Design of microwave direct-coupled cavity waveguide filter for VSAT communication at c-band using MathCAD software

Waveguides are robust structure and handle high power well, compared to transmission line filter such as coplanar lines, microstrips and striplines. As such, it is used in a very small aperture terminal (VSAT) communication system operating at C-band. In this paper, the mathematical computations for the design dimensions of a direct-coupled cavity waveguide bandpass filter are implemented using MathCAD mathematical software, based on the Insertion loss method. Firstly, the design specifications are set. These include operating frequency, operating bandwidth, minimum attenuation, ultimate attenuation, and type of filter response. An optimum number of filter order will be determined. The cavity waveguide filter consists of vertical inductive diaphragm of circular holes, which represent the cavity. Computation of the filter performances in terms of the insertion and return losses were successfully achieved. Comparisons with electromagnetic simulations were also made. Good correlation can be observed between the computed performances using MathCAD and simulated performances using simulation software.