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This paper clarifies the radiation characteristics of a tension truss-type deployable antenna based on measurements made on its solid model and presents its experimental method. The main reflector of the model antenna is constructed by many triangular plates approximating a paraboloid. As the aperture shape of a tension truss-type deployable antenna is a hexagon, the difference between the circular aperture of the model antenna and the hexagon is covered with radiowave absorbers. The distribution of mechanical reflector t:rrors which are projected on the aperture plane is formulated and their relations to electrical errors is shown. Data on reduction of gain and grating lobes in the radiation pattern arising from periodic reflector errors are obtained. The measured results are compared with calculated values of radiation characteristics and good agreement is obtained. It is shown that radiation characteristics can be estimated by the aperture integration method by neglczting the disturbance of current distribution at seams of facets.

In most of the deployable antennas to be placed on board a satellite, the main reflector is made of planar facets or ruled surface. Therefore, an anomaly can be expected in the electric field distribution on the aperture in comparison with the smooth reflector. This paper presents the near-field measurement method, relevant problems, and measurement results for a polyhedron approximated antenna with a reflector made of planar facets. The near-field measurement system is of a polarplane scanning type, and the two polar components of the electric field can be measured simultaneously. With this system, the near-field of the polyhedron approximated antenna is measured. It is experimentally shown that the amplitude is maximum at the junction of the facets; thus, the validity of the previously reported theoretical analysis is proven. Although the near-field distribution depends on the measurement plane, the results of the transform of Presently with Toyo Communications. 79 such a distribution to the far-field by the aperture distribution method are identical regardless of the measurement plane. Further, reduction of the near-field measurement points is discussed. In the case of the present antenna, it is shown to be necessary to use 30 points and 36 points, respectively, of the number of measurement points in the radial and circumferential directions with the measurement scan range at the circumscribing circle of the hexagonal aperture, if the far-field paraxial radiation characteristics obtained are accurate to within 1 dB.