GB2479151A

GB2479151A - A hollow ridge dual channel waveguide that is operable using at least two bands comprising at least a first waveguide and a second waveguide.

Info

Publication number: GB2479151A
Application number: GB1005360A
Authority: GB
Inventors: John Grant; Steve Mccabe; Rob Urwin; Alan J Sangster
Original assignee: NewWave Broadband Ltd
Current assignee: NewWave Broadband Ltd
Priority date: 2010-03-30
Filing date: 2010-03-30
Publication date: 2011-10-05
Also published as: GB201005360D0

Abstract

A waveguide apparatus comprising at least a first waveguide and a second waveguide, wherein the first waveguide comprises a ridge waveguide and the second waveguide is at least partially comprised in at least one ridge of the first waveguide. The waveguide apparatus may comprise a hollow ridge waveguide, such as a hollow ridge dual channel waveguide. The first waveguide may comprise a conduit which may be a hollow metal conduit and may be contained within a circular, cylindrical or square envelope. The first waveguide may be adapted to support or propagate a first frequency signal or frequency band and the second waveguide may be adapted to support a second frequency signal or frequency band. The ridged waveguide propagates best for wide ridges with small gaps between the ridges, i.e. a large ridge depth. It may be used as a feed for a microwave horn antenna or as a dual channel microwave transmission filter.

Description

Waveguide Apparatus The present invention relates to a waveguide apparatus, for example, a waveguide apparatus for use as a feed for a microwave horn antenna or as a dual channel microwave transmission filter. In particular, the invention relates to a hollow ridge dual channel waveguide that is operable using at least two bands and/or using at least two polarisations.

Background of the Invention

Parabolic dish antenna systems are used in a variety of applications, such as radar tracking systems or in telecommunications.

Parabolic dish antenna systems typically comprise a radiation source, such as a feed horn, arranged to emit a signal and reflect the signal from a reflector, such as a parabolic dish. The feed and the horn, and its associated microwave components, can seriously limit the operational bandwidth of the intrinsically wideband reflector.

For satellite communications, wide band operation is essential in order to provide spectral coverage of widely spaced communication bands. When a single broadband device is used to access transmit and receive channels that may be widely separated (such as C-band and Ku-band, as non-limiting examples) the overall bandwidth of the antenna must by wide enough to accommodate both channels. Channels can also be linearly polarised and/or circularly polarised, which dictates that the feed system is preferably multi-moded to permit polarisation switching.

The usual solution to this problem is to employ separate feeds in a dual feed * arrangement, with one feed designed to operate at a low frequency band while the * S. 50* * other is optimised for a high frequency band. However, for a ship-borne antenna, which in many cases will be enclosed in a compact protective radome structure, the 5*�S complexity of the dual-feed approach is generally impractical, as such devices can be bulky as they typically require lengthy convoluted waveguide support structures. In S...

addition, such dual feed devices require separate feeds that cannot be co-located at the focus of the reflector. This results in well recognised and well understood radiation pattern difficulties.

The alternative is to use a very broad-band feed source at the focus of the reflector.

The feed source needs to be wide enough to transmit and receive the required channels (for example C-band and Ku-band). These broad band feed sources are usually of circularly symmetric design to accommodate polarisation switching. This combination of requirements restricts the feed sources that can be used. Examples of sources that are used for such applications include very wideband sinuous antennas, a wideband tapered quad-ridge horn and a wideband corrugated horn.

The sinuous antenna was rejected for the satellite communication application, since it is limited to circular polarisation, while the quad-ridge horn and the corrugated horn fail to provide sufficient bandwidth to accommodate more than one broadband channel widely separated in frequency. Furthermore, they do not physically separate the channel signals and therefore space consuming filtering is required.

Several dual-band, parabolic reflector feed horns have been proposed to provide channel separation in a compact structure. Various problems may be associated with the prior art feed horns, for example, the prior art devices may comprise resonant antennas that may be capable of selecting only narrow portions of the C-band and Ku-band, or the prior art devices may use frequency selected surfaces, wherein the frequency separation may be dictated by the resonances of the frequency selective surface and the bandwidth may be narrow at each frequency, the prior art feed horns may comprise a co-axial waveguide which may be non-radiating for the fundamental TEM mode or space consuming and orthogonal mode transducers may be required to set up the radiating TE11 mode.

Summary of Invention

According to a first aspect of the invention is a waveguide apparatus comprising at least a first waveguide and a second waveguide, wherein the first waveguide comprises a ridge waveguide and the second waveguide is at least partially comprised in at least one ridge of the first waveguide.

