Optimum design of 6‐18 GHz ultra‐wideband microstrip filters with arbitrary source and load impedances by the least mean squares Method

Abstract

In this article, the method of least mean squares (LMS) is employed to design ultra-wideband (UWB) filters with various input and output port impedances in 6-18 GHz frequency range. Optimization process on the circuit dimensions is done by MATLAB and AWR microwave office softwares utilizing exact closed-form relations for microstrip transmission lines and microstrip T-junction discontinuities. The advantages of this method are its simplicity, fast design time, including impedance matching. Two design examples are depicted in the article. To validate the designed structures, the circuit model results are compared with full-wave analysis and measurements. The first design example corresponds to equal source and load impedances. For this design, maximum measured transmission coefficient in the frequency range 5.9-16.6 GHz is obtained as −12 dB, upper out-of-band rejection around image frequency is better than −17 dB and lower out-of-band rejection at 5 GHz is obtained better than −30 dB. The second design example describes the case of unequal source and load impedances.