Antennae
On the satellite, phased-element array antennas were chosen to provide the communications link. A phased-element array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.[1] While both hardware and software are relatively complex compared to a large dish antenna, the advantages that phased arrays provide far outweigh its complexity. The two main advantages of array antennas for the IRIS communications subsystem are:
- Electronically configurable gain pattern
- Fault tolerance
Since the array antenna is electronically controlled, the gain pattern can be manipulated to achieve beam steering. This reduces the need for moving parts that might possibly fail as well as having a significant speed advantage over mechanical parts. As for fault tolerance, in addition to mechanical failure, should one element in the array fail, it does not drastically hinder the antenna as a whole.
Figure C1. Gain pattern from a phased-element array. [Figure Reference 1]
Current solutions for phased array antennas can be used even at Geostationary Earth Orbit [2], providing evidence that the solution will work for our Medium Earth Orbit space solar power system.
There is more flexibility in choosing Earth station antennae, and as such large aperature dish antennas, on the order of 2-5meters can be used to attain high gain for transmission and reception.
