Radiation patterns of a paraboloidal reflector fed by a pyramidal horn with lossy walls

Abstract

normalized input impedances of standing-wave dipoles having the same half-lengths are also shown in Fig. 5; note the large variation of the input impedance for this type antenna. This behavior indicates that the mutual coupling between antenna elements having a traveling-wave distribution of current is weaker than that for standing-wave antennas. For more than two elements, the mutual impedance will still be smaller for traveling-wave elements as compared to standing-wave elements; however, the locus of points of the input impedance as a function of the phase difference between array elements will no longer be a circle.Admittedly, there is a price to be paid for this reduction in the mutual coupling; about 50 percent of the input energy is dissipated in the resistive load [ 11. However, there are applications, particularly for receiving arrays, for which this trade-off is warranted.E. E. Altshuler, "The traveling-wave linear antenna," IEEE Trans.Abstract-A reduction of 7 dB in cross polarization in pyramidal horns is achieved by covering the walls of the horn with a dissipative material. The corresponding loss in co-polar gain is found to be less than 1 dB. The effect of dissipative material is to reduce wall surface currents and hence cross polarization. INTRODUCTIONExperimental studies indicated that far-field cross polarization in pyramidal horns is brought about by surface currents on the walls normal to the direction of polarization [l], [ 2 ] . This suggests that if radiation from the walls is attenuated, then far-field cross polarization can be reduced. Attenuation of fields radiated by the walls can be achieved by coating the inner surface of the horn walls with some absorbing material or by placing absorbing slabs against the interior surface of the walls.The presence of the absorbing material within the horn cavity is expected to reduce not only the cross-polarized fields but also the copolarized ones. The effect on the co-polar field is, however, much less than that on the cross-polarized field. Besides loss in co-polar gain, one also expects the co-polar radiation pattern to be affected due to possible changes in aperture field distribution as dictated by the boundary conditions at the lossy walls [3].It is the purpose of this communication to report some recent measurements carried out on a small pyramidal horn, to verify the above theory, and to study the effect of absorbing the walls on the copolar gain and radiation pattern.

Power Transport Theorem Based Decoupling Mode Theory for Wave-Port-Fed Transmitting Antennas

“…Besides the metallic horn antenna, PTT-DMT can also be used to analyze the other kinds of wave-port-fed metallic antennas. Here, the metallic parabolic reflector antenna reported in [45] is analyzed by using PTT-DMT, and its radius and focal depth are 31 cm and 11.5 cm respectively, and it is fed by a wave port locating at the focal point of the reflector antenna. The JE-DoJ-based modal resistance curves are shown in Fig.…”