. Airborne radar. Airplanes; Guided missiles. 558 ANTENNAS AND RF COMPONENTS tional to frequency, gyromagnetic resonance occurs and the permeability for the positive sense of circular polarization reverses abruptly between extreme values. In this same region the positive circularly polarized wave experiences a high resonance absorption. Except in the region of resonance, the ferrite is practically lossless for both senses of circularly polarized waves. Various regions of the unusual and controllable permeability charac- teristics shown in Fig. 10-29 and the resonance loss characteristic are ex
. Airborne radar. Airplanes; Guided missiles. 558 ANTENNAS AND RF COMPONENTS tional to frequency, gyromagnetic resonance occurs and the permeability for the positive sense of circular polarization reverses abruptly between extreme values. In this same region the positive circularly polarized wave experiences a high resonance absorption. Except in the region of resonance, the ferrite is practically lossless for both senses of circularly polarized waves. Various regions of the unusual and controllable permeability charac- teristics shown in Fig. 10-29 and the resonance loss characteristic are exploited in many ways to achieve the remarkable reciprocal as well as nonreciprocal properties of the microwave ferrite devices.^^'^^ Most of these new devices depend upon the differential permeability for their operation, while the resonance absorption isolator^^ exploits the high absorption differential between positive and negative circularly polarized waves in the region of gyromagnetic resonance. Faraday Rotation. A linearly polarized wave incident on a longitudi- nally-magnetized ferrite element, as shown in Fig. 10-30, will undergo a Output Polarization. Solenoid To Current Supply Fig. 10-30 Principle of the Ferrite Microwave Faraday Rotator. rotation of its plane of polarization. This is because of the different permeabilities seen by the positive and negative circularly polarized components of the linearly polarized wave. (A linearly polarized wave can be resolved into two oppositely rotating circularly polarized waves of equal amplitudes.) Each circularly polarized component manifests a different phase delay in traversing the ferrite section; and if losses are negligible, they combine in a linearly polarized wave rotated by some angle 6 from the input wave. The microwave Faraday effect, which permits electronic ?i^C. E. Hogan, "The Elements of Nonreciprocal Microwave Ferrite Devices," Proc. IRE44:j 1345-1368 (1956). ''^Henjamin Fax, "Frequency and Eoss C
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