Daniel H. Schaubert

Professor of Electrical and Computer Engineering
University of Massachusetts
 

Radar Antenna Research


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Multi-frequency Dual-Polarized Cloud Radar Antenna


The University of Massachusetts Microwave Remote Sensing Laboratory is building a multi-frequency radar to measure particle sizes and density of clouds as part of global warming and climatology studies. Three radars operating at 13, 35 and 94 GHz will use a single antenna system mounted on a large truck for transportability. The antenna was designed, assembled and tested by the Antenna Laboratory. A single, dual-polarized, two-frequency feed was designed for 13 and 35 GHz. The feed illuminates the subreflector of a dual-offset Gregorian antenna. The 2-meter main reflector is fully utilized for the 13 GHz beam, yielding 0.75-deg beamwidth H and V polarized beams with identical shapes and boresight directions. At 35 GHz, only the central portion of the main reflector is used to produce 0.75-deg H and V polarized beams that are aligned with the 13-GHz beams. The design of the feed insures that the four beams (two frequencies + two polarizations) are matched for all look directions. The 95-GHz beam requires only a 30-cm aperture, which is provided by a small dielectric lens antenna mounted securely to the main reflector.
The new antenna system is smaller and lighter than a multiple-antenna system with similar performance, and it eliminates problems of parallax and alignment that have plagued previous multiple-antenna systems.

Wide Bandwidth Phased Arrays


The Antenna Laboratory at UMass has studied wide bandwidth Tapered Slot Antenna antennas and arrays, often called Vivaldi antennas, for two decades. Efficient computational electromagnetic (CEM) codes have been developed and used to design wide bandwidth scanning arrays and to uncover key phenomenology that governs the behavior of these antennas. The early work of the laboratory provided quantitative estimates of the radiation characteristics of single Tapered Slot Antennas (TSAs). Our frequency domain CEM codes for infinite arrays provided the first antenna designs with bandwidths exceeding 5:1 and scan volumes exceeding 450 from broadside. For several years, UMass has supported the efforts of international radio astronomers to design a radio telescope with one square kilometer of collecting area. The antenna should operate 0.2 – 2.0 GHz, providing 1 square degree field of view and 0.1 arcsec resolution at 1.4 GHz. Many visitors and collaborators contributed to our understanding of wide bandwidth antenna arrays and enriched the educational experience of our students.

 

Time-Domain Integral Equation Analysis


Time-domain computational methods are particularly useful for studying wide bandwidth radiation and scattering because the computations are performed without matrix inversion and Fourier transformation of the transient response yields the entire frequency range at once. The UMass Antenna Lab has developed an efficient time-domain integral equation code exploiting the efficiencies of surface integral formulations and incorporating several techniques from advanced signal processing to maintain stable solutions even for large structures that require a very long time history to accurately characterize their behavior. Using TDIE, ordinary desktop computers can analyze the input impedances of a 16x16 array of Vivaldi tapered slot antennas in a couple of hours. A convenient user interface permits entry of many common antenna types with a few mouse clicks and the post-processor provides easy to interpret graphical displays of key antenna and scattering parameters.

 

Ultrawide Bandwidth Antenna Systems


In collaboration with the UMass Wireless Communication Center, the University of Southern California, and UC Berkeley, the Antenna Laboratory is developing antennas and analysis techniques for UltraWide Bandwidth (UWB) communication, tagging and location systems. UWB systems use extremely wide bandwidth signals with low power spectral density so that they can coexist with narrow bandwidth signals without significant degradation of those signals. Typically, UWB antennas must effectively radiate or receive signals with more than an octave of frequency bandwidth, and they should be small and inexpensive to fulfill objectives of many proposed applications. Time-domain analysis of UWB antennas yields necessary information for the ultrawide bandwidth signals. Easy to use computer codes based on Marching-in-Time algorithm for Maxwell's equations permit quick and accurate characterization of existing antennas and helps to design new antennas with improved performance.