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* The waveguide apparatus may comprise a hollow ridge waveguide, such as a hollow * S....

* 30 ridge dual channel waveguide. S... S...

The first wave guide may comprise a conduit, which may be a hollow metal conduit.

The conduit may have a complex cross-section. The conduit may be provided with at least one ridge extending internally from an inner surface of the conduit. The ridge may extend toward a centre of the conduit. The conduit may comprise an even number of diametrically opposed ridges, such as two, four or eight ridges.

The conduit may be contained within a circular, cylindrical or square envelope.

The at least one ridge may extend longitudinally along the conduit. At least one and preferably each ridge may extend in parallel to at least one and preferably each other ridge. The ridges may be evenly spaced around the periphery of the conduit. The ridges may extend partially across the conduit.

The ridges may be provided in coplanar pairs. At least one pair of ridges may be oriented perpendicularly to at least one other pair of ridges. The ridges forming a coplanar pair may extend partially across the conduit, such that a gap is formed between the ridges.

The ridges may comprise a pair of protruding members defining a channel therebetween. The channel may have a substantially rectangular cross-section. The channel may extend longitudinally along the ridge.

The second waveguide may be comprised in or formed within at least one, and preferably each, ridge of the first waveguide. The second waveguide may be embedded within at least one and preferably each ridge of the first waveguide. The second waveguide may be at least partially defined by at least one ridge of the first waveguide The second waveguide may comprise the channel in at least one, and preferably each, ridge of the first waveguide. The second waveguide may be a waveguide having a rectangular cross section.

The second waveguide may comprise at least two waveguides. Each waveguide may comprise facing or opposing channels. At least one of the second waveguides may be substantially orthogonally oriented in respect of at least one other second **IS..

* 30 waveguide. *S..

S S...

In an optional embodiment, the second waveguide or waveguides may be open to the conduit. S...

S S...

In an optional embodiment, the second waveguides may be isolated from the first waveguide. The second waveguides may be closed to the conduit.

The waveguide apparatus may be provided with at least one conductive member, such as foil strips, which may be located at an interface between the first and second waveguides. The at least one conductive member may be located at the apex of at least one and preferably each ridge of the first waveguide. The conductive member may be arranged to isolate or close at least one second waveguide. The conductive member may be adapted to substantially prevent an electromagnetic wave propagated by the first waveguide from entering at least one second waveguide.

The first waveguide may be adapted to support or propagate a first frequency signal or frequency band and the second waveguide may be adapted to support a second frequency signal or frequency band. The first and second frequency signals or frequency bands may be distinct or separated from each other.

The first frequency signal or frequency band may comprise a higher frequency or frequencies than the second frequency signal or frequency band. The first frequency band may comprise or belong to the Ku-band, i.e. between 10.7 and 14.5GHz. The second frequency band may comprise or belong to the C-band, i.e. between 3.6 and 7.025GHz.

The first waveguide may be adapted to support one or more signal propagation modes, which may comprise quasi-TEM modes. The first waveguide may be adapted to support two or more signal propagation modes. The first waveguide may be switchable between propagation modes. Each mode may be supported by a pair of opposing ridges. The first waveguide may be adapted to support orthogonal signal propagation modes.

The second waveguide may be adapted to support or propagate one or more signal propagation modes, which may comprise at least one TE10 mode. The second waveguide may be adapted to support two or more signal propagation modes. The * ***** * 30 second waveguide may be switchable between propagation modes. Each mode may be supported by a pair of opposing channels. The second waveguide may be adapted to support orthogonal signal propagation modes. ** S.

: The waveguide apparatus may be adapted to support orthogonal modes. The waveguide apparatus may be switchable between mutually orthogonal linear polarisations and/or between linear and circular polarization.

The waveguide apparatus may be operable as a feed.

According to a second aspect of the present invention is a waveguide apparatus comprising at least one first waveguide and at least one second waveguide, wherein the first waveguide comprises a ridged waveguide and the second waveguide comprises a rectangular cross sectioned waveguide.

The waveguide apparatus may comprise a hollow ridge waveguide, such as a hollow ridge, dual channel waveguide.

The waveguide apparatus may be a waveguide apparatus for a horn antenna.

The second waveguide may be at least partially comprised in at least one ridge of the first waveguide.

A skilled person would appreciate that optional and preferred features described above in relation to the first aspect may also apply to the second aspect.

According to a third aspect of the invention is a feed or feed horn comprising the waveguide apparatus as defined above in relation to the first and/or second aspects of invention.

The feed horn may comprise a transition section for transitioning between the waveguide and a radiating aperture. The transition section may comprise a horn.

