Electronically-scanned phased-array antennas
Electronically-Scanned Large Aperture Membrane Arrays
L-band interferometric synthetic aperture radar (InSAR) is critical for measuring surface deformation caused by seismic and volcanic phenomena and for hazard monitoring. It also has broad application to other high-priority science, including soil moisture, biomass, glaciology and cold land process measurements.
16 x 16 element active membrane array being developed by Radar Science & Engineering.
We need increased accessibility and coverage to improve the science return of the next-generation InSAR missions, which require operation from higher vantage points  . However, operation at higher orbits requires many new capabilities such as very large (>400m2) lightweight antennas with distributed electronics and wavefront control techniques that are currently not possible. Conventional phased-array antenna technologies have a mass density of 8-15 kg/m2 (for antenna, electronics, and structure) [2, 3] . Existing launch vehicles are not capable of supporting the payload requirements of such a large antenna. Current systems use rigid manifolds where electronic components are individually packaged and integrated onto panels. One method to dramatically reduce the weight, stow volume, and associated cost of space-based SAR is to replace the conventional rigid manifold antenna architecture with a flexible membrane. Using this approach we expect to achieve a mass density of 2 kg/m2  .
We are currently developing a 16 x 16 element active membrane array (see figure at right). The active portion of the array is 2.3 m x 2.3 m. This membrane phased array consists of a repeating pattern of patch antennas and the patch feed.
The membrane is 125-µm-thick Pyralux®AP™ (DuPont’s copper-clad all-polyimide flexible circuit material) with 18-µm copper layers. The transmit/receive (T/R) electronics, located on the backside of the ground plane, are coupled to the radiating patches via slot feeds. The T/R module for this antenna is a hybrid multi-layer module that is assembled and packaged independently and attached to the membrane array. For more details see  .
Other technologies in this area include:
- Embedding of thinned die inside membrane materials using flip-chip assembly techniques (see [6, 7] ). This work is in collaboration with Prof. R. Wayne Johnson at Auburn.
 C. W. Chen, A. Moussessian, “MEO SAR system concepts and technologies for Earth remote sensing,” AIAA Space Conference, September 2004.
 W. Edelstein, S. Madsen, A. Moussessian, C. Chen, “Concepts and Technologies for Synthetic Aperture Radar from MEO and Geosynchronous Orbits,” SPIE International Asia-Pacific Symposium, Remote Sensing of the Atmosphere, Environment, and Space, November 2004, Honolulu, Hawaii, USA.
 A. Moussessian, C. Chen, W. Edelstein, S. Madsen, P. Rosen, “System Concepts and Technologies for High Orbit SAR,” Invited paper, The IEEE MTT-S International Microwave Symposium, Long Beach, CA, June 2005.
 A. Moussessian, L. Del Castillo, J. Huang, G. Sadowy, J. Hoffman, P. Smith, T. Hatake, C. Derksen, B. Lopez, E. Caro, “An Active Membrane Phased Array Radar,” The IEEE MTT-S International Microwave Symposium, Long Beach, CA, June 2005.
 A. Moussessian, L. Del Castillo, M. Zawadzki, U. Quijano, V. Bach, E. Weininger, J. Hoffman, P. Rosen, “An Electronically Scanned Large Aperture Membrane Array,” NASA Science Technology Conference, Adelphi, MD, June 2007.
 T. Zhang, Z. Hou, R.W. Johnson, A. Moussessian, L. Del Castillo, C. Banda, “Flip Chip Assembly of Thinned Silicon Die on Flex Substrates,” APEX 2005, Anaheim, CA, February 2005.
 B. Holland, R. McPherson, T. Zhang, Z. Hou, R. Dean, R.W. Johnson, L. Del Castillo, A. Moussessian, “Ultra-thin, flexible electronics,” Electronic Components and Technology Conference, May 2008.
 W. Kuhn, M. Mojarradi, A. Moussessian, “A resonant switch for LNA protection in Watt-level CMOS transceivers,” IEEE Trans. Microwave Theory Tech., pp. 2819-2825, September 2005.
