GB1591719A

GB1591719A - Orthogonal mode transducers

Info

Publication number: GB1591719A
Application number: GB5330776A
Authority: GB
Original assignee: ARCONI CO Ltd
Current assignee: ARCONI CO Ltd
Priority date: 1976-12-21
Filing date: 1976-12-21
Publication date: 1981-06-24
Also published as: DE2709565A1; DE7706758U1; JPS5381047A

Description

(54) ORTHOGONAL MODE TRANSDUCERS (71) We, The MARCONI COMPANY LIMITED, a British Company of Marconi House, New St. Chelmsford, Essex CMi 1PL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a waveguide orthogonal mode transducer. Such transducers may be used to combine or separate orthogonal polarised waves where it is required, for example, to transmit on one of the orthogonal modes of wave propagation and to receive on the other orthogonal mode of wave propagation.

A known orthogonal mode transducer is shown in Figure 1 of the drawings accompanying the Provisional specification in which a square sectioned common waveguide channel 1 is connected to a first auxiliary waveguide channel 2 through the intermediary of a smooth tapering, impedance transition 3, and a second auxiliary waveguide channel 4 forms a narrow wall coupler to one side of the common waveguide channel 1. In operation, a TE10 mode shown by the arrow headed line a, representing the direction of the E-field in the common waveguide channel, does not couple with the channel 4, since the channel 4 is dimensioned to be cut-off to this mode, but passes through the transition 3 to be coupled into the channel 2. Conversely, a TE01 mode, polarised orthogonally to the TE1o mode, (shown by the arrow headed line b) is reflected by the channel 2 due to the narrow height of this channel and couples to the channel 4 with the same direction of E-field.

The channel 4 thus forms an H-plane junction with channel 1 with regard to the TE01 mode which, it has been found, provides a mis-match between these two channels. In some circumstances, to provide a wider bandwidth, it is necessary to have a further auxiliary waveguide channel (not shown) on the opposite wall of the common waveguide channel 1 from the channel 4, so that an H-plane T-junction is formed, but this has the disadvantage that the impedance match between the H-plane junction channels is worsened because in the equivalent circuit of such an H-plane T-junction the impedances are connected in parallel.

The present invention seeks to provide an orthogonal mode transducer in which the foregoing mis-match problems are at least partially reduced.

According to this invention, an orthogonal mode transducer includes a common waveguide channel for propagating the two orthogonal modes, a first auxiliary waveguide channel dimensioned so as to propagate only one of the orthogonal modes and connected to one end of the common waveguide channel, and, connected to the common waveguide channel, second and third auxiliary waveguide channels each of which form an E-plane junction for the other orthogonal mode and which are dimensioned to be cut-off to the said one mode, the second and third auxiliary channels being connected to mutually opposite sides of the common waveguide channel, and wherein the total impedance of the second and third auxiliary waveguide channels is substantially the same as the impedance of the common waveguide channel.

Preferably, the impedance of each of the second and third auxiliary waveguide channels is one half that of the common waveguide channel.

Conveniently, the first auxiliary waveguide channel is connected to the common waveguide channel through the intermediary of an impedance transition, such as a smooth taper.

Preferably, septums are provided in the connecting paths of the auxiliary channels to ensure that the auxiliary channels are cut-off to the appropriate unwanted mode.

The ports connecting the second and third auxiliary waveguide channels to the common waveguide channel may lie directly opposite one another in the common waveguide channel or be offset in the direction of the longitudinal axis of the common waveguide channel, by keg/4 or a multiple thereof where kg is the guided wavelength of the frequency to be coupled.

In one preferred embodiment, the common waveguide channel is formed from square sectioned waveguide and the auxiliary waveguide channels are formed from rectangularly sectioned waveguide, although the cross-sections of the common waveguide channel may be circular with elliptical waveguide channels for the auxiliary waveguide channel dimensioned to ensure that the appropriate unwanted mode is not propagated therein.

The invention will now be described, by way of example, with reference to Figures 2 to 5 of the drawings accompanying the Provisional specification in which, Figure 2 shows a perspective view of an orthogonal mode transducer in accordance with this invention, Figure 3 is a plan view of the transducer shown in Figure 2, Figure 4 is a side view of the transducer shown in Figure 2 and Figure 5 is a plan view of a further embodiment of a transducer in accordance with this invention.

In the Figures 2 to 5, parts corresponding with those shown in Figure 1 have been given like references.

