| Aerospace

Broadband Circularly Polarized Antenna Array for Mars Rover Direct-to-Earth Communications

Printed circuit board technology is used, which requires almost no hand assembly.

Mars rovers and other landers typically use UHF relay to return their science and engineering data to Earth. Direct-To-Earth (DTE) communications are typically used for commanding. If future UHF relay capability becomes diminished, Mars landers may be forced to use DTE communications to meet their data return requirements. An augmented DTE capability with a high-gain antenna and a higher-power transmitter are required to support the relatively high data volume returned in a typical mission. The research for this innovation has developed an antenna architecture that can support such an augmented DTE capability. This antenna architecture comprises an array of microstrip patch subarrays fed by a waveguide corporate feed network, producing a net gain of 30 dBic at the array input.

The antenna sub-array is a key component of such an antenna, and is designed to be manufactured using printed circuit board technology, which requires almost no hand assembly. This makes for an easy-to-manufacture component that reduces risk if a future flight development is needed. The challenge in this design lies primarily in implementing the patch element sub-arrays, chiefly in implementing good circular polarization performance at both the X-band transmit frequency of 8.4 GHz, and the receive frequency of 7.1 GHz (which is a relatively wide percentage bandwidth) in an antenna that is compact, simple to fabricate, and low loss. To meet these challenges, a 4×4 sub-array architecture composed of half-E-shaped patch antennas fed by an integrated corporate stripline feed network was developed. Stripline feeds are highly isolated, resulting in a very low distortion to the desired antenna pattern characteristics. A probe-fed, half-E-shaped patch design was chosen for enhanced performance. The patch element design was optimized using particle swarm optimization to obtain the required RF performance. The half-E-shaped element is compact, allowing it to fit within the required footprint while meeting pattern performance requirements. It also has a single probe feed that greatly simplifies the feed design as well as minimizing insertion loss, which is approximately 0.5dB for this design.

The waveguide feed network affords much higher power handling capability than circuit board based techniques such as microstrip or stripline. The power handling capability is estimated to be at least 100 W nominal, allowing operation of the antenna with a high-power transmitter source to facilitate higher data rates for returned data. Array antennas with high gain have higher feed losses because feed size increases with aperture, therefore it is important to utilize a feed approach that minimizes loss. The waveguide feed network in this design has an insertion loss of 0.1 dB, which is 10% of the overall array insertion loss of approximately 1dB, while comprising 95% of the overall path length of the feed. This estimate does not include gimbal losses, rotary joint losses, and implementation margins, which would be the same for a waveguide feed or a transmission line feed.

This work was done by Neil F. Chamberlain, Richard E. Hodges, Sam Valas, and Jeffrey M. Srinivasan of Caltech; and Yahya Rahmat-Samii of UCLA for NASA’s Jet Propulsion Laboratory. NPO-49695