Jacqueline C. Chen

AirMOSS: An Airborne P-band SAR to measure root-zone soil moisture

A keystone of the Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) investigation is the P-band Synthetic Aperture Radar (SAR), which will provide calibrated polarimetric measurements that will be used to retrieve the root-zone soil moisture (RZSM) over regional scale (250 kha) areas imaged. The radar is based on JPLs L-band Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) system. It is currently under development and scheduled to begin flights in mid-2012. The AirMOSS P-band SAR inherits UAVSARs existing L-band RF and digital electronics subsystems. New up- and down-converters convert the L-band signals to UHF frequencies (280-440 MHz). The passive antenna is based on the legacy GeoSAR design.

THz dichroic plates for use at high angles of incidence

The design of a high-frequency dichroic plate consisting of an electrically thick self-supporting metallic mesh that can be used in a linearly polarized quasi-optical system at high angles of incidence is described. The measured and computed performance of a 2.5-in-aperture mesh is given. This mesh has a 3-dB cutoff frequency of 875 GHz and less than 0.75 dB of transmission loss from 950-1350 GHz at incidence angles of 0, 30, and 45 degrees . The results of a multimode waveguide analysis corroborate the measured data.<<ETX>>

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.

X/Ka-band dual frequency horn design

The Deep Space Network has a need for a dual frequency horn for simultaneous dual frequency operation in a beam waveguide antenna. The dual frequency horn will receive X-band (8.4-8.5 GHz), KABLE frequency (33.6-33.8 GHz), and DSN Ka-band downlink (31.8-32.3 GHz) signals simultaneously. The horn is designed to receive circularly polarized waves. Low loss (noise) in the dual frequency horn is a prime consideration since the horn is employed in the reception of signals from deep space.<<ETX>>

Gaussian beam and physical optics iteration technique for wideband beam waveguide feed design

A novel approach is demonstrated which involves iterating Gaussian beam and beam waveguide (BWG) parameters to obtain a wideband BWG feed. The result is further improved by making a comparison with the physical-optics result and repeating the iteration. The basic goal was to design a BWG feed system with good performance from 2 to 32 GHz, utilizing mirror sizes of 20 lambda at the low frequency. The BWG antenna performance (e.g. gain, efficiency, noise temperature) at S, X, and Ka-bands is presented. It is noted that higher-gain horns are needed for higher frequencies.<<ETX>>

Juno microwave radiometer all-metal patch array antennas

This paper focuses on the design and RF performance of metal patch antenna arrays for the Juno microwave radiometer (MWR) instrument [1]. Juno is a NASA New Frontiers mission to Jupiter scheduled to launch in 2011. Metal patch antenna elements contain no dielectric. This is attractive for the Juno application because the elimination of dielectric prevents electrostatic discharge due to high-energy electrons in the Jovian orbital environment. Dielectric materials can be engineered to bleed static charge by doping them with carbon powder, but it can be difficult to obtain the desired balance of DC, RF, structural, and thermal performance. All-metal patches side-step these materials issues and provide a design that is amenable to predictable performance, both from an electrical and mechanical point of view. The metal patch design has good pattern performance and other advantages, including wide bandwidth, precise tuning, low mass, and good thermal and emissivity properties.

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.

Theoretical and experimental results for a thick skew-grid FSS with rectangular apertures at oblique incidence

Theoretical and experimental results for the reflection characteristics of a thick plate containing rectangular holes on a skew grid at oblique angles of incidence are presented. By including a large number of waveguide modes in the solution, excellent agreement between theory and experiment has resulted. The use of a corrugated horn and lens allowed a high-quality test of the theory using a relatively small plate in the near field of the horn. The software is now being used to design thick frequency selective surfaces for high-power low-noise applications in the Deep Space Network.<<ETX>>

Accurate insertion loss measurements of the Juno patch array antennas

This paper describes two independent methods for estimating the insertion loss of patch array antennas that were developed for the Juno Microwave Radiometer instrument. One method is based principally on pattern measurements while the other method is based solely on network analyzer measurements. The methods are accurate to within 0.1 dB for the measured antennas and show good agreement (to within 0.1dB) of separate radiometric measurements.

Design of thick frequency selective surfaces with complex apertures: dichroics with cross-shaped and stepped rectangular apertures

Recent work has shown the successful demonstration of design techniques for straight, rectangular apertures at an incident angle of 30 degrees . In the present work, some of the cases in which the straight rectangular shape may have limited usefulness are addressed. For example, grating lobes become a consideration when the bandwidth required to include the new frequency of 7.165 GHz conflicts with the desired incident angle of 30 degrees . For this case, the cross shapes increased packing density and bandwidth could make it desirable. When a sharp frequency response is required to separate two closely spaced Ka-band frequencies, the stepped rectangular aperture might be advantageous.<<ETX>>