The orthogonal mode transducer shown in Figures 2 to 4 has a square sectioned common waveguide channel 1 having one end connected to a rectangularly sectioned waveguide 2 through the intermediary of a smooth tapering, impedance transition 3 so that the TE10 mode a is propagated as described in Figure 1. However, instead of the TEol mode b coupling via an H-plane junction, an E-plane junction to this mode is formed by rectangularly sectioned auxiliary waveguide channels 5, 5' being connected directly opposite one another in the common waveguide channel 1. Consequently for the TEol mode b, broad wall coupling is effected with the phases of the dominant mode in the channels 5, 5' being phase reversed, b' and b" respectively. Because E-plane junction impedances add in series the impedance of each of the channels 5, 5' is arranged to be one half the impedance of the common waveguide channel 1 so that the channels 5, 5' match the impedance of the common waveguide channel 1.

To ensure that the unwanted TE10 mode is not propagated in the channels 5, 5', septums 6, 6' respectively are provided in the mouths of these channels so that the longitudinal edge of the septums 6, 6' facing the channel 1 are in alignment with the wall current lines of the TElo mode a. Similarly, to ensure that the TEol mode b is reflected before reaching the channel 2, three septums 7 each having a longitudinal edge which aligns with the wall current lines of the TE01 mode, are connected at the mouth of the channel accepting the TE1o mode.

Thus, in operation, orthogonally polarised modes a, b fed into the common waveguide channel 1, are divided so that the mode a passes into the channel 2 and the mode b is split into two halves which are phase reversed with respect to one another b' b" and which, in a practical embodiment, are combined in phase by a known transducer (not shown) for utilisation.

In an alternative embodiment, shown in Figure 5, the channels 5, 5' are displaced along the longitudinal axis of the common waveguide channel 1 by keg/4 where kg is the guided wavelength of the frequency to be coupled so that if any disturbance should be caused by the channels 5, 5' this will be cancelled due to a total path length difference of keg/2 between the channels 5, 5'. The direction of the electric field in the channel 2 has not been shown, since this will be orthogonal to the plane of the drawing.

Although the embodiments of the invention thus far described have been provided with two E-plane junctions, it should be understood that this is not essential and that only one junction need be employed provided that the impedance of the auxiliary channel leading from the E-plane junction is the same as that of the common waveguide channel 1. Furthermore, although described above as being formed from square sectioned waveguide the common waveguide channel may be circular and the auxiliary channels may be elliptical, dimensioned such that the appropriate unwanted mode is not propagated in the auxiliary channels.

