Title: High Frequency PIN-Diode Switches for Radiometer Applications
Author: Oliver Montes
Organization: Caltech / Jet Propulsion Laboratory
Co-Authors: Douglas E. Dawson, Pekka Kangaslahti, Steven C. Reising, Kwok Loi, Augusto Gutierrez

Dicke switching radiometers utilize an RF switch to modulate the input of the receiver between the signal from the antenna and the signal from a fixed reference load internal to the radiometer. Subsequent demodulation makes the radiometer much less susceptible to fluctuations in the gain or loss of components downstream from the switch in the receiver chain. Therefore, the stability of the radiometer is greatly improved, resulting in improved noise measurement capability. The Jet Propulsion Laboratory (JPL) has designed and tested high frequency single-pole double-throw (SPDT) switches fabricated on monolithic microwave integrated circuits (MMIC) that can be easily integrated into radiometers that utilize microstrip technology. The use of MMIC and microstrip technology, as opposed to waveguide technology, greatly reduces the mass and volume of the instrument, which are important for space applications. In particular, the switches developed at JPL can be used for a radiometer such as the one proposed for the Surface Water and Ocean Topography (SWOT) Satellite Mission with three channels at 92, 130, and 166 GHz to allow for wet-tropospheric path delay correction in coastal areas and over land, a feat not possible with the current Jason-class radiometers due to their lower measurement frequencies and thus lower spatial resolution.

Indium Phosphide (InP) PIN diode technology was used for the development of the high frequency microwave switches due to the low loss and very fast switching speed (< 1 μsec) of PIN diodes. The low capacitance when reverse biased and low resistance when forward biased makes the PIN diode ideal for microwave switch applications. The MMIC switch circuits were designed with Agilentís Advanced Design System (ADS) microwave circuit simulation software using PIN-diode models provided by Northrop Grumman Space Technology (NGST). The MMIC chips were fabricated at NGST using their InP PIN diode process and measured at JPL using high frequency test equipment. Simulation and measurement results will be presented.