Microwave Recursive and Transversal Active Filters using Lange Couplers

This paper proposes new recursive and transversal implementation techniques based upon the use of Lange couplers at microwave frequencies. We show how Lange couplers with various coupling values, can be effectively employed in the design of recursive and transversal structures. Wepresent analytical, computer-simulated and experimental results for two passive band-pass filters, implemented on a Duroid substrate in the 3-5 GHz frequency range. Good agreement is obtained between the theoretical and the measured S-parameters. The results of an active recursive filter, including a balanced amplifier in the 3-4 GHz range, are also shown.