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Title:
HIGH POWER - LOW LOSS ANTENNA SYSTEM AND METHOD
Document Type and Number:
WIPO Patent Application WO/2014/127422
Kind Code:
A1
Abstract:
A medium to high power wideband antenna waveguide feed for interconnecting electromagnetic signals to a coaxial output antenna waveguide, the feed including: a first input feed inputting a first polarised electromagnetic signal; a second input feed inputting a second signal, substantially orthogonal to the first polarised electromagnetic signal; a first electromagnetic power splitting unit for splitting power fed from the first input feed into a first and second polarised output signals, a second electromagnetic power splitting unit for splitting power fed from the second input feed into a first and second orthogonal polarised output signals; a first and second interconnecting waveguides interconnecting the first and second polarised output signal to a first and second port of the coaxial output antenna waveguide; a third and fourth interconnecting waveguide interconnecting the first and second orthogonal polarised output signal to a third and fourth port of the coaxial output antenna waveguide.

Inventors:
POPE GREGORY STEVEN (AU)
GRANET CHRISTOPHE JEAN-MARC (AU)
KOT JOHN SEWARD (AU)
DAVIS IAN MAXWELL (AU)
Application Number:
PCT/AU2014/000156
Publication Date:
August 28, 2014
Filing Date:
February 20, 2014
Export Citation:
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Assignee:
BAE SYSTEMS AUSTRALIA LTD (AU)
International Classes:
H01Q13/00; H01Q15/00
Foreign References:
US5818396A1998-10-06
US6812807B22004-11-02
CN101997173A2011-03-30
Attorney, Agent or Firm:
SHELSTON IP (60 Margaret StreetSydney, New South Wales 2000, AU)
Download PDF:
Claims:
CLAIMS:

1. A medium to high power wideband antenna waveguide feed for interconnecting electromagnetic signals to a coaxial output antenna waveguide, the feed including:

a first input feed inputting a first polarised electromagnetic signal;

a second input feed inputting a second orthogonal polarised electromagnetic signal, substantially orthogonal to the first polarised electromagnetic signal;

a first electromagnetic power splitting unit for splitting power fed from the first input feed into a first and second first polarised output signals;

a second electromagnetic power splitting unit for splitting power fed from the second input feed into a first and second orthogonal polarised output signals;

a first interconnecting waveguide interconnecting the first polarised output signal to a first port of the coaxial output antenna waveguide;

a second interconnecting waveguide interconnecting the second polarised output signal to a second port of the coaxial output antenna waveguide;

a third interconnecting waveguide interconnecting the first orthogonal polarised output signal to a third port of the coaxial output antenna waveguide; and

a fourth interconnecting waveguide interconnecting the second orthogonal polarised output signal to a fourth port of a coaxial output antenna waveguide.

2. A wideband antenna waveguide feed as claimed in claim 1 wherein said first and second port arc diametrically opposed to one another.

3. A wideband antenna waveguide feed as claimed in claim I wherein said third and forth port are diametrically opposed to one another.

4. A wideband antenna waveguide feed as claimed in any previous claim wherein said first, second, third and fourth ports are arranged around the circumference of a cylindrical waveguide.

5. A wideband antenna waveguide feed as claimed in any previous claim wherein said coaxial output antenna waveguide further includes:

a tapered elongated cavity defined by a first and second wall,

a first proximal end of the cavity having a waveguide interconnected to the first, second, third and fourth ports:

a second distal end of the cavity being electromagnetically transparent; the first wall having a sectional profile being axially tapered to a point: and the second wall being substantially monotonically increasing, to a first order, in radial diameter in section from the proximal to distal ends.

Description:
High Power - Low Loss Antenna System and Method FIELD OF THE INVENTION

[0001] The present invention relates to the field of antenna devices and, in particular, to an antenna device having a wide frequency and high power range of operation.

[0002] Antenna device of the present invention have a wide range of applications, including, but not limited to Radio Astronomy, Multi-band Satellite Communications (SATCOM) Systems, Signal Surveillance and Intelligence, Spectrum Surveillance, and Electronic Warfare.

BACKGROUND

[0003] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0004] Antenna devices efficiently couple energy to and from an oscillating electrical signal into a corresponding oscillating electromagnetic field normally initially operational within an associated waveguide. Ideally, the devices arc operational over a wide range of frequencies of interest.

