The Development Of Ka Band Nonreciprocal Ferrite Phase Shifter

Phase shifter is one of the key components of T/R section in Phase Array Radarsystem. Development of phase shifter with high performance, miniaturization and lowcost is very important for the development of Phase Array Radar system. Ferrite phaseshifter is worthy of important research value due to its high power capacity, lowinsertion loss, wide bandwidth, and low cost. The LiZn ferrite preparation and thestructure design for Ka band phase shifter were investigated.The LiZn ferrite were manufactured by using conventional ceramic process, andthe effects of Bi₂O₃and sintering process on microstructure and magnetic properties ofLiZn ferrite were investigated. The results are as follow. The density and grain growthare improved by moderate addition of Bi₂O₃, thus LiZn ferrite with high saturationmagnetization, high remanence ratio and low coercivity is achieved. However, a secondphase appears at grain boundary resulting from excess Bi₂O₃, which decreases the grainuniformity. A rapid heating rate results in the increase of coercivity and remanence ratioof LiZn ferrite. A subatmospheric pressure of oxygen atmosphere enhances saturationmagnetization and remanence ratio and decreases coercivity.The simulation design of Ka band nonreciprocal ferrite phase shifter is carried outby Ansoft HFSS. The simulation results of ferrite phase shifter （the grooved waveguideis used for ferrite phase shifter and the length of ferrite toroid is30mm） are as follows.The difference phase shift is420°, and the insertion loss and Voltage Standing WaveRatio （VSWR） is less than1.6dB and1.7, respectively, in the frequency range of34GHz±1GHz. The VSWR simulation of two kinds of impedance match dielectricmaterials （Al₂O₃and GaAs） were performed. At the same time, the simulations ofPolytetrafluoroethene （PTFE） and air filled to the center slot of ferrite toroid wereperformed. As a result, the VSWR of two kinds of impedance match dielectric are bothless than1.2. Comparing with air filling, an increase of20°is achieved by loadingPTFE in the center slot of ferrite toroid, furthermore, the insertion loss and VSWRdecrease slightly. Then, based on the simulation results, the Ka band nonreciprocalferrite phase shifter was fabricated by utilizing the LiZn ferrite materials. At33³5GHz, the difference phase shift is284°, the insertion loss is lower than1.8dB, and the VSWRis less than1.4, respectively.