Abstract: To track an object such as a space probe or a satellite emitting an electromagnetic radio signal, the signal received at a ground antenna is passed through a circular waveguide section propagating modes TE.sub.11 and TE.sub.21. Polarized signal components of the higher TE.sub.21 mode are extracted from the waveguide through two pairs of lateral slots and their differences are multiplied by an r-f reference signal of the same frequency obtained from a preamplifier coupled to an output port to which the signal of mode TE.sub.11 is transmitted by way of a rotatable polarization changer. Corrective signals resulting from these multiplications are proportional to spatial coordinates of the tracked object in a predetermined Cartesian system, one of whose axes coincides with that of the waveguide section, and serve to keep the antenna trained upon the object.

Abstract: A parabolic reflector antenna, designed to discriminate between incoming and outgoing waves having mutually orthogonal planes of polarization, has a ratio R between focal distance f and diameter D which, for optimum efficiency and cross-polarization decoupling, lies between 0.46 and 0.5 and operation in the TE.sub.11 mode and above 0.6 for operation in the dual TE.sub.11 +TM.sub.11 mode. An associated feed, in the shape of a slightly tapering horn of circular cross-section connected to a waveguide of square cross-section, has a relative aperture .alpha., defined as the ratio between its aperture radius r and the wavelength .lambda..sub.o at the center of the operating frequency band, which in the first instance ranges between 0.52 and 0.6 and in the second instance is given by kR+h with k.apprxeq.1 and h between about 0.1 and 0.15.

Abstract: An antenna designed to emit a beam of generally elliptical cross-section has a reflector with a parabolic-elliptical concave surface conforming to the formula(x/p)+(y/q)=2zwhere p and q are the parameters of its parabolic cross-section in the xz and yz planes, respectively. A microwave feed located on a line interconnecting the foci of these two parabolas, preferably at the outer focus separated from the surface vertex by a distance q/2, generates a beam parallel to the axis whose ellipticity depends on the ratio q/p.