[0005] Examples of antenna devices (operational in a Multiband frequency domain) include those disclosed in: United States Patent 6,720,932 entitled "Multi-Frequency Antenna Feed", United States Patent 8.089, 415 entitled "Multiband Radar Feed System and Method", and United States Patent 6,982,679 entitled: "Coaxial Horn Antenna System".

[0006] The desire for efficient transmission and reception of antenna signal over a wide frequency domain and high operational power places restrictions on the particular antenna feed design. In particular, any form of non-linear frequency response for devices used in forming a wideband driving feed are likely to have detrimental effects on the performance of the antenna feed system. Further, the design is preferably operational over a very wide frequency range and at medium and high powers.

SUMMARY OF THE INVENTION

[0007] It is an object of the invention, in its preferred form to provide an improved form of antenna design for operation at medium and high powers.

[0008] In accordance with a first aspect of the present invention, there is provided a medium and high power wideband antenna waveguide feed for interconnecting electromagnetic signals to a coaxial output antenna waveguide, the feed including: a first input feed inputting a first polarised electromagnetic signal; a second input feed inputting a second orthogonal polarised electromagnetic signal, substantially orthogonal to the first polarised electromagnetic signal; a first electromagnetic power splitting unit for splitting power fed from the first input feed into a first and second first polarised output signals; a second electromagnetic power splitting unit for splitting power fed from the second input feed into a first and second orthogonal polarised output signals; a first interconnecting waveguide interconnecting the first polarised output signal to a first port of the coaxial output antenna waveguide; a second interconnecting waveguide interconnecting the second polarised output signal to a second port of the coaxial output antenna waveguide; a third interconnecting waveguide interconnecting the first orthogonal polarised output signal to a third port of the coaxial output antenna waveguide; and a fourth interconnecting waveguide interconnecting the second orthogonal polarised output signal to a fourth port of a coaxial output antenna waveguide.

[0009] hi some embodiments, the first and second ports are preferably diametrically opposed to one another. In some embodiments, the third and forth port are preferably diametrically opposed to one another. The first, second, third and fourth ports are preferably arranged around the circumference of a cylindrical waveguide.

[0010] In some embodiments the coaxial output antenna waveguide includes: a tapered elongated cavity defined by a first and second wall; a first proximal end of the cavity having a waveguide interconnected to the first, second, third and fourth ports; a second distal end of the cavity being electromagnetically transparent; the first wall having a sectional profile being axially tapered to a point; and the second wall being substantially monotonically increasing, to a first order, in radial diameter in section from the proximal to distal ends.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0012] Fig. 1 Olustrates the wideband coaxial launcher concept;

[0013] Fig. 2 illustrates a perspective view of the feed portions of the wideband launcher;

[0014] Fig. 3 illustrates a sectional view through the feed portions of the wideband launcher;

[0015] Fig. 4 is a graph of the simulated measured frequency response of the wideband launcher;

[0016] Fig. 5 illustrates a schematic sectional view of the upper portion of a substantially symmetric 'Bullet' horn arrangement;

[0017] Fig. 6 illustrates a schematic sectional view of the Bullet Horn arrangement; [0018] Fig. 7 illustrates a schematic sectional view of a first portion of a cornigaled Bullet Horn arrangement;

[0019] Fig. 8 illustrates a schematic sectional view of a second operative portion of a corrugated Bullet Horn arrangement;

[0020] Fig. 9 illustrates a side perspective sectional view of an antenna design;

[0021] Fig. 10 illustrates a close up view of the feed portion of the antenna of Fig. 9;

[0022] Fig. 1 1 illustrates a further close up view of the feed portion of the antenna of Fig. 9;

[0023] Fig. 12 illustrates a higher power waveguide feed;

[0024] Fig. 13 illustrates further portions of the higher power feed; and

[0025] Fig. 14 illustrates a shortened medium to power waveguide feed able to take probe inputs. DETAILED DESCRIPTION

[0026] The preferred embodiment provides for an efficient coupling over a wideband balanced excitation of a coaxial waveguide at medium to high power.

