Zhan Zhang

This paper presents a low-profile compact cavity frequency scanning antenna that utilizes coupled characteristic modes to enable wide-angle beam scanning. The core advantage of this design lies in its utilization of characteristic mode analysis (CMA) to distinctly identify and excite both E-dipole and M-dipole modes within the structure. By integrating these modes into adjacent frequency bands and leveraging their coupling relationships and superposition, the array achieves continuous cross-quadrant scanning. By controlling the mode spectrum distribution through adjustable slots and coupling windows, the proposed antenna realizes a $103^{\circ }$ scanning range ($-60^{\circ }$ to $+43^{\circ }$) within a 7% bandwidth, a peak gain of 9.26 dBi, radiation efficiency of 77.6%, and a scanning rate of $15^{\circ }/\%$. This design overcomes the quadrant limitation of single-mode arrays and avoids high complexity, demonstrating the superiority of CMA for wide-angle frequency scanning antennas.

This paper proposes two types of phase gradient metasurfaces, named as non-centrosymmetric beam metasurface (NCSM) and centrosymmetric beam metasurface (CSM), which exhibit remarkable performance in reducing radar cross-section (RCS). For the NCSM, when a circularly polarized (CP) wave is incident, it scatters incident wave into 45 beams accompanied by polarization conversion. When a linearly polarized (LP) wave is incident, the NCSM can generate total of 90 beams, including 45 left-circularly polarized (LCP) beams and 45 right-circularly polarized (RCP) beams. In contrast, when either CP or LP waves are incident on a CSM, it scatters incident wave into 36 beams and simultaneously achieves polarization conversion. The NCSM achieves over 10 dB multi-polarization RCS reduction across frequency range from 14.3 GHz to 33.4 GHz (80.1% relative bandwidth). Similarly, the CSM achieves over 10 dB multi-polarization RCS reduction within a frequency range from 14.9 GHz to 33.5 GHz (76.8% relative bandwidth). The proposed metasurfaces provide an efficient way to achieve multi-polarization RCS reduction, which can be adapted to the complex radar detection environment.

This paper presents a novel dual‐band circularly polarised (CP) filtering antenna designed using electromagnetic coupling theory. First, characteristic mode analysis (CMA) is employed to verify that introducing different types of coupling between two adjacent patches significantly modifies the resonant frequencies of the inherent modes. Consequently, by applying specific coupling configurations between the patches, a desired modal distribution is achieved, enabling dual‐band CP filtering performance across the two operational frequency bands. Subsequently, the analysis of the magnetic field distributions of the characteristic modes leads to the selection of slot‐coupled feeding as the optimal excitation method to effectively activate the desired modes and achieve the intended functionality. Finally, to further enhance the filtering response without degrading the CP performance within the passbands, slots and open‐circuit stubs are integrated into the feedline. This modification offers additional control over out‐of‐band suppression and improves selectivity. Following fabrication and measurement, the proposed antenna exhibits dual‐band impedance bandwidths of 3.3–3.67 GHz (10.6%) and 4.74–5.28 GHz (10.7%). The corresponding axial ratio (AR) bandwidths are 1.4% (3.47–3.52 GHz) and 1.2% (4.86–4.92 GHz), respectively. These results validate the effectiveness of the synergistic integration between the guided patch coupling mechanism and the parasitic feedline elements. The proposed design approach enables the realisation of the multifunctional antenna structure, achieving dual‐band operation, CP and intrinsic filtering characteristics within a single structure.

In this letter, a broadband metasurface-loaded periodic leaky-wave antenna (PLWA) based on substrate integrated coaxial line (SICL) is proposed for frequency scanning applications in millimeter-wave (mmWave) band. The -1st spatial harmonic radiation is excited and a wide operating band covering from 20 to 40 GHz is obtained. The open stopband (OSB) is effectively suppressed by utilizing wide dumbbell-shaped slots, so the beam can scan continuously from backward to forward directions. Moreover, a metasurface (MTS) is loaded on the antenna aperture to enhance the radiation performance. The antenna is fabricated, and the measured results show that the proposed antenna has the capability of continuous frequency scanning and the peak gain can reach 16.28 dBi. By loading the MTS, the gain and radiation efficiency is improved effectively. The method proposed in this paper can be used to design high performance LWAs with conventional dimensions.

