A Millimeter Wave PLL Oscillator for Optical Receivers E.Udvary 1 , A.Zólomy 1 , A.Hilt 1 , G.Járó 1 , S.Mihály 1 , T.Berceli 1 1 Technical University of Budapest, Dept. of Microwave Telecommunications H-1111 Budapest, Goldmann György tér 3, Hungary, Phone: +(361) 463 1559, Fax: +(361) 463 3289 udvary@ nov.mht.bme.hu Abstract. The design and experimental investigations of a harmonic microwave oscillator is presented. The transistor oscillator was designed to operate at the fundamental frequency with high third harmonic output. The final goal is to utilize the constructed circuit in a combined millimeter- wave / optical system for picocell applications presented below. I. Introduction Optical generation of millimeter waves is relevant for many practical applications, and there is an increasing demand for higher and higher carrier frequencies. However, millimeter- wave generation is very expensive and complex by the known and used methods. In the new approach instead of transmitting the millimeter-wave signal, one of its subharmonic is optically transmitted and at the reception side the millimeter-wave is generated utilizing the subharmonic signal as a reference frequency. The main advantage of this system is the simplicity and the relative low cost [1]. The block diagram of this system is shown in Fig.1. Amplifier LP Filter HarmonicVCO Phase Detector Freq. Divider Amplifier Branching Filter fVCO/n = fref PhotoDetector fref MW Amplifier optical fiber k·fVCO Fig. 1. Block diagram of millimeter wave generation using the optically transmitted reference A harmonic Voltage Controlled Oscillator (VCO) is used with a fundamental oscillation frequency around n·f ref . This frequency is divided before comparing to the optically transmitted reference signal (f ref ) in the phase detector. The error signal is amplified, filtered and used to control the harmonic VCO frequency. One of the harmonic frequencies k·f VCO is coupled out of the oscillator and utilized after proper amplification. The most important device of the system is the harmonic VCO. The output power at fundamental frequency and at the selected mm-wave harmonic frequency must be optimum. II. Oscillator design principles Two well-known linear methods, the negative conductance and the maximum instability oscillator design method were applied in the calculations [2].