562 ANTENNAS AND RF COMPONENTS 



electrical symmetry of this device permits high switching ratios to be 

 achieved over a broad band. 



Off attenuations of 30 db over a 10 per cent band are readily obtained in 

 ferrite switching devices, and 40 db can be achieved with special care in 

 design, construction, and operation of the device. Insertion losses of a 

 fraction of a decibel are often realized. Switching speed of microwave 

 ferrite devices is usually limited not by the ferrite, but by eddy-current 

 induction effects in the waveguide structure. Switching times of a fraction 

 of a microsecond have been achieved by pulsing specially designed Faraday 

 rotation type switches.^^ Ferrite switches capable of handling peak powers 

 of 100 kw and more have been made for X-band. New low-loss materials 

 with improved high-level characteristics will make feasible devices of still 

 higher power. 



Phase Shifters. The controllable microwave permeability of ferrites 

 (Fig. 10-29) can be utilized to obtain either reciprocal or nonreciprocal 

 phase shift in either circular or rectangular waveguides.^"* The phase of a 

 circularly polarized wave passing through a longitudinally magnetized 

 ferrite element in circular waveguide can be controlled by varying the 

 applied magnetic field. The fact that there are regions in a rectangular 

 waveguide where circularly polarized components exist^°'^^ permits phase 

 control by magnetically biased ferrites in a TEio mode waveguide as well. 

 Cross-sectional configurations of three different phase shift elements of this 

 type are shown in Fig. 10-36. The nonreciprocal type is known as a dijferen- 



GZl [m CH] 



Nonreciprocal Reciprocal Nonreciprocal 



(a) (b) (c) 



Fig. 10-36 Various Configurations for Ferrite Phase Shifters in Rectangular 



Waveguide: (a) Nonreciprocal. (b) Reciprocal, (c) Non-Reciprocal. Arrows 



Indicate Direction of Biasing Magnetic Field. 



tial phase shifter, as the phase shift is different in opposite directions 

 through the device. If this phase differential is made 180° the element has 

 the property of a gyrator. Two 90° differential phase shifters, sometimes 

 c2i\\&<\jayrators, can function as a gyrator as illustrated in Fig. 10-37. This 

 shows schematically the construction of the circulator of Fig. 10-34, which 

 utilizes two 90° differential phase shift elements to perform the gyrator 

 function required in any circulator. 



53R. C. LeCraw, "High-Speed Magnetic Pulsing of Ferrites," J. Appl. P/iys. 25, 678-679 

 (1954). 



54A. G. Fox et al., "Behavior and Applications of Ferrites in the Microwave Region," Be// 

 System Tech. J. 34, 5-103 (1955). 



55M. L. Kales et al., "A Nonreciprocal Microwave Component," J. Appl. Phys. 24, 816-817 

 (1953). 



