In this paper, a new frequency selective surface (FSS) is proposed, which is mainly applied to 5G communication. The equivalent circuit method is used to provide assistance for structural design. This structure can generate dual-frequency passbands that resonant frequencies are 28.1 GHz and 39.5 GHz. And it acquires large enough bandwidths to cover 27.5-28.35 GHz and 38.6-40 GHz which are bands of 5G communication. In addition, this structure is a multi-layer structure composed of one metallic layer and two dielectric layers, and its unit size is 0.56λ×0.56λ where λ is the wavelength corresponding to the first resonant frequency. Simulated results show that this structure has excellent filtering properties with respect to polarization stability as well as angular stability. Finally, the prototype of this structure is fabricated. The measured results and simulated results have consistent filtering characteristics within the tolerance of error.

This letter proposes a dual-stopband frequency selective surface (FSS) with tightly spaced frequency response characteristics. The metal layer of this FSS structure is composed of a metal strip of a bow-type ring and a metal strip of a square ring type, which forms the center symmetric ring structure. This dual-band FSS can achieve reflection characteristics at 6.29 and 8.35 GHz, which belong to C-band and X-band, respectively. In addition, two resonant frequencies can be independently controlled for good flexibility. This structure has excellent polarization stability and angular stability. Furthermore, a prototype sample of the proposed structure in this letter is processed and produced, and the test results are highly consistent with the simulation structure after being measured in a microwave anechoic chamber.

In this letter, a miniaturized frequency selective rasorber (FSR) based on complementary bandpass frequency selective surface (FSS) for fifth generation applications is designed. It is formed by the superposition of tortuous annular resistive layer and complementary bandpass FSS layer. The tortuous annular resistive layer consists of a regular octagonal patch and two bent metal rings. Four lumped capacitors and eight chip resistors are loaded to achieve impedance matching and wave absorption. In the bandpass layer, a complementary Jerusalem cross structure is adopted to realize electromagnetic wave transmission and structural miniaturization. The proposed FSR exhibits A-T-A filtering characteristics. The center frequency of passband is located at 2.6 GHz and transmission rate reaches 87.5%. Under 80% absorption rate, low-frequency absorption band ranges from 1.64 to 2.36 GHz, and high-frequency absorption band ranges from 1.64 to 2.36 GHz. Finally, a 500 mm × 500 mm prototype is fabricated, and the measured results are highly consistent with the simulated results.

This letter presents an active frequency-selective rasorber (AFSR) with switchable dual operating modes at Lband. The proposed frequency-selective rasorber (FSR) comprises of a resistive layer and a frequency-selective surface (FSS) layer loaded with PIN diodes, separated by an air spacer. The operating mechanism is elaborated by analyzing the equivalent circuit model (ECM). By controlling the states of the PIN diodes, the AFSR can be switched from the absorption-transmissionabsorption (A-T-A) to absorption-reflection-absorption (A-R-A) modes. In the A-T-A mode, the transmission peak is 0.21 dB at 1.89 GHz, while the absorption band is 0.87 GHz to 3.42 GHz. In the A-R-A mode, the reflection peak is 0.15 dB at 1.91 GHz, while the absorption bands are 0.95−1.34 GHz to 2.1−3.51 GHz. A prototype of the proposed FSR was fabricated and measured to verify the design concept.

This letter proposed a miniaturized frequency selective rasorber (FSR). This FSR consists of a conducting sheet layer with embedded dual-bow resonators and a bandpass frequency selective surface (FSS) layer with cross-ring slot. The structure exhibits absorption-transmission-absorption (A-T-A) characteristics which shows excellent transmission performance in 2.4GHz band. The unit size of structure is 0.113 $\lambda _{L}$ and the thickness is 0.071 $\lambda _{L}$ , where $\lambda _{L}$ is the lowest frequency of the absorption band satisfying 80% absorption rate. The simulation results show that the centre frequency of the transmission band is located at 2.42GHz with 0.24dB insertion loss. Under the condition of 80% absorption rate, the absorption bandwidth is 58.82% for low frequency absorption band, and 58.6% for high frequency absorption band. The concept of slope in mathematics is introduced into FSR for the first time to define steep drop characteristics. Finally, in order to verify the correctness of the analysis results, a prototype of FSR with 20×20 units is processed and measured, and the measured results are in good agreement with the simulation results.

A dual-passband frequency-selective rasorber (FSR) with high selectivity is proposed in this letter. By analyzing the equivalent circuit model (ECM), the design approach improving the selectivity of the dual-passband is introduced. The FSR is formed by a lossy layer and two frequency-selective surface (FSS) layers. The lossy layer is composed of two parallel resonance units embedded in a rhombic patch, which is connected with four resistors loaded on the T-shape metal strips. The lossless layer consists of two layers of double square slots to provide highly selective passbands with second-order response. The simulated results show that two transmission bands are achieved at 7.2 and 10.8 GHz with the insertion loss of 0.86 and 0.57 dB, and the fractional bandwidth for |S₁₁| < −10 dB is 94.8%. Both sides of the transmission bands exhibit steep roll-off characteristics, with the coefficient of steep drop (CSD) being 41.18, 77.78, 31.82 and 17.5, respectively. The unit cell size is 0.18λ × 0.18λ × 0.19λ (λ is the wavelength at the lowest operating frequency). A prototype of the proposed FSR was fabricated and measured, the measured results are consistent with the simulation results