Inner Workings of High-Gain Mars Rover Antennas?

cavac asks: "I've been searching for detailed info on how the high gain antennas on the Mars Rovers work, but did not find much useful information except that they DO work. I've been wondering: they are disc-shaped and are approximately the size of a CD. They somehow reassemble parabolic antennas but actually aren't, are they? Anyway, how much use would a parabolic antenna that size have? When I first saw them, they reminded me of the old antennas[*] (enclosed in plastic) used on vacuum tube based radio projects[*]. So, what's really inside the Mars Rovers high gain antennas? Note: Links marked with [*] are german language but the pictures should be self explaining."

Comments

X-band, and other matters.

[mlyle]

The MERs use X-Band for high data rate communications back to earth-- which has a wavelength of 3cm, making high gain antennas considerably smaller and more practical.

It's my understanding that the high gain antenna on MER is a compact phased array design. Even parabolic antennas could be practical at the 3cm wavelength, though they wouldn't be flat (which was obviously preferable for footprint issues).

Re:X-band, and other matters.

[stienman]

The X-Band Phased Array Antenna has one major benefit. Phased array antennas are meant to mimic the directivity and gain of a parabolic antenna, with the ability to aim it, in an array of antennas that does not move and is flat.

So basicly you take a bunch of flat antennas, do some 'magic' between the array and the signal source (or destination) and you can effectively aim the antenna as though you were actually moving a parabolic antenna.

Since the antenna on spirit is aimed mechanically, and phased array antennas are, IIRC, still pretty power hungry, then it may be that they are not using a phased array. However, it would make a lot of sense to use a phased array for fine control aiming and the machanical link for coarse control.

-Adam

You mean like this?

[JCMay]

Before Harris sold it to JetBlue, they developed LiveTV, a system to bring DirecTV to airliners in-flight. The receiver includes a phased array antenna that scans in elevation while sitting on a gimble that allows the beam to be scanned in azimuth.

Phased arrays use lots of power, but that's because each antenna element in the array requires its own amplifier(s) and phase shifter (or time delay unit). Fortunately, those amplifiers cam be much smaller than the monolithic amplifier required to drive a dish (since the signals from each amplifier in the array are summed together).