Design and simultaneous analytical optimization of microwave filters with superimposed rectangular cavities for radar applications

In this paper, a method for the rapid design of filters with superimposed rectangular cavities is proposed. It starts with a good initialization of the filter dimensions from the targeted coupling matrix, which serves as the basis for calculating the bandwidth of the inter-cavity couplings (CBW) and the group delay (GD) of the input/output couplings. Next, an analytical and simultaneous optimization of all filter dimensions is applied. It is based on the extraction of the S-parameter coupling matrix from Model-based Vector Fitting (MVF) coupled to the Generalized Isospectral Flow Method (GIFM). The differences between the coefficients of the targeted matrix and the extracted matrix are then calculated, and depending on their positive or negative signs, appropriate adjustments are applied to the filter dimensions. This computer-aided design (CAD) process was successfully used to design one single-band and one dual-band 6th-order microwave filters with superimposed- cavity, with respective center frequencies of 10 GHz and 9.99 GHz, and taking into account milling constraints for eventual manufacture.