WO2007141561A1 - Antenna array - Google Patents

Abstract

An antenna arrangement comprising a circular array of element wherein said elements are arranged around a periphery and wherein said elements are point inwards. The elements are so arranged such that elements which lie opposite to each other are at an angle and/or are linearly polarised to each other.

Description

Antenna Array

This invention relates to antenna arrays comprising a plurality of individual elements and has particular, but not exclusive application, to tapered slot antenna such as Vivaldi antennas.

A known antenna arrangement comprises a circular phased array of linearly polarised elements; a difficulty in creating such a phased array at high frequencies is getting centres within half a wavelength of each other in order to prevent grating lobes. A known solution to this is either to use a large number of elements or very small elements. Both of these options have drawbacks. Using large numbers of elements means that the beam former required will be large and complicated, whilst very small elements are difficult to manufacture and feed.

An alternative is to have several small sub-arrays each of which takes the form of a small concaved arc such that the bore-sights of the elements converge at a point in front of the array; this unfortunately requires a beam- former for each sub-array.

It is an object of the invention to overcome these problems.

The invention comprises an antenna arrangement comprising an array of element wherein said elements are arranged around a periphery and wherein said elements are point inwards. Preferably the periphery is circular.

The elements are preferably arranged such that element which lie opposite to each other are at an angle or are linearly polarised at 90 degrees to each other and the elements are arranged at an angle of 45 degrees to the plane of the periphery

In a further embodiment, a further array of elements is interleaved with the elements where the further array point outwards. Figure Ia and b shows embodiments of the invention. It shows a full 360 degree circular array 1 of inward facing antenna elements 2. In the figure these are shown as Vivaldi type antenna elements. They are rotated at 45 degrees, either clockwise of anti clockwise about their boresight relative to the plane of the array (that is to say at 45 degrees to the plane of the circle they form when viewed circumferentially). This means the elements do not block each other because opposite elements 2a and 2b are consequentially at 90 degrees to each other.

As can be seen for any particular element, the element directly opposite it is at right angles to it and so invisible from it in electromagnetic terms because it an orthogonal polarisation. The feed points (connectors connected to cables for power etc (not shown)) for the antenna are in line with the bore-sight of the antenna (i.e. at also 45 degrees). Therefore the feed-line routing around the antenna is preferably parallel to the antenna polarisation so as not to block the antenna looking through it. It is of course possible to produce an array with an orthogonal polarisation, see figure Ib, by rotating the elements by 90° relative to the array of figure Ia.

A further known technique in antenna arrays in general is to use two different antenna types interleaved in an array; the small antennas located close to the centre of the array so that their phase centres are close together for the high frequencies while the large antennas would have their phase centres further out for the lower frequencies. The problem with this solution is that the large antennas interfere with the field of view of the smaller antennas.

This problem is solved in a further embodiment of the invention by forming the 360 degree array with interleaved inward facing high frequency antennas and outward facing low frequency antennas, see figures 2a and 2b. As before the antennas at an angle of 45 degrees to the plane of the array. The arrows again show the direction the antennas are pointing in.

Furthermore with the high and low frequency antennas being interleaved then although the high and low frequency arrays are two separate arrays they only take up as much space as the larger of the two arrays. In an example ultra-wideband antennas are used for both the high frequency and low frequency portions of the array which is possible due to the lack of size constraints on the high frequency antennas. As before for any particular inward looking antenna the antenna directly in front of it is at right angles to it and so invisible from it in electromagnetic terms because it has an orthogonal polarisation.

Claims

Claims

1. An antenna arrangement comprising an array of element wherein said elements are arranged around a periphery and wherein said elements are point inwards.

2. An arrangement as claimed in claim 1 wherein said periphery is circular.

3. An arrangement as claimed in claim 1 or 2 wherein said elements are so arranged such that elements which lie opposite to each other are at an angle and to each other.

4. An arrangement as claimed in claims 1, 2 or 3 wherein said elements are /or are linearly polarised

5. An arrangement as claimed in claim 3 wherein said angle is 90°.

6. An arrangement as claimed in claims 1 to 5 wherein the elements are arranged at an angle of 45° to the plane of the periphery.

7. An arrangement as claimed in claims 1 to 6 having a further array of elements interleaved with said elements and where said element of the further array point outwards.

8. An arrangement as claimed in claim 7 wherein outward pointing and inward pointing elements are interleaved alternately.

9. An arrangement as claimed in claims 7 or 8 wherein said elements of the further array are a different size.

10. An arrangement as claimed in claims 1 to 9 wherein the feed connections for an element are arranged parallel to the element.

11. An arrangement as claim in any preceding claim wherein said antenna elements are tapered slot antenna elements.