A Microstrip Phase Locked Oscillator for Digital Radio

Abstract

A simple microstrip oscillator with a 70-MHz mechanical tunabiliiy in the 550/650 MHz band, phase-locked to a 100 MHz (nominal) reference developed by the Indian Telephone Industries Limited Bangalore, is described. This is specifically designed to meet the power output, frequency stability and the noise requirements for the UHF Digital Radio. The microstrip oscillator has the fabrication advantage over the cavity oscillators. A seven-section elliptic function low-pass filter at the output of the voltage controlled oscillator suppresses the harmonics by 45 dBc. The UHF oscillator and the phase lock circuitry is housed in an aluminium box and works on a single negative 20 V supply at 125 mA current.