Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2002-02-15
2003-12-09
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S373000, C342S383000
Reexamination Certificate
active
06661375
ABSTRACT:
BACKGROUND OF THE INVENTION
Phased array antennae are used in communications systems and radar systems to provide adjustable directionality of transmission and reception, without the need to physically displace the antenna.
A phased array antenna consists of many individual antenna elements arranged in an array, typically a linear (one-dimensional) or matrix (two-dimensional) Layout. The elements are typically spaced from each other by a distance equal to one half of the wavelength of interest.
In reception mode, the signals received by each element are summed together to provide an overall received signal. With no phase difference introduced into the signals from the various elements, the antenna is most sensitive to signals arriving from a direction perpendicular to the plane of the antenna array. By introducing a progressive phase delay into the various elements, the direction of maximum sensitivity may be adjusted.
For example,
FIG. 1
shows a one-dimensional array
10
of antenna elements
12
-
1
to
12
-
7
in which each element is associated with a phase delay
14
-
1
to
14
-
7
of a greater than that of the preceding element. A wave-front
20
is shown, arriving in the direction of maximum sensitivity. The path length
16
-
1
to
16
-
7
to be travelled by the wave-front increases from zero at element
12
-
1
to 6&bgr; at
16
-
7
. The path length &bgr; is the distance travelled by wave-front
20
in the time taken for a phase angle of &agr; to be travelled by wave-front
20
. That is, &bgr;=&lgr;.&agr;/2&pgr;, where &lgr; is the wavelength of the signal producing wave-front
20
. The effect of this and the phase delays
14
-
1
to
14
-
7
is that summing unit
22
receives signals corresponding to wave-front
20
from each antenna element at the same time. These signals will sum
38
to produce a large response to wave-front
20
. For signals arriving from different directions, such as wave front
30
, the summing unit
22
will receive signals corresponding to wave-front
30
at different times, since the phase delay introduced by phase delay elements
14
is not compensated by a corresponding difference in path length. The signals received at the summing unit
22
will arrive at different times, and will not add up
38
to a large response. Signals corresponding to wave-front
34
will arrive over an even wider spread of timings, and the sensitivity of the array
10
to the wave-front
34
is even less than to wave-front
30
.
The summer
22
may apply a weighting scheme to the various signals from antenna elements
12
to provide a degree of aperture shading.
By analogy, similar considerations may be applied to transmission of signals. That is, a single outgoing signal is applied to each of the phase delay elements
14
-
1
to
14
-
7
. Due to the phase delays, the signal is transmitted from the various elements
12
-
7
to
12
-
1
with an increasing delay. The corresponding wave fronts produced by each of these elemental antennae will effectively sum to produce a wave-front principally orientated as in the direction of wave
20
shown in FIG.
1
.
The above principles may be applied to a two-dimensional matrix array, whereby the directional sensitivity of the phased array antenna may be adjusted in both azimuth and elevation by suitably setting the various phase delays.
A great advantage of the phased array antenna is in that the directional response of the antenna may be altered electronically, by suitable control of electronic phase delay elements
14
. The antenna may therefore be “pointed” in a required direction without any mechanical movement of the antenna. This allows for simplification of antenna installation, and allows the direction of the antenna to be changed very rapidly.
Another advantage of phased array antennae is in the improved signal
oise ratio in the final output signal. As the number n of elements in the array increases, the noise signal increases as n, while the signal strength increases as n. The improvement in signal-to-noise ratio, as compared to a single antenna element, is n. Accordingly, a high number of antenna elements should be used to give a good signal
oise ratio. Depending on the application, seven elements (as shown in FIG.
1
) may provide sufficient directionality and signal-to-noise ratio. However, it is common to use much larger numbers of antenna elements. Some communications or radar receivers are known having tens of thousands of elements, each with their own associated phase delay. Such an arrangement obviously provides a much increased signal-to-noise ratio, but can lead to problems in processing such a large amount of data.
Since the antenna array can only receive or transmit one signal at a time, all of the signals from the numerous elements must be added together to produce a single output signal. As shown in
FIG. 2
, the antenna elements
12
may be arranged into sub-arrays
36
. Each sub-array will contain the equipment illustrated in
FIG. 1
, that is, the associated antenna elements
12
, their phase delay units
14
, and a summing unit
22
. Each sub-array
36
then produces a single output signal,
38
, and these signals from the sub-arrays are summed in a further summing unit
40
to produce the required single output signal
42
, representing a combination of the signals from all of the antenna elements. This arrangement avoids the need for a single summing unit to sum the possibly very numerous signals from the antenna elements
12
. The use of sub-arrays also allows certain advanced types of signal processing to be carried out, such as blocking a jamming signal by adjusting the antenna response to ignore the jamming signal, as is known to those skilled in the art.
The phase delays &agr;,
14
applied to each antenna element are the same across all elements
12
in all subarrays.
Another known advantage of arranging the antenna elements into sub-arrays is in that the directional response of the antenna may be adjusted by adjusting the phase of the signals
38
produced by each sub-array.
As shown in
FIG. 3
, a different phase delay &phgr;1-&phgr;9 may be applied
48
to each of the sub-array signals
38
. By treating each sub-array signal
38
in the same way as the element signals of
FIG. 1
, it can be seen that the response of the whole antenna may be adjusted by adjusting the phase delays &phgr;1-&phgr;9
48
appropriately. In a two-dimensional antenna such as that shown in
FIGS. 2-3
, the antenna response in both azimuth and elevation may be adjusted by adjusting the phase delays &phgr;1-&phgr;9
48
.
Analogue-to-digital converters
44
may be introduced to convert the signal
38
from each sub-array
36
into a corresponding digital representation
46
, allowing the phase delays &phgr;1-&phgr;9 to be introduced by digital phase shifters
48
before being summed by a digital summing unit
40
.
While it is possible to adjust the directionality of the antenna by introducing appropriate phase delays into the sub-array signals
38
, this is only possible within the response defined by the phase delays of the individual elements within the subarrays. For example, as shown in
FIG. 4
, the response of the antenna as defined by the phase delays of the individual elements in one dimension (azimuth or elevation) as already discussed with relation to
FIG. 1
, is shown as outer envelope
50
in this polar diagram. By introducing appropriate phase delays into the sub-array signals
38
, the direction of maximum sensitivity may be controlled by introducing suitable phase delays &phgr;1-&phgr;9
48
, but the range of this adjustment is limited by the overall response
50
of the antenna as defined by the phase delays
14
of the individual elements
12
. For example, by adjusting phase delays &phgr;1-&phgr;9
48
to provide maximum response in directions
52
or
54
, the sensitivity will be reduced by about half and significant side lobes will be produced. If phase delays &phgr;1-&phgr;9 were adjusted further to provide maximum response in a direction
56
, for example, the antenna response wou
Carter Nicholas Alfred
Rickett Bryan Stephen
Wright Peter John
Mull Fred H
Roke Manor Research Limited
Tarcza Thomas H.
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