C-band direct-coupled cavity waveguide filter design using MathCAD software

This paper presents the design of a direct coupled cavity waveguide bandpass filter operating at C-band, with the aid of a mathematical software. The application chosen is for the receiving circuitry of a high power communication system. The basis of the design is the insertion loss method. The direct-coupled cavity bandpass filter can handle high power compared to transmission line filter such as microstrip and striplines. The design procedure starts by computing the relevant prototype parameters based on the required specifications. The design specification includes the operating frequency, cut-off frequency, ultimate attenuation, minimum attenuation, and response type. The computation involves varying the number of orders and determining the optimum number of order. The design focuses on the equi-ripple response. The dimensions of a rectangular waveguide having inductive diaphragm with circular holes were then designed. The inductive diaphragm represents the cavity. Computation of the filter performances in terms of the insertion and return losses were successfully achieved. Good agreements between the theoretical computations and electromagnetic simulations have been achieved.