WHAT WE CLAIM IS: 1. An orthogonal mode transducer including a common waveguide channel for propagating the two orthogonal modes, a first auxiliary waveguide channel dimensioned so as to propagate only one of the orthogonal modes and connected to one end of the common waveguide channel, and, connected to the common waveguide channel, second and third auxiliary waveguide channels each of which form an E-plane junction for the other orthogonal mode and which are dimensioned to be cut-off to the said one mode, the second and third auxiliary channels being connected to mutually opposite sides of the common waveguide channel, and wherein the total impedance of the second and third auxiliary waveguide channels is substantially the same as the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. to the appropriate unwanted mode. The ports connecting the second and third auxiliary waveguide channels to the common waveguide channel may lie directly opposite one another in the common waveguide channel or be offset in the direction of the longitudinal axis of the common waveguide channel, by keg/4 or a multiple thereof where kg is the guided wavelength of the frequency to be coupled. In one preferred embodiment, the common waveguide channel is formed from square sectioned waveguide and the auxiliary waveguide channels are formed from rectangularly sectioned waveguide, although the cross-sections of the common waveguide channel may be circular with elliptical waveguide channels for the auxiliary waveguide channel dimensioned to ensure that the appropriate unwanted mode is not propagated therein. The invention will now be described, by way of example, with reference to Figures 2 to 5 of the drawings accompanying the Provisional specification in which, Figure 2 shows a perspective view of an orthogonal mode transducer in accordance with this invention, Figure 3 is a plan view of the transducer shown in Figure 2, Figure 4 is a side view of the transducer shown in Figure 2 and Figure 5 is a plan view of a further embodiment of a transducer in accordance with this invention. In the Figures 2 to 5, parts corresponding with those shown in Figure 1 have been given like references. The orthogonal mode transducer shown in Figures 2 to 4 has a square sectioned common waveguide channel 1 having one end connected to a rectangularly sectioned waveguide 2 through the intermediary of a smooth tapering, impedance transition 3 so that the TE10 mode a is propagated as described in Figure 1. However, instead of the TEol mode b coupling via an H-plane junction, an E-plane junction to this mode is formed by rectangularly sectioned auxiliary waveguide channels 5, 5' being connected directly opposite one another in the common waveguide channel 1. Consequently for the TEol mode b, broad wall coupling is effected with the phases of the dominant mode in the channels 5, 5' being phase reversed, b' and b" respectively. Because E-plane junction impedances add in series the impedance of each of the channels 5, 5' is arranged to be one half the impedance of the common waveguide channel 1 so that the channels 5, 5' match the impedance of the common waveguide channel 1. To ensure that the unwanted TE10 mode is not propagated in the channels 5, 5', septums 6, 6' respectively are provided in the mouths of these channels so that the longitudinal edge of the septums 6, 6' facing the channel 1 are in alignment with the wall current lines of the TElo mode a. Similarly, to ensure that the TEol mode b is reflected before reaching the channel 2, three septums 7 each having a longitudinal edge which aligns with the wall current lines of the TE01 mode, are connected at the mouth of the channel accepting the TE1o mode. Thus, in operation, orthogonally polarised modes a, b fed into the common waveguide channel 1, are divided so that the mode a passes into the channel 2 and the mode b is split into two halves which are phase reversed with respect to one another b' b" and which, in a practical embodiment, are combined in phase by a known transducer (not shown) for utilisation. In an alternative embodiment, shown in Figure 5, the channels 5, 5' are displaced along the longitudinal axis of the common waveguide channel 1 by keg/4 where kg is the guided wavelength of the frequency to be coupled so that if any disturbance should be caused by the channels 5, 5' this will be cancelled due to a total path length difference of keg/2 between the channels 5, 5'. The direction of the electric field in the channel 2 has not been shown, since this will be orthogonal to the plane of the drawing. Although the embodiments of the invention thus far described have been provided with two E-plane junctions, it should be understood that this is not essential and that only one junction need be employed provided that the impedance of the auxiliary channel leading from the E-plane junction is the same as that of the common waveguide channel 1. Furthermore, although described above as being formed from square sectioned waveguide the common waveguide channel may be circular and the auxiliary channels may be elliptical, dimensioned such that the appropriate unwanted mode is not propagated in the auxiliary channels. WHAT WE CLAIM IS:

1. An orthogonal mode transducer including a common waveguide channel for propagating the two orthogonal modes, a first auxiliary waveguide channel dimensioned so as to propagate only one of the orthogonal modes and connected to one end of the common waveguide channel, and, connected to the common waveguide channel, second and third auxiliary waveguide channels each of which form an E-plane junction for the other orthogonal mode and which are dimensioned to be cut-off to the said one mode, the second and third auxiliary channels being connected to mutually opposite sides of the common waveguide channel, and wherein the total impedance of the second and third auxiliary waveguide channels is substantially the same as the

impedance of the common waveguide channel.

2. An orthogonal mode transducer as claimed in claim 1 and wherein the impedance of each of the second and third auxiliary waveguide channels is one half that of the common waveguide channel.

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3. An orthogonal mode transducer as claimed in claim 2 and wherein septums are provided in the connecting paths of the auxiliary channels to ensure that the auxiliary channels are cut-off to the appropriate unwanted mode.

4. An orthogonal mode transducer as claimed in any one of claims 2 to 3 and wherein the ports connecting the second and third auxiliary waveguide channels to the common waveguide channel lie directly opposite one another in the common waveguide channel.

5. An orthogonal mode transducer as claimed in any one of claims 2 to 3 and wherein the ports connecting the second and third auxiliary waveguide channels to the common waveguide channel are offset in the direction of the longitudinal axis of the common waveguide channel, by keg/4 or a multiple thereof where kg is the guided wavelength of the frequency to be coupled.

6. An orthogonal mode transducer as claimed in any one of claims 2 to 5 and wherein the common waveguide channel is formed from square sectioned waveguide and the auxiliary waveguide channels are formed from rectangularly sectioned waveguide.

7. An orthogonal mode transducer as claimed in any one of claims 2 to 5 and wherein the cross-section of the common waveguide channel is circular with elliptical waveguide channels for the auxiliary waveguide channel dimensioned to ensure that the appropriate unwanted mode is not propagated therein.

8. An orthogonal mode transducer substantially as illustrated in and described with reference to Figures 2, 3 and 4 of the drawings accompanying the Provisional specification.

9. An orthogonal mode transducer substantially as illustrated in and described with reference to Figure 5 of the drawings accompanying the Provisional specification.