ABSTRACT This work investigates the characteristic mode analysis (CMA) along with the performance evaluation of a circularly polarized Hexa-Slot circular patch antenna integrated with an annular ring construction for millimeter-wave (mmWave) 5G communication. The proposed antenna geometry design combines six symmetrically distributed slots with an annular ring resonator to make a wideband circular polarization and strong mode excitation. CMA performed at 24 GHz, through CMA identifies 10 dominant modes contributing significantly to radiation, with modal significance values close to unity and characteristic angles aligned near 180° that confirming effective modal resonance. The single-element configuration attains a gain of 8 dBi and a radiation efficiency of 93.9%, while the 2 × 2 MIMO arrangement enhances the peak directivity to 10.5 dBi and efficiency to 96.7%. The design is made on a Rogers RT5880 substrate that is 2.8λ 0 × 2.8λ 0 × 0.15λ 0 in size. It has a wide impedance bandwidth from 23.32 GHz to 43.84 GHz and an axial ratio below 3 dB from 27 to 36 GHz. The envelope correlation coefficient (ECC) stays below 0.00133, which means that MIMO diversity is quite good. These properties make the suggested architecture a good choice for mmWave 5G frequency bands like n257, n258, and n260.

ABSTRACT This article introduces a broadband dual-band RF crossover employing coupled transmission lines (CLs) and transmission line stubs. Even-odd mode analysis was initially conducted for the design. Subsequently, simulations were utilized to validate and optimize the theoretical analysis. The proposed crossover is fabricated on a 1.524 mm substrate with a permittivity of 3.55. The low-frequency range starts from 1.48 to 2.08 GHz with a 600 MHz bandwidth (BW). As for the high frequency, it covers the 4.40 to 5.16 GHz frequency range with a BW of 760 MHz. The low-frequency range exhibits an insertion loss of less than 1.2 dB, return loss better than 12 dB, and isolation higher than 13 dB. Whereas the high-frequency range shows an insertion loss of less than 1.5 dB, input return loss better than 13 dB, and isolation more than 14 dB. The size of the crossover is 40 × 42.8 mm2. The experimental results demonstrated excellent agreement with the simulated results. The proposed device is well suited for a wide range of applications, such as 5 G smartphone systems and satellite communication systems.

ABSTRACT In this paper, a single-substrate dual-band transmissive metasurface (MS) for independently adjusting the amplitude and phase is proposed. The metasurface consists of two nested ring resonators (RRs) printed on both sides of the substrate. By tuning the geometries and orientations of the outer and inner RRs, the amplitude and phase in lower and higher bands can be regulated, respectively. Based on this element, a dual-beam transmitarray antenna (TA) employing a single-substrate is constructed. The measured result is shown at 7.5 and 17.2 GHz. At 7.5 GHz, two beams pointing to the (θ 1 = 0°, φ 1 = 90°) and (θ 2 = 30°, φ 2 = 90°) are observed, with a power ratio of P 1: P 2 = 1:1. At 17.2 GHz, two beams are steering to (θ 3 = 25°, φ 3 = 0°) and (θ 4 = 35°, φ 4 = 90°) with the measured gains of 19.56 and 16.57 dBi. In other words, their power ratio is 2:1. The test results are in good agreement with the simulation results. The proposed dual-band transmitted array antenna has a good application in multi-band wireless communication and satellite communication.

ABSTRACT A novel DC and AC hybrid-modulated reconfigurable bandpass filter (BPF) with switchable filter-isolator dual functionality is proposed in this paper. The proposed BPF is realized by interdigital capacitors and microstrip inductors based on the printed circuit board (PCB) technology to achieve low cost and compact size. Besides, it consists of a conventional BPF topology based on LC parallel resonators and capacitive coupled J-inverters, where parallel capacitors are replaced with varactor-based tunable elements, along with integrated DC and AC hybrid bias networks. Next, the proposed BPF dynamically switches between two operational states by integrating spatiotemporal modulation (STM) with varactor-based capacitors: (1) a tunable BPF with DC bias network, offering an operating frequency range from 350 MHz to 400 MHz with a fixed fractional bandwidth of 16.5%, insertion loss below 2 dB, and return loss above 10 dB; (2) a non-reciprocal isolator under AC modulation, achieving 48 dB reverse isolation at 310 MHz. For verification, a prototype for the proposed BPF is designed, simulated, fabricated, and measured. This BPF has a compact size of 0.15 λg ×0.08 λg. The measured results show that the proposed BPF exhibits fixed bandwidth, two operational states, compact size, and low insertion loss.

