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.