Development of Components and Subsystems for Low Noise Receivers at Micro- andMillimeter Waves

摘要

The development of low noise receivers at micro- and millimeter wave frequenciesmainly intended for radio astronomical studies and remote sensing applications are discussed. The work is divided into three parts: design and construction of cryogenic, low noise MESFET (Metal Semiconductor Field Effect Transistor) and HEMT (High Electron Mobility Transistor) amplifiers, studies on semiconductor local oscillators and phase locking of mm wave Gunn oscillators. The basic theory of low noise transistor amplifiers employing scattering and noise parameters of an active device is reviewed. Stability problems of amplifiers and noise measurement techniques especially applicable to cryogenic systems are discussed. Several low noise amplifiers were constructed for the frequency range of 1 to 22 GHz. As an example, a 4 GHz cryogenic MESFET IF amplifier with 20 K noise temperature was developed. A two stage coaxial HEMT amplifier with T(sub A) = 300 K at room temperature was constructed. Various designs of semiconductor local oscillators needed for mm wave receivers are reviewed. Experimental verification of the theoretical model for the waveguide mounting structure of Gunn diodes is given at frequencies of 35 to 53 GHz. Fundamental frequency local oscillators with an output power of approximately 50 mW and mechanical tuning range of 5 to 10 GHz (center frequency of 45 GHz) were constructed. Description of the phase locking scheme (exploiting bias tuning of Gunn oscillators) of the 72 to 115 GHz receiver is given. The additional factors needed in application of the basic phaselock theory to mm wave oscillators are discussed.