Introduction to the Design and Simulation of Reflectionless Filters

One novel approach to improving filter performance is to use so-called reflectionless filters which have recently been proposed. In this paper we demonstrate how to design, simulate and manufacture a reference reflectionless low-pass filter with the corner frequency of 188 MHz. We have found very good agreement between measurements, simulations, and published data, which validates our implementation of the design procedure. We have also designed a comparable diplexer so that we can examine the relative advantages and disadvantages of the reflectionless filters vs. diplexers. Measurements, simulations and published data, all agree very well in this case as well. This agreement extends into multi-GHz range, far into the filter stopband, which illustrates the high quality of the modeling tools used. The reflectionless filter has been verified to provide low return loss for all ports in the stopband which enables cascading. It also has a much simpler bill-ofmaterials and uses only three unique components, whereas the diplexer uses 32 unique components. On the other hand, the diplexer exhibits steeper initial fall-off after the 3-dB corner frequency and somewhat improved attenuation in the stopband