[0027] hi the preferred embodiment there is provided an antenna waveguide for operation in a TE1 1 mode. The waveguide is led to a coaxial horn antenna, herein after known as a 'Bullet Horn' antenna device.

[0028] The waveguide can then be used to feed various antenna devices, for example, a coaxial horn antenna. The preferred embodiment can be described as a further development on a coaxially fed waveguide. The preferred embodiment acts as an extension on a coaxially fed waveguide and will be initially described with reference to the coaxially fed waveguide.

[0029] For typical coaxial waveguide dimensions used in the preferred embodiment, the mode spectrum of the waveguide, in order of increasing cut-off frequency is: TEM, TEn, TE21, TE31, . . ., TEIVI,. By exciting the coaxial waveguide with a pair of balanced probes, the TEtnl modes with m even are nulled-out, as is the TEM mode.

[0030] This leaves the El 1 mode as the first significant excited mode, with the TE 3; mode as the next significant higher-order mode. To a good approximation, the cut-off frequency of the TE31 mode is three-times the cut-off frequency of the TE n mode. This fixes the practical upper limit for the operating frequency bandwidth of such a feed as 3:1. However, practical considerations mean that the waveguide should be operated somewhat above the TE, , cut-off frequency, so a more realistic limit for the frequency bandwidth is probably closer to 2.5: 1. [0031] The spectrum of the coaxial waveguide can be modified by including ridges or corrugations into the waveguide, and this approach has the potential to extend this limit.

[0032] A significant practical limit of this type of transition is the need for a balanced feed to the two probes, i.e. they need lo be driven with signals of equal amplitude that are 180° out of phase. Generating this equal amplitude split with a 180° phase shift is possible with a component such as a hybrid junction or a Balun, but these components are also frequency-dependent, and their bandwidth limits tend to limit the overall performance of the wideband transition.

[0033] The topology of the coaxial waveguide allows connection via the inner and outer conductors, to allow in-phase excitation of the junction. The resulting in-phase power divider can be made to operate over a very wide bandwidth, so that the frequency dependence of the wideband transition is not limited by the performance of the power splitter.

[0034] A wideband coaxial launcher concept 1 of the preferred embodiment is illustrated initially in Fig. 1. In this case, a pair of coaxial concentric waveguides 2, 3 is provided. Waveguides 2, 3 extend circumferentially and coaxially about a central axis with waveguide 2 being disposed within waveguide 3, which has a larger radius than waveguide 2. The region between waveguides 2, 3 defines an annulus shaped cavity centred about the central axis and extending along the axis. The annulus cavity is substantially axially symmetric about the central axis.

[0035] Two probes 5, 6 located within the annulus at substantially diametrically opposed positions are driven from opposite ends with respective in-phase signals 8, 9 to generate a balanced excitation. In this way, the need for 180° phase shift circuitry is removed. If the probes 5, 6 are matched usmg a system coaxial impedance of 100Ω, the two probes can be connected in parallel to a standard 50Ω coaxial line 10 using a tee-junction 11 to generate the in-phase signals. Because the match of the tee-junction depends only on characteristic impedance of the transmission lines, it is inherently frequency-independent, allowing for a wideband driving signal. However, the arrangement of Fig. I is only suitable for low power implementations.

[0036] The arrangement of Fig. 1 also deals only with a single polarization. However, the orthogonal polarization can be generated using a set of orthogonal probes. An advantage over the known circular ridged waveguide wideband orthomode transducer (OMT) is that it is simple to locate the probes for both polarizations in a common plane. This can also apply to a ridged coaxial OMT.

[0037] One possible implementation of a low power wideband junction arrangement 20 is shown in Fig. 2. The arrangement 20 utilises a symmetrical double-tapered probe structure 21, 22 that can be fed either via a transmission line 23 connected to the inner conductor or a transmission line 24 connected to the outer conductor of the large coaxial waveguide. Each probe has a structure that is widest at a point intermediate the inner and outer conductors and which tapers in width towards each conductor. The probe 21 , 22 are connected to equal lengths of J 00Ω coaxial transmission line 23, 24, and then via a tee-junction 25 to a 50Ω coaxial line 26 and input connector.

[0038] In the embodiment illustrated in Fig. 2, probe 22 is driven by transmission line 24 from a position external to the outer conductor of the coaxial waveguide and probe 21 is driven by transmission line 23 from a position internal to the inner wall of the coaxial waveguide.

