This paper presents a high-performance 4 × 1 dual-polarized square-ring patch antenna array operating in the Ku-band for Ground-Based Synthetic Aperture Radar (GB-SAR) applications, with a compact size of 90mm × 30mm. The proposed design achieves compact integration by implementing dual-port polarization on a single substrate, enabling significant size reduction while effectively controlling mutual coupling and suppressing surface-wave propagation. To further enhance isolation and radiation performance, metamaterial unit cells (MTMLs) are introduced between adjacent elements to mitigate surface waves, while strategically positioned metallic vias improve port isolation. The antenna exhibits a wide impedance bandwidth from 16.3 to 18.5GHz; however, the performance is specifically optimized within the 16.8-17GHz band of interest for GB-SAR applications, where it achieves mutual coupling below - 12.5 dB, radiation efficiency exceeding 93%, and ECC values below 0.006. A two-layers dielectric superstrate are incorporated to improve radiation characteristics, resulting in a peak gain of 12 dBi, sidelobe suppression of - 16.8 dB, and a half-power beamwidth of 38.3°. These additional layers enhance gain and beam focusing while also serving as a protective shield against harsh automotive environmental conditions such as temperature variations, vibration, moisture, and mechanical stress. This protective layer ensures mechanical durability and stable RF performance without compromising radiation efficiency. The antenna array is fabricated and experimentally validated, with measured results showing strong agreement with simulations. The proposed configuration provides a compact, low-loss, high-efficiency, and environmentally effective solution suitable for advanced Ku-band radar applications.

ABSTRACT A monolithically integrated on-chip THz emitter is demonstrated by directly bonding an InGaAs/InP uni-traveling-carrier photodiode (UTC-PD) onto a silicon carbide (SiC) substrate and coupling it to a series-fed microstrip patch array (MPA) antenna. The device is fabricated using an adhesive-free flip-wafer bonding technique that transfers the InGaAs/InP epitaxial layers of the UTC-PD onto the SiC platform, overcoming the lattice and thermal mismatch limitations. The SiC substrate provides both C-band optical transparency and high thermal conductivity, allowing efficient backside illumination and stable high-power operation of the UTC-PD. The UTC-PD performs optical heterodyne mixing of two laser tones to generate a tunable signal in the 0.6 THz band, which is guided and radiated through a weakly leaky traveling-wave MPA array. The eight-element MPA array produces a directional fan-beam with a mainlobe angle of 14°, exhibiting a passive beam squint of about 10° as the beat frequency varies from 0.60 to 0.62 THz. The total radiated power at 0.6 THz is estimated to be 22 µW at a photocurrent of 15 mA under a −1 V bias. This monolithic SiC-based integration enables on-chip optical-to-THz conversion and free-space THz radiation, offering a compact platform for beam-scannable THz transmitters in next-generation photonic THz wireless systems.

Reliable and fast radiation pattern prediction is critical for large-scale tightly coupled linear antenna arrays. Strong mutual coupling and finite-array edge effects limit the accuracy of conventional array factor methods, while full-wave simulations become computationally prohibitive for large arrays. To address this issue, a fast and efficient radiation pattern prediction method (FERPP) is proposed. For central elements, the far-field response is obtained from a calibrated reference array and extended through position-dependent phase compensation. For edge elements, responses are extracted from independent local full-wave simulations. All element responses are assembled into a global far-field response matrix, enabling direct radiation pattern synthesis using the extended method of maximum power transmission efficiency. Simulation results obtained with a 1024-element linear microstrip patch antenna array operating at 3.5 GHz, with small inter-element spacing, demonstrate close agreement with full-wave simulations. For a broadside single-beam case, the predicted peak gain is 29.10 dBi, compared with 29.02 dBi from full-wave simulation. For a scanned beam at 30°, the predicted peak gain is 28.22 dBi, while the full-wave result is 28.99 dBi. For an equal-weight three-beam configuration at −30°, 0°, and 30°, the proposed method yields a peak gain of 23.87 dBi, compared with 24.21 dBi from full-wave simulation. In terms of computational efficiency, the proposed method requires only about 1.8% of the computational time required for a full-wave simulation. These results demonstrate that the proposed FERPP method provides a practical and efficient solution for radiation pattern prediction and beamforming analysis of large-scale tightly coupled linear antenna arrays.

