Demonstration of Ultrawideband Hyperspectral Microwave Interferometer by True Time Delay

Abstract

JAXA has conducted earth observations using the AMSR series of satellite-borne microwave radiometers (MWRs) for 20 years. Although design of the AMSR series poses problems in terms of lifetime, spatial resolution, and artificial radio frequency interference (RFI), the same design has been carried over to the AMSR2 successor (AMSR3) currently under development. In response to the need for technological development to solve these problems, we began studying a satellite-borne MWR based on a new concept. We recently developed a new-type MWR, DSμRAD. This is the world's first hyperspectral MWR that can receive microwave power from L- to Ka-band with an ultrawideband antenna and measure the spectrum of brightness temperature in high-frequency resolution by ultrahigh-speed A/D converters. Based on the development of DSμRAD, we believe that a hyperspectral microwave interferometer (MWI) with a phased array antenna (PAA) composed of ultrawideband antennas is the most ideal MWR that can solve all the problems at once. This MWI controls pointing by true time delay (TTD) taking advantage of ultrahigh-speed sampling. As the first step to demonstrate this idea, we developed and tested the most basic two-element ultrawideband hyperspectral MWI based on DSμRAD. As a result, the sharp main lobe of the MWI was simultaneously formed over the 4-16 GHz range at the same position, and its pointing and width could be controlled as intended. In particular, the azimuthal shift of the main lobe caused by the time delay given to the signal of either element did not depend on the frequency.