High-efficiency power oscillator using harmonic-tuned matching network

This paper presents a high-efficiency power oscillator, which uses LDMOS (Laterally Diffused Metal Oxide Semiconductor) transistor for high output power and a harmonic-tuned matching network to obtain high efficiency characteristic for RF power source application. A hair-pin resonator was designed and employed into the high efficiency power oscillator in order to improve phase noise characteristic and frequency selectivity. Measurement results show that output power of the power oscillator is 38.1 dBm, corresponding to a conversion efficiency of 73% at 981 MHz which is the highest efficiency reported in microwave power oscillator. Experiments performed with the hair-pin resonator show that output power is 36.9 dBm and conversion efficiency is 65%. Phase noises are measured to be 78.9 dBc/Hz and 103 dBc/Hz at 10 kHz offset without and with the hair-pin resonator, respectively.

I. Introduction

The oscillator is an important active device widely used in various microwave and millimeter-wave applications for wireless communication or RF power source. And high power oscillator was studied for single transmitter like man-portable radar transponder [1]. Especially, for using RF power source [2], the dc-to-RF conversion efficiency is an important characteristic in connection with a power loss and reliability of transistor according to thermal stress and the cost of system [3]. The high efficiency oscillator using switch-mode like class E, F amplifiers has been studied. In a few GHz and a few hundreds MHz, the conversion efficiency was accomplished about 48% to 67% [2]–[6].