GB1377742A - Waveguide coupler arrangements - Google Patents

Abstract

1377742 Directional filters MARCONI CO Ltd 30 March 1972 [8 May 1971] 13905/71 Heading H1W A band-separating filter comprises a narrowwall waveguide directional-coupler provided with symmetrically positioned reactances near the opposite narrow walls of the coupler within the coupling zone. In the self-explanatory arrangement of Fig. 3, the reactances take the form of two arrays of ports 8, 9 and in a modification (Fig. 5, not shown) solid conductive members bounded by the same line as is defined in Fig. 3 by the ports. Within the coupling zone, the waveguides are wide enough to support both the TE 10 and TE 20 modes and the reactances are so dimensioned that the TE 20 waves are close to cut-off. The TE 10 mode is propagated as a wave having co-phasal components in respective waveguides and the TE 20 as a wave having components in antiphase in respective waveguides (the two modes are sometimes referred to as "odd" and "even" modes in some accounts of this kind of coupler). The two modes are indicated respectively by dashed and chain dotted lines, the resultant by a solid line. Because of frequency dispersion, a band centred on f 1 near the cut-off frequency of the TE 20 mode is coupled between ports 3 and 5, whilst a band centred on a higher frequency f 2 is coupled between ports 4 and 5 (Fig. 4, not shown). The ports are matched to the coupling zone by steps. The ports 9 are spaced by #/8 (at the mean working frequency) over the greater part of the coupling zone. At the edges the ports 8 diminish in diameter and the spacing is gradually reduced according to a Chebyshev or binomial coefficient law.