WO2008104456A1 - End- fed array antenna - Google Patents

End- fed array antenna Download PDF

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Publication number
WO2008104456A1
WO2008104456A1 PCT/EP2008/051652 EP2008051652W WO2008104456A1 WO 2008104456 A1 WO2008104456 A1 WO 2008104456A1 EP 2008051652 W EP2008051652 W EP 2008051652W WO 2008104456 A1 WO2008104456 A1 WO 2008104456A1
Authority
WO
WIPO (PCT)
Prior art keywords
end
array antenna
fed
antenna according
plurality
Prior art date
Application number
PCT/EP2008/051652
Other languages
French (fr)
Inventor
Anthony Kinghorn
Original Assignee
Selex Sensors & Airborne Systems Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB0703870.6 priority Critical
Priority to GB0703870A priority patent/GB0703870D0/en
Priority to EP07251239.5 priority
Priority to EP07251239 priority
Application filed by Selex Sensors & Airborne Systems Limited filed Critical Selex Sensors & Airborne Systems Limited
Publication of WO2008104456A1 publication Critical patent/WO2008104456A1/en

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/2682Time delay steered arrays
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00Antenna arrays or systems
    • H01Q21/0006Particular feeding systems

Abstract

The present invention relates to an array antenna. More specifically, the present invention relates to an electronically scanned end-fed array antenna. The present invention provides an end-fed array antenna comprising: a plurality of radiating elements (10); a plurality of communication modules (60), each in communication with one of said radiating elements; an input line (30) having a plurality of junctions (50), each junction being connected to one of said communication modules; and control means for individually controlling each of said communication modules by applying a respective delay to each communication module,- wherein a signal is fed into the input line via each said junction to said plurality of communication modules and each of the plurality of communication modules transmits said signal after the respective delay applied by the control means to that communication means.

Description

END- FED ARRAY ANTENNA

The present invention relates to an array antenna. More specifically, the present invention relates to an electronically scanned end-fed array antenna. Before electronically scanned array antennas became prevalent, there were two ways to feed an antenna having a plurality of radiating elements: using either a "corporate" feed or an "end" feed.

A "corporate" feed, shown in Figure 1 , provides a symmetrical path to each radiating element 10, so that there is an identical distance from the collective input to the array and each radiating element 10. The path comprises a multitude of branches 30 repeatedly splitting into two branches 30 at each junction 40. A signal 20 transmitted to the array, therefore, reaches every radiating element 10 in the array at the same time, in turn leading to such an array producing a uniform-shaped beam in a direction perpendicular to the array face.

An "end-fed" arrangement, shown in Figure 2, has a single input line 30 that is connected to a plurality of radiating elements 10 via a number of junctions 50 in the input line 30. The power of the signal 20 transmitted down the input line 30 is filtered at every junction 50 to provide each radiating element 10 with a signal having the same power.

When electronically scanned array antennas replaced conventional antennas and conventional array antennas, the "end-fed" arrangement shown in Figure 2 was no longer considered a viable structure for feeding the radiating elements 10 of electronically scanned array antennas because there is a delay between the input signal reaching the first radiating element 10 and the last radiating element 10. This delay causes an electronically scanned array antenna beam to be emitted at an angle to the array antenna face, rather than in a perpendicular direction to the array antenna face. The "corporate" feed structure shown in Figure 1 did, however, provide an antenna beam to be emitted in a perpendicular direction to the array face so was adopted as the standard mechanism to feed electronically scanned array antennas. A problem with the "corporate" feed structure is that it is complicated due to the large number of junctions 40 needed to provide symmetrical paths. This arrangement thus takes up a larger volume of space than the "end-fed" structure and as a result is heavier than the "end-fed" structure. Prior arrangements were based on separate plug-in modules, using a planar manifold for RF distribution, control and power, and an entirely separate cooling manifold. The approach was abandoned because of weight, excessive number of connectors (which caused reliability problems) and a failure to find a solution to the RF/DC manifold problem; it proved impossible to squeeze all the required interconnect into the area available, even using very difficult multi- layering.

The next step was to adopt the 'plank' approach. This solved the manifolding problem (at the expense of increased depth) by placing half the RF manifold and all of the DC manifold on a plank; the remaining RF manifolding was provided on separate combiners at right angles. This approach also allowed a significant reduction in connector count. However the interconnection of the manifolds has remained a problem; the present solution of connectorised Duroid boards, interconnected with semi-rigid co-ax, is at best inelegant and, at worst, a major reliability hazard. Further steps were all to do with plank optimisation- depth has been reduced by folding some of the interconnect layers, and the ribbon bonds to the T/R modules have been replaced by vertical interconnect using fuzz-buttons.