This letter presents a Ku-band 2 × 2 patch array antenna that supports dual-polarization operation using a simple cooperative feed network. Depending on the selected input port of the proposed simple feed network, the 2 × 2 array antenna radiates either vertically or horizontally polarized waves. The proposed feed structure consists of two serially connected power dividers placed on the same geometrical plane, enabling dual-polarization without additional multilayer routing. The microstrip line-based feed network also enables a 180° reversed placement of the radiating elements thereby improving the cross-polarization ratio of the proposed array antenna, achieving better than 30 dB across the operating band. The fabricated antenna, designed for a center frequency of 14.9 GHz with a 6.8% fractional bandwidth, demonstrates a realized gain higher than 10 dB for both polarization modes. Measurement results in terms of the input impedance bandwidth, isolation, gain, and cross-polarization ratio are in good agreement with simulation results.

Abstract This work presents the design, optimization, fabrication, and measurement of a $$2 \times 2$$ 2 × 2 circularly polarized microstrip patch antenna array intended as an elementary radiator for 76–77 GHz MIMO radar prototype validation. Circular polarization (CP) is achieved using a sequential rotation phase technique with four linearly polarized patches arranged on a square grid and excited with $$90^\circ $$ 90 ∘ progressive phase shifts. Aperture-coupled feeding is employed to isolate the radiating patches from the feed network, enhancing pattern stability and impedance bandwidth. A series–parallel microstrip network is synthesized to deliver equal power to all elements with the required phase progression, using a $$32.5~\Omega $$ 32.5 Ω quarter-wave transformer for $$50~\Omega $$ 50 Ω input matching. The antenna is implemented on Rogers 3003 substrates with truncated-corner patches to improve axial ratio and matching. Measurements using a vector network analyzer (VNA) with mmWave frequency converters confirm a $$-10$$ - 10 dB impedance bandwidth of 10.9 GHz, good matching at 76.5 GHz ( $$S_{11} \approx -23$$ S 11 ≈ - 23 dB), peak realized gain of 10.9 dBi, and axial ratio below 3 dB over 74–77.5 GHz at boresight. Radiation patterns exhibit broadside coverage with $$\sim 40^\circ $$ ∼ 40 ∘ half-power beamwidth in both principal planes, suitable for imaging radar. Sensitivity analysis shows robust performance against feed-line width tolerances and $$\pm 0.1$$ ± 0.1 variations in substrate permittivity, with maintained gain and circular polarization across the target band. The results validate the proposed element as a compact, peak realized gain of 10.9 dBi at 76.5 GHz, as a compact CP radiator for MIMO antenna array prototype measurements and anechoic chamber validation.

Abstract Wireless sensor networks are increasingly deployed in Internet of Things (IoT) applications, demanding self‐powered solutions to overcome the limitations of conventional batteries. Radio frequency energy harvesting (RFEH) offers a practical means to scavenge ambient RF power from ubiquitous sources such as mobile base stations, enabling sustainable operation of remote or inaccessible devices. This work presents a complete RFEH system integrating a microstrip patch antenna array, impedance matching network, and rectifier circuit, optimized for the 2.1 GHz 3G downlink band. Full‐wave simulations predict a resonance at 2.1 GHz, realized gain of 5.1 dBi, 60 MHz bandwidth, and half‐power beamwidth of . Circuit‐level simulations indicate a rectifier DC output of 3.575 V under nominal excitation. Experimental measurements in an anechoic chamber confirm the predicted antenna performance and demonstrate a 706 m output under ambient 3G exposure, sufficient to illuminate an LED load. The discrepancy between simulation and measurement is attributed to lower ambient power levels, propagation losses, and rectifier nonlinearity. In contrast to prior RFEH studies centered on single‐element rectennas, multi‐band harvesting circuits, or controlled‐source demonstrations, the present work emphasizes a complete 2.1 GHz UMTS harvesting prototype based on a compact patch array. The measured antenna performance and the ambient 3G experiment, which produced 706 m and illuminated an LED, confirm the feasibility of system‐level RFEH for low‐power IoT nodes without a dedicated RF power transmitter.

This work presents a novel T-shaped transmission line structure designed for physical size reduction. It is analytically demonstrated that, for a specific operation frequency, the proposed structure behaves exactly like a λ/4 transmission line. Furthermore, the open-ended part of the structure can be tuned for controlled frequency rejection, thus exhibiting a built-in low-pass filtering behavior. The applicability of the network is illustrated through a practical design of the miniaturized 4 × 4 Butler Matrix (BM). As a result, the obtained BM is reduced in size by 65% compared to the classic implementation and is also capable of low-pass filtering. The theoretical and simulated return loss, insertion loss, and phase difference are in close agreement with the corresponding measured values, which proves the effectiveness of the proposed design. The designed BM has been further investigated for practical applicability as a beamforming network using patch array antennas in a simulation environment. The designed antenna array system achieves a maximum gain of 10 dBi in boresight with a possible output steering angle of ±40°.