The feed horn may comprise a signal launching section.

The waveguide apparatus, in conjunction with the horn and/or signal launching sections may form a single structural unit.

** The signal launch section may comprise at least one signal transmitter and/or receiver, such as an electromagnetic coupling apparatus, for providing a signal to, and/or receiving a signal from, at least one of the first and second waveguides. S...

The signal launch section may comprise a ridged launch waveguide. The launch waveguide may comprise a conduit having a plurality of ridges, such as four ridges.

The ridges of the launch section may be solid.

The cross-section of the conduit of the signal launch section may be substantially the same as that of the first waveguide.

The signal launching section may comprise a first waveguide launch section for providing signals to and/or receiving signals from the first waveguide.

The first waveguide launch section may comprise at least one and preferably two or more coaxial line connectors. The coaxial line connectors may be orthogonally located. Each line connector may be located at or on a ridge of the launch waveguide. Each connector may be connected to a probe. The probes may be arranged to pass through a port in the launching section and may pass through a ridge of the launch waveguide. The probe may enter the gap between opposing ridges of the launch section. The probe may extend at least partially across the gap.

The probes may be adapted to generate andlor receive signals in the first (high) frequency band.

The probes are adapted to be axially off-set from each other. The axial off set may substantially correspond to a quarter wavelength at the centre frequency of the high frequency band.

The waveguide apparatus may comprise a second waveguide launching section for providing signals to and/or receiving signals from the second waveguide.

The second waveguide launching section may comprise one or more magnetic loops, which may be connected or connectable to coaxial cable. The magnetic loops may be adapted to generate or detect electromagnetic signals, such as TE10 electromagnetic waves. The magnetic loops may be located in the channels of the second waveguides. The magnetic loops may be adapted to generate a signal, which may be a signal in the second (low) frequency band for propagation by the second waveguides. At least one magnetic loop may be located in a channel of a second waveguide that is orthogonal to a channel of a second waveguide in which at least one further magnetic loop is located. S... S...

The signal launching section may comprise tunable shorting walls, which may be located behind the probes. The tunable shorting walls may be adapted to match the launching section to at least one of the waveguides.

The first waveguide launching section may comprise a tunable short located between two ridges and behind at least one probe.

The signal launching section and the radiating aperture may be connected by the waveguide apparatus, such that signals generated by the signal launching section may be transmittable via the waveguide apparatus to the radiating aperture.

The waveguide apparatus may be adapted to terminate in the radiating aperture, which may be adjusted to emit radiation externally of the feed horn. The radiating aperture may be circular and between 50 and 100mm in diameter. The radiating aperture may be a TE11 mode waveguide aperture The signal launching sections may be coupled to the radiation aperture via at least the first and second waveguides.

The transition section may be adapted to transform a mode associated with the first waveguide to an emission mode associated with the radiating aperture. The transition section may comprise a cylindrical dielectric insert with a conical or hemispherical tip, which may comprise a dielectric rod. In an alternate embodiment, the rod may have a square cross-section. The first waveguide electromagnetic signal may ideally be wholly transferred to the transition section and radiate efficiently from the conical or hemispherical tip. For a rod with a slowly tapering conical tip, wave power in the rod may leak progressively from the tapering surface, (like water from the surface of a perforated hose) thus narrowing the radiated beam. The tip may have a tip angle in the range of 5° to 150 At least a portion of the second waveguide may transition outwardly toward the emission aperture, which may be by stepping, tapering or flaring. At least a portion of the second waveguide may transition toward the emission aperture by decreasing a dimension that the channel of the second waveguide extends into the conduit and/or increasing a dimension of the channel of the second waveguide that is circumferential in the conduit. The transition between the second waveguide and the S...

emission aperture may be adapted to achieve a matched transition. . 35

According to a fourth aspect of the present invention is an antenna comprising a waveguide apparatus according to either of the first or second aspects and a feed horn for providing and/or receiving a signal and a reflector for reflecting the signal.

The feed horn may be a feed horn according to the third aspect.

The reflector may be a parabolic reflector.

The antenna may be a radome enclosed antenna. The antenna may be a ship-borne antenna.

According to a fifth aspect of the present invention is a method of manufacturing a waveguide apparatus, the method comprising providing a first waveguide, wherein the first waveguide comprises a conduit and one of more ridges extending inwardly from the conduit, the method also comprising providing a second waveguide embedded in and/or at least partially formed by the one or more ridges of the first waveguide.

The waveguide apparatus may be a waveguide apparatus according to either the first and/or second aspects.

