a stable gain of dBi. An equivalent circuit model is optimized via particle swarm optimization (PSO). The optimized MED antenna is utilized to investigate various CP-MIMO configurations and wideband sequential arrays. Next, a CP-MIMO antenna system is developed, employing polarization diversity in parallel and mirror configurations. Isolation is improved by etching a ground slot between the MED elements, yielding isolation levels of below dB and dB, respectively. Further, a CP-MIMO configuration is designed and evaluated. This arrangement demonstrates an envelope correlation coefficient (ECC) of and a diversity gain of approximately 10 dB across the operating bandwidth. Finally, a sequential array is designed that applies a sequential rotation and phase excitation to MED elements for high-gain CP 5G communications. Here, various array sizes are evaluated, with an MED array providing CP radiation ( dB) from 20 to 30 GHz with enhanced impedance and axial ratio bandwidths and stable gain with a peak value of dBi.