TABLE OF CONTENTS This chapter discusses RF transformer devices and circuits. Topics include conventional transformers, core material for RF transformers, IF amplifier transformers, HF wideband conventional transformers, transmission-line transformers, and power combiners and splitters. Some of the information presented is based on [1], [2], [3].
Figure 15.1 shows a conventional two-winding transformer with windings on a ferrite core. In an ideal transformer, the following relationships apply:
In practice in a real transformer, winding loss, leakage inductance, and magnetizing inductance must be taken into account. That may be done using the equivalent circuits in Figure 15.2.
Nomenclature for these circuits is as follows:
C p = primary equivalent shunt capacitance
C s = secondary equivalent shunt capacitance
E g = rms generator voltage
E out = rms output voltage
L m = magnetizing inductance
L p = primary leakage inductance
L s = secondary leakage inductance
R c = core-loss equivalent shunt resistance
R g = generator resistance
R L = load resistance
R p = primary winding resistance
R s = secondary winding resistance
The LF response of a conventional transformer is degraded by a shunt susceptance that appears across the primary winding. The magnetizing inductance, L m, of the transformer is given by
where:
n
