Mark Zawadzki

Design, Analysis, and Development of a Large Ka-Band Slot Array for Digital Beam-Forming Application

This paper discusses the design, analysis, and development of a large Ka-band slot array for digital beam-forming application. The array consists of 160 times 160 elements in 16 subarrays for producing 16 digital beams in the receive mode. Infinite array mutual coupling model has been employed in the design and analysis models. Challenges posed in meeting the pattern and return loss specifications because of manufacturing tolerances are discussed. Measured return loss and pattern characteristics of 10 times 40 slot array modules as well as results on a 1 m times 1 m demonstration array are presented.

Waveguide-Slot Array Antenna Designs for Low-Average-Sidelobe Specifications

This paper discusses the design, analysis, and development of waveguide-fed planar slot arrays to achieve low-average-sidelobe specifications, as may arise in radiometer applications. Such antennas may be required to meet strict average sidelobe levels in different angular regions, and low average return loss over a specified bandwidth. In addition to Elliotts design technique, we used a Moment-Method analysis program, Ansofts HFSS code, and results of tolerance studies using Monte Carlo simulations to meet the design objectives. Comparisons of simulated results and experimental results are also presented.

The Glacier and Land Ice Surface Topography Interferometer: An Airborne Proof-of-Concept Demonstration of High-Precision Ka-Band Single-Pass Elevation Mapping

As part of the NASA International Polar Year activities, a Ka-band cross-track interferometric synthetic aperture radar (SAR) recently demonstrated high-precision elevation swath mapping capability. This proof-of-concept instrument was achieved by interfacing two Ka-band slotted-waveguide antennas in a cross-track geometry and Ka-band electronics with the Jet Propulsion Laboratorys L-band uninhabited aerial vehicle SAR. Deployed on the NASA Gulfstream III, initial engineering flights in March and April 2009 marked the first airborne demonstration of single-pass cross-track interferometry at Ka-band. Results of a preliminary interferometric assessment indicate height precisions that, for a 3 m × 3 m posting, range from 30 cm in the near range to 3 m in the far range and greater than 5 km of swath over the urban areas imaged. The engineering flights were followed by a comprehensive campaign to Greenland in May 2009 for ice-surface topography mapping assessment. Toward that end, coordinated flights with the NASA Wallops Airborne Topographic Mapper lidar were conducted in addition to establishing ground calibration sites at both the Summit Station of the National Science Foundation and the Swiss Camp of the Cooperative Institute for Research in the Environmental Sciences. Comparisons of the radar-derived elevation measurements with both in situ and lidar data are planned for a subsequent paper; however, at this stage, a single data example over rugged ice cover produced a swath up to 7 km with the desired height precision as estimated from interferometric correlation data. While a systematic calibration, including assessment and modeling of biases, due to penetration of the electromagnetic waves into the snow cover has not yet been addressed, these initial results indicate that we will exceed our system requirements.

The UAVSAR phased array aperture

The development of a microstrip patch antenna array for an L-band repeat-pass interferometric synthetic aperture radar (InSAR) is discussed in this paper. The instrument will be flown on an unmanned aerial vehicle (UAV) and will provide accurate topographic maps for Earth science by 2007. The antenna operates at a center frequency of 1.2575 GHz and with a bandwidth of 80 MHz, consistent with a number of radar instruments that JPL has previously flown. The antenna is designed to radiate orthogonal linear polarizations for fully-polarimetric measurements. Beam-pointing requirements for repeat-pass SAR interferometry necessitate electronic scanning in azimuth over a range of plusmn20degrees in order to compensate for aircraft yaw. Beam-steering is accomplished by transmit/receive (T/R) modules and a beamforming network implemented in a stripline circuit board. This paper focuses on the electromagnetic design of the antenna tiles and associated interconnects. An important aspect of the design of this antenna is that it has an amplitude taper of 10dB in the elevation direction. This is to reduce multipath reflections from the wing that would otherwise be detrimental to interferometric radar measurements. The amplitude taper is provided by coupling networks in the interconnect circuits as opposed to using attenuators in the T/R modules. Details are given of material choices and fabrication techniques that meet the demanding environmental conditions that the antenna must operate in. Predicted array performance is reported in terms of co-polarized and cross-polarized far-field antenna patterns, and also in terms of active reflection coefficient. Measured performance of a 4-element by 2-element antenna tile is presented

