GB1018923A - Waveguide filters - Google Patents

Abstract

1,018,923. Channel-dropping filters. STANDARD TELEPHONES & CABLES Ltd. Jan. 10, 1964 [Jan. 14, 1963], No. 1590/63. Heading H1W. A channel-dropping filter comprises a main waveguide 4 having first and second resonant slots 5, 6 spaced such that the impedance of the second slot as seen from the first is in inverse relationship to the impedance of the first slot, the waveguide 4 being coupled to a branch waveguide 7 through the first slot. The waveguide is coupled by the second slot to an adjustable short-circuited stub 9 whereby an effective open-circuited impedance is presented at the second slot. The slots may both be transverse (as shown) or longitudinal and are spaced apart an odd number of quarter wavelengths at the resonant frequency. Alternatively, a transverse and a longitudinal slot spaced by an odd number of half wavelengths may be used. The main waveguide and the branch waveguide may contain multiple-section filters and several branch guides for differing channels may be coupled to the main guide. The apparatus may be connected through an appropriate transformer to a circular waveguide utilizing the H 01 circular-electric mode. Where longitudinal slots centred on the guide are used, the main waveguide may be dimensioned to support the H 02 mode which will not be excited by the slots. The slots may be formed by sparkerosion techniques.