According to a sixth aspect of the present invention is a method of manufacturing a feed horn comprising providing a waveguide apparatus according to either of the first or second aspects.

According to a seventh aspect of the present invention is a method of manufacturing an antenna comprising providing a waveguide apparatus according to either of the first or second aspects and a horn, or a feed horn according to the third aspect, and a reflector, wherein the feed horn is arranged to transmit and/or receive a signal and * 30 the reflector is arranged to reflect the signal. S..

The antenna may be an antenna according to the third aspect. S.'.

: According to a eighth aspect of the present invention is a filter comprising a * 35 waveguide according to the first or third aspects of invention.

The microwave filter may be a dual channel microwave filter.

According to an ninth aspect of the invention is a method of manufacturing a filter comprising providing waveguide apparatus according to either the first or second aspects.

The microwave filter may be a dual channel microwave filter.

In shipborne, airborne or spaceborne applications where microwave systems such as communication systems or radar systems have to be installed in very restricted spaces, the microwave filter as defined above provides a single compact microwave filter through which the microwave signals of a plurality of frequency channels, such as two low frequency and two high frequency channels, can be passed, rather than using four different waveguides or cables.

Brief Description of the Drawings

Various aspects of the invention will now be described by way of example only with reference to the accompanying drawings, of which: Figure 1 is a waveguide apparatus according to an aspect of the invention; comprising a launching section, a hollow ridge dual channel waveguide feed, and a radiating horn section.

Figure 2(a) is a cross sectional view of the waveguide apparatus of Figure 1 taken through the plane 2-2 shown in Figure 1; Figure 2(b) is a detail view of part of the cross section of Figure 2(a); Figure 3 is a cross sectional view of a feed horn according to another aspect of the invention * .*... * S

Figure 4 is cross sectional view of the mid point of the feed horn of Figure 1; and Figure 5 is a mode diagram associated with the waveguide apparatus of Figure 1. Se..

Detailed Description of the Drawings

The waveguide apparatus of the present invention is described herein, as an exemplary application, in terms of its use in a feed horn for an antenna. However, it will be appreciated that the waveguide apparatus described herein may also be applicable to other applications, such as a microwave filter.

Figure 1 shows a waveguide apparatus configured as a feed horn 5 comprising a signal launching section 10 at a first end of a hollow ridge dual channel waveguide 15 and a radiating section 20 in the form of a horn at a second end of the waveguide feed 15. In this way, dual-mode electromagnetic waves in two bands may be propagated from the signal launching section 10 to the radiating section 20 via the hollow ridge dual channel waveguide 15. The radiating section 20 is arranged to transform the signal propagated by the propagation section 15 into a form for emission from the waveguide apparatus 5.

The signal launching section 10 is operable as a signal source and/or receiver and is in communication via coaxial lines 25a, 25b with an external controller (not shown) comprising suitable control circuitry.

The signal launching section 10 is arranged to provide two signals, namely a low frequency band signal and a high frequency band signal, to appropriate sections of the hollow ridge dual channel waveguide section 15. In the example described herein, the low frequency band comprises the C-band (i.e. a having a frequency in the range 3.6GHz to 7.025GHz) and the high frequency band comprises the Ku-band (i.e. between 10.7GHz and 14,5GHz). However, it will be appreciated that other frequency bands may be used.

The hollow ridge dual channel waveguide 15 comprises, in this embodiment, a circular cylinder 30 defining a conduit 35 extending between the signal generating/receiving section 10 and the radiating section 20. The conduit 35 is provided with four evenly spaced ridges 40a, 40b, 40c, 40d extending longitudinally with, and inwardly from, the walls of the conduit 35. This ridged conduit 35 forms a first waveguide 45 in the form of a quad-ridge waveguide.

As the ridges 40a, 40b, 40c, 40d are evenly spaced and lie in parallel to each other, the ridges can be considered as forming two ridge pairs, each pair comprising a pair of opposing ridges 40a and 40c, 40b and 40d lying in the same plane. It will be appreciated that the two ridge pairs 40a and 40c, 40b and 40d lie orthogonally to each other.

Each ridge 40a, 40b, 40c, 40d of the first waveguide 45 is formed from a pair of protruding members 50a, 50b (shown in Figure 2(b)) extending in parallel to each other from the circular conduit wall and extending longitudinally along the conduit 35.

Each pair of protruding members 50a, 50b has a rectangular cross sectioned channel therebetween. In this embodiment, the channel 55 is open towards the conduit 35. In this way, opposing pairs of channels 55 act as rectangular cross sectioned waveguides 60a, 60c and 60b, 60d, i.e. second waveguides.

