GB761763A - Microwave filters - Google Patents

Abstract

761,763. Microwave filters. STANDARD TELEPHONES & CABLES, Ltd. May 1, 1953 [May 8, 1952], No. 12112/53. Class 40 (8). A microwave filter comprises a transmission line of the parallel conductor type described in Specifications 704,050, 708,601 and 761,764, pairs of obstacles being disposed along one or both of the conductors to form resonant sections. The transmission line comprises a " line " conductor 1, Fig. 1, separated from a comparatively wide " ground " conductor 2 by a layer of dielectric 3 a small fraction of a quarter-wavelength thick. The obstacles 4, 5, 6, 7 consist of short lengths of conductive material disposed cross-wise to form two resonant cavity sections of length l. These sections are tuned by means of short pieces of wire 9, 10 soldered in adjusted positions on the line 1 or the cross-pieces 4, 5, 6, 7. Fig. 4 shows in cross-section another method of tuning by means of conductive posts 11, 12 embedded in the dielectric layer 3. A further method of tuning (Fig. 3, not shown) consists in varying the width of the line 1. In a modified form of the filter of Fig. 1, the " ground " conductor 2 is of the same width as the " line " conductor 1 and is provided with cross-pieces corresponding to the cross-pieces 4. 5, 6, 7. The ends of corresponding crosspieces on the conductors 1, 2 may be joined or left open-circuited. A filter of this type may be tuned by off-setting corresponding crosspieces on either side of the dielectric layer with respect to each other. In the filter of Fig. 9, cross-pieces of different length are provided, the cross-pieces 28, 29, 30, 31 representing transformer couplings between adjacent resonant sections whilst cross-pieces 32, 33, 34 determine the susceptance of the resonant sections. The filter is tuned by means of capacitative posts 35. Modified forms of filter may be made by cutting the " line " conductor 1 to various configurations such as that shown in Fig. 11. Tuning is carried out by cutting away portions of the small projections 38, 39. The filter may also be made by severing the " line " conductor 1 (Figs. 14, 15, not shown) into separate lengths, the adjacent pieces being coupled by small pieces of wire which are adjusted to tune the filter. Specifications 761,761 also is referred to.