Constraints for antennas selection¶

The type of antenna and associated performances are strongly linked to the considered central frequency. However, constraints are not the same for the aircraft antenna or for the ISAE antenna as we will describe below.

ISAE antenna:¶

Given the distance and the bit rate required to fulfil the specifications, a tracking antenna might be needed on the roof on the antenna. Nevertheless, as this solution is considerably increasing the system complexity, we will try to design a system with a fixed mounted antenna if possible.

In fact, the need (or not) for tracking will be determined by the required figure of merit (G/T) of the antenna (computed in part III).

*As increasing the gain of the antenna decreases its coverage (theta 3 dB), if the required gain of the antenna leads to a coverage smaller than the aircraft action zone, a tracking antenna will be required.

Aircraft action zone limited
Increase gain ->> increase G/T but decrease coverage. If no tradeoff can be found between the coverage and the gain, a tracking antenna has to be used

Rq: high gain easier to realize for high frequencies, T decreasing when G increasing*

Aircraft antenna:¶

The connection between the aircraft and the ISAE building shall remain available for an inclination of 45° and an attitude of 15° at a distance of at least 50 km.

As tracking antennas are not an option for the aircraft because of the complexity of integration, these availability requirements dictate a given radiation pattern for the aircraft antenna.

Graph pattern, idée antenne, mais masquage de l’avion …