The propagation section 15 is formed by machining, spark eroding or otherwise suitably fabricating the ridges 40a, 40b, 40c, 40d and channels 55 from an electrically conducting cylindrical rod, such as an aluminium or copper rod. The dimensions of the propagation section 15 are dependent on the chosen operating bands.

The rectangular waveguides 60a, 60c and 60b, 60d are adapted to preferentially propagate radiation from a lower frequency radiation band than the ridged waveguide 45. In this case, the rectangular waveguides 60a, 60c and 60b, 60d are arranged to propagate microwave radiation from the C-band, whilst the first ridged waveguide 45 is arranged to propagate microwave radiation from the Ku-band. The low frequency radiation propagated independently by the second waveguides 60a, 60c and 60b, 60d is linearly polarised, whilst the high frequency radiation propagated by ridges 40a,40c, or 40b, 40d, of the first waveguide 45 is also linearly polarised.

As the first waveguide 45 is a quad-ridged waveguide, it can support two independent orthogonal quasi-TEM ridge modes, each mode supported between a different pair of opposing and aligned ridges 40a and 40c, 40b and 40d. This provision of two orthogonal propagation modes permits polarisation agility or switching between the orthogonal modes. *. ..

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I.. S* Similarly, the second waveguides 60a, 60c and 60b, 60d are each capable of supporting a linearly polarized signal, the facing pairs of channels 55 each also S..

support independent orthogonally oriented TE10 modes. This permits polarisation switching of the low frequency band between these two orthogonal modes.

A wave launched on the first waveguide 45 in the gap between ridges 40a and 40c will be linearly polarised in the y-direction (see fig. 1), while a wave launched on the second waveguide 55 in the channels 60b and 60d will also be linearly polarised in the y-direction. Linear polarisation in the orthogonal direction (x-direction) is procured by launching a wave in the gap between ridges 40b and 40d at the high frequency, and in channels 60a and 60c at the low frequency. Simultaneous excitation of ridge gaps 40a, 40c and ridge gaps 40b, 40d, at the high frequency, will produce linear polarisation at 450 to the x and y directions, if the launched waves are in phase, and circular polarisation if they are in quadrature phase. Similarly, at the low frequency, simultaneous excitation of channels 60a, 60c and 60b, 60d generates a wave polarised at 45° to the x and y directions if the launched waves are in phase, and circular polarisation if they are in quadrature phase.

The relationship between the rectangular (low frequency) waveguides 60a, 60c and 60b, 60d and the quad-ridged (high frequency) waveguide 45 is shown more clearly in figures 2a and 2b, which show a cross section taken through the plane 2-2 in Figure 1. The dimensions of the four central ridges 40a, 40b, 40c, 40d, and the hollow inner conduit 35, in which they are located, are dependent on the desired operating frequency and operating bandwidth of the upper passband of the hollow ridge dual channel waveguide feed 15. In determining the dimensions of these elements, it is presumed that the ridges 40a, 40b, 40c, 40d appear solid' for the high frequency electromagnetic waves, in which case standard design procedures for ridge waveguides can be employed. First waveguide dimensions are typically determined by using mode diagrams, such as the one shown in Fig. 5. The frequency range of operation for a quad-ridge structure with h/R-0.2 is shown by the vertical bar. The ridged waveguide 45 propagates best for wide ridges 40a, 40b, 40c, 40d with small gaps between the ridges, i.e. a large ridge depth.

I

The low frequency electromagnetic waves of the dual-band system are supported by the perpendicularly orientated rectangular waveguides 60a, 60c and 60b, 60d (see *.J. . . . . . . fig 2a), which are machined or etched into the metallic conduit cylinder, such that they form the channels 55 within the high frequency ridge structures. The dimensions of the rectangular waveguides 60a, 60c and 60b, 60d are determined by a.

: the low band operating frequency and the thickness of the ridges 40a, 40b, 40c, 40d oftheridgedwaveguide45.

The rectangular waveguides 60a, 60c and 60b, 60d are preferably air filled.

However, in an optional embodiment shown in Figure 3, metallic foil strips 65 are located at the junctions between the rectangular waveguides 60a, 60c and 60b, 60d and the conduit 35 of the ridge waveguide 45. The channels 55 between the protruding members 50a, 50b are filled with polystyrene or similar low relative permittivity material to provide support for the strips 65. The foil strips 65 have negligible influence on the independent TE10 modes which propagate within the orthogonally orientated, rectangular cross-section, channel waveguides 60a, 60c and 60b, 60d.

