In this communication, a metasurface-based antenna array with wideband radiation and broadband radar cross section (RCS) reduction is constructed. Without introducing additional radiators, the broadband radiation performance of the antenna array is achieved by inspiring the metasurface itself. In addition, the characteristic mode theory is introduced to analyze the radiation mechanism of the radiator elements and the proposed antenna array. Both simulations and measurements are carried out to verify the performance of the proposed antenna array. The results show that the impedance bandwidth and 3 dB gain bandwidth of the proposed antenna array are 5.1–9.0 and 5.1–8.0 GHz, respectively, with a peak gain of 12.1 dBi. Monostatic RCS reduction more than 10 dB is achieved within the frequency band of 6.0–26.2 GHz.

In this paper, a novel composite metasurface (MS) with diffuse scattering and absorbing characteristics is proposed to reduce the radar cross section (RCS) of a metal target in a broad band. The combination of absorption and diffusion is realized based on lossy Pancharatnam-Berry (PB) phase particles. The units are arranged according to a coding sequence which is obtained by an optimization algorithm based on simulated annealing algorithm. Simulation results show that the MS obtained based on the optimized coding sequence is insensitive to polarization. Due to the combination of absorption and diffusion, the MS has good performance in both monostatic and bistatic scenarios. Finally, the proposed MS is fabricated and measured, and the experimental results are in good agreement with simulation results. A 10 dB backward reflection reduction can be achieved from 21GHz to 38GHz and a 15 dB backward reflection reduction can be achieved from 22GHz to 35GHz under normal incidence. Furthermore, the MS has good performance under large angle (<45°) incidence.

This paper presents a simple split ring resonator excitation to realize a multi-mode wideband bandpass filter in a rectangular waveguide cavity. The proposed resonator employs two rectangular split rings attached with two coaxial probes extended into the cavity to excite two resonant modes, unlike the conventional cavity resonators which employ conductive cylinders in the cavities to achieve the same results. A hybrid magnetic (HM) mode and a hybrid electric (HE) mode are the two hybrid modes excited to realize the wideband bandpass filter. The filter operates at 2.5 GHz center frequency with 53% fractional bandwidth. Finally, the prototypes of a second and a fourth order filter are fabricated for results validation. Measured results are in good agreement with the simulated ones.

In this chapter, Fano resonances in simple structures with high permittivity such as spheres or core-shell particles are analyzed by Mie theory. The Mie scattering coefficients can be decomposed into slow varying backgrounds and narrow resonances, which cause the Fano resonances in scattered field. For structures of arbitrary shapes, temporal coupled-mode theory is applied to explain the Fano resonances found in the scattering cross section. At last, we analyze the periodic structures by using band diagram, and it shows that the Fano resonances can be viewed as the superposition of the Bloch wave and the Mie scattering wave.

A broadband circularly polarized (CP) antenna with enhanced gain and low profile is proposed. Two identical dipoles with full wavelength are placed orthogonally to generate radiation waves with equal amplitude and orthogonal polarization. The arms of the dipoles are designed as stepped patches to enlarge the impedance matching bandwidth and axial ratio (AR) bandwidth. Crossed-dipoles with full wavelength are utilized as the main radiators to provide a wide operating bandwidth and enhanced gain, and an artificial magnetic conductor (AMC) structure is introduced as the reflector to reduce the profile of the whole antenna. Due to the introduction of the AMC structure, the antenna profile is reduced from 12.8 to 6.9 mm, that is, reduced to 0.14${\lambda }_0$ (where ${\lambda }_0$ denotes the wavelength corresponding to the center frequency of the passband, 4.0–8.5 GHz). A simulation and experiment were carried out to verify the performance of the proposed antenna. Experimental results showed that the antenna realized an impedance bandwidth of 74%, an AR bandwidth of 67.7%, a peak gain of 12.1 dBic, and an average gain of 10.69 dBic.

This paper proposes a method for designing a quadruple-mode wideband bandpass filter using off-centered perturbed metallic cylinders in a rectangular waveguide cavity with compact size and improved out-of-band rejection. Two off-centered perturbation cylinders were placed at the bottom of the rectangular waveguide cavity along with a pair of perpendicularly-fed coaxial lines, which excited four quasi-transverse magnetic (TM) modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders were exploited to achieve an all quasi-TM modes filter with good out-of-band rejection and sharp skirt selectivity. The proposed filter operates at 2.93 GHz center frequency with 38% wide fractional bandwidth (FBW). The proposed filter is fabricated using aluminum. The measured and simulated results are in good agreement with each other.