The increasing demand for integrated communication and sensing has led to the development of Joint Communication and Sensing (JCAS) systems. However, strong self-interference (SI) between transmitting (TX) and receiving (RX) antennas remains a major obstacle, significantly degrading system performance in compact MIMO arrays. Traditional signal-processing-based cancellation methods face limitations in wideband scenarios due to high complexity and potential signal distortion. In this work, a novel metasurface-assisted decoupling structure is presented. The metasurface based on modified split-ring resonators (MSRRs) can suppress surface currents and reduce the coupling between TX and RX arrays. To further enhance isolation and reduce front-end self-interference in sensing-centric full-duplex JCAS, a multi-frequency null-space projection (NSP) beamforming algorithm is integrated with the antenna array design, forming a hardware-algorithm co-optimization framework. As proof of concept, a 2 × 2 patch antenna array incorporating the proposed metasurface operating in the 9-10 GHz band has been designed, fabricated, and characterized. The measurement results validate effectiveness. The findings suggest that the proposed decoupling approach offers a promising solution for enhancing electromagnetic isolation and overall system performance in next-generation JCAS applications such as intelligent transportation and indoor wireless sensing.

ABSTRACT This paper presents a linearly polarized, ground‐defected 2 × 2 rectangular patch antenna array with microstrip inset feeding. A simple structure is realized by placing the rectangular patches and the feeding network on the same layer. The proposed microstrip inset‐fed configuration facilitates proper impedance matching and easy array formation. This work provides an in‐depth examination of the antenna array's characteristics and performance. The antenna array is fabricated on an RT Duroid substrate and integrates a dumbbell‐shaped defected ground structure (DGS) in a triangular form with four radiating elements. The primary objective of incorporating the DGS is to improve the return loss. The proposed compact antenna array has overall dimensions of 106.3 × 112 × 1.575 mm 3 and is intended for wireless communication applications. The designed array operates over the desired frequency band of 3.52–3.61 GHz, achieving a reflection coefficient better than −10 dB and an impedance bandwidth of 25.09%. The antenna exhibits stable radiation characteristics with a peak gain of approximately 13.08 dBi across the operating band. The array is analyzed using HFSS, and fabrication and measurements are carried out to validate the simulated results. The measured outcomes show good agreement with the simulations, demonstrating the suitability of the proposed antenna for 5G midband mobile broadband wireless communication applications.

ABSTRACT This paper presents the design and implementation of a high‐gain 1 × 2 active microstrip patch antenna array for sub‐6‐GHz 5G wireless communication applications. Three structures set apart the modified conventional patch design: an octagonal conductive patch embedded in a square frame and a circular ring. This patch shows improvements in critical parameters such as radiation efficiency, gain, impedance matching, directivity, bandwidth, and half‐power beamwidth. With a bandwidth of 200 MHz, an HPBW of 44°, and a radiation efficiency of 82.3%, the measured results show that the suggested passive antenna array may achieve maximum gain and directivity of 6.1 and 7.27 dBi, respectively. The antenna array combines a new coupling‐loss compensation method, an RF amplifier, and a redesigned circular patch construction. With passive components, such as an RF splitter and an RF combiner, the two antenna elements are connected to a common amplifier via 50‐Ω arc transmission coupling lines. The methodology used in its development includes compact antenna geometry, prototype construction of a low‐loss substrate, and experimental verification. Improvements in impedance matching, bandwidth, gain, and radiation efficiency can be achieved by combining amplifier coupling with structural optimization. With a maximum gain of 18.15 dBi, directivity of 19.2 dBi, bandwidth of 320 MHz, HPBW of 73°, and radiation efficiency of 94.7%, the experimental findings show a 99.9% increase in matching efficiency. The excellent radiation characteristics of the active antenna array establish an efficient pathway for advancing fifth‐generation wireless communication systems, such as those used in tablets.