The present invention provides an end-fed array antenna comprising: a plurality of radiating elements; a plurality of communication modules, each in communication with one of said radiating elements; an input line having a plurality of junctions, each junction being connected to one of said communication modules; and control means for individually controlling each of said communication modules by applying a delay to each communication module; wherein a signal is fed into one end of the input line and a portion of said signal reaches each said communication means and the communication means transmits the portion of the signal after the delay applied by the control means to that communication means.

Thus the present invention provides a smaller, lighter and less complicated structure than when using a "corporate" feed structure as described above.

The new concept is a breakthrough idea which, it is believed, will make 'tiled' arrays technically feasible and economic, and offer major size and weight advantages.

To date, all RF manifolding concepts have been based on corporate feed structures. Furthermore these structures have been multi-layered to support sub-arraying. The nature of the corporate feed is that it occupies a great deal of space, due to its multi-level structure and the large number of power dividers.

The new approach is to use end-fed structures. These have been commonly used in ground radar, and these systems have commonly exhibited the generally undesirable feature of end-fed arrays: frequency squinting. Essentially, because each element of an end-fed array is, usually, equally spaced, an end-fed system has an equal time delay to each element, which results in a frequency-dependent beam squint. Whilst acceptable for a single frequency radar, the requirement for any form of frequency agility has tended to rule it out as an option. As a result the approach has been almost totally neglected in airborne radar.

However, with a T/R module at each element, there exists all of the control capability necessary to correct the beam squint (and indeed to steer the beam as required)- hence an end-fed arrangement is perfectly acceptable. It will have a limited instantaneous bandwidth, but this is also true of corporate-fed arrays so this is not considered a discriminating factor.

This approach is advantageous as it offers the possibility of greatly simplifying the RF feed structure, which has (so far) been seen as the Achilles' heel for low profile planar arrays. Although this approach is incompatible with arbitrary sub-arraying, which has been the industry standard for many years, the merits of arbitrary sub-arraying are less clear now; the early motivation of arbitrary sub-arraying was anti-jamming against a highly complex 'Cold War' threat, which is less of an issue now; also, the costs of the necessary receiver and processor structures for such systems remain high and the cost/benefit trade-off for sub-arrayed systems remains questionable, Another reason is that this has simply been the way the technology has evolved from planar passive antennas, and that no-one (up to now) has thought to question it.

Specific embodiments of the invention will now be described, by way of example only and with reference to the accompanying drawings that have like reference numerals, wherein:- Figure 1 is a diagram showing a portion of a conventional "corporate" feed to an antenna array;

Figure 2 is a diagram showing a portion of a conventional "end-fed" antenna array;

Figure 3 is a diagram showing the feed structure of an embodiment of the present invention;

Figure 4 is a diagram showing a transmit/receive module of an embodiment of the present invention;

Figure 5 is a diagram showing an antenna assembly using the transmit/ receive module of Figure 4; Figure 6 is a diagram showing an example RF distribution arrangement of an embodiment of the present invention; and

Figure 7 is a diagram showing of a cross-section of a complete array of an embodiment of the present invention,

A specific embodiment of the present invention will now be described in more detail with reference to Figures 3 to 7.

The feed structure of the specific embodiment of the present invention, as shown in Figure 3, is an electronically scanned end-fed arrangement. There is provided a single input line 30 having a plurality of junctions 50 along the length of the input line 30. Input signal 20 is fed into the input line 30. Each junction 50 allows a predetermined amount of the input signal 20 to flow from the input line 30 into a transmit/receive module 60. Transmit/receive module 60, as seen in Figure 4, then transmits the portion of input signal 20 through a respective radiating element 10.

In accordance with the widely understood workings of an electronically scanned array antenna, each radiating element 10 can be controlled to delay the transmission of its respective signal by a processing unit (not shown).

Without any compensation, this feed arrangement will cause the beam formed by the array antenna to form at an angle relative to the array face because of the delay between the input signal 20 reaching the first junction 50 and the last junction 50 along the input line 30.

The aforementioned processing unit (not shown) can automatically delay the respective transmit/receive modules 60 by a respective calculated or predetermined delay time in addition to the required respective delays to cause the beam to be formed as required by the apparatus.

The new approach, is capable of exploiting many of the technologies that have been developed for more conventional array structures. The following description outlines the key elements of the concept and how, as currently envisaged, such technology would be built.

