Radio frequency signal power amplifier

TLDR: In this paper, a multistage radio frequency (RF) signal power amplifier is described that utilizes microstrip transmission line techniques for realizing essentially all of the matching circuitry for each stage of amplification.

Abstract: A multistage radio frequency (RF) signal power amplifier is described that utilizes microstrip transmission line techniques for realizing essentially all of the matching circuitry for each stage of amplification. The power amplifier includes a variable gain predriver, a driver amplifier and a pair of paralleled final amplifiers, all of which are intercoupled by microstrip coupling circuitry. A power detector senses the magnitude of the final amplifier output and provides a forward power signal having a magnitude proportional thereto. A power output regulator is responsive to the forward power signal for providing a drive signal for varying the gain of the predriver amplifier to maintain the magnitude of the final amplifier output at a preset magnitude. The RF signal power amplifier further includes spurious signal suppression circuitry coupled to the output of the driver amplifier and final amplifiers for suppressing spurious signals generated by regenerative modes of oscillation occurring therein. The spurious signal suppression circuitry includes a resistor coupled to a microstrip transmission line having a length such that the line is a relatively low impedance at the spurious signal frequencies and a high impedance at the RF signal frequency. Thus, the spurious signals are attenuated by the resistor, while the RF signal is essentially unaffected. The RF signal power amplifier embodying the present invention may be advantageously utilized in a radio communication system for amplifying signals to be transmitted by a base station radio.