Broad-band three-port and four-port stripline ferrite coupled line circulators

The broad-band characteristics of a stripline ferrite coupled line (FCL) section are verified through measurements, for the first time. Subsequent simulations and measurements on a 17-GHz three-port circulator employing a stripline FCL section shows a 65% bandwidth, from 11.5 to 22.5 GHz. A four-port FCL circulator, which is a modification of that proposed earlier by Masur and Mrozowski and Queck and Davis is also realized by connecting the two lines together at the center of the FCL section, i.e. within the ferrite region. Compared to the four-port circulator consisting of an FCL section and a hybrid coupler, it has the advantage of much broader bandwidth. Simulations and measurements confirm its circulating behavior and also show a similar 65% bandwidth, from 12.0 to 23.5 GHz.