A transistor amplifier stage in which two identical single-ended amplifier circuits ("channels") are used, and the input signal and output power are equally divided between them. This technique produces approximately twice the output power of a single-ended amplifier stage with generally improved dynamic range and reduced VSWR.|
In a balanced microwave transistor stage two identical amplification channels are used with quadrature (90o) couplers to equally divide the input signal and combine the output of the channels. The major advantage of the balanced amplifier stage is that, using the same transistors, a balanced stage can produce approximately twice the output power of a similar single-ended stage. In addition, the third-order intercept point is about 3 dB higher. Thus, with available microwave transistors, balanced amplification can provide significantly higher power output levels.
The quadrature couplers or Lange couplers also have the inherent ability to cancel reflected energy at both their input and output ports and tend to improve the VSWR of each stage in which they are used. This improved VSWR is obtained without the need for trading off gain or noise figure in stage tuning. The degree of VSWR improvement depends on how well the two amplifier channels are matched and on the degree of balance of the coupler.