A transmit/receive (T/R) module 400, shown in Figure 4, remains at the heart of any phased array, and this technology is no different. However a key aspect of a 'tiled' array is that the module 'footprint' is necessarily constrained to an area of about λ2 x λ2, in order to avoid the formation of grating lobes. So, for example, in the X-band the footprint would be about 1 .5cm. This has led others to investigate very complex and expensive 3-D packaging technologies. Instead, this embodiment uses a simple, low cost 3-D packaging technology, which might be described as a 'Heterogeneous System-in- Package'. It consists of a surface- mounted ball grid array LTCC package 420, containing two active layers: a single large GaAs MMIC 435 implementing all RF functions; overlaid by a single Si ASIC 425 implementing all digital functions. The two devices are directly wire-bonded to each other. In order to use this approach for the 'tiled' array, two steps are needed: 1 ) Incorporate a radiating element 410 into the lid- this is seen as a relatively straightforward task based on previous experience with LTCC antennas for other applications, such as the Meteor datalink; and

2) Modify the heat-sinking arrangements to be more compatible with the low profile planar array concept.

A cross-section of the new package concept, approximately to scale, is shown in Fig.4 below:

The key new features of the package, are the surface-mounted LTCC radiating element 410 and the 'thermal stud' 440. The latter is brazed to the LTCC package as the final part of package manufacture. The completed package is then populated and wire bonded, before lidding with lid 415 to provide a hermetic enclosure for long-term reliability. The radiating element 410 is then attached using solder balls 405; this process is self-aligning and will provide mechanical attachment and RF interconnect to the antenna, connecting to RF vias in the main LTCC package 420. This provides the final stage of T/R module manufacture.

The complete antenna assembly is then made, as shown in Figure 5, and will now be described:

The basic antenna assembly consists of a multilayer RF/digital/power distribution circuit board and a 'cold plate' 505. The circuit board is drilled for the 'thermal studs' on each T/R module; these holes are deliberately oversized.

In the first stage of assembly, the circuit board is populated with T/R modules which are then soldered in place, again with solder balls 430. The BGA attachment is self-aligning, the clearance in the circuit board ensures that the 'thermal stud' 440 does not interfere with this alignment.

The completed circuit board is then offered up to the 'cold plate' 505 and bolted in place via the 'thermal studs'. A good thermal path is achieved through a combination of thermal compound 510 within the clearance holes and a good metal-to-metal conduction path via the stud 440, nut 515 and spring washer 520. This construction also provides a very strong construction but with some compliance to accommodate thermal mismatches.

The 'cold plate' 505 may be realised in several possible ways. It may take the form of a metal panel with meandering liquid cooling channels between the rows of studs. This is probably the best option if it is desired to minimise hardware at the edges of the panel, and probably offers the best thermal management. Another concept is to use a panel of encapsulated thermalised pyrolitic graphite (TPG). This will provide excellent thermal conductivity to the edges of the array, where the heat may be removed either by air or liquid cooling. A third possibility is to provide finning for air cooling on the back of the array, although this may interfere with mountings for support equipment (power supplies etc.).

The surface layout of the board is where the unique advantages of this approach are most readily apparent. However, to take full advantage of the approach, it will also probably be necessary to use an addressable serial link to the modules for control, to avoid the plethora of control lines that would otherwise be necessary using current practices.

The approach lends itself to a conventional quadrant monopulse architecture. The overall concept is most conveniently realised as a rectangular array, but other shapes are possible with a little more complexity. Fig. 6 illustrates an example layout for a four-quadrant monopulse antenna. Note that whilst a corporate feed is illustrated for the vertical power combining, it could also use another end-fed arrangement. The vertical power combining could, as illustrated, be coplanar with the main RF distribution network, or it could be folded around the back (employing flexible RF interconnect, probably based on current AR work on Liquid Crystal Polymer (LCP) RF substrates. Note that Fig. 6 shows a 'square' grid array- a 'hexagonal' grid may be preferred; this will depend on several factors, including the radiating element design. Either grid layout is possible. Overall digital control will be provided from a separate control and power supply board, probably most conveniently located behind the array, as illustrated in Fig. 7. Interconnection to the array would be by conventional flexible PCB technology.

This outlines a concept and key features for an ultra-low profile AESA technology which builds on a wealth of past experience. The additional steps needed to realise this concept appear to be reasonably low risk. The key developments needed are:

1 ) Integrated radiating element in module lid;

2) End-fed stripline power distribution network; and

3) Use of addressable serial digital control for T/R modules. The technology appears well suited to large area arrays (which could be built up in a series of panels) or small, low cost arrays. It is likely, at least initially, that the power density per unit area will be lower than with conventional technology (perhaps 1W-2W per element) but this may be entirely adequate for many applications. Future use of Gallium Nitride could redress this limitation. It is likely that high-end fighter aircraft applications, wideband arrays and sub-arrayed digital beamforming systems will be better served by the more conventional 'plank'-based technologies, but for low cost systems this new concept looks very attractive.

