Abstract: In a temperature-stabilized microwave filter, each resonant cavity (5) is tuned by means of a tuning rod (10) of a thermally stable material. A first end of each tuning rod (10) extends into the respective cavity (5) without touching its surface. A second end is clamped, remotely of the cavity (5), into the filter body (1-2). At the position of this second end the filter body (1-2) has a bore (13) of substantially the same diameter as the tuning rod (10). The tuning rods (10) are clamped by pairs of retaining screws (15) accommodated in clearance holes in the filter body on one side of a longitudinal groove (21) intersecting the bore (13) and anchored into the filter body (1-2) on the other side of the groove (21).

Abstract: A hyperfrequency filter comprises a series connection of an inlet length of waveguide (1), a plurality n of resonant cavities (3, 4, 5) and an outlet length of waveguide (2). All these units are of rectangular cross-section and they are interconnected by coupling irises (16, 17, 18, 19). Each resonant cavity includes a dielectric tuning screw (13, 14, 15) for adjusting the resonant frequency of the cavity. Each tuning screw is located in the middle of one of the largest faces of its resonant cavity.The longer dimension a of the cross-section of each cavity is longer than the longer dimension of the cross-section of the waveguide lengths so that the optimum width of the coupling irises is substantially at its minimum possible value for a given set of design conditions on the other filter parameters. This has the effect of broadening the range of frequencies over which a given structure can be tuned without detrimental repercussions on the frequency characteristic of the filter.

Abstract: Two main rectangular wave guides e.g. for telecommunications in GHz frequency bands are coupled by arms inclined for example at 60.degree.. This simultaneously simplifies machining of the coupler in the form of two symmetrical shells and also improves the electrical characteristics of the coupler.

Abstract: A millimetric wave high-pass filter is assembled from two axially-separate halves. Each half comprises a cast metal body having a channel which is divided to form two wave guides by means of a metal strip. The dimensions of the wave guides of the filter as a whole decrease towards a constriction at their centers while the strip is relatively thick at the constriction and tapers towards the ends. This configuration makes it possible to cast the filter in two halves with the body and the strip of each half being cast in a single piece. When assembled the halves meet at the level of the constriction.

Abstract: A series connection of n diplexers is used as a multiplexer for separating a hyperfrequency band into n + 1 sub-bands (or vice-versa). Each diplexer comprises a semi-circular inlet coupler followed by a semi-circular high-pass filter and by a semi-circular outlet coupler, the filter at each stage is dimensioned to reflect only the lowest of the sub-bands which it receives from the previous stage. The creation of unwanted parasitic modes in the reflected sub-band is avoided by so choosing the radius of the inlet coupler that the reflected sub-band lies between the frequencies at which the parasitic TE.sub.12 and TE.sub.22 modes occur. This is achieved by use of the relationship ##EQU1## WHERE V IS THE SPEED OF LIGHT, FMAX AND FMIN ARE THE UPPER AND LOWER LIMIT FREQUENCIES OF THE REFLECTED SUB-BAND AND P'.sub.12 and P'.sub.22 are the second zeros of the first and second order Bessel functions characterising the respective semi-circular TE.sub.12 and TE.sub.22 modes.

Abstract: The invention relates to a microwave mode transducer for changing between e rectangular TE.sub.10 mode and the semi-circular or circular TE.sub.01 mode. It comprises a microwave mode transducer comprising a semi-circular wave guide and a rectangular wave guide, the wave guides having substantially parallel longitudinal axes and being separated by a web which forms at least a part of the plane wall of the semi-circular guide and one of the smaller side walls of the rectangular guide, the guides being coupled by orifices in the web which orifices are substantially contiguous and are substantially as wide at their maximum width as the wall of the rectangular guide in which they are made.