High power broadband ferrite circulator for air traffic surveillance radar

Signal routing at watts and kilowatt levels is primarily handled by using waveguide or stripline structures containing magnetised ferrite materials. Current radar applications require the design of high power circulators with increased bandwidth and reduced insertion loss. A technique called ldquomode segregationrdquo is used to select a bias field region above ferrimagnetic resonance, which avoids low-field loss, resonance damping and high power nonlinear loss to achieve optimal power/bandwidth and temperature stability. A finite element magnetostatic/microwave procedure is used to implement this technique for the differential phase shift section of a 4 port circulator to be used in air traffic control surveillance. The magnetostatic solver calculates the D.C state of the ferrite prior to calculating the microwave solution for this low loss mode of operation. This study dictates that the differential phase shift is reduced and larger magnetic bias fields are required. The circulator phase shifting section has an operating bandwidth from 9.6-10.4 GHz, handles peak power of 0.60 MW, and 1.8 KW average power above ferrimagnetic resonance. Minimum 20 dB isolation with insertion loss less than 0.2 db over the operating frequency band was achieved. Calculations agree well with the experimental data.