Abstract This work presents the design, simulation, and fabrication of microstrip patch antenna arrays for 24 GHz automotive radar applications. Beginning with a single-element patch, the design was progressively extended to 1 × 2, 2 × 2, 2 × 4, and 4 × 4 configurations to enhance key parameters such as gain, impedance matching, and directivity. The single patch achieves a moderate gain of 5.62 dB, while the final 4 × 4 array reaches a high realized peak gain of 19.1 dB, a deep impedance matching level (S11 = −55 dB), a bandwidth of 3.1% and a radiation efficiency of approximately 85%. The antennas are implemented on a Rogers RO3006 substrate ( ε r = 6.15, h = 0.254 mm) and designed using CST Studio Suite. Fabricated prototypes are experimentally characterized using a vector network analyzer, and the measured results show good agreement with simulations, validating the proposed design approach.The originality of this work lies in the combination of a progressive array design strategy, a simple planar architecture, and a complete experimental validation, providing a practical and reproducible solution that achieves an effective trade-off between high gain, compact size, and fabrication simplicity, making the proposed antenna arrays well suited for short-range 24 GHz automotive radar systems.

Non-contact monitoring of human vital signs using microwave radar has attracted increasing attention due to its capability to operate unobtrusively and through clothing or light obstacles. In vector network analyzer (VNA)-based radar systems, vital signs can be extracted from phase variations in the forward transmission coefficient , whose sensitivity strongly depends on the electromagnetic performance of the antenna system. This work presents the design, optimization, fabrication, and experimental validation of a high-gain 12 GHz 4 × 4 microstrip patch antenna array specifically developed for phase-based vital signs monitoring. The antenna array was progressively optimized through coaxial feeding, slot-based impedance control, stepped transmission line matching, and mitered bends, achieving a simulated gain of 17.8 dBi, a measured gain of 17.06 dBi, a reflection coefficient of −26 dB at 12 GHz, and a total efficiency close to 74%. The antenna performance was experimentally validated in an anechoic chamber and subsequently integrated into a continuous-wave VNA-based radar system. Comparative measurements were conducted against a commercial biconical antenna, a single patch radiator, and an MIMO antenna under identical conditions. Results demonstrate that while respiration can be detected with moderate-gain antennas, reliable heartbeat detection requires high-gain, narrow-beam antennas to enhance phase sensitivity and suppress environmental clutter. The proposed array significantly improves pulse detectability in the (1–1.5) Hz band without relying on advanced signal processing. These findings highlight the critical role of antenna design in -based biomedical radar systems and provide practical design guidelines for high-sensitivity non-contact vital signs monitoring.

This paper introduces a broadband 45° slant dual-polarized series-fed microstrip patch antenna array with low VSWR, based on magnetic current feeding technology. Conductive strips connect the radiating elements, minimizing out-of-phase currents to improve broadside directivity. A ring resonator is introduced by slotting the microstrip line, adding new resonant frequency bands, while the feed network design enables the formation of radiation modes similar to a magnetic current-fed array. The series-fed array’s wide bandwidth is achieved by combining the fundamental mode of side-shorted microstrip patch antennas with additional modes from the feed structure. A fabricated three-element linear array with central feeding demonstrated an impedance bandwidth of 3–6 GHz (67%) and a minimumVSWR of 1.007, offering simple feeding and low loss. This design is well-suited for applications requiring high directivity and dual polarization, such as 5G communication, drones, radar systems, satellite communications, and IoT networks.

Abstract In this paper, a low-profile and wideband patch antenna and its 2 × 3 antenna array are proposed to be suitable for X/Ku partial band applications. A bowtie slot is incorporated into the radiating patch to broaden the operating bandwidth. This configuration combines the modes of the rectangular patch with an additional mode from the bowtie structure, exciting a triple-resonant response. Based on the proposed design, a linearly arranged antenna array was fabricated and tested to further enhance the gain for long-distance communication, while array miniaturization was achieved by integrating U-shaped slots into the gaps between the antenna elements. The designed array size is 1.99 λ 0 × 0.83 λ 0 × 0.06 λ 0 (where λ 0 is the free-space wavelength at the center frequency), the measured results indicate a 37.15% impedance bandwidth, spanning a frequency range of 9.6 GHz–13.98 GHz, while the peak gain is improved to the range of 10.47–12.06 dBi.

In this letter, a dual-band, dual-beam shared-aperture antenna combining a variable inclination continuous transverse stub (VICTS) antenna and a patch antenna array (PAA) is proposed for simultaneous connections with two satellites. The VICTS generates a Ku-band scanning beam, whereas the PAA provides a K-band fixed-direction beam. By mounting the PAA on the surface of the radiating layer of the VICTS antenna, a shared-aperture configuration is achieved. The feeding network of the PAA is specially designed, and long slots are etched on both the substrate and the ground plane to effectively mitigate the interference. To verify the proposed design, a prototype was fabricated and measured, showing good agreement between the measured and simulated results.

