[0001] The present invention relates to an antenna choke suitable for use in the field of
radar antenna arrays.
[0002] Radar antenna arrays are composed of a number of radiating elements which are connected
to each other. A problem with such arrays is that an electric current mutually couples
the adjacent radiating elements. It is therefore desirable to reduce this current
so that the performance of the array is increased.
[0003] Antenna array chokes are known, and one such example is discussed in a book entitled
"Theory and Analysis of Phased Array Antennas" by M Amitay, V Galindo and C P Wu,
and published by Wiley Interscience. At page 308 of the above reference book, there
is shown a planar array of compound elements. The array is shown in Figure 1 herein
and includes a plurality of circular waveguides 1, and each circular waveguide has
an associated rectangular waveguide 3 which together make up a unit cell. The effect
of the rectangular waveguide is to break up the path of the ground plane currents
which travel between the circular waveguides, and therefore these rectangular waveguides
act mainly as chokes. While the small rectangular waveguides have been found to be
effective in choking the ground plane currents, their manufacture has proved to be
quite difficult.
[0004] It is an object of this present invention to provide an antenna choke which is easily
manufactured and which reduces the current which mutually couples adjacent sections
of a radar array.
[0005] According to the present invention there is provided an antenna choke for an antenna
array, the array comprising a plurality of linear array sections containing a plurality
of individual radiating elements, each array section having a channel of predetermined
depth formed throughout its length in an edge thereof, so that when the array sections
are stacked with the channels facing the same direction to form the array, the channels
between adjacent array sections act as a choke to reduce an electric current which
mutually couples adjacent array sections.
[0006] The present invention has the advantage of simplicity of construction and therefore
is more easily manufactured.
[0007] An embodiment of the present invention will now be described with reference to the
accompanying drawings, wherein;
FIGURE 1 shows a prior art antenna array;
FIGURE 2 shows a partial front view of an antenna array according to the present invention;
and,
FIGURE 3 shows a partial side view of an antenna array according to the present invention.
FIGURE 4 shows a partial side view of an antenna array incorporating a different type
of radiating element; and
FIGURE 5 shows a partial plan view of the array shown in Figure 4.
[0008] Referring to Figures 2 and 3, the antenna array comprises a plurality of linear array
sections 2, 4. Each section is of rectangular cross section and has a plurality of
rectangular radiating elements 10 positioned along its length. Each section has a
rectangular channel 6 cut into an edge of each element which extends along the entire
length of the section. The channel 6 is machined into each section prior to assembly
of the antenna array and therefore the manufacture of such arrays is made very much
easier than the array discussed in the prior art.
[0009] The channel 6 has a depth equal to a quarter of the wavelength of the operating frequency
of the array. This mount of depth effectively chokes or reduces the ground plane currents
which exists between the adjacent sections of the array.
[0010] Since the array is made up of a number of linear array sections, such as 2, 4, the
array is built by sequentially placing one section on top of another section and placing
a conductive type sealant 8 between each section. The sections are secured together
by suitable bolts, for example, with the channels all facing in the same direction
to give an assembled array.
[0011] The array therefore inherently has the necessary chokes incorporated in it by virtue
of the channels.
[0012] Figures 4 and 5, show an antenna array in which the radiating elements are of different
shape to those shown in Figures 2 and 3. The array is composed of a number of linear
array sections 2, 4 similar to those shown in Figures 2 and 3, connected together
with sealant 8 between adjacent sections. Each section has a channel 6 cut into it
along its length at a depth equal to a quarter of the wavelength of the operating
frequency of the array. The radiating elements 10, each comprise a pair of dipoles
12 printed on a substrate 14. The radiating elements 10 extend from the array sections
2, 4 in the same direction as shown in Figures 4 and 5.
[0013] It will readily be appreciated by those skilled in the art that radiating elements
of different shape to those described above may be used.
[0014] It will be readily appreciated by those skilled in the art, that while the above
description has been to an antenna array being composed of array sections which have
rectangular cross sections, cross sections of a different shape may be used. The array
sections may be curved throughout their length so that an antenna array of a dish
form is produced.
[0015] It will also be readily appreciated by those skilled in the art that any radiating
elements combined in the form of a linear array may be used providing that the body
of rectangular cross section can be formed. It will also be readily appreciated by
those skilled in the art that any lattice, rectangular, triangular or random may be
used provided it can be formed from linear arrays in either horizontal or vertical
form.
1. An antenna choke for an antenna array, the array comprising a plurality of linear
array sections containing a plurality of individual radiating elements, each array
section having a channel of predetermined depth formed throughout its length in an
edge thereof, so that when the array sections are stacked with the channels facing
the same direction to form the array, the channel between adjacent array sections
act as a choke to reduce an electric current which mutually couples adjacent array
sections.
2. An antenna choke as claimed in Claim 1, wherein the array sections are of rectangular
cross section, and the channel is cut into an edge of the array section and is substantially
right angular in form.
3. An antenna choke as claimed in Claim 1 or Claim 2, wherein the array sections are
stacked with an electrically conductive sealant therebetween.
4. An antenna choke as claimed in any preceding claim, wherein the depth of the channel
is a quarter of the operating wavelength of the antenna array.
5. An antenna choke as claimed in any preceding claim, in which the radiating elements
are of rectangular cross section.
6. An antenna choke as claimed in any of the claims 1 to 4, in which the radiating elements
are dipoles.