Patent GB-541634-A (GB)
Title: Improvements in or relating to electric wave transmission networks
IPC: H01P5/04
Filed: 1940-06-27
Abstract: 541,634. Impedance networks; electric resonators. ELECTRICAL RESEARCH PRODUCTS, Inc. June 27, 1940, No. 10953. Convention date, Aug. 4, 1939. [Class 40 (iii)] Co-axial transmission lines are combined with variable condensers to form a wide-band filter having a uniform impedance-transformation ratio, adjustable band-width and a pass band, which can be shifted in the frequency scale. Fig. 7 shows the equivalent circuit of a structure 16, 17, 18, Fig. 6, in which the image impedances bear a high ratio to the characteristic impedances of the co-axial resonators employed. The short-circuit 19, Fig. 6, of the middle section 18 is adjustable, and the corresponding shunt arm LB, 21 is so shown in Fig. 7. According to the invention, variable lumped capacitances 10, 11, Fig. 6 are shunted across the input and output terminals, 1, 2 and 3, 4 of the structure. The band-width is varied by adjusting the short-circuit 19, and the location band can 6e shifted by adjusting the capacitances 10, 11. A similar network in which the inductances in the equivalent circuit form a delta instead of the tee LA, LB, LC is described (Figs. 1-4, not shown). Similar networks having a high image impedance at one end (the condenser 10 being in shunt) and a low impedance at the other (the condenser 11 being in series) are described with reference to Figs. 8, 9 (not shown) which show inductances in delta formation, and Figs. 10, 11 (not shown) which show inductances in T formation. Networks having at each end an image impedance which is low in comparison with the characteristic impedances of the co-axial resonators are described (Figs. 12 to 14, 15, 16, not shown) which respectively show a delta connection and a T-connection of the three inductances, which both show a series connection of the lumped capacitances 10, 11 instead of the shunt connections seen in Fig. 6. The Specification explains how to calculate and adjust the magnitudes of the elements of the networks, and gives numerical values for the practical embodiment shown in Fig. 17, which is of the type illustrated in Figs. 6, 7, but has the end resonator 17 in line with the middle shunt resonator 18 and at right angles to the other end resonator 16, instead of the arrangement shown in Fig. 6. The characteristic impedance of the resonators 17, 18, as determined by the diameters of the inner conductor 33 and outer conductor 32 are the same, while that of the resonator 16, comprising conductors 53, 54, is different. The short-circuiting connection 19, Fig. 6, of the resonator 18 comprises a metal annulus 37 with springs 38 and a handle in the form of a disc 41 of insulating material. The terminal connections of the end resonators 17, 16 are made respectively to a feeder 31, connected as shown and to a diode 30 whose plate 59 is connected to the inner conductor 54 while its cathode 57 and heater 58 are connected to external circuits through insulated plates 61 which are capacitively related to the terminal plate of the outer conductor 53. The end lumped capacitance 22, Fig. 7, comprises a fixed capacitance between the end plate 43 of the inner conductor and an annular flange 44 on the end plate 45 of the outer conductor, together with a variable capacitance between the end plate 43 and a screw-adjustable plate 49. Alternatively, Fig. 18 (not shown) the screw-adjustable plate may be mounted on the inner conductor. The other lumped capacitance 20 is furnished by an adjustable screw 69 on the outer conductor and a disc 68 on the inner conductor.