Design of 140GHz Narrow Band-pass Planar Filters Based on Open Loop Resonators

In this paper, a universal design procedure for narrow-band filter based on square open-loop resonators is established. The square open-loop resonator is partitioned into microstrips and coupled microstrips which are characterized separately. The coupled microstrips are represented as a four-port device and a BP neural network is established to map the entire S-parameter while the gap and folded microstrips are modeled simply by lumped parasitic-included equivalent circuits. The entire design procedure is demonstrated by implementing a planar D-band narrow band band-pass filter. The measurement results show that the filter exhibits insertion loss around 4.3dB at 140GHz and FBW about 6% which are close to most waveguide filters. To the best of the authors’ knowledge, this is the narrowest bandwidth in D-band filter with relatively low insertion loss among planar solutions.