The Space Exploration Synthetic Aperture Radar (SESAR) is an advanced P-band beamforming radar instrument concept to enable a new class of observations suitable to meet multiple Decadal Survey science goals for planetary exploration. The radar is capable of providing unprecedented surface and near subsurface measurements at full polarimetry and fine (meter scale) resolution, and achieves beam agility through programmable waveform generation and digital beamforming. The radars highly flexible modular architecture employs a novel low power, lightweight design approach to meet stringent planetary instrument requirements, all while minimizing cost and development time

Carter, Lynn M.

du Toit, Cornelis F.

Lu, Daniel

Perrine, Martin

Rincon, Rafael F.

NASA Technical Reports Server

 BEAMFORMING P-BAND                            
SYNTHETIC APERTURE RADAR FOR 
PLANETARY APPLICATIONS 
 
Rafael F. Rincon, Daniel Lu, Martin Perrine,      
Cornelis F. du Toit                                  
NASA/Goddard Space Flight Center 
Greenbelt, MD, USA 
rafael.rincon@nasa.gov 
Lynn M. Carter 
Lunar and Planetary Laboratory 
University of Arizona 
Tucson. AZ, USA  
 
 
 
Abstract—The Space Exploration Synthetic Aperture Radar 
(SESAR) is an advanced P-band beamforming radar instrument 
concept to enable a new class of observations suitable to meet 
multiple Decadal Survey science goals for planetary exploration. 
The radar is capable of providing unprecedented surface and near-
subsurface measurements at full polarimetry and fine (meter scale) 
resolution, and achieves beam agility through programmable 
waveform generation and digital beamforming. The radar’s highly 
flexible modular architecture employs a novel low power, 
lightweight design approach to meet stringent planetary instrument 
requirements, all while minimizing cost and development time. 
(Abstract) 
Keywords— P-band SAR; Digital Beamforming; MIMO radar.  
I. INTRODUCTION 
The Space Exploration Synthetic Aperture Radar (SESAR) 
is a “next generation” P-band (70 cm wavelength) radar 
instrument with capabilities beyond current planetary 
instruments [1] and ideally suited to meet a number of Decadal 
Survey Science Goals [2], [3]. The instrument’s operation, 
characterized by full polarimetry, high resolution (< 6 m), and 
programmable beams, have the potential to provide 
unprecedented planetary surface and near-subsurface 
measurements. The instrument design is based on a modular, 
low power, lightweight architecture that allows the instrument 
to be configured and optimized for a specific planetary 
mission, such as a Mars or a Moon mission. Advanced 
features, such as multiple RF channels, programmable 
waveform generation, and digital beamforming provides 
SESAR with enhanced capabilities to help answer key 
questions in planetary science.   
Multiple decadal survey science goals require fine 
resolution views of subsurface stratigraphy, and the ability to 
expose bedrock and search for buried features that hold clues 
about the geologic history. For example, locating habitable 
regions, finding water, and determining the hydrology and 
cryosphere evolution is a primary goal of the Mars exploration.  
Fig. 1. SESAR is a P-band (70 cm wavelength) digital beamforming radar 
system that is modular and can be used for imaging polarimetry of Earth and 
rocky planets and moons, as well as asteroids and comets. 
SESAR’s long wavelength signals would penetrate through 
meters of material, image buried surfaces at fine spatial 
resolution and full polarimetry, and provide information to 
identify signatures of buried ice and water [2],[4]. 
On the Moon, SESAR would be able to image through 
meters of surface-covered regolith and provide information to 
characterize the near-surface stratigraphy and geology, crucial 
in the understanding of lunar processes and in the identification 
of landing sites for future lunar missions. SESAR’s fine 
resolution mapping and polarimetry would also provide details 
about the volcanic processes that built the lunar mare and to 
locate and track lava tubes [5], important for both science and 
future exploration purposes. 
II. INSTRUMENT ARICHITECTURE  
SESAR employs a multiple-input multiple-output (MIMO) 
and modular approach that distributes the radar systems into 
instrument panels composed of “smart” active subarrays, as 
illustrated in Figs 2 and 3. The radar architecture is fully 
programmable and capable of multi-mode radar operation 
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including polarimetric SAR imaging, nadir SAR altimetry, and 
scatterometry. Some of other advanced programmable features 
include single, dual, or full polarimetry; multi-look angle data 
collection; selectable resolution and swath width; digital beam 
steering (no moving parts); and beam pattern control; among 
others. This radar design is based on the successful P-band 
EcoSAR and L-band DBSAR airborne radars that were 
developed at the NASA Goddard Space Flight Center [6], [7]. 
Table 1 lists some of SESAR’s main characteristics. 
SESAR will use a distributed digital and RF electronics 
architecture that implements advanced waveform modulation 
techniques to provide the full beam steering agility while 
significantly reducing the system power consumption. Under 
the technology-development program awarded by NASA’s 
Planetary Instrument Concepts for the Advancement of Solar 
System Observations program (PICASSO), the SESAR team is 
developing an innovative Frequency Domain Multiplexing 
(FDM)  techniques to reduce the mass and power consumption 
of the Radar Digital Unit (RDU). Through other R&D efforts, 
the SESAR team is also developing innovative techniques to 
reduce the mass of the antenna, and increase the efficiency of 
the RF electronics.  
SESAR’s highly innovative architecture will allow 
synthesis of multiple antenna beams, simultaneously or 
interleaved, enabling the implementation of non-conventional 
imaging that can overcome fundamental limitations of 
conventional radar systems [8], [9], [10].  Some of its benefits 
include an increase in the measurement swath without reducing 
the received antenna gain, and the suppression of ambiguities 
or localized interference in the receiver signal by appropriate 
null-steering of the antenna pattern. The antenna gain, beam 
pointing angle, and sidelobe structure can be programmed to be 
controlled in real-time for specific tasks. Furthermore, multiple 
beams can be synthesized on both sides of the flight-track, as 
well as nadir, using a single nadir-looking antenna, thus 
increasing the coverage area. 
 
