IEEE - Aerospace and Electronic Systems - May 2020 - 28

Feature Article:

DOI. No. 10.1109/MAES.2020.2981795

Multifrequency Spaceborne Deployable Radiometer
Antenna Designs
Wang Hongjian, Key Laboratory of Microwave Remote Sensing, National
Space Science Center, Chinese Academy of Sciences;
University of Chinese Academy of Sciences

INTRODUCTION
Recognizing the importance of global sea wave and its
applications, atmospheric correction microwave radiometer (ACMR) of ocean dynamic satellites is employed to
correct atmospheric path delay in the radar altimeter.
Microwaves operating at frequencies of 18.7, 23.8, and 37
GHz are sensitive to atmospheric water vapor, precipitation
over oceans, cloud liquid water, snow or ice coverage, and
other geographical parameters [1]-[3]. Therefore, radiometer working at these bands with dual polarizations is of
great importance for data retrieval. Calibration of the radiometer in-orbit was achieved by viewing the cold space
and internal matched loads for each channel of the radiometer. High main beam efficiency (MBE) (usually above
90%) is required for the radiometer antenna to achieve
sharp contrast of the scene-brightness variation [2]. An offset dish is chosen as the observing antenna (OA) to eliminate the blockage by the feed, at the same time large focal
length to aperture (f/D) is helpful to reduce the cross-polarization (CP) levels of the antenna [4]. Multifrequency dual
polarization function reflector antenna can be realized by
three feed horns [3]. However, the swaths for different frequencies do not coincide with each other; in addition, the
two lower frequency antenna patterns (18.7 and 23.8 GHz)
have inevitable severe distortions. Therefore, the retrieval
accuracy is decreased. A common feed with tri-band is
needed to overcome these errors. Wideband polarization
grids are not suitable for this OA common feeding

subsystem because of the limited structure space for the
quasi-optics approximation [4], [5]. Therefore, a multiplexer is employed to separate the multifrequency dualpolarization waves. Several key technologies put high
demand on wideband corrugated horn (2:1 band ratio)
design, ultra-wideband OMT design, and filter design.
Three corrugated horns followed with three OMTs are
selected as the ACMR calibration antennas.
A curved-profile horn is chosen instead of one with a
common straight profile [6] in order to have the phase
centers as close to the horn aperture as possible for triband; nevertheless, the feed phase center's deviation
from the focal point results in the offsets axially and laterally. The horn aperture is designed with appropriate
edge tapers (ET) for high MBE requirements at all
bands. Tradeoff should be made to diminish the discrepancy between the focal point and horn's phase centers at
tri-band. The ACMR OA imposes some unique mechanical, thermal, and RF design challenges in stability
requirements. Two hinges are utilized for the deployment of the reflector dish. All in all, this ACMR has
some similarities with the Jason-2 advanced microwave
radiometer [7] but with a much wider frequency band.
This article presents the mechanical and electrical
designs of the tri-band dual polarizations OA with a
common feed subsystem. Measurement of the patterns
and deployment, together with the pointing accuracy,
are also outlined.

KEY ELECTRICAL DESIGN OF THE OVERALL ANTENNA
Authors' current address: Wang Hongjian, Key Laboratory of Microwave Remote Sensing, National Space Science
Center, Chinese Academy of Sciences, Beijing 100190,
China; University of Chinese Academy of Sciences, Beijing
100490, China (e-mail: wanghongjian@mirslab.cn).
Manuscript received October 14, 2019, revised February 3,
2020, and ready for publication March 18, 2020.
Review handled by Mauro De Sanctis.
0885-8985/20/$26.00 ß 2020 IEEE
28

The schematic block diagram of the ACMR is shown in
Figure 1. The ACMR is calibrated by employing the hot
blackbody around the temperature of 293 K and the cold
sky horns that detect the stable and uniform cold cosmic
radiation. The three calibration horns (each horn for only
one frequency band) are mounted on the satellite deck
towards the cold sky, while the ACMR OA is mounted on
the direction facing the earth. Take vertical pol, for

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