[0039] Impedance matching can be done using three structures: the coaxial cavity 28 behind the probes, the shape of the probes 21 , 22 themselves, and a pair of impedance matching stubs 29, 30 placed in front of the probes at a predetermined distance from the respective probes within the annulus. Although a pair of matching stubs 29, 30 is shown in Fig. 2, alternative matching mechanisms can be used, like ridges, irises, steps, etc.

[0040] Fig. 3 illustrates a sectional view through the arrangement 20 of Fig. 2. As the probes 21, 22 are fed from different ends and arc located in a coaxial structure, they are only approximately symmetrical in structui'e and so the two probes will be slightly different to achieve a balanced feed.

[0041] An example coaxial feed launcher of the arrangement of Fig. 3 was analysed using the software package CST Microwave Studio. The initial, non optimised results for S- parameters arc shown in Fig. 4. A first curve 41 shows Sn at the 50Ω input, and the second curve 42 shows S31 which is the coupling from the 50Ω input to the TEn mode at the output. The target frequency band was 1 to 2 GHz, but a slight overall frequency shift has occurred, giving an operating frequency band of approximately 1.1 to 2.3 GHz.

INTERFACE TO A WIDEBAND COAXIAL HORN ANTENNA

[0042] In the design of the coaxial waveguide feed, the primary function of the wideband coaxial junction is to feed a mated wideband coaxial hom antenna. In the coaxial waveguide feed the coaxial horn includes a profiled surface, hereinafter referred to as a "Bullet Horn", which interfaces directly with the wideband coaxial junction.

[0043] Given the coaxial waveguide input parameters of the wideband coaxial junction, a set of parameterized profile curves (like splines for example) can be defined to generate the Bullet Horn shape. Two profiles are required, an inner profile and an outer profile. An example resultant design of the structure can be as illustrated in Fig. 5, which illustrates a sectional view though an upper portion of a substantially axially symmetric Bullet Horn 50. The Bullet Horn arrangement, includes two profiled surfaces 51, 52 defined by a number of spline-nodes e.g. 53 that are used as parameters to define the surface geometry. Tn the case where spline curves are used to define the profiles, the spline nodes are the parameters that can be utilized to optimize the overall performance of the combined wideband coaxial junction and Bullet Horn. Fig. 6 illustrates a sectional profile view of ' one form of Horn geometry, illustrating its substantially symmetric nature.

[0044] The optimization process can take into account a set of user defined performance requirements such as the overall input return loss, gain, cross-polarization maximum and sidelobe levels. An optimization procedure adjusts the inner and outer profiles and "shapes" the Bullet Horn profile to meet or come as close as possible to a desired performance targets.

[0045] The Bullet Horn geometry can be, at present, either smooth-walled or corrugated. Whilst Fig. 5 and Fig. 6 illustrate a smooth walled design. Fig. 7 and Fig. 8 illustrate a corrugated wall design. Fig. 7 illustrates a first sectional view 70 of the top portion of an axially symmetric Bullet Horn design. The top portion initially includes tapered spline profiled surfaces 72, 73, which then feed out to a corrugated horn profile end. The corrugations provide for low cross polarisation of the antenna system. Fig. 8 illustrates the overall geometry of the corrugated horn arrangement.

MECHANICAL DESIGN CONCEPTS

[0046] A mechanical design for a wideband coaxial launcher and associated Bullet Horn was investigated from a manufacturing perspective. Fig. 9 to Fig. 1 1 illustrate sectional views through one investigated design. Turning initially to Fig. 9, in this design, a corrugated horn arrangement 90 is illustrated having a front end 91 with a corrugated and radially expanding outer profiled surface and a back end 92 having a radially tapered inner profiled surface 93. The coaxial feed in is provided in back section 94. The front end 91 and back end 92 are connected at a point where the inner surface 93, which is conical in shape, tapers to a point. In one embodiment, front end 91 includes a series of corrugated slots along the outer profiled surface. Fig. 10 illustrates an enlarged view of the back portion of the Bullet Horn antenna, showing the stepwise profiled surfaces 92, 93. In preferred embodiments, the surfaces 92, 93 are stepwise tapered so as to include a series of distinct but interconnected taper levels. Similarly, surfaces 72, 73 of Fig. 7 can include stepwise profiled sections. In various embodiments, the profiles surfaces can include various degrees of smoothing, which define the size of each taper level. As such, in some embodiments, the outer profiled surface increases substantially monotonically in radial diameter from a proximal end adjacent the back end 92 to a distal end adjacent front end 91. At the distal end, the cavity is electromagnetically transparent.

