GB1444540A - Electrical filters - Google Patents

Abstract

1444540 Filters PLESSEY CO Ltd 28 Aug 1973 [13 Sept 1972] 42414/72 Heading H1W Filters are formed by connecting shortcircuited stubs in pairs to spaced common points on a main transmission line. Each pair of stubs forms a complete loop which is shortcircuited at an intermediate point. The connection points are spaced apart by an odd number of quarter-wavelengths at the centre frequency of the filter and the aggregate length of the stubs forming each pair is equal to a multiple of one wavelength at this frequency. Each stub, however, varies from a half-wavelength (or appropriate multiple) by a small amount which determines the band-width of the filter. Thus a filter consists of successive pair of stubs of lengths # 0 /2 Œ# r where r is different for each pair and runs through 1 to n where n is order of the filter. In the 2nd order filter of Fig. 3, the pairs of stubs 1, 2 and 3, 4 (shown as single lines) are each constituted by a loop having a short-circuit realized in the form of a slider which is common to both loops. As shown in Fig. 4a, a rotary slider 15 adjustably connects tracks 10, 11 to a conductive disc 14 to which the earth conductors of all the stubs are connected in common. The "live" conductors of lines 1, 2 are connected respectively to terminals 12 and those of lines 3, 4 to terminals 13. The loops shown in Fig. B are thus completed by the tracks 10, 11. Where there are more than two pairs of stubs, a slider using a number of concentric tracks may be used.