GB2218854A - Waveguide apparatus - Google Patents

Abstract

Waveguide apparatus includes a rotating joint 5 across which microwave power is transmitted. One microwave signal is transmitted via ports 6 and 7 in the TM01 mode and another signal at a different frequency is transmitted across the joint 5 in the TE10 mode. The transition from a TE10 mode to the TE01 mode is achieved by applying a signal to the E-plane port of a Magic-T 10 and arranging the outputs of the Magic-T 10 to be adjacent one another. The outputs are then applied via a short taper and an iris to a resonant cavity at the joint 5. <IMAGE>

Description

WAVEGUIDE APPARATUS This invention relates to waveguide apparatus and more particularly to a waveguide rotating joint.

In some applications it is desirable that microwave energy be transmitted between relatively rotating members.

This can be accomplished by transmitting power across a waveguide rotating joint using a waveguide mode having characteristics of which tend to remain constant as rotation occurs between the two waveguide members of the rotating joint.

The present invention arose in an attempt to provide an improved rotating joint.

According to the invention there is provided waveguide apparatus comprising a waveguide rotating joint capable of transmitting two signals across the joint in respective different waveguide modes. By employing the invention, only one rotating joint is required for the transmission of two signals between relatively rotating members, whereas using previously known apparatus, a separate rotating joint would have been required for each signal. Thus, the size of waveguide apparatus can be reduced by using the invention. This is particularly important for example, in applications such as satellite communication equipment and in radar apparatus. The waveguide modes chosen must be such that there is little or no coupling between them. It is preferred that the two signals are at respective different frequencies.These frequencies might be, for example, 4 GHz and 6 GHz which are typical frequency bands for satellite communication down and up paths. By using widely spaced frequency bands for the two signals, any coupling between them tends to be further reduced.

It is preferred that the waveguide at the joint is circular, and that one mode is the TMO1 mode and the other is the TEol mode. The TMol mode is illustrated in Figure 1 and has a radial electric field, as shown. The TEO mode has circumferential electric field lines as shown in Figure 2. Thus, when a signal in one of these modes is imposed on another signal in the other mode, the electric field lines of the two modes are orthogonal and there is substantially no coupling between them. Another advantage in employing these two modes is that there is only a very small electric field along the longitudinal axis in the TEO1 mode so that, for example, a cable could be positioned along it.

It might be thought that the use of the TEO1 mode in a rotating joint would not be practicable, because to obtain a signal in this mode from the usual rectangular TElo mode, illustrated in Figure 3, a large transition section is normally required and for this reason, the TE mode is typically used only where a signal is to be transmitted over a long distance. The use of a conventional transition section would tend to cause difficulties where part of the apparatus is required to rotate. However, the inventor has discovered that the TEol mode can be produced using a relatively small transition section which includes a Magic-T and which may be, for example, of the order of five times shorter than a conventional transition section.

Although such a small transition section tends to be somewhat inferior in its bandwidth capability and mode purity compared with a conventional transition section, it has good matching characteristics and offers sufficiently good performance for it to be usefully included in a rotating joint. Advantageously, therefore, a Magic-T is included at a port for one of the signals, a signal in the TElo mode being arranged to be applied to the Magic-T via its E-plane port, and its outputs being arranged adjacent one another to produce a signal in the TE20 mode.

Normally the input to a Magic-T is applied via its H-plane port and the E-plane is connected to a load for matching purposes. When the input to the Magic-T is applied to the H-plane port, the signals at its outputs are in the same sense. However, by terminating the H-plane port and applying the input signal to the E-plane port in accordance with the inventive feature, the signals at the two outputs of the Magic-T have their E-fields in opposite directions. By arranging the outputs adjacent to one another, the two, opposite, TE10 modes combine to form a TE20 mode as shown in Figure 4, where one output of the Magic-T is shown at 1 and the other is referenced 2. The production of the TE20 mode is a starting point for the eventual translation of the signal into the TEol mode.

Preferably, a taper section is arranged to follow the outputs of the Magic-T, the taper section having an aperture therethrough which is of substantially rectangular section at one face and substantially cruciform section at its other face, the face having the rectangular section aperture therein being arranged adjacent the outputs of the Magic-T. An iris having a cruciform aperture therein is preferably included, being arranged adjacent the face of the taper section having the cruciform aperture therein.

