Millimeter Wave Solid State Devices
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Millimeter Wave Solid State Devices Steven A. Rosenau, Cheng Liang, Weikang Zhang†, Bihe Deng†, Weiying Li†, Chia-Chan Chang, Pei-Ling Hsu†, Richard P. Hsia‡, Fan Jiang↓, Calvin W. Domier†, Neville C. Luhmann, Jr.* Department of Electrical and Computer Engineering, University of California, Davis, CA 95616 † Department of Applied Science, University of California, Davis, CA 95616 ‡ Microwave Communications Division, Harris Corporation, Redwood Shores, CA 94065 ↓ Wytec, Inc., 3385 Scott Blvd, Santa Clara, CA 95054 * Author for Correspondence: Tel: 530-752-5414 Fax: 530-754-9070 Email: [email protected] ABSTRACT Examples of novel solid state devices are presented, together with descriptions of their applicability to the diagnosis of laboratory, processing and fusion plasmas. GaAs varactor diodes can be arranged in large monolithic grid arrays, forming millimeter wave frequency multiplier based sources and high speed switches, or embedded in transmission lines to provide a true time delay for phased antenna array beam steering. Micro-electromechanical systems (MEMS) switches are exciting new devices with numerous applications, including low loss millimeter wave switches, phase shifters and mechanically tunable structures. INTRODUCTION Millimeter wave technologies have been widely utilized for fusion plasma diagnostics, such as interferometers for the measurement of plasma electron density profiles, reflectometers for the measurement of plasma density profiles and fluctuations, radiometers for the study of plasma electron temperature profiles and fluctuations, and cross polarization scattering diagnostics for the measurement of magnetic field fluctuations. Recently, there are growing demands for high spatial resolution imaging diagnostics, such as Electron Cyclotron Emission (ECE) Imaging and Microwave Imaging Reflectometry (MIR), for advanced plasma fluctuation studies [1, 2]. Traditionally, pyramidal horns are utilized to transmit/receive millimeter waves to/from the plasma. However, due to their relatively large (compared to the wavelength) sizes and limited access to the plasmas contained in experimental devices, pyramidal horns are not suitable for plasma imaging diagnostics. Therefore, compact, low cost, wide bandwidth millimeter wave imaging arrays are developed, and presented, together with the successful applications. Solid state devices offer a clear advantage in size, weight and cost when compared to vacuum electron devices. However, as frequency increases, the power handling capabilities of solid state devices diminishes considerably. Thus, vacuum electron devices continue to dominate the market for high power sources in the millimeter wave region. Quasi-optical grid arrays offer a possible solid state solution for a high power millimeter wave source. A quasi-optical grid array consists of thousands of solid state devices and antennas on a single wafer. Using spatial power combining, such an array provides a thousand-fold increase in power handling capacity over single devices. This approach is extremely
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