 
 
Fig. 2. SESAR employs a modular approach that permits customizing the 
architectures for a given planetary mission.  
 
TABLE 1 SESAR’S MAIN CHARACTERISTICS 
Frequency 435 MHz (P-band) 
Wavelength 0.69 m 
Max Bandwidth 100 MHz 
Pulse Width 40 μs 
Polarization HH, VV, VH, HV 
Noise Equivalent σo  < -29 dB 
Slant Range Resolution 1.5 m 
Max. Transmit Power 300 W  
Beam Steering Range ± 45 degrees 
Antenna Panel Size 3.5 m x 2.1 m 
Number of Antenna Panels Configurble (e.g., 3 for Mars) 
 
III. SYSTEM CHARACTERISTICS 
SESAR concept permits the configuration of the radar 
instrument to meet specific mission requirements. This is 
possible by the modularity of its four main subsystems: A) the 
Antenna arrays, B) the RF Transceiver Modules (RTMs), C) 
the Radar Digital Units (RDUs), and D) the Frequency Domain 
Multiplexing electronics (FDM), as illustrated in Fig. 3. Each 
subsystem is designed to be reusable and to minimize mass, 
size, and power consumption.    
A. Antenna Arrays: 
SESAR employs arrays of antenna elements distributed 
over  antenna panels, as shown in Figs 2, 3 and 4. The panels 
stow around the spacecraft during launch, and once deployed 
form a large array. The number of panels employed depend on 
the mission’s target and measurement requirements. 
 
 
Fig. 3. SESAR architecture distributes digital and RF electronics over 
arraysof antenna elelemts to provides system flexibility, and reduce power 
and mass.  
 
 
Fig. 4.  Illustration of SESAR antenna panel architecture. The elements in 
each antenna form subarrays that enable cross track scanning. The linearly 
polarized antenna elements (H and V pol) are based on a proven stack-patch 
design. 
  
After deployment, the antenna is oriented towards nadir, as 
illustrated in Fig. 2, permitting beamforming across the track 
over a large field of view (>45°). The antenna elements are 
based on a stacked-patch element design (see Fig 4) that 
permits horizontal (H) and vertical (V) polarization 
measurements over a 100 MHz bandwidth, and cross-
polarization isolation greater than 30 dB [11]. The antenna 
elements are grouped as subarrays aligned in the flight 
direction, permit cross-track beam steering over a range of ± 45 
degrees. 
 
B. Radar Trasnvceiver Modules (RTMs): 
SESAR’s RTMs build on the heritage of Goddard’s Digital 
Beamforming Synthetic Aperture Radar (DBSAR) and 
EcoSAR which miniaturized radar transceivers while 
improving system performance [6] [12]. SESAR’s RTMs 
employ surface mount components on printed circuit board 
(PCB) which yields a compact and robust design (see Fig. 5). 
The RTMs were designed for high efficiency and light weight. 
Ongoing efforts with the University of Oklahoma seek to 
increase the solid state power amplifiers (SSPA) to RF power 
while improving the efficiency to reduce the DC power.  
   
 
 
Fig. 5. SESAR’s compact and highly effcient Radar Trasncever Modules are 
distributed over the antenna panels drving each of the antenna elements.  
 
The primary function of the transceivers is to amplify the 
transmit signal to the necessary power level to feed the antenna 
subarrays and to amplify the very low power RADAR return 
signal for processing. In addition, the transceivers provide 
accurate means to calibrate the transmitter and receiver 
independently, and to reject out-of-band interference to the 
receiver. 
 
C. Radar Digital Units (RDUs): 
 
Each subarray in the radar is controlled by an RDU, as shown 
in Fig. 6. The RDUs are capable of arbitrary waveform 
generation, data acquisition, and onboard processing (see fig. 
5). These units are designed with Xilinx Kintex UltraScale 
FPGAs, low power digital-to-analog converters (D/As) and 
analog-to-digital converters (A/Ds). They synthesize based 
band signals with the appropriate phase and amplitude weights 
for transmit beam steering and side lobe control.  
Beamforming on receive is performed by coherently acquiring 
the raw complex data and processing them on board. They are 
also responsible for system synchronization, radar timing, and 
data transfers. 
 
D. Frequency Domain Multiplexing (FDM) Electronics. 
  SESAR achieves further reduction in power consumption by 
employing a novel FDM technique [13]. The FDM approach 
reduces the number of DACs and ADCs and enables 
centralized waveform generation and data acquisition with 
reduced power and mass (see Fig. 5). This approach preserves 
full array steering capabilities while reducing the number of 
DACs and ADCs by a factor of 5 or higher, resulting in a 
significant reduction of SESAR's power consumption. 
 
 
 
 
 
Fig. 6. SESAR’s RDUs designed for low power consumption, employ 
Kintex 7 FPGAs, and low power digital-to-analog converters (D/As) and 
analog-to-digital converters (A/Ds). Significnat power reduction is achieved 
by employeing a Frequency Domain Mutliplexing (FDM) Technique, which 
reduces the number of DACs and ADCs in the system.   
IV. CONCLUSION  
The SESAR instrument approach would be a first in 
planetary exploration. SESAR’s agile radar operation, 
modularity, and multimode operation, while using technology 
that can be optimized to produce the best possible data set for 
the individual science goals, will help pave the way for the 
next generation planetary radar systems. SESAR’s innovative 
approach to lower mass and power consumption will make 
these future missions feasible. 
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