It is preferred that the rotating joint includes ports for the signal in the TMO1 mode located between ports for the signal in the TEol mode. The TMol ports are arranged to feed the signal in this mode into a resonant cavity across the rotating joint and the ports for the TEO1 mode are preferably arranged so that they act as short circuits for the TMO1 mode, thus suppressing the undesirable TE11 mode which could otherwise result.

One way in which the invention may be performed is now described by way of example with reference to the accompanying drawings, in which: Figure 5 is a schematic perspective view of apparatus in accordance with the invention; Figure 6 is a schematic sectional view of the apparatus as shown in Figure 5; and Figure 7 is an exploded view of part of the apparatus of Figure 5.

With references to Figures 5 and 6, apparatus in accordance with the invention includes two circular waveguide sections 3 and 4 which are relatively rotatable at a rotating joint 5 about axis X-X. Two ports 6 and 7 are included for transmission of microwave energy across the rotating joint 5 in the TMO1 waveguide mode. Power in the TEo1 mode can also be transmitted across the rotating joint 5 via ports 8 and 9, between which the TMo1 ports 6 and 7 are located. The frequency of the TEo1 mode signal is different from that of the TMO1 mode signal.

TEo1 port 8 is the E-plane input port of a Magic-T 10, the H-plane input port having a termination 11. As is more clearly shown in Figure 7, the two output ports 12 and 13 of the Magic-T 10 are arranged adjacent one another. Microwave energy applied in the TE10 mode to the port 8 reaches one of the outputs 12 in the TE10 mode, as illustrated by the arrows, and the other output port 13 in the TE10 mode in the opposite sense. Thus, the output of the Magic-T 10 is effectively in the TE20 mode. The output of the Magic-T 10 is applied to a short taper 14 which has an aperture therethrough. The transverse section of the aperture gradually changes from being rectangular at the face arranged adjacent the outputs 12 and 13 of the Magic-T 10 to being substantially cruciform at its other face. The TE20 signal applied to the rectangular section part of the aperture results in a mode being produced at the other face of the taper 14 as illustrated by the arrows. The taper 14 is followed by a spacer 15 and an iris 16 having a cruciform aperture 17 therein. Application of a signal in the TE10 mode at the E plane part IB sets up a mode at the iris 16 as illustrated by the arrows. A similar transition section 19 is included on the other side of the rotating joint 5 and includes the port 9, which again is the E-plane port of a Magic-T.

The taper 14, or iris 16 where this is included, is arranged to present a short circuit at 20 (as shown in Figure 6) to energy passing through ports 6 and 7 so as to inhibit the TE11 mode.

Claims (8)

1. Waveguide apparatus comprising a waveguide rotating 'joint capable of transmitting two signals across the joint in respective different waveguide modes.

2. Waveguide apparatus as claimed in claim 1 wherein the two signals are at respective different frequencies.

3. Waveguide aparatus as claimed in claim 1 or 2 wherein the waveguide at the joint is circular and one mode is the TMO mode and the other is the TEol mode.

4. Apparatus as claimed in claim 3 wherein the rotating joint includes ports for the signal in the TMO1 mode located between ports for the signal in the TEO1 mode.

5. Waveguide apparatus as claimed in claim 4 wherein the signal in the TEol mode is transmitted into a resonant cavity at a distance from a port for the signal in the TMO mode such that it acts as a short circuit for the signal in the TMol mode.

6. Waveguide apparatus as claimed in any preceding claim and including a Magic-T at a port for one of the signals, a signal in the TE10 mode being applied to the Magic-T via its E-plane port and its outputs being arranged adjacent to one another to produce a signal in the TE20 mode.

7. Waveguide apparatus as claimed in claim 6 and including a taper section having an aperture therein, the transverse section of which is substantially rectangular at one face, and substantially cruciform at the other face, the taper section being arranged such that the face having the rectangular section aperture therein is adjacent the outputs of the Magic-T.

8. Waveguide apparatus substantially as illustrated in and described with reference to Figures 5, 6 and 7 of the accompanying drawings.