C-Ku-Band Dual-Polarized Array Element for Shared-Aperture Frequency-Scanning Array

Accurate now-casting and forecasting could prevent losses and reduce risks caused by severe weather. Key observation to improve our knowledge of the weather is the ocean vector wind. National Oceanic and Atmospheric Administration (NOAA) is embarking on an ambiguous but needed effort to launch a new satellite-based instrument called the Dual Frequency Scatterometer (DFS) that will provide accurate global mapping of the ocean vector wind in a timely manner. The Advanced Wind and Rain Airborne Profiler (AWRAP) can play a pivotal role for this mission by providing critical measurements to improve the geophysical model function that DFS will relay on to estimate the winds. AWRAP requires a novel antenna to collect dual-polarized, dual-wavelength measurements. This work develops a subarray for the AWRAP antenna that will enable it acquire the necessary measurements from the NOAA WP-3D aircraft. By sharing the aperture for both C (5.3 GHz) and Ku (13.8 GHz) bands, this antenna array utilizes the given circular area as efficiently as possible. In both bands, the array is capable of forming and scanning a narrow beam in the x-z plane in the range 40°-60° o normal within 10% of frequency bandwidth, for both vertical and horizontal polarizations. Each subarray consists of nine dual-polarized Ku-band microstrip patch antennas and two perpendicular C-band slot antennas, sharing the aperture. Microstrip patches and their stripline feed networks are integrated into an 8-layer printed circuit board (PCB) and the slots are formed on an aluminum plate under the PCB. The PCB covers the slots, but they can radiate through the openings in the ground planes of the PCB. The C-band slots are positioned between Ku-band patches every third patch spacing. In total, four separate feed networks are required to drive the antenna elements in two bands for two polarizations. In order to achieve lower loss and higher antenna efficiencies in a small space, several transmission line technologies (namely, rectangular waveguides, suspended striplines and striplines) are used to deliver the power to the antenna elements. In order to pass the signal between different media, a broad-band perpendicular E-plane waveguide-to-suspended stripline transition is designed and fabricated in Ku band. A frequency bandwidth of 12% and an insertion loss as low as 0.09 dB are achieved in measurement. Measured input return loss of the Ku-subarray is more than 9 dB in the entire frequency bandwidth and realized gains are better than 10 dBi. Cross-polarization levels are less than -20 dB in the lower frequencies. However, in the higher frequencies, cross-polarization levels increase to -15 dB. It is proposed to use mirrored feed technique to improve cross-polarization levels of the array. For the C-subarray, measured input return loss is better than 12 dB in the entire frequency bandwidth. Measured realized gain at the center frequency is -12 dBi, and cross-polarization level is better than -20 dB

NASA Tech Briefs, October 2001

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Air Force Institute of Technology Research Report 2016

This Research Report presents the FY16 research statistics and contributions of the Graduate School of Engineering and Management (EN) at AFIT. AFIT research interests and faculty expertise cover a broad spectrum of technical areas related to USAF needs, as reflected by the range of topics addressed in the faculty and student publications listed in this report. In most cases, the research work reported herein is directly sponsored by one or more USAF or DOD agencies. AFIT welcomes the opportunity to conduct research on additional topics of interest to the USAF, DOD, and other federal organizations when adequate manpower and financial resources are available and/or provided by a sponsor. In addition, AFIT provides research collaboration and technology transfer benefits to the public through Cooperative Research and Development Agreements (CRADAs)