A ridge mode launching section 70 for generating and detecting signals propagated by the first (ridge) waveguide is attached coaxially to the waveguide 15. The first (ridge) waveguide is fed from coaxial lines 25a, 25b through wideband coax-ridge-waveguide transitions. The ridge mode launching section 70 has a reduced outer diameter compared to the conduit of the hollow ridge dual channel waveguide 15, which permits clearance for tuning screws 75. The ridge mode launching section 70 comprises a launching conduit 80, having four solid launch ridges 85 extending along and into the launch conduit 80. The two orthogonally located coaxial connectors 25a, 25b are positioned at perpendicular launch ridges and are employed to enable selective generation of orthogonal fields and thus secure polarisation agility. Each connector 25a, 25b is attached to a coaxial probe (not shown) which passes through a cylindrical hole in the body of the launching section 70 and through a solid launch ridge 85. Each probe enters a ridge gap between the opposing launch ridges 85 and partially or wholly crosses the ridge gap, depending on matching requirements.

The coaxial probes are normally off-set axially from each other by one quarter wavelength at the centre frequency of the high frequency band, but co-location at the same transverse plane can be used by using bent' probes. An adjustable shorting e:... wall to provide match optimisation is provided by a tuning screw 90, encroaching into the ridge gap, and is approximately the same diameter as the ridge gap width. * 30

The low frequency band signal propagated by the second (rectangular) waveguides 60a, 60c and 60b, 60d is provided by two coaxial line connectors 95a and 95b, located in the same x-y plane (i.e. transversely of the conduit direction) but spatially displaced by 90° on the outer surface of the conduit (i.e. so that they are arranged perpendicularly). This arrangement permits orthogonal fields to be selectively generated by selectively applying appropriate signals to the perpendicularly oriented line connectors 95a 95b to achieve full polarisation control.

Each connector 95a, 95b is attached to a coaxial line inner wire 100 which is threaded through a cylindrical hole to the rectangular waveguides 60a, 60c and 60b, 60d. The impedance of this coaxial feed line 100 is preferably as close as possible, in magnitude, to the impedance of each rectangular waveguide 60a, 60c and 60b, 60d. The threaded wire 100 is terminated in a magnetic field coupling loop (not shown) located within each rectangular waveguide 60a, 60c and 60b, 60d. The coupling loop is responsive to signals provided by the controller via the coaxial lines 95a, 95b in order to generate the low frequency TE10 mode signal for propagation by the second waveguides 60a, 60c and 60b, 60d.

Match optimisation is secured through the formation of the adjustable shorts 105 at the non-radiating ends of the rectangular waveguides 60a, 60c and 60b, 60d. These shorts 105 will generally be about one quarter guide wavelength from the plane of the loops. Adjustability of the shorts 105 is achieved by means of screws 75 which bear on the movable shorts 105. Alternative coupling arrangements employing transverse E-field probes or axial slots may also be used.

In use, once the signals have been generated and propagated via the ridged 45 and rectangular 60a, 60c and 60b, 60d waveguides, the signals are emitted from the waveguide 15 via the radiating section 20. The radiating section 20 is adapted to transition the signals propagating in the waveguides 45, 60a, 60c and 60b, 60d to an emitted signal propagating through free space with the minimum of loss. The radiating section 20 comprises a radiating aperture 110 at a terminal end of the feed horn 5 and transition apparatus 115, 120 for transitioning the signals propagated by the first 45 and second 60a, 60c and 60b, 60d waveguides to the aperture 110.

The transition apparatus for the high frequency signal propagated by the first waveguide 45 comprises a leaky wave radiator 120. The leaky wave radiator 120 is SI...

* 30 formed from a high permittivity tapered cylindrical polyrod that is cantilever mounted securely in the throat (emission) end of the waveguide apparatus 5 and at the centre I...

of the conduit 35 that forms the high frequency band ridge waveguide 45, as shown in Figure 1. The rod 120 is positioned coaxially with the conduit 35 and in firm *.*.

contact with the ridges 40a, 40b, 40c, 40d. The end of the rod 120 facing the propagation section forms 15 a conical taper 125 to secure a match between the quad-ridge waveguide 45 and the polyrod 120. This conical taper 125 is arranged to have a length in a range corresponding to one to two wavelengths of a frequency at the lower end of the high frequency band. At the throat end, the length of the leaky rod radiator 120 and its flare angle are chosen to produce a radiating beamwidth, which optimally illuminates a parabolic reflector over the entire range of upper band frequencies.

