In order to reduce the effect of gain and noise instabilities in the RF chain of a microwave radiometer, a Dicke radiometer topology is often used, as in the case of the proposed surface water and ocean topography (SWOT) radiometer instrument. For this topology, a single-pole double-throw (SPDT) microwave switch is needed, which must have low insertion loss at the radiometer channel frequencies to minimize the overall receiver noise figure. Total power radiometers are limited in accuracy due to the continuous variation in gain of the receiver. Currently, there are no switches in the market that can provide these characteristics at 92, 130, and 166 GHz as needed for the proposed SWOT radiometer instrument.
High-frequency SPDT switches were developed in the form of monolithic microwave integrated circuits (MMICs) using 75-ìm indium phosphide (InP) PIN-diode technology. These switches can be easily integrated into Dicke switched radiometers that utilize microstrip technology. The MMIC switches operate from 80 to 105 GHz, 90 to 135 GHz, and 160 to 185 GHz. The 80- to 105-GHz switches have been tested and have achieved 15-dB return loss (>18 dB for the asymmetric design), and >15-dB isolation. The isolation can be tuned to achieve >20-dB isolation from 85 to 103 GHz. The 90- to 135-GHz SPDT switch has achieved 15- dB return loss, and 8- to 12-dB isolation. However, it has been shown that the isolation of this switch can also be improved. Although the 160- to 185- GHz switch has been fabricated, it has not yet been measured at the time of this reporting. Simulation results predict this switch will have 20-dB return loss, and >20-dB isolation. /p>
The switches can be used for a radiometer such as the one proposed for the SWOT Satellite Mission whose three channels at 92, 130, and 166 GHz would allow for wet-tropospheric path delay correction near coastal zones and over land. This feat is not possible with the current Jason-class radiometers due to their lower frequency signal measurement and thus lower resolution.
The design work was done by Oliver Montes, Douglas E. Dawson, and Pekka P. Kangaslahti of Caltech for NASA’s Jet Propulsion Laboratory. The processing of the InP MMIC circuits was done by Kwok Loi and Augusto Gutierrez from NGST. NPO-48083
This Brief includes a Technical Support Package (TSP).
Single-Pole Double-Throw MMIC Switches for a Microwave Radiometer
(reference NPO-48083) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package for Single-Pole Double-Throw (SPDT) MMIC switches designed for microwave radiometers, developed under NASA's Commercial Technology Program. It presents the results of research and technology advancements in microwave switch design, particularly focusing on high-frequency applications.
The work described in the document was conducted by Montes et al. and presented at the SWOT-ACT ESTF 2011 conference in Pasadena, California. The primary objective was to design microwave switches that operate across three frequency ranges: 80-105 GHz, 90-135 GHz, and 160-190 GHz. These switches were realized using monolithic microwave integrated circuit (MMIC) technology, fabricated with Northrop Grumman’s 75-μm thick InP MMIC PIN diode process. The use of PIN diodes was crucial due to their low insertion loss and fast switching speeds, making them ideal for high-frequency applications.
The document details the design topology and the specific characteristics of the switches, including microstrip and coplanar waveguide technologies. Variations of the SPDT designs were fabricated with different PIN diode sizes ranging from 3 to 8 μm. As of the report, the 80-105 GHz and 90-135 GHz switches had been tested, while the 160-190 GHz switches were still pending evaluation.
In addition to the technical details, the document acknowledges the support received from NASA's Earth Science Technology Advanced Component Technology ACT-08 Program, led by Steven C. Reising of Colorado State University. The research was carried out at the Jet Propulsion Laboratory (JPL) and involved collaboration with various individuals from Northrop Grumman and NASA's Earth Science Technology Office.
The document serves as a resource for those interested in the technological advancements in microwave switch design and their potential applications in aerospace and other fields. It emphasizes the importance of innovative partnerships and the ongoing support from NASA in advancing research and technology in this area.
For further inquiries or additional information, the document provides contact details for the Innovative Technology Assets Management at JPL, encouraging engagement with the ongoing developments in aerospace-related technologies.
