Data processing system for a phased array antenna

[54] DATA PROCESSING SYSTEM FOR A PHASED ARRAY ANTENNA

[75] Inventor: Robert W. Kress, Saugerties, N.Y.

[73] Assignee: Grumman Aerospace Corporation, Bethpage, N.Y.

[21] Appl. No.: 240,960

[22] Filed: Sep. 6,1988

[51] Int. Q.* G01S 3/16; G01S 3/28

[52] U.S. a 342/380; 342/383;

342/372

[58] Field of Search 342/380, 383, 372

[56] References Cited

U.S. PATENT DOCUMENTS

4,415,902 11/1983 Redlich 343/844

4,489,324 12/1984 Blume 342/372

4,516,126 5/1985 Masak et al 342/383

4,736,460 4/1988 Rilling 342/380

Primary Examiner—Theodore M. Blum

Attorney, Agent, or Firm—Scully, Scott, Murphy &

Presser

[57] ABSTRACT

A data processing system for a phased array antenna consisting of an array of transmit/receive elements which result in a significant reduction in the data pro

cessing requirements for the received signals. In operation, the RF transmitted and received beams are formed and steered in a conventional manner with a phase shifter and amplitude weighting for each element. However, a simplifying approximation is made in the signal processing of the received signals for interference suppression, which results in minimal degradation of the system performance. In such a system, interference suppression is obtained by generating nulls in the receive antenna pattern in the direction of the interference. The nulls are produced by adjusting the phase and amplitude (weight) of the received signal from each array element just enough to null the interference with minimal impact on the rest of the antenna pattern. Pursuant to the present invention, the signal processing requirements are significantly reduced by summing the outputs of adjacent array elements to produce a lesser number of summed signals, less than the number of elements in the array. Each summed signal is then directed to a weighted amplifier controlled to weigh the contribution of the particular summed signal to a composite output signal formed by a composite summing circuit, which sums the weighted output signals of all of the weighted amplifiers.

6 Claims, 2 Drawing Sheets

DATA PROCESSING SYSTEM FOR A PHASED
ARRAY ANTENNA

BACKGROUND OF THE INVENTION 5

1. Field of the Invention

The present invention relates generally to a data processing system for reducing the data processing requirements for a phased array radar antenna, and more particularly pertains to a data processing system for reduc- 10 ing the data processing requirements for signals received by an electronically scanned radar antenna system formed by a linear array of endfire elements.

2. Discussion of the Prior Art

Ganz, et al. U.S. Pat. No. 4,336,543 discloses an elec- 15 tronically scanned antenna system having a linear array of endfire elements of the type for which the data processing system of the present invention was developed. In this antenna system, the endfire elements are laterally spaced between about 0.3X to 0.9X apart, preferably 20 about 0.55X apart, to enhance the effects of mutual coupling therebetween for broadening the radiation signal pattern of the elements in the plane of the array. Advantageously, the endfire elements may be of the Yagi type with each endfire element including a com- 25 mon reflector, a driver, and a plurality of directors. This provides an antenna array of very small elevation so as to be suitable for conformal installation on or within the airfoil surfaces of an aircraft, e.g., wing leading edges and the horizontal stabilizer trailing edge. Such a 30 phased array antenna system offer tremendous surveillance and missile guidance capability with., high levels of jam resistance at reduced weight, power and volume.

One of the major developmental and production problems associated with such conformal linear phased 35 array radars is accomplishing the level of interference suppression processing required for the many transmit/receive modules in the system array. Some current development work has focused on the UHF band at approximately 450 MHz. However, for some applica- 40 tions, operation at the L band, at approximately 900 to 1,200 MHz, is more desirable, but at the higher frequencies the relative signal processing requirement or load increases by a factor of two to three, or more, tending to mitigate against operation at the L band. 45

In conventional signal processing techniques for the signals received by each element of such a phased array antenna, the antenna is first operated to transmit, and by varying the transmitted gain and phase of each element module, the transmitted beam can be formed and 50 steered in azimuth. Similarly, the receiver gain is varied, and the received signals phase shifted "to match the transmitted beam pattern. In conventional signal processing techniques, the outputs of all of the element receivers are initially processed independently. In ef- 55 feet, the signal processing in the prior art was considered to be a function of the transmitted frequency, which determines the number of transmit/receive element modules required.

A conventional data processing technique would 60 initially process separately the signal received from each of the twelve receive elemenjs. Interference suppression is obtained by generating nulls in the receive antenna pattern in the direction of the interference. The nulls are produced by adjusting the phase and amplitude 65 (weight) of the received signal from each array element just enough to null the interference with minimal impact on the rest of the antenna pattern. The extent that

2

this can be accomplished depends upon the number of weights that are available for adjustment, usually referred to as the number of degrees of freedom.

If the phased array had twelve element modules therein, then twelve separate signal processing channels were required, each having a phase shifting circuit and a weighted amplifier controlled by an interference suppressor processor, and the twelve controlled signals were then summed to form a composite output signal. This technical approach resulted in a significant and burdensome signal processing requirement for the received signals.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to provide a data processing system for a phased array antenna as described hereinabove which results in a significant reduction in the data processing requirements for the received signals.

The present invention greatly reduces the signal processing requirement at a given frequency. For example, operation at the L band could be accomplished, in effect, with a data processing requirement typical of the UHF band. Or a UHF system would have a reduced data processing requirement corresponding to that of a system with half the frequency or less.

Pursuant to the teachings of the present invention, the RF transmitted and received beams are formed and steered in a conventional manner with phase shifters and possible amplitude weighting in each module. However, a simplifying approximation is made in the signal processing for interference suppression, which results in minimal degradation of the system performance. Consider an array consisting of twelve L band elements. Conventional data processing would initially process separately the signal received from each of the twelve receive elements. Interference suppression is obtained by generating nulls in the receive antenna pattern in the direction of the interference The nulls are produced by adjusting the phase and amplitude (weight) of the received signal from each array element just enough to null the interference with minimal impact upon the rest of the antenna pattern. The extent that this can be accomplished depends upon the number of weights that are available for adjustment, usually referred to as the number of degrees of freedom.

In the subject invention, the necessary number of degrees of freedom are obtained with a major reduction in the signal processing over that of a conventional prior art system. An explanation of the process follows. If the twelve elements are regarded as points on a continuous curve of received signals along the array, it becomes apparent that a twelve point curve fit is substantially more than necessary to define adequately almost any function (twelve points yield an 11th power curve fit). In a radar system, the function is a radar beam with nulls in the side lobes for the interference. Therefore, it becomes possible to sum (average) the outputs from adjacent elements and describe the function with a lesser number of points. Summing each two adjacent outputs for the twelve element array results in a six point, 5th power curve fit as shown in FIG. 3. For a fifteen element array, each three adjacent outputs could be summed, resulting in a 5 point, 4th power curve fit. The extent to which the reduction in signal processing can be obtained depends upon the level of