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COUPLING add-on

COUPLING is an add-on object to GRASP for calculating the complex coupling ratio between two independent sources. Both the transmitting and the receiving source may be given as feeds, feed arrays and current distributions.

A few applications:

Telemetry antennas

The simplest case deals with two small antennas which could be intended for telemetry or command purposes and have wide angle patterns. In such a case it is of interest to be able to calculate the level of received power in one of the antennas when the other is transmitting. When mounted on a scattering structure, such as a satellite, the different structural parts may be taken into account through a series of interactions.

Centre-fed dual reflector configuration

Another application is the centre-fed dual reflector configuration. In such a case a feed illuminates the subreflector which in turn radiates onto the main reflector. However, the induced currents on the subreflector also radiate back into the feed horn and cause a degradation in the return loss of the feed. An even more severe situation occurs in radar systems if circular polarization is employed and if the receiver is attached to the orthogonal port of the transmitter. In this case the reflected field from the subreflector will be directed to the receiver, and since the level can be very high relative to the signal level for which the receiver is intended, it is important to determine this level so that adequate protection of the receiver can be implemented. The level can be determined by performing a coupling analysis between the current elements on the subreflector and the feed system.

Conjugate field matching

The 'conjugate field matching' method is used when a reflector is illuminated by a plane wave from some direction. This gives rise to a current distribution on the reflector, and if the reflector is equipped with a feed array in the focal plane it is possible to perform a coupling analysis between each feed and the current distribution. The results of such analyses can be used to determine a beam forming network for the feed array, so that the array will generate the desired beam. This procedure, though, requires knowledge of both amplitude and phase of the coupling.