Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
2000-02-17
2001-08-14
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C342S014000, C342S378000
Reexamination Certificate
active
06275188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a nulling antenna system and, more particularly, to a nulling direct radiating array antenna that employs auxiliary antenna arrays positioned around a main array for increasing the nulling resolution.
2. Discussion of the Related Art
Various communications systems, such as certain telephone systems, cable television systems, internet systems, and military communications systems, make use of satellites orbiting the Earth to transfer communication signals. A satellite uplink communications signal is transmitted to the satellite from one or more ground stations, and the satellite retransmits the signal to another satellite or to the Earth as a downlink communications signal to cover a desirable reception area depending on the particular use. The satellite is equipped with an antenna system including an array of antenna feeds that receive the uplink signals and transmit the downlink signals to the Earth.
Satellite-based phased array antenna systems have been developed that provide signals to communication areas using pixel beams designed to cover specific areas on the Earth's surface. Typically, the pixel beams are organized into a matrix of evenly shaped and spaced beams to provide a total coverage area for a large geographical area, such as the visible Earth. One particular phased array suitable for this purpose is the “Enhanced Direct Radiating Array” disclosed in U.S. patent application Ser. No. 09/443,526, filed Nov. 19, 1999, assigned to the assignee of this application and herein incorporated by reference.
FIG. 1
is a hexagonal coverage area
10
including cells
12
defined by a phased array antenna system, where each cell
12
represents a pixel beam. The antenna system may provide a plurality of communications channels where each channel includes a plurality of pixel beams. In this example, each channel includes a hexagonal group
14
of seven cells
12
, where each cell
12
in each group
14
is labeled A-G. The particular user may be located in the center cell
12
of the group
14
, where the perimeter cells
12
in the group
14
provide for increased communications performance. Communications signals from locations in the group
14
are received by the antenna system on the satellite, and then retransmitted to another group
14
for communications purposes. The phased array antenna system provides beam steering for all of the groups
14
.
Intentional and unintentional jamming of satellite uplink signals occurs in various situations. For example, in a military situation, satellite communications are used to transmit signals and information to and from a warfare theatre or hostile environment. The reception area for the uplink communications signals in the hostile environment may be jammed by the enemy using a high powered transmitter. If the jamming signal comes from with-in the channel area for the uplink signal, it is referred to as in-beam jamming, and if it comes from outside of the channel area for the uplink signal, it is referred to as out-of-beam jamming. The jamming signal must be at the frequency of the uplink signal to be effective for jamming purposes. Jamming signals can also come from unintentional or friendly sources that inadvertently interfere with the satellite uplink signals.
In order to eliminate or reduce the effects of jamming signals in both hostile and friendly scenarios, it is known to employ nulling antenna systems that detect the presence of a jamming signal, and provide an antenna null in the antenna radiation or reception pattern so that the jamming signal does not significantly affect the uplink signal. Particularly, nulling antenna systems are able to determine the direction of the jamming signal and create a null or void in the radiation pattern of the antenna so that it in effect does not see the jamming signal. In order to be able to block or null the jamming signal so that it does not affect the ability to transmit the downlink signal, it is necessary to determine the location of the signal, whether it be from an in-beam or out-of-beam jamming source, and then provide the null at that location.
An adaptive weighting system is generally used in nulling antenna systems to sample the received pixel beams in a particular channel to determine if a jamming signal is present. The weighting system then weights the pixel beams in the channel to block the jamming signal. The weighting system generally includes a correlator to correlate each of the pixel beams with the combined beam for the channel to determine if a jamming signal is present. Once the correlator determines that a jamming signal is present, algorithms are used to determine the location of the jamming signal. The algorithm goes through each pixel beam separately using a weighting function to determine where the jamming signal is being received from. The weighting function provides the null by inverting the phase of the received signal at the appropriate location. When the weighting of the pixel beams blocks the jamming signal and the image is cleared up, the antenna system knows where the jamming signal is being received from, and can make weighting adjustments accordingly. Various algorithms that perform this function are known to those skilled in the art.
The nulled area of the radiation pattern of the antenna has a width and a depth which determines its effectiveness in nulling the jamming signal. However, creating a null in the radiation pattern of the antenna also creates a “blind spot” in the uplink signal. Therefore, it is desirable to limit the size of the null while still blocking the jamming signal. In other words, it would be desirable to provide higher nulling resolution to tightly define the null in the radiation pattern so that more of the uplink signal can be processed by the antenna system. This would minimize the area of the radiation pattern that is nulled, and still provide effective anti-jamming. In this manner, it is possible to provide communication to a wider area around the jamming source.
It is known by antenna theory to narrow the antenna radiation pattern by increasing the aperture size of the antenna, i.e., providing more antenna elements. However, adding more antenna elements to increase the aperture size significantly increases the cost and complexity of the antenna system. It would be desirable to increase the aperture of the nulling antenna, without significantly increasing the number of elements to provide more effective nulling capabilities. It is therefore an objection of the present invention to provide such a nulling antenna.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a nulling direct radiating array is disclosed that includes a main phased array and a plurality of auxiliary arrays symmetrically disposed around and spaced apart from the main array. The main array includes a plurality of antenna elements and a beam forming system that generates one or more channels made up of pixel beams. The pixel beams from the main array are connected to a nulling processor along with the combined signal from the antenna elements of the auxiliary arrays. An adaptive weighting network and an adaptive weight generator within the nulling processor determine whether a jamming signal exists in the channel, and weights the pixel beams from the main array accordingly to block the jamming signal. The auxiliary arrays provide a wider beam aperture that is able to more narrowly define the null in the radiation pattern of the main array.
Additional objects, features and advantages of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3706998 (1972-12-01), Hatcher et al.
patent: 4495502 (1985-01-01), Masak
patent: 4516126 (1985-05-01), Masak et al.
patent: 4628321 (1986-12-01), Martin
patent: 4673943 (1987-06-01), Hannan
patent: 4937584 (1990-06-01), Gabriel et al.
patent: 5185608 (1993-02-01), Pozgay
patent: 573434
Keller Robert W.
Phan Dao
TRW Inc.
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