A TRIPLE BROADBAND MICROWAVE FILTER SYNTHESIS USING NONUNIFORM LINES

摘要

In this article, we propose a mapping method in which the system function of the filter in the z-domain is found by discrete-time domain techniques as well as by chain-scattering matrices of various transmission-lines to achieve a triple broadband microwave filter based on equal-length nonuniform coupled lines. The main methodology for designing a triple band filter is using a wideband band-pass filter to cascade two symmetrical band-stop filters together to reach the desired bandwidth and low insertion loss. The band-stop filter and band-pass filter are five-order Butterworth ones implanted and placed with a coupled-serial-shunted lines structure. The design process is finished by using optimization algorithms to tune the values of the characteristic impedances of each transmission line section. Experimental results agree significantly with the theoretical values. Measurement shows that the 3 dB pass bandwidths are about 650 MHz (1.35-1.8 GHz), 1.15 GHz (3.45-4.6 GHz), and 600 MHz (5.5-6.1 GHz) for Duroid substrates. The insertion loss is about 1.03, 1.15, and 2.05 dB at frequencies of 1.8, 3.45, and 5.85 GHz, respectively.