With the rapid development of terahertz applications in recent years, numerous devices and circuits have been designed to operate at millimeter-wave and terahertz frequencies. Frequency-selective-surface (FSS) structures, for example, have been proposed for bandpass filtering at these frequencies. A new class of FSS structures, known as miniaturized-element FSSs (MEFSSs), is constructed of multi-layer arrays of non-resonant metallic elements with much smaller dimensions than the operational wavelength. Researchers from Australia recently proposed an MEFSS with a second-order filter response at terahertz frequencies. The proposed structure achieves a wide rejection band and large angular tolerance.
The structure is composed of two periodic metallic arrays that are separated by a dielectric spacer. Its response was modeled by means of an equivalent lumped-element circuit. The synthesized lumped-element component values were mapped to the geometrical dimensions of the FSS. The performance of the fabricated FSS was then measured, demonstrating good agreement with the simulation results. A center frequency of 0.42 THz was achieved along with a 3-dB bandwidth of approximately 45%. Out-of-band signals to 1.5 THz were attenuated by more than 25 dB. In addition, the maximum loss in the passband was less than 5 dB.
See “Second-Order Terahertz Bandpass Frequency Selective Surface With Miniaturized Elements,” IEEE Transactions on Terahertz Science and Technology, Sept. 2015, p. 761.