Waveguide filters

Claim 2

A microwave reflection filter including two waveguide channels, an input port and an output port for each said channel, tapers between said input and output ports such that the channel dimension reduces from said input ports to a region between said ports, down to dimensions corresponding to a predetermined upper cut-off frequency such that signals with frequencies above said cut-off frequency pass through the output ports and signals with frequencies below said upper cut-off frequency are reflected through the input ports, the taper from the input port of one of said channels being dimensioned in accordance with a predetermined law and the taper from the input port of said other channel being dimensioned such that the distance from the input port to the point of cut-off for any frequency in the reflected band is substantially a quarter waveguide wavelength, at that frequency, greater than the distance from the input port of said one channel to the corresponding cut-off point in said one channel.

Claim 3

A microwave reflection filter as claimed in claim 1 wherein said predetermined law is of any desired suitable form and the shape of the other taper is obtained by calculating said distance for a number of discrete frequencies and interpolating the shape of the taper between the discrete values obtained by such calculation.

Claim 4

A microwave reflection filter as claimed in claim 1 wherein the channels are semicircular in cross-section with a decreasing radius taper and the incident electromagnetic waves are in the TE01 mode of wave propagation.

Claim 5

A band branching network including a bifurcation, for transferring energy at one end thereof from a circularly sectioned waveguide to two semicircularly sectioned waveguides at the other end thereof, which is coupled to a centre excited coupler, for transferring energy below a predetermined frequency from two semicircularly section waveguides to an axially, centrally disposed waveguide having a further different cross-section, and which in turn is coupled to a reflection filter as claimed in claim 1 the combination being capable of operating such that an incident wave possessing the TE01* mode in circularly sectioned waveguide is transferred to the TE01 mode in each of the two semicircularly sectioned waveguides of the bifurcation, the TE01 mode waves in each said semicircularly sectioned waveguide being in phase opposition so that they pass through the centre excited coupler to the reflection filter, whereupon energy above said predetermined frequency passes through the reflection filter substantially unaffected thereby and energy below said predetermined frequency is reflected by the reflection filter so as to provide an in-phase relationship between the reflected TE01 mode waves which are then coupled into the waveguide having the further different cross-section.

Claim 6

A band bRanching network as claimed in claim 4 wherein said further, different cross-section is rectangular with the narrow walls thereof connected to the flat sides of the semicircular waveguides and is capable of supporting TE10 mode waves.

Claim 7

A band branching network as claimed in claim 4 wherein a diplexer known per se is connected to the output of the waveguide having the different cross-section to provide further band branching.

Claim 8

A microwave reflection filter as claimed in claim 1 wherein the waveguide channels include tapers between said region and the output ports, the taper in said other channel from the output port to said region being in accordance with said predetermined law and the taper in said one channel from the output port to said region having the same dimensions as the taper in said other channel from the input port to said region.

Claim 9

A microwave reflection filter as claimed in claim 7 wherein the predetermined law with which the taper from the input port of said one channel and from the output port of said other channel is dimensioned is a cos2 law.