During the launch, landing and orbit phases of the proposed HERMES spacecraft, telecommand data (10 kb/s) and telemetry data (25 kb/s) are transmitted between HERMES and the ground by a relay satellite. An analysis of operational requirements resulted in the selection of four switched antennas, integrated within the plane structure, each of which may comprise several antennas. The two software packages used assess the performance of these antennas are briefly reviewed. The first package is for implementing the boundary element method (BEM). The program is executed on a DEC VAX 8600 and the linear system, whose matrix is complex, symmetrical and complete, is solved on an array processor, FPS 164/MAX. The electromagnetic characteristics (radiation patterns, surface currents, etc.) of the antenna are displayed graphically. The other package, SARGASSES, is an interactive simulator for antennas on structures such as aircraft or spacecraft.<>

A general finite-element method is applied to compute the skin current of a perfectly conducting surface illuminated by an incident electromagnetic wave. Surface charges over any element and currents flowing through any edge are approximated by polynomials of degree m. Some radiation patterns of two horns are calculated and compared with those obtained from experiment.