UAVSAR Phased-Array Antenna
The UAVSAR airborne repeat-pass interferometric SAR provides rapid-revisit as well as long-term surface change detection capabilities. Collecting high-precision repeat-pass radar measurements requires accurate repetition of the aircraft track and radar look angle over widely varying atmospheric conditions. This is achieved by using an electronically-steered phased-array antenna.
UAVSAR phased-array antenna on test range.
The electronically-steered phased-array antenna transmits over 2 kW total from 24 T/R modules. Both transmit and receive antenna patterns are adjusted in real time to compensate for the changing yaw angle of the aircraft. Switching within the feed networks provides a choice of transmit polarizations and simultaneous dual-polarization receive. Built-in calibration networks are used to continuously monitor transmit and receive phase delays so that phase drifts can be removed. The entire system is designed to operate robustly over a wide temperature range using stable low-CTE material for critical circuits. The antenna is also designed for high-reliability and easy field serviceability, allowing the UAVSAR system to effectively collect science data even on extended campaigns to remote locations.
UAVSAR phase-array antenna installed in instrument pod on NASA G-III aircraft.
Millimeter-wave antennas and electronics
GLISTIN Digitally-Beamformed Array Antenna
The “Glacier and Land Ice Surface Topography Interferometer” (GLISTIN) is an instrument concept for a single-pass, single platform interferometric synthetic aperture radar (InSAR). GLISTIN uses an 8.6-mm wavelength, which minimizes snow penetration yet has relatively low atmospheric attenuation. Such a system has the potential for delivering topographic maps at high spatial resolution, high vertical accuracy, independent of cloud cover, with subseasonal updates. This will greatly enhance current observational and modeling capabilities for studying ice mass-balance and glacial retreat.
1m x 1m Ka-band DBF antenna on test range.
GLISTIN uses a cross-track digitally-beamformed (DBF) antenna to provide a wide measurement swath. To demonstrate this concept and advance the technology readiness of this design JPL has developed a 1 m x 1 m digitally-beamformed Ka-band (35.6 GHz) slotted waveguide antenna with integrated digital receivers. This antenna provides 16 simultaneous receive beams, effectively broadening the swath without reducing receive antenna gain. The implementation of such a large aperture at Ka-band presents many design, manufacturing and calibration challenges that are addressed as part of this program.
The 1 m x 1 m aperture is divided into 16 “sticks” along the elevation dimension. Each stick has a Ka-band to L-band downconverter and subsampling L-band digital receiver. Data from all 16 receivers is captured for later processing. Sixteen simultaneous beams are formed across the swath. The L-band digital receivers are also suitable for using in L-band DBF arrays, by omitting the downconverter stage.
L-band digital receivers.
G-Band Landing Radar
Landing on a planet or other body presents many challenges, requiring precision navigation and guidance from initial entry all the way to touchdown. Delivering large payloads with very small landing error ellipses requires advanced sensors to supply critical data to the autonomous guidance systems. In partnership with JPL’s Instrument Electronics and Sensors Section (389), we are developing technology for millimeter-wave landing radar systems operating in the 140-160 GHz (G-band) frequency range. The small wavelength enables highly accurate velocity sensing using substantially smaller antennas than are currently employed. However, the small wavelength presents many technological challenges in the areas of MMIC design and array packaging. To demonstrate the feasibility of G-band landing radar systems, we have develop a range of systems designs to meet the needs of future missions along with laboratory demonstrations of packaged transmit/receive modules.
150-GHz transmit/receive module (L. Samoska, D. Pukala, Sec. 389).
Transmit/receive modules and RF pulsed power amplifiers
In order to support future missions requiring electronically-steered arrays or solid-state power amplifiers (SSPA), we are developing a range of transmit/receive (TR) modules, SSPAs and pulsed power conditions. Much of this work is performed in partnership with industry, academia and other JPL sections (including Flight Communications Systems , Instrument Electronics and Sensors , and Power and Sensor Systems ). T/R module or SSPA demonstrations have been produced at L-band (1.2 GHz), Ku-band (13.6 GHz), Ka-band (35.6 GHz) and G-band (150 GHz) with transmit power levels from milliwatts to over 100 W.
