7 W Microwave Transistor Amplifier for High Capacity 4 GHz Radio Links

This paper describes the basic aspects for the design of wideband microwave transistor power amplifiers making use of advanced transistor technology. A novel measuring procedure for the accurate determination of the large signal impedances of microwave transistors is presented. For the matching networks special lumped elements are used which have nearly ideal, predictable frequency characteristics, low loss and are easy to manufacture. A new automatic control of the transistor operating point ensures minimum AM-PM conversion and maximum gain. In addition, a temperature controlled overload protection is achieved. These procedures are applied to the design of a six-stage 7W-4GHz transistor amplifier. Although packaged transistors without internal matching are used, the total amplifier gain of 30 dB is flat to 0.5 dB within a bandwidth of 7.5 %.. The experimental data for group delay distortion, thermal and intermodulation noise show that the amplifier is suitable for the use in 1800-channel FDM-FM radio relay systems.