[0047] The coaxial feed in is provided by means of coaxial cable 98 which is split into two cables 96, 97 which deliver signals to the probes phased appropriately to excite the TE11 mode. The tapering of inner profiled surface 93 corresponds to a tapering of the inner surface of the annulus between conductors. Therefore, an inner core of the annulus tapers down to a point beyond which the region within waveguide 3 is circular in radial cross section. [0048] Fig. 1 1 illustrates the feed in portion 94 of Fig. 10 in more detail. The coaxial cable 98 is split with two equal lengths 96, 97 being fed to corresponding probes 101 , 102. The coaxial cable 97 passes through a core cavity 106 and attaches to the probe 102. Cavity tuning is provided by tuning stubs 103, 104.

USE OF ALTERNATIVE FEED STRUCTURES FOR M ED I UM TO HIGH-POWER AND

LOW-LOSS OPERATION

[0049] The foregoing arrangement will only apply up to a particular power limit. These arrangements use traditional coaxial transmission lines to drive the probes 101 , 102 that are used to excite the large coaxial waveguide. Coaxial lines may not be ideal for some applications, due to limited power-handling or high loss. One alternative approach would be the direct replacement of the coaxial transmission lines with an alternative TEM-mode transmission line, such as slab-line.

[0050] When dealing with high power environments, a preferred approach is to utilise a wideband waveguide structure, such as a ridged rectangular waveguide. This second approach would be facilitated by the replacement of the probe feeds by coupling slots.

[0051] Fig. 12 illustrates one form of Electromagnetic (EM) model of a coaxial OMT 120 with double ridged waveguide ports including ports 121 to 124. The double ridged waveguide ports can be fed with a double ridged waveguide network containing wideband E-planc Tec junctions. Such an arrangement 130 is illustrated in Fig. 13, wherein the coaxial OMT 120 is fed by double ridged waveguide ports 121 to 124 which are in turn coupled to E-plane Tee junctions 131 , 132. Tee junctions 131, 132 can be respectively configured to deliver input electromagnetic signals in orthogonal polarisations. Tee junctions 131, 132 split the power from each of the orthogonal polarised signals to deliver a frrst. polarisation along waveguide ports 121 and 122, and a second polarisation along waveguide ports 123 and 124. As illustrated in Fig. 13, ports 121 and 122 are diametrically opposed to each other. Ports 123 and 124 are similarly diametrically opposed to each other. All four ports are arranged around the circumference of a cylindrical waveguide. The cylindrical waveguide is able to be interconnected with the feed portion of the Bullet Horn antenna described above.

[0052] In an alternative medium to high power arrangement 140, as illustrated in Fig. 14, the double ridged waveguide output ports are transformed into standard coaxial ports 141 to 144. The coaxial ports are on opposing sides which results in each pair of ports being in anti-phase if fed by the same simple coaxial splitter as proposed for the wideband coaxial launcher.

[0053] It can be seen that the described arrangements provide for the utilisation of symmetrical probes fed from opposite ends, which gives the desired balanced feed, and provides for a practical implementation concept, for example, for a feed for a wideband coaxial horn antenna. A similar concept can be realised using ridged waveguides coupled via slots, for example, in high-power applications.

[0054] The wideband coaxial junction and Bullet Horn design can be used together to achieve user defined wideband performance in terms of return loss, radiation pattern and gain.

INTERPRETATION

[0055] Reference throughout this specification to "one embodiment", "some embodiments" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the ptoses "in one embodiment", "in some embodiments" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0056] As used herein, unless otherwise speci fied the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, cither temporally, spatially, in ranking, or in any other manner.

[0057] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[0058] As used herein, the term "exemplary" is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment" is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

[0059] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[0060] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0061] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[0062] hi the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0063] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0064] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.