Cham Kiong Queck

Microstrip and stripline ferrite-coupled-line (FCL) circulator's

Measurements on an 11-GHz four-port microstrip ferrite-coupled-line (FCL) circulator, employing a broad-band hybrid coupler and an improved air bridge, confirm that only a weak biasing field of 3-4 kA/m (35-50 Oe) is required. By cascading the S-matrices of the FCL section and hybrid coupler using signal flow graphs, the measured and predicted bandwidth and losses are compared for the first time. Simulated results for stripline FCL sections exhibit broader bandwidths than those obtained with microstrip FCL sections. Using such a structure, the simulated performance of a three-port circulator indicates that, in principle, bandwidths of at least 3:1 or 4:1 may be possible.

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.

Novel folding technique for planar ferrite-coupled-line circulators

A novel folding technique for a longitudinally magnetized ferrite-coupled-line (FCL) section is reported in this paper. The results from Ansoft HFSS simulations of a single-folded structure are presented for a 17-GHz folded stripline FCL section and the measurements on the 17-GHz folded stripline three-port FCL circulator confirm the folding concept and demonstrate that nonreciprocal behavior is retained.

Bandwidth and losses of 4-port ferrite coupled line circulators

For the first time, the bandwidth and the losses of a 4-port Ferrite Coupled Line (FCL) circulator are analysed and reported. A broadband hybrid coupler with an improved air-bridge has been designed for the circulator and the performance of a 4-port microstrip FCL circulator is predicted by cascading the S-matrices of the FCL and hybrid coupler using signal flow graphs. The possibility of realising a broadband circulator is investigated and it is found that there is a trade-off in performance between bandwidth and loss.

Butterfly-shape Folding of a Ferrite Coupled Line

A new butterfly-shape folding technique for ferrite coupled line (FCL) is proposed as an alternative to that reported in Queck and Davis (2004). The advantage of this new folding technique is easier fabrication for the folded FCL and high isolation between the feeder lines. The predicted performance of the single-folded lossless FCL is close to that of the unfolded version in the frequency range 10-11 GHz

4-port Microstrip Ferrite Coupled-Line Circulator

A 4-port microstrip Ferrite Coupled-Line (FCL) circulator is designed at 11.4 GHz by cascading a longitudinally-magnetized FCL structure with a 180° hybrid coupler. A broadband 180° hybrid ring with a bandwidth of approximately 7 GHz is realised by employing stepped impedance sections on the hybrid coupler. The simulated results of the respective sections are presented in this paper. The scattering matrix of the cascaded 4-port microstrip FCL circulator is predicted using a power flow diagram.