Slot array antennas for the Juno radiometer application

In this paper, the design and analysis of two planar array geometries, the conventional one and a symmetric design that exhibits significantly lower sidelobe levels is discussed.

Technology Demonstration of Ka-band Digitally-Beam formed Radar for Ice Topography Mapping

GLISTIN (Glacier and Land Ice Surface Topography Interferometer) is a spaceborne interferometric synthetic aperture radar for topographic mapping of ice sheets and glaciers. GLISTIN will collect ice topography measurements over a wide swath with sub-seasonal repeat intervals using a Ka-Band digitally-beamformed antenna. This paper will give an overview of the system design and key technology demonstrations including a Im x Im digitally-beamformed Ka-band waveguide slot antenna with integrated digital receivers. We will also detail the experimental scenario that we will use to demonstrate both the beamforming and interferometric performance of this system.

The design of H- and V-pol waveguide slot array feeds for a scanned offset dual-polarized reflectarray

A unique experimental mission being designed by NASA/JPL is the wide swath ocean altimeter (WSOA). A unique offset-fed reflectarray antenna design was developed to meet the requirements of the missions two antennas. Each antenna has two feeds located off-focus to produce two beams scanned /spl plusmn/3.3/spl deg/ from nadir. Waveguide slot arrays were selected as the feeds for the reflectarray for their efficiency, low mass, high power-handling capability, and the relative ease with which to implement amplitude and phase tapers. Amplitude tapers are required to achieve the required secondary beamwidths and phase tapers are required to focus the feed energy on the reflectarray, since the reflectarray is located in the near-field of the feeds. While the design of waveguide slot arrays is not new, this particular design effort shows that very good results can be achieved on a first attempt using established slot array design techniques and commercial software for the waveguide power divider network. The design process is discussed in detail.

Juno Microwave Radiometer patch array antennas

The requirements, design, and performance of the Juno Microwave Radiometer patch array antennas were discussed. The antennas meet both the electrical performance and environmental requirements. There is generally good agreement between measurements and calculations.

A reflectarray antenna for use in interferometeric ocean height measurement

A deployable reflectarray antenna is developed for use in a Ku-band dual polarization cross-track interferometer instrument. It is found that the reflectarray antenna provides unique, mission enabling advantages for a large dual polarized antenna in terms of stowage, dual beam aperture efficiency and cost. This paper presents experimental results to demonstrate that reflectarray antenna technology is sufficiently mature for flight applications

Low-sidelobe slot arrays for the Juno Microwave Radiometer

Juno is a NASA New Frontiers mission to Jupiter scheduled to launch in 2011. One of the instruments on board is called the Juno Microwave Radiometer (MWR), which will peer into the outer layers of Jupiter with the goal of determining the composition of ammonia and water in its atmosphere. This information will contribute to the knowledge of Jupiters formation and evolution. The instrument uses six frequency bands, each requiring an antenna with very low sidelobes. Three of the antennas are 8×8 waveguide slot arrays with approximately 30dB Taylor slot amplitude distributions operating at 2.6GHz, 5.2GHz and 10GHz, and each requiring bandwidths of 4%. This paper presents a practical overview of the design and analysis of these antennas and compares measurements with the predictions, including those of finite element models on a finite ground plane using HFSS - a relatively large problem electrically. It was found that there was very good agreement between the HFSS predictions and the measured patterns down to at least −35dB. Due to limited time and space constraints, the paper will focus on the largest and most difficult to fabricate of these antennas, the 2.6GHz “A3” slot array.