For the low frequency band the TE10 rectangular waveguide modes are transformed into TE11 cylindrical waveguide modes by adopting a horn arrangement 115. The design of the enclosing horn 115 also has a bearing on the beamwidth of the radiations in the higher frequency band. In the horn 115, the rectangular waveguides 60a, 60c and 60b, 60d are terminated by a portion comprising stepped or convex surfaces 130 so that the channel widths of the rectangular waveguides 60a, 60c and 60b, 60d increase and the rectangular waveguide 60a, 60c and 60b, 60d heights reduce from the propagation section 15 towards the radiating aperture 110, optimising the match between the TE10 mode in each waveguide 60a, 60c and 60b, 60d, and the TE11 mode radiating aperture 110, so maximising radiation efficiency.

Figure 1 depicts a stepped embodiment to best illustrate the way in which the transition is achieved. It shows quarter-wavelength step transitions 130 (three in number) transforming the structure from the original rectangular waveguide 60a, 60c and 60b, 60d dimensions to the cylindrical waveguide aperture 110.

A cross-sectional view of the structure at the mid-section of the transformer transition section 20 (on plane 3-3) is shown in figure 4. The various dimensions of the transition section 20, such as number of steps, step sizes, horn diameter at the aperture are chosen to provide a good match to the horn over the chosen bands, and to provide a balance between low frequency band, high frequency band, gain and beamwidth. An alternative embodiment of the transition section could comprise smooth flaring of the structure from the quad-ridge guide 45 to the horn aperture 110.

In this case horn flare angle and surface shapes (linear taper or convex taper) contribute to the efficiency of the transition.

* S.... * 30

As an example of the apparatus 5 in use, the apparatus 5 is adapted to illuminate a S...

circularly symmetric parabolic dish (not shown) with orthogonally polarised waves in both the upper and lower bands. The quad-ridge waveguide 45 is arranged to *SSS : radiate from the aperture 110 of a circularly symmetric TE11 mode cylindrical waveguide horn 20. The horn 20 is arranged such that the radiated electromagnetic wave is intercepted by a parabolic reflector.

Whilst an exemplary application of a hollow ridge dual channel waveguide 15 is described above in relation to a feed horn and antenna system, it will be appreciated that the waveguide may be used for other applications. For example, the hollow ridge dual channel waveguide 15 may be used as a microwave filter. The frequency channels that are passed by the filter can be selected based on the dimensions of the waveguide.

A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the scope of the invention. For example, although the first waveguide 45 is described in terms of a quad-ridged waveguide, it will be appreciated that other numbers of ridges may be used, such as two ridge or eight ridge waveguides. Furthermore, although the first waveguide 45 is advantageously described as having a circular cross section, it will be appreciated that waveguides having other cross sections may be used. Similarly, although the second waveguide 60a, 60c and 60b, 60d is described as advantageously having a rectangular cross section, it will be appreciated that waveguides having other cross sections may be used. In addition, although the waveguide feed and horn 5 is described in terms of signal generation and emission, it will be appreciated that the feed and horn 5 may also be operable as a receiver and the emission or radiating section 20 may be operable as a receiving section and apparatus associated with signal generation or launch 10 may be operable to receive/detect signals.

* ** *** * 30 It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the S...

invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claims

CLAIMS1. A waveguide apparatus comprising at least a first waveguide and a second waveguide, wherein the first waveguide comprises a ridge waveguide and the second waveguide is at least partially comprised in at least one ridge of the first waveguide.
2. A waveguide apparatus according to claim 1, wherein the first wave guide comprises a conduit, the conduit being provided with at least one ridge extending internally from a wall of the cavity.
3. A waveguide apparatus according to claim 2, wherein the conduit of the first waveguide is formed in a metallic block.
4. A waveguide apparatus according to claim 2 or claim 3, wherein the first wave guide comprises four ridges.
5. A waveguide apparatus according to any of the preceding claims, wherein the second waveguide has a substantially rectangular cross section.
6. A waveguide apparatus according to any of the preceding claims, wherein the second waveguide comprises at least two waveguides, at least one of the second waveguides being substantially orthogonally oriented in respect of at least one other second waveguide.
7. A waveguide apparatus according to any of the preceding claims, wherein the second waveguides are isolated from the first waveguide.I.....

