SOURCEFORGE » RALF » 2014 Dimensioning and budgeting of TM/TC link

h1. Constraints for antennas selection

The type of antenna and associated performance 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. 

h2. 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 (cf part _"compution of (G/T)"_). As increasing the gain of the antenna will decrease its coverage ( $\theta_{3dB}$ ), if the required gain of the antenna leads to a coverage smaller than the aircraft action zone, a tracking antenna will be required. 

h2. 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. However, a tracking antennas is not an option for the aircraft because of its possible fast angular motion and the integration complexity.

These availability requirements impose huge constraints on the radiation pattern of the aircraft antenna. In fact, we couldn't find a slot were the antenna would never be masked by the aircraft for the given specifications. Then, a system with two antenna might be considered, but a study of interferences between them should be performed.

As the antenna integration is not the aim of our project, we will suppose that a such system can be performed, but we won't detail it.