GB1419635A - Waveguide filters electronic circuit for activating - Google Patents

Abstract

1419635 Band-separation filters MARCONI CO Ltd 25 Oct 1973 [11 Nov 1972] 52189/72 Heading H1W A waveguide band-separation filter 13 comprises two channels 1, 2 which taper from input ports 3, 4 to a minimum cross-section corresponding to a chosen cut-off frequency, and expand from the minimum cross-section to the output ports 5, 6. The tapers 7 from the input port 3 and the output port 6 may be designed in accordance with a cos<SP>2</SP> law. The tapers 8 from the input port 4 and the output port 5 are designed such that for any frequency in the reflected band the distance of the point of cut-off from the input or output port is greater than the corresponding distance in tapers 7 by one quarter wavelength. Hence the reflected waves suffer a 180 degrees differential phase-shift and the transmitted waves are substantially unaffected. The channels 1, 2 may be of semicircular cross-section and (as shown) are connected to a coupler 12, and to a bifurcation 11. Wave energy in the circular electric TE<SP>0</SP> 01 mode at the input 14 of the bifurcation is divided in antiphase between the (semicircular) channels 17, 18 of the coupler and passes unaffected into the filter 13. The reflected waves are in phase in the coupler channels 17, 18 and hence are coupled into the rectangular waveguide 19.