Another potential advantage is weight- an initial appraisal suggests that it could be between 5x and 10x lighter than current solutions.

A particularly attractive aspect of the design is that it almost totally eliminates connectors. This offers major savings in cost and weight, and will enhance reliability. However consideration will need to be given to servicing and testing, but this might well be the point at which the antenna panel becomes the replaceable item- especially if the cost is low enough.

An interesting non-radar application that has recently started to emerge is for low cost, high gain steerable microwave antennas for high bandwidth mobile communications. More investigation into this application area is required, but the initial view is that this technology approach may be very attractive. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

Claims
1. An end-fed array antenna comprising:
a plurality of radiating elements;
a plurality of communication modules, each in communication with one of said radiating elements;
an input line having a plurality of junctions, each junction being connected to one of said communication modules; and
control means for individually controlling each of said communication modules by applying a respective delay to each communication module;
wherein a signal is fed into the input line via each said junction to said plurality of communication modules and each of the plurality of communication modules transmits said signal after the respective delay applied by the control means to that communication means.
2. An end-fed array antenna according to claim 1 , wherein said communication modules are transmit/receive modules.
3. An end-fed array antenna according to any of claims 1 or 2, wherein the input line is end-fed.
4. An end-fed array antenna according to any preceding claim, wherein the control means comprises an addressable serial link.
5. An end-fed array antenna according to any of claims 1 to 3, wherein the control means comprises a serial digital control.
6. An end-fed array antenna according to any preceding claim, wherein each radiating element and respective communication module are provided in one unit and the radiating element is integrated into a lid of said unit.
7. An end-fed array antenna according to any preceding claim, further comprising cooling means.
8. An end-fed array antenna according to claim 7, wherein cooling means comprises each radiating element being attached to a thermal stud.
8. An end-fed array antenna according to any of claims 7 or 8, wherein cooling means comprises liquid cooling channels in a plate.
9. An end-fed array antenna according to any of claims 7 or 8, wherein cooling means comprises encapsulated thermalised pyrolitic graphite.
10. An end-fed array antenna according to any of claims 7 or 8, wherein cooling means comprises a plurality of cooling fins mounted to an external surface or the array antenna.
11. An end-fed array antenna substantially as hereinbefore described with reference to Figures 3 to 7.
PCT/EP2008/051652 2007-02-28 2008-02-12 End- fed array antenna WO2008104456A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
GB0703870.6 2007-02-28
GB0703870A GB0703870D0 (en) 2007-02-28 2007-02-28 Antenna
EP07251239.5 2007-02-28
EP07251239 2007-02-28

Publications (1)

Publication Number Publication Date
WO2008104456A1 true WO2008104456A1 (en) 2008-09-04

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2008/051652 WO2008104456A1 (en) 2007-02-28 2008-02-12 End- fed array antenna

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4445119A (en) * 1981-04-30 1984-04-24 Raytheon Company Distributed beam steering computer
US4939527A (en) * 1989-01-23 1990-07-03 The Boeing Company Distribution network for phased array antennas
JPH042207A (en) * 1990-04-19 1992-01-07 Nec Corp Phased array antenna
US5821901A (en) * 1996-05-17 1998-10-13 Raytheon Company Antenna system
US6184832B1 (en) * 1996-05-17 2001-02-06 Raytheon Company Phased array antenna
WO2001077706A1 (en) * 2000-04-07 2001-10-18 The Chief Controller, Research And Development Transmit/receiver module for active phased array antenna
US6377217B1 (en) * 1999-09-14 2002-04-23 Paratek Microwave, Inc. Serially-fed phased array antennas with dielectric phase shifters

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4445119A (en) * 1981-04-30 1984-04-24 Raytheon Company Distributed beam steering computer
US4939527A (en) * 1989-01-23 1990-07-03 The Boeing Company Distribution network for phased array antennas
JPH042207A (en) * 1990-04-19 1992-01-07 Nec Corp Phased array antenna
US5821901A (en) * 1996-05-17 1998-10-13 Raytheon Company Antenna system
US6184832B1 (en) * 1996-05-17 2001-02-06 Raytheon Company Phased array antenna
US6377217B1 (en) * 1999-09-14 2002-04-23 Paratek Microwave, Inc. Serially-fed phased array antennas with dielectric phase shifters
WO2001077706A1 (en) * 2000-04-07 2001-10-18 The Chief Controller, Research And Development Transmit/receiver module for active phased array antenna

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