Abstract: A microwave antenna has a circularly symmetrical reflector made of a material having a liquid phase and a solid phase, with the reflector being obtained by centrifuging the material while in its liquid phase and then allowing it to pass into its solid phase. This results in a convex paraboloidal reflector face having a very high degree of surface accuracy. When housed inside a microwave absorbing ring connecting the reflector face to a microwave-transparent window and used with a suitable source held at a predetermined focus position between the reflector and the window by means of microwave absorbent triangular struts, the antenna demonstrates improved radio and mechanical properties. Alternately, the centrifugally cast convex paraboloidal reflector may be used as the main reflector in a hybrid Cassegrain optical system in which the subreflector has a "conformed" non-paraboloidal surface that is machined from a solid piece of material.

Abstract: An antenna is provided equipped with a device which rotates the direction of the rectilinear polarization of a wave transmitted to a receiver (or transmitted by a transmitter) associated with the antenna, with respect to this same wave such as it is received by the antenna (or transmitted by the antenna). The device is formed from a square cross-section wavequide which is twisted in steps and which steps may be adjustable and which is twist guide inserted in the primary source of the antenna, between the horn of the antenna and the receiving (or transmitting) means associated with the antenna.

Abstract: A multiplexing device for a multiband antenna. It essentially comprises, in series from the coupling input to the antenna: a common guide permitting the passage of a high frequency band and a low frequency band, into which issue by means of two coupling holes staggered with respect to one another along the common guide, two orthogonal guides which constitute the inputs for the two orthogonal polarizations of the lower band; a junction; and a polarization duplexer for the higher band. The coupling holes contain resonators forming a short-circuit for the higher band frequencies.

Abstract: A primary source for a space communications antenna requiring a mode extractor means comprises more especially a horn with two types of evenly spaced alternate corrugations whose depth decreases, for each of the types, from the neck to the opening, followed by a band separator of the quasi-optical filter type, followed by a mode extractor means placed in series in the reception channel of the primary source.

Abstract: A transducer for coupling to an antenna with a first polarizing duplexer for working in a low-frequency band, a between-guide transition element formed from a variable-section guide and a second polarizing duplexer for working in a high-frequency band. In the polarizing openings of the first duplexer are placed dipoles resonating at the mean frequency of the high band which cause a short-circuit for the high frequencies and let the low frequencies pass. A set of quasioptical filters, situated in the body of the first duplexer, between the polarizing openings of this first duplexer and the transition element, causes a short-circuit for the low frequencies and lets the high frequencies pass.

Abstract: A cylindrical metal sheath surrounds the beam rays between the antenna and the passive reflector of a periscope arrangement; this sheath forms the support of the periscope arrangement as well as a screen against parasitic radiation.

Abstract: A corrugated horn of the exponential type is provided with corrugations whose depth decreases exponentially from the throat of the horn towards its mouth. Such corrugations have the effect of reducing the stationary wave ratio.

Abstract: An antenna is made operative for two frequency bands, .DELTA.F.sub.B and .DELTA.F.sub.H, the latter higher than the former, by means of a frequency selective absorber, covering, in its edge region, a reflector of the antenna in order to reduce the diameter of the reflecting surface of the reflector and therefore the gain of the antenna for frequency band .DELTA.F.sub.H.

Abstract: In an antenna of the Cassegrainian or Gregorian type including a periscope arrangement, the auxiliary reflector has a longer focal distance than the auxiliary reflector of a conventional antenna of this type and the length of the optical path between the auxiliary reflector and the primary source of the antenna is choosen substantially equal to the distance between the auxiliary reflector and that one of its two foci which is the more remote therefrom. This makes it possible to use only plane mirrors in the periscope arrangement.

Abstract: A multiplexer-demultiplexer operates in the 3.6 to 4.2, 5.9 to 6.4, 6.4 to 7.1 and 10.7 to 11.7 kmc. The multiplexer-demultiplexer first picks off the signals of the first frequency band, and thereafter separates the signals of the fourth frequency band from other frequency bands, comprising the second and third frequency band, of the input signals, all these operation being performed for each one of the vertical and horizontal polarizations. The aforesaid other frequencies are thereafter separated according to polarization only before it is demultiplexed according to frequency.