ABSTRACT In this paper, a dual-level compressive sensing (CS) method is proposed to efficiently solve wideband and wide-angle electromagnetic scattering problems by accelerating the ultra-wideband characteristic basis function method (UCBFM) on two levels. At the first level, a multiple-measurement-vectors (MMV) CS model is established, aiming to reconstruct the entire set of ultra-wideband characteristic basis functions (UCBFs) from a limited number of measurements. As a result, not only is the computation time of UCBFs reduced, but also the number of UCBFs is decreased. At the second level, another MMV-CS model is constructed to solve the induced current at each frequency point, through which not only can the measurement matrix be constructed by filling the impedance matrix with just a few rows, but also the complicated construction process of the reduced matrix is avoided. Numerical simulation results show that the computational efficiency is significantly improved by the proposed method.

ABSTRACT This paper presents a 3D printed lightweight conformal broadband frequency selective surface (FSS)-based electromagnetic absorber. The proposed geometry is designed using a periodic pattern of resistive inks deposited on a perforated dielectric substrate, supported by an air gap and a ground plane, which demonstrates a wide absorption bandwidth ( > 90% absorptivity) of 109.81% covering the X, Ku, and K bands (8.5–29.2 GHz). The topology is polarization-insensitive as well as maintains stable performance under oblique incidence up to 45° for TE mode and 30° for TM mode. An equivalent circuit model and surface current analysis are presented to elucidate the underlying absorption mechanism. A prototype has been developed using a cost-effective 3D printing technology, and its measured responses show excellent agreement with the simulated results. Furthermore, the geometry has been conformed to a cylindrical shape with different curvature angles, and its absorption responses are verified, demonstrating promising real-world applications in radar cross-section (RCS) reduction and electromagnetic shielding.

ABSTRACT Reflection paths present in folded transmitarray antennas (FTAs) can cause feed blockage and lead to increased return loss and gain degradation. In this letter, a method of loading a metal rectangular pyramid in FTA is proposed. This method changes the reflection path of electromagnetic waves and reduces electromagnetic waves reflected to the source. Based on this method, the simulated return loss is reduced by an average of 2.0 dB, and the simulated gain is improved by an average of 0.6 dB in the frequency range of 12–15 GHz. Furthermore, the compensation phase of FTA is optimized by an electric field sampling method to improve gain. The fabricated FTA achieves a height-to-diameter ratio of 0.21, a −1.5 dB gain bandwidth of 17.6%, a peak gain of 26 dBi, and a maximum aperture efficiency of 51.7%.

ABSTRACT This paper proposes a slot-coupled feeding patch antenna which works at TM 30 mode with reshaped radiation pattern. By analyzing the surface current distribution, it was found that the generation of sidelobes is closely related to the out-of-phase current region. To reduce the sidelobes, firstly, the size of the out-of-phase current region was symmetrically reduced along the X-axis. Secondly, 14 short-circuit vias were symmetrically loaded along the Y-axis. The re-distribution of surface currents effectively suppressed the sidelobes. The measurement results show that the proposed patch antenna improves the radiation pattern and reduces energy loss in unwanted directions. Ultimately, the sidelobe level of the antenna is significantly reduced to about −17 dB.

ABSTRACT This paper proposes a novel method for enhancing the half-power beamwidth (HPBW) of an end-fire circularly polarized (CP) terminal antenna, whereby the end-fire CP antenna is designed for 6 G satellite communication. First, the CP property is realized by allocating the resonances of both In-phase mode (IM) and out-of-phase mode (OM) based on the theory of characteristic mode (TCM). The HPBW of OM and IM is enhanced by layering the radiator, which introduces interlayer currents for OM and substrate thickness for IM. Besides, by using the stepped ground edge to regulate field distribution in the radiator, the HPBW is further broadened. The proposed wide HPBW CP antenna is manufactured and measured to validate the novel design concept. The measured results show that −6 dB impedance bandwidth is 2.45 ~ 2.56 GHz, and 3 dB axial ratio (AR) bandwidth is 2.48 ~ 2.50 GHz. The measured HPBW in the xoy and yoz planes are 76° and 94°, respectively. The high normalized comprehensive coefficient (NCC), considering AR bandwidth, Gain, HPBW, and antenna size, proves that the proposed antenna is especially suitable for 6 G terminal satellite communication.

ABSTRACT A compact, single-layer reconfigurable leaky-wave antenna capable of both linear polarization (LP) and circular polarization (CP) with beam scanning is presented in this study. The antenna utilizes copper strips inserted between shorted stubs and a patch to achieve LP and CP states. An H-shaped arrangement of horizontal and vertical slots enables wideband CRLH characteristics, supporting dual-polarization operation from 10 GHz to 20 GHz for LP state and from 12.8 GHz to 20 GHz for CP state. The dimensions of the proposed antenna are relatively small, with a size of (3.25 × 0.4 × 0.07) λ3 and provided continuous beam scanning across a range of −70° to 37° for CP states with the maximum gain of 10.37 dB. However, LP state is offered from −69° to 61° with the peak gain of 10.42 dB. The antenna exhibits an axial ratio below 3 dB within the CP bandwidth and efficiency exceeding 90% for both LP and CP states.