In this paper, we combine the design of band-pass frequency selective surfaces (FSSs) with polarization converters to realize a broadband frequency-selective polarization converter (FSPC) with lowbackward scattering, which consists of the top polarization conversion layer backed by a multi-layer bandpass FSS. It is numerically demonstrated that the 1 dB transmission window can be obtained from 8.5 GHz to 11 GHz with a 25.6% fractional bandwidth (FBW), and the bandwidth of reflection below -10 dB is up to 92% from 5.6 GHz to 15.13 GHz. Moreover, the proposed device can achieve two polarization conversion bands (5.66-6.9 GHz and 12.8-15.2GHz) with the polarization conversion ratio over 90%. Besides, by arranging the proposed structure in a checkerboard-like distribution, the backward scattering energy can be reduced in a wide frequency band ranging from 4 to 16 GHz. Both simulation and experimental results are in good agreements, which demonstrates our design strategy. Compared with the conventional polarization conversion designs, the proposed design presents an extra frequency-selective performance and hence can be applied to various practical situations, for instance, working as radomes to transmit the in-band signals with high-efficiency while keeping low-backward scattering for the out-of-band waves.
Herein, a tunable metamaterial absorber was realized by using two-dimensional (2D) plasma photonic crystals (PPCs). A photonic band gap (PBG) can be obtained in the proposed 2D PPCs, which runs at frequencies from 1.7 to 1.93 GHz. The fabricated absorber is tunable and is composed of excited plasma tubes with 2D square lattices. The resonances originate from the all-dielectric resonances. The plasma frequency is also measured. The experimental results agree with the simulation results. The fabricated absorber shows excellent absorption (up to 84.3%). Hence, it can be used to design various devices, such as tunable microwave devices, stealth devices, and reconfigurable antennas.
This paper presents a single-feed wideband circularly polarized (CP) antenna with tapered crossed slots and corner directors. According to the multimode resonance concept, the antenna uses two identical cross placed Vivaldi-like tapered slots as the wideband radiating elements, and four rectangular parasitic patch directors are connected on each corner of the ground for further enhancing the bandwidth. A simple second-order stepped microstrip line with a via on the other side of the substrate is used to feed the antenna. Two pairs of capacitors and inductors are placed on each slot to realize a 90 phase difference for CP operation. The proposed antenna is designed, fabricated and measured. Simulation results are in good agreement with the measured results that demonstrate a 10 dB impedance bandwidth (IMBW) from 1.98 to 5.71 GHz (3.73 GHz, 97.01%) and a 3 dB axial ratio bandwidth (ARBW) from 2.13 to 3.91 GHz (1.78 GHz, 58.94%). The antenna outperforms most of the reported cross slot antennas for its wide IMBW and ARBW.
K E Y W O R D Smulti-mode resonance, parasitic patch directors, wideband circularly polarized (CP) antenna
A reflective metasurface based on the quasi‐spiral element is proposed to achieve broadband orbital angular momentum vortex beams for multi‐polarisations. The quasi‐spiral element can provide linear and smooth phase responses covering about 360° from 10 to 15 GHz with a relative bandwidth about 40% by adjusting the length of four phase delay lines. Additionally, the metasurface can generate vortex beams with optional charges in vertical, horizontal and circular polarisations which are determined by the polarisation of feed antenna. Finally,we have designed and fabricated a 24 × 24 cm2 metasurface prototype. The simulated and measured results show that the reflective metasurface can generate broadband vortex beams with orbital angular momentum effectively. As the structure is simple, lightweight and easy to fabricate, the proposed method is applicable to generate broadband vortex beams for multi‐polarisations.
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