Study on Third-Order Wide Band Miniaturized Element Frequency Selective Surface with an Ultra Wide Stopband

In view of the problems of large area, narrow bandwidth, low stopband rejection and narrow stopband of frequency selective surface unit, this paper proposed a novel third-order ultra wide stopband miniaturized frequency selective surface element based on three symmetrical interdigital microstrip metal layer, square metal layer coupled loop and four dielectric layer. The symmetrical interdigital structures is equivalent to capacitance, the square coupling rings is equivalent to inductor, and the dielectric layer is equivalent to short lines. The hybrid parameter equivalent circuit with lumped and distributed parameters was obtained. According to the circuit theory, the frequency response characteristics of the third-order Chebyshev band pass filter and the frequency characteristics of the ultra wide band stopband were calculated. The third-order frequency selective surface was designed by combining the circuit theory calculation with the electromagnetic simulation software HFSS. The results of the theoretical calculation are in agreement with those of the electromagnetic simulation software HFSS, and has a frequency response characteristic curve of third-order band-pass filter and ultra wide stopband. The size of the ultra wide stopband miniaturized frequency selective surface element is 6 mm×6 mm, and the thickness is 7 mm. A 41×41 third-order wide band miniaturized element frequency selective surface was machined and tested. The measured center frequency is 2.48 GHz, the relative bandwidth is 11.2%, the in-band insertion loss is less than 0.5 dB, the return loss is greater than 18 dB, the stopband exceeds 55 GHz, and the rejection in the stopband is greater than 25 dB in the frequency range from 2.8 GHz to 55 GHz. It has good frequency stability in the angle of incidence from 0° to 70°. The experimental results are in good agreement with the simulation results, indicating that the design method and the structure of the three-order frequency selective surface adopted in this paper are correct.