*
8. A waveguide apparatus according to claim 7, wherein the feed is :: 30 provided with at least one conductive vane at an interface between the first and second waveguides.
9. A waveguide apparatus according to any of the preceding claims, wherein the first waveguide is adapted to support or propagate a first frequency **** * 35 signal or frequency band and the second waveguide is adapted to support a second frequency signal or frequency band.
10. A waveguide apparatus according to claim 9, wherein the first frequency signal or frequency band comprises a higher frequency or frequencies than the second frequency signal or frequency band.
11. A waveguide apparatus according to claim 10, wherein the first frequency band comprises or belongs to the Ku-band and/or the second frequency band comprises or belongs to the C-band.
12. A waveguide apparatus according to any of the preceding claims, wherein the first and/or second waveguide is adapted to support a plurality of signal propagation modes.
13. A waveguide apparatus according to claim 12, wherein the signal propagation modes supported by the first waveguide comprise quasi-TEM modes.
14. A waveguide apparatus according to claim 12 or claim 13, wherein the signal propagation modes supported by the second waveguide comprise at least one TE10 mode.
15. A waveguide apparatus according to any of claims 12 to 14, wherein the first and/or second waveguide is switchable between propagation modes.
16. A waveguide apparatus according to any of claims 12 to 15, wherein the first and/or second waveguide is adapted to support orthogonally polarised signal propagation modes.
17. A waveguide apparatus according to any of claims 12 to 16, wherein the waveguide apparatus is switchable between mutually orthogonal linear polarisation modes and/or between linear and circular polarization modes.
18. A feed comprising a waveguide apparatus according to any of the preceding claims, a radiating aperture and a transition section for S..: transforming a mode associated with the first waveguide to an emission mode associated with the radiating aperture.
19. A feed according to claim 18, wherein the transition section comprises a tapered dielectric rod.
20. A feed according to claim 18 or claim 19, wherein the transition section comprises leaky wave characteristics.
21. A feed according to any of claims 18 to 20, wherein the feed comprises a radiating aperture and at least a portion of the second waveguide transitions toward the emission aperture.
22. A feed according to claim 21, wherein at least a portion of the second waveguide transitions toward the emission aperture by decreasing a dimension that a channel of the second waveguide extends into the cavity and/or increasing a dimension of the channel of the second waveguide that is circumferential in the conduit.
23. A feed according to any of claims 18 to 22, comprising at least one signal transmitter and/or receiver for providing a signal to and/or receiving a signal from at least one of the first and second waveguides and a ridged launching section.
24. A feed according to claim 23, wherein the signal transmitter and/or receiver comprises two or more orthogonally positioned probes for providing and/or receiving signals, the probes being located in a gap between opposing ridges of the ridged launching section.
25. A feed according to claim 25, wherein the probes are adapted to generate and/or receive signals in the Ku frequency band for propagation by the first waveguide.

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26. A feed according to claim 24 or claim 25, wherein the probes are axially **S.off-set from each other.
27. A feed according to any of claims 23 to 26, wherein the signal transmitter and/or receiver comprises one or more magnetic loops adapted to generate or detect electromagnetic signals, the magnetic loops being located in channels of the second waveguides.
28. A feed according to claim 27, wherein the magnetic loops are adapted to generate a signal in the C frequency band for propagation by the second waveguides.
29. A feed according to any of claims 27 to 28, wherein the signal transmitter and/or transceiver comprises a plurality of magnetic loops and at least one magnetic loop is located in a channel of a second waveguide that is orthogonal to a channel of a second waveguide in which at least one other magnetic loop is located.
30. A feed according to any of claims 24 to 29, wherein the ridged launching section comprises tunable shorting walls located behind the probes.
31. A feed for an antenna, the feed comprising at least one first waveguide and at least one second waveguide, wherein the first waveguide comprises a ridged waveguide and the second waveguide comprises a rectangular cross sectioned waveguide.
32. An antenna comprising a waveguide apparatus according to any of claims ito 17 or a feed according to any of claims 18 to 31 for providing and/or receiving a signal and a reflector for reflecting the signal.
33. A method of manufacturing an antenna feed, the method comprising providing a first waveguide, wherein the first waveguide comprises a conduit and one of more ridges extending inwardly from the conduit, the method also comprising providing a second waveguide embedded in and/or at least partially formed by the one or more ridges of the first waveguide.* ** S.. * 30
34. A method according to claim 33, wherein the feed comprises a waveguide apparatus according to any of claims 1 to 17, a horn section, and a launching section and/or is a feed according to any of claims 18 to 31. *..* * S...
35. A method of manufacturing an antenna comprising providing an waveguide apparatus according to any of claims 1 to 17 or a feed according to any of claims 18 to 31 and a reflector wherein the feed is arranged to transmit and/or receive a signal and the reflector is arranged to reflect the signal.
36. A microwave transmission system or filter comprising a waveguide apparatus according to any of claims 1 to 17. * SS* ***** * S all.I I...S *.S * I.I