4.2.6 Isolators
Ferromagnetic processes, particularly faraday rotation, allow us to create nonreciprocal modules in which the electromagnetic wave behaves dofferently depending on its direction of propagation.
Circulators and isolators are components that make use of this phenomenon. Commercially available devices typically provide directivity values around 20 dB, again varying with frequency and show something around 1 to dB as insertion loss in the wanted (forward) direction.
There-port circulators have similar performance figures but applied to all three connections and naturally following the appropriate direction of rotation. Then practical bandwdths available often match those of standardized waveguide ranges, but coaxial modules are also available for the lower microwave bands.
Many millimeter-wave amplifiers and oscillators require the use of an isolator at their output to reduce load.pulling effects and oscillators require the use of an isolator at their output to reduce load- pulling effect and to make the output stage withstand posible RF open/short circuit; see figure 4.10.
Of course this means that we deliberately accpet losing a bit more that 1 dB of power. A ferrite circulator can be effectively used as a part of an RX/TX switch in a radar or communication system having one antenna interface as illustrated in figure 4.11 the loss and NF calculations must be performed accordingly.
Libro: Circuits and Components for System Evaluations and Design
Autor: Pekka Eskelinen
Nombre: Josmar Eduardo Depablos Rodriguez
Asignatura: Circuitos de Alta Frecuencia
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