A wideband high-efficiency millimeter-wave (mm-wave) circularly polarized (CP) array which is constituted by novel planar SIW-fed S-dipoles is presented in this paper. The proposed mm-wave CP S-dipole consists of two rotational symmetric curved arms and is fed differentially through aperture coupling, which features simple configu-ration and excellent performance. Detailed analysis is given to explain the operating principles of this element. It is noted that superior element performance including a wide impedance bandwidth of 43%, a wide 3-dB axial ratio (AR) bandwidth of 36% and 1-dB gain bandwidth of 38% is achieved by the planar SIW-fed S-dipole. By feeding 64 in-phase S-dipole elements through a full-corporate SIW feeding network, a planar wideband highly efficient mm-wave 8 × 8 CP array is realized. To verify the design concept, a prototype operating at Ka-band is fabricated and measured. Measurement results indicate that the proposed array achieves a wide overlapped bandwidth of 27.6%, a high antenna gain of 25.2 dBic and a high aperture efficiency of 89.9%. Attributed to the planar and robust array structure as well as its excellent performance, the presented array is a good candidate for various mm-wave applications.

A novel ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is presented in this paper. This reflectarray antenna consists of a wideband feed and a wideband reflecting surface. The feed is a log-periodic dipole array antenna. The reflecting surface consists of 26×11 unit cells. Each cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is 8 mm, which is about 1/10 wavelength at the lowest operating frequency. By combining the advantages of reflectarray antennas and those of tightly coupled array antennas, the proposed TCDR antenna achieves ultra-wide bandwidth with reduced complexity and fabrication cost. A method to minimize the phase errors of the wideband reflectarray is also developed and the concept of equivalent distance delay is introduced to design the unit cell elements. To verify the design concept, a prototype operating from 3.4 to 10.6 GHz is simulated and fabricated. Good agreement between simulated and measured results is observed. Within the designed frequency band, the radiation pattern of the TCDR antenna is stable and the main beam of the antenna is not distorted or split. The side lobe levels of the radiation patterns are below -11.7 dB in the entire operating band. It is the first time a tightly coupled reflectarray is reported.

In order to design the wideband patch antenna, a hybrid method based on the artificial neural network (ANN) and the simulated annealing (SA) algorithm is proposed in this paper. The ANN is employed to describe the nonlinear relationship between the geometric parameters and the S-parameters of the antenna. The ANN is trained by the dataset got by the High Frequency Structure Simulator (HFSS). More importantly, the dataset is divided into three groups according to their own characteristics so that the ANN can be trained faster and better. The SA is employed to broaden the bandwidth of the patch antenna with the required center frequency. Then three wideband patch antennas with different center frequencies are designed to demonstrate the feasibility of the proposed method. Several slots are added to the patch to achieve the wide bandwidth. The results prove that the proposed method can obtain the wideband patch antenna quickly and efficiently.

This paper presents a single-layer circularly polarized reflectarray which achieves large bandwidth (BW) in terms of axial ratio (AR), gain, aperture efficiency (AE) and radiation pattern. By using a novel wideband S-shaped phasing element, an offset-fed reflectarray with 20° offset beam is designed based on the element angular rotation method. Theoretical analysis is given to analyze the effect of angular rotated elements on the performance of the reflectarray, which indicates that the AR BW of the reflectarray can exceed the AR BW of the feed horn. Furthermore, the influence of the differential spatial phase delay is analyzed quantitatively, and the performance of S-elementbased reflectarrays with different aperture sizes are investigated and discussed. To verify these concepts, a 180 mm × 180 mm prototype with 15×15 elements is fabricated and measured. The measured results confirm that the proposed reflectarray achieves a 68.5% 3-dB AR BW (7 to 14.3 GHz) and a 47.8% 3-dB gain BW (8.6 to 14 GHz). Moreover, the AE is larger than 50% in a 33% BW and larger than 30% in a 64% BW.

A high roll-off, third-order frequency selective surface (FSS) with quasi-elliptic bandpass response is presented. It is based on substrate integrated waveguide technology. Its unit cell includes three cavities that support at the TE ₁₀₁ mode. Interactions of resonators are dominated by magnetic couplings. The coupling matrix is analyzed and used to design FSS. Guidelines for a coupling-matrix-based FSS design are given. Transmission zeros realized close to the lower and upper narrow passband lead to high roll-off characteristics. In addition, a cross-polarization feature is easily achieved. Finally, a prototype is designed and fabricated to validate the proposed structure. A stable frequency response in passband has been obtained with an oblique incidence of 40° for TE polarization. Good agreement between the simulated and measured results verifies the design concept of bandpass FSS.

Ideally, the orthogonal port can be effective to eliminate the TE₁₀₂/TE₂₀₁ spurious passband of a fundamental substrate integrated waveguide (SIW) filter using the orthogonality. However, it was not feasible in practical applications because the orthogonality of TE₁₀₂/TE₂₀₁ is deteriorated by the orthogonal port. Here, we propose an approach to repair the orthogonality which makes the practical orthogonal port work as the ideal one and thereby avoid the TE₁₀₂/TE₂₀₁ spurious passband in an SIW filter. The repair is achieved using ports' offset almost without affecting the fundamental passband. A guideline of using the proposed technique to design a wide stopband filter based on square SIW resonators is provided. Four SIW filters with three, four, five, and six resonators, respectively, are then experimented. The measured results agree with the expectations well. An empirical equation is finally given to initialize the critical ports' offset to facilitate the design. Compared with counterparts, the proposed technique uses a much simpler design, obtains better performance, and can be more easily implemented in practical applications.