In this work, a phaseless equivalent source reconstruction method based on a two-stage physics-informed neural network (PINN) is proposed. Unlike conventional dipole-based equivalent source artificial neural networks that rely on Green's functions, the proposed approach is capable of recovering the phase information of the equivalent sources while simultaneously predicting both near-field magnitude and phase. By leveraging the physical mapping relationship between equivalent sources and near-field magnitudes, the proposed framework enables the joint reconstruction of the magnitude and phase of the equivalent sources. Moreover, through a phase-information constraint, it effectively alleviates the multi-solution problem inherent in phase retrieval. Compared with traditional iterative phase-retrieval algorithm, the proposed method exhibits superior performance in both magnitude prediction accuracy and phase recovery capability. Two numerical examples are provided to validate the effectiveness of the proposed approach. Simulation results show that for a 2×2 patch antenna array and a microstrip line on glass-base substrate, the method achieves magnitude prediction errors of 0.7% and 2%, respectively, while recovering relatively accurate phase distributions. These results indicate that the proposed method is well suited for near-field measurement, as well as antenna analysis and design applications.

This paper proposes a fast phaseless inversion method based on characteristic mode analysis (CMA) for nearfield measurement systems. Targeting applications such as antenna characterization and EMC diagnostics, the method reconstructs mode currents on an equivalent surface by combining surface integral equations with characteristic mode solutions. It replaces the basis functions used in traditional techniques, significantly reducing the number of unknowns. Crucially, by utilizing magnitude-only data, this approach eliminates the need for complex phase calibration, thereby enhancing measurement robustness and quality in practical environments. To validate the effectiveness, near-field magnitude data are collected from simulations of a filtering magneto-electric dipole antenna, a dualpolarized dipole filtenna, and a planar inverted-F antenna, as well as measurements of a patch antenna and a patch antenna array. The results show that the proposed method is approximately 100 times faster than traditional methods with a relative data error below 1%, demonstrating its potential for high-efficiency and calibration-free radiation prediction.

Graphene-enhanced printed star-shaped patch array antenna with high gain and multi-resonant characteristics for advanced THz 6G wireless systems

In this paper, we propose a novel dual-band metasurface (MS) designed to enhance 5 G mm-wave antenna performance when integrated with a smartphone glass cover. Unlike prior works that focus on either mm-wave or sub-6 GHz bands, the proposed MS supports both, addressing a key gap in the literature. Through simulations and measurement results, we demonstrate that the MS significantly improves antenna gain and mitigates radiation pattern distortions caused by superstrate loading. A 1× 4 mm-wave patch antenna array operating in the 24–27 GHz band is fabricated and evaluated with and without the MS-loaded glass cover, confirming the performance enhancement. In addition, the integration of a sub-6 GHz antenna on the same substrate verifies multi-band compatibility relevant to practical 5 G smartphones.

This work presents an integrated design framework for compact series-fed microstrip patch antenna arrays (SF-MSPAAs) enabling scalable sub-arrays for planar and MIMO configurations. In the proposed framework, an artificial neural network (ANN) based surrogate model is utilized as a computational accelerator to eliminate repeated full-wave simulations, while the subsequent array design is carried out using deterministic, physics-based electromagnetic design procedures. Phase equalization is achieved through S-parameter based optimization of feed-line lengths using sequential nonlinear programming (SNLP), resulting in quasiuniform inter-element spacing without additional phase compensation structures. The desired sidelobe level (SLL) is realized via width-scaled Taylor amplitude tapering, and robust input matching is ensured using an adaptive two-section microstrip impedance transformer. Unlike conventional approaches that primarily optimize one or few performance metrics aggressively, for example, maximum sidelobe suppression, the proposed framework provides specification-driven control over key parameters such as operating frequency, SLL, gain and array footprint. This allows designs to precisely meet application-specific requirements within a structured and computationally efficient workflow. A five element prototype is designed using the proposed framework to meet an application requirement of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SLL</i> ≤ −15dB and a gain of ≥ 10 dBi operating at 6.4 GHz. The designed prototype is fabricated and experimentally validated. The measured results demonstrated a gain of ∼12 dBi, 75% radiation efficiency, 1.6% bandwidth, −18 dB SLL and return loss better than 35 dB across the bandwidth, showing close agreement with simulations.