Ka-band array module with 8 x 2-W transmit channels and 26 receiver channels (C. Andricos, Sec. 337).
2.5-W L-band T/R module membrane array (J. Hoffman, Sec. 334).
UAVSAR 100-W L-band dual-polarized T/R module (REMEC Defense and Space).
30-W L-band T/R module (C. Andricos, Sec. 337).
Highly miniaturized RF electronic systems
Advancing radar science goals requires development of compact, high- performance, high-frequency electronics, such as Ku-band, Ka-band, and W-band. Miniaturization is also critical to lower frequency missions that require large phased array antennas, such as L-band interferometric synthetic aperture radar (InSAR). A large number of transmit/receive modules are required for these antennas, so reductions in size and mass are important for mission cost and feasibility.
Our focus is on miniaturization and risk reduction of Radar System RF components – reducing their mass, volume, power, and cost. Reducing the resources required by a single instrument also enables new instrument architectures and mission configurations, increasing science return and the possibility of cross-discipline science. As part of this effort we are developing common architectures and components addressing multiple upcoming missions requiring multiple, compatible frequency plans and architectures.
This effort is reducing risk for near-term radar missions, such as SMAP and NISAR; reducing risk and increasing TRL for mid-term missions, such as SWOT and XOVWM; as well as reducing risk and increasing TRL and driving innovations for far-term missions, such as SCLP and ACE.
We are currently testing several hybrid sub-circuits that will make up our complete compact Ka-band radar, such as the front-end receiver with receive protection and calibration ports, shown below, left, and the radar’s transmitter electronics, shown below, right.
Ka-band receiver front-end test fixture using hybrid components.
Design (top) and prototype hardware (bottom) for a hybrid Ka-band radar transmitter.
Real-time data processor systems
On-Board Processor for Synthetic Aperture Radar Interferometry
On-board imaging radar data processor for single-pass and repeat-pass interferometry will enable:
- The observation and use of surface deformation data over rapidly evolving natural hazards, both as an aid to scientific understanding and to provide timely data to agencies responsible for the management and mitigation of natural disasters.
- The use of topographic mapping radar for planetary missions where the interplanetary downlink data rate is the limiting factor.
Functional flow for the repeat-pass interferometric SAR on-board processor.
This technology is being developed for the following ongoing and future projects:
- UAVSAR: UAV-based L-band SAR for repeat-pass interferometry
- Provide real-time high resolution SAR imagery
- Provide near real-time disturbance detection capability
- NISAR: L-band for repeat-pass interferometry (InSAR)
- Selective onboard processing will increase science coverage
- Surface Water Ocean Topography (SWOT) mission: Ka-band wide swath radar for surface water measurements
- Onboard processing is necessary to achieve wide swath coverage within available downlink data rate
- Lunar Mission Opportunities:
- On-board processor technology is critical in using Ka-band imaging radar for landing and science applications
With funding from the NASA ESTO AIST program, we developed a compact, reconfigurable real-time interferometric SAR processor by combining both FPGA and microprocessor technologies. This processor features:
- Europa Orbiter Mission Concept:
- On-board processor technology for Ka-band single-pass InSAR is critical in reducing the downlink data rate to < 670 kbps
- High throughput front-end to ingest raw data from data storage device via fiber-channel interface with maximum data rate of 1 Gbps
- Real-time reconstruction of airborne platform trajectory by using a 6-state Kalman filter to ingest 3-dimensional position and velocity data
- Dynamic Doppler parameter updates for motion compensation and azimuth compression via VME bus
- Presummer to decimate and re-align range compressed data in the along track direction to provide flexibility in:
- Reducing corner-turn memory size and azimuth FFT length
- Matching processor output data rate to spacecraft downlink data rate
- Capability to handle both spaceborne and airborne SAR data
Custom FPGA board for the OBP (left); Envisat image of Mt. Etna generated by the real-time OBP (right).