During the evolution from 5G to 6G, integrated space-air-ground communication has become a hotspot for research. Among them, unmanned aerial vehicle (UAV) communication and millimeter-wave (mmW) technology play important roles. UAV communication requires high-gain, wide-angle coverage, and flexible beam-steering antenna arrays. In this paper, we propose a compact antenna array with wide coverage and beam steering capability for mmW applications. The array is composed of three layers and fed through substrate integrated waveguide (SIW) with three ports. The antenna features a simple, horizontally symmetrical structure. By independently exciting each of the three ports, and combinations where port 2 is excited simultaneously with port 1 or port 3, the antenna generates currents that complement equivalent magnetic currents to produce beams pointing in different directions. The wide beams of the antenna can steer and cover a total range from -${60}^{\circ }$ to ${240}^{\circ }$ across five states. Based on this design, a four-element array is fabricated and tested. Measurement results demonstrate the gains of 10.03, 10.8, and 10.5 dBi within the operational frequency range (23.7-28 GHz), with a radiation efficiency of 87.3%. The proposed antenna features a low-profile and compact structure, achieving a coverage range of approximately 300 degrees. It is highly suitable for UAVs, and small mobile devices when integrated with an integrated chip circuit. Additionally, if matched with a phase shifter, the antenna can achieve two-dimensional scanning capability.

Based on the characteristic mode analysis (CMA), our earlier study [1] introduced a theoretical method for designing frequency-scanning antennas using coupled patch antenna arrays: adjacent mode pair can be superimposed under specific conditions to achieve a high-gain, low-sidelobe beam whose direction scans with frequency. As an extended study of the above method, to improve the scanning rate and range, the design of a tightly coupled SIW-based slot array is proposed in this paper. With the aid of CMA, this paper provides an effective way of controlling the spectral characteristics of certain modes by adjusting the window size between cavities, which in turn enhances the scanning rate and scanning range. Simulation and experimental results validate the proposed approach. Over the sub-6 GHz band from 5.19 to 5.39 GHz, the proposed antenna has achieved a scanning range from $15^{\circ }$ to $75^{\circ }$ , and a scanning rate of 15.9%. It maintains an average gain of 9.5 dBi with a radiation efficiency of 79%.

A compact broadband loop complementary source antenna with four switchable tilted beams is proposed in this paper. The antenna is constructed by adding vertical quarter wavelength shorting pins to a horizontal four-leaf-clover-shaped loop patch. A packaged microstrip line structure is developed to excite different ports of the antenna. The complementary antenna features a wide impedance bandwidth of 56.5%, covering from 6.07 to 10.85 GHz, and the profile height of the proposed structure is 0.165λ0 at the operating frequency of 8.46 GHz. In addition to its broadband and tilted radiation performances, the antenna can generate four switchable tilted beams in different directions to cover the entire hemispheric space. Measured results show that a gain of 7.89 dBi is achieved. Compared to available works, the proposed antenna demonstrates a notable bandwidth improvement, making it a preferable candidate for future intelligent wireless communication.

A co-design approach is proposed in this communication for an efficient design of frequency scanning coupled-patch arrays (CPAs) with wide scanning range and high scanning rate. It combines characteristic mode analysis (CMA) and coupling matrix analysis, where the former is employed for radiation pattern synthesis while the latter tunes the feeding reflection and mode excitation based on a coupled-resonator network model. With this systematic approach, it becomes efficient to control both beam scanning properties and feeding reflection. 3 ^rd -order and 6 ^th -order design examples are provided to validate the proposed method. The 6 ^th -order CPA achieves a wide scanning range of 73° (from -45° to 28° across broadside) and a high scanning rate of 26.1°/1%. Both are higher than other reported CPAs.

A novel electrically controlled leaky-wave antenna (LWA) with capability of fixed frequency beamforming scanning is proposed in this communication. The antenna is designed on substrate-integrated waveguide (SIW), and the slot period of the antenna can be changed electronically by switching between “ON” and “OFF” states of PIN diodes connected to two edges of slots. Based on the reconfigurable property of slot period, the phase constant of the -1th spatial harmonic can be modified, thus the beam direction of antenna can be changed and continuous beam scanning can be realized. For specific applications in linear confined space, scanning beam with almost the same field strengths along a straight path is commonly required. Therefore, a hybrid coding method is proposed in this paper and applied to a 2×1 antenna array to realize bilateral beamforming scanning. Simulation and measurement results show that a wide beam scanning range of 99° at 5.98 GHz can be obtained in both cases of continuous beam scanning and beamforming scanning. The proposed LWA array is suitable for the future application of smart mobile communication.