GB1469152A - Circular te-on mode filter - Google Patents

Abstract

1469152 Mode filters FUJIKURA CABLE WORKS Ltd 14 March 1974 [24 March 1973 14 April 1973 18 May 1973 18 June 1973] 11506/74 Heading H1W A mode filter for a circular waveguide system propagating the circular-electric TE 01 mode comprises a waveguide section with crosssectional deformations defined by a = a 0 (1 + #p#) where a 0 is the radius of the circle, p the number of deformations which is greater than 5, # the maximum amplitude of the deformations and (a, #) are angular co-ordinates. The deformations may be in the form of longitudinal ridges. The cross-section of the filter for p = 5 is shown in Fig. 3. It is stated that mode conversion TE on (n#2)#TE pm is much greater than mode conversion from TE 01 to other modes. The desired conversion attains a maximum when the difference in phase constants of the two modes attains a minimum and this gives a criterion for choosing p, details of which are tabulated in the specification. It is stated that the attenuations of the TE on modes is many times greater than that of the TE 01 mode for values of p equal to 5, 6 and greater numbers. The specification gives an expression for calculating the optimum length of the filter. Instead of a plain conductive waveguide, a helix waveguide as shown in Fig. 5, where p = 5, may be used. The waveguide consists of a helix 12-1 of insulated wire spaced from an outer conductor 12-3 by a dielectric layer 12À2. It is shown that a filter with p=5 (as shown) is most effective for conversion of the TE 02 mode and the specification gives a detailed numerical example including the criteria used in choosing the dimensions of the ridges. The invention may also be applied to the kind of circular TE 01 waveguide using a dielectric liner (see Fig. 8, not shown). In order to deal with a wide band of frequencies, the filter may be split into several sections each effective over a subband, the sections being separated by ordinary helix waveguide sections capable of absorbing TE pq modes (see Fig. 10, not shown). In a further embodiment, Fig. 13, also designed for a wide frequency band, two filters of identical cross-section (p = 9) are arranged immediately adjacent each other and are rotated with respect to each other through an angle #=2#/4p. It is stated that the two filters operate without mutual interference.