Demonstration of a terahertz integrated planar network synthesis filter

At terahertz (THz) frequencies, there are few experimental works that demonstrate the viability of all-pole network synthesis filters to obtain desired frequency characteristics (i.e., Chebyshev, Butterworth, Bessel, etc.) using planar waveguides. This capability has been proven with non-planar waveguides, but has yet to be demonstrated using planar waveguides, which are desirable due to their integration capabilities similar to printed circuit board or monolithic microwave integrated circuit structures. In this paper, we use network synthesis methods from microwave engineering to fabricate three integrated planar low-pass filters for THz applications that have the same cut-off frequency (fc = 0.8 THz) but different orders (N = 3, 4, 5). We measure their response to a THz-bandwidth excitation pulse and find that the experimental results exhibit increasing roll-off rates with increasing filter order without incurring significant pulse distortion, which is aligned with theory.