Dynamic signal routing in electronically scanned antenna systems

An antenna array system with dynamic signal routing to a set of receivers. A monopulse electronically scanned antenna (ESA) has a plurality of antenna elements divided into subarrays. ESA beam steering phase shifters are associated with the respective subarrays of antenna elements, such that the output signals from the respective antenna elements associated with the respective quadrants are phase shifted and summed to provide respective subarray signals. A monopulse network responsive to the subarray signals provides monopulse outputs to a set of receivers. A beam steering controller provides phase shift commands to the ESA phase shifters to set the phase shift associated with the respective phase shifters of the subarrays. The controller commands the ESA phase shifters to modulate the phase shift of selected quadrants. The phase shifts associated with the subarrays are selectively set to either 0 or 180 degrees relative to one of the subarrays by adding the desired subarray phase shift (0 or 180 degrees) to the beam steering phase command at each element. This produces the main array signals. By setting the subarrays's phase shifts, the main array signals are appropriately steered to the desired receivers. The dynamic signal routing can also be used with non-electronically scanned systems.

TECHNICAL FIELD OF THE INVENTION

This invention relates to antenna systems, and more particularly to techniques for dynamic signal routing in Electronically Scanned Antenna (ESA) systems.

BACKGROUND OF THE INVENTION

In a multifunction tactical radar, dynamic signal routing between a multiport antenna and a bank of receivers is usually accomplished by an RF switch network. Unavoidable switch non-idealities such as impedance mismatches, signal attenuation, signal leakage, and dynamic range limitations are drawbacks to this approach and usually have significant radar system performance implications. The switches themselves also introduce undesirable single point failure modes.

FIG. 1 shows a conventional system architecture having an electronically scanned antenna partitioned into four quadrants (Quad 1 , Quad 2 , Quad 3 , Quad 4 ) feeding a conventional monopulse combiner. The outputs of the monopulse combiner are Sum (Quad 1 Quad 2 Quad 3 Quad 4 ), Delta Azimuth (Quad 1 Quad 3 Quad 2 Quad 4 ), Delta Elevation (Quad 1 Quad 2 Quad 3 Quad 4 ), and Delta X (Quad 1 Quad 4 Quad 2 Quad 3 ). These signals are typically connected to a bank of receivers via a switch network, as shown. The switch network provides the desired dynamic routing of the antenna outputs to the individual receivers. In some cases, the sum channel would be directly connected to a receiver to avoid the switch losses, reflections, distortions, and leakage in the sum signal path resulting in a loss of system availability if that receiver fails.

The conventional approach has several drawbacks overcome by this invention. The non-idealities of the RF circuits and switches used in the switch network degrade the radar return signals at a critical point in the signal path, significantly affecting radar performance. The switch network includes single point failure mechanisms that could render one or more of the critical antenna monopulse signals inoperative, likely degrading system performance below useful levels. The addition of the switch network increases system cost and complexity.

SUMMARY OF THE DISCLOSURE

An array system with dynamic signal routing is described, and includes a plurality of antenna elements divided into a plurality of subarrays. A summing network for each subarray combines the signals from each antenna element in a subarray to provide for each subarray a subarray signal. Phase shifting apparatus selectively introduces a signal routing phase shift of 0 or 180 to the respective subarray signals. A monopulse combiner is responsive to the subarray signals to provide a plurality of combiner outputs. The system can include a plurality of receivers each having an input connected to receive a corresponding combiner output for processing the monopulse combiner outputs. A controller providing phase shift commands to the phase shifting apparatus to modulate the phase shift of the phase shifters of selected subarrays by adding a subarray phase shift of 0 or 180 to dynamically effect the routing of the monopulse array output signals to desired ones of the receivers.

Modern multifunction tactical radars employ ESAs that are partitioned into subarrays. The ability to dynamically rout the various antenna array and subarray outputs to a bank of receivers is very desirable. Dynamic signal routing in accordance with the invention allows the antenna outputs to be time multiplexed between fewer receivers than the total number of antenna outputs. This flexible signal routing also allows reconfiguration to compensate for failed receivers.

In accordance with an aspect of the invention, an ESA is described with dynamic signal routing to a set of receivers. A monopulse ESA has a plurality of antenna elements divided into subarrays. ESA beam steering phase shifters are associated with the respective subarrays of antenna elements, such that the output signals from the respective antenna elements associated with the respective subarrays are phase shifted and summed to provide respective subarray signals. A monopulse combiner responsive to the subarray signals provides monopulse outputs to the set of receivers. A beam steering controller provides phase shift commands to the ESA phase shifters to set the phase shift associated with the respective phase shifters of the subarrays. In addition to supplying a beam steering phase shift to each ESA phase shifter, the controller commands the ESA phase shifters to modulate the phase shift of selected subarrays. The phase shifts associated with the subarrays are selectively set to either 0 or 180 degrees relative to the one of the subarrays by adding the desired subarray phase shift (0 or 180 degrees) to the beam steering phase shift at each element.

In an exemplary embodiment, the subarrays represent quadrants, and the monopulse output signals are Sum, Delta Azimuth, Delta Elevation, and Delta X; by setting the quadrant phase shifts, the monopulse output signals are appropriately steered to the desired receivers.

The dynamic signal routing technique can also be applied to arrays which are not electronically scanned.

DETAILED DESCRIPTION OF THE DISCLOSURE

The disclosed invention is an approach for dynamically routing the main array signals (in this embodiment, Sum, Delta Azimuth, Delta Elevation, and Delta X) using the monopulse combiner instead of a conventional RF switch network. This results in a simpler, lower cost design and avoids the performance and reliability drawbacks of the conventional approach.

FIG. 2 illustrates in block diagram an ESA 50 employing aspects of this invention. The system includes an ESA 60 divided into four subarrays, in this case quadrants 1 - 4 . The invention is not limited to ESAs with quadrant partitioning, and can be employed with subarrays other than quadrants. The antenna element outputs within the first quadrant are all phase shifted and summed to provide a first quadrant output signal S 1 on line 62 - 1 . The antenna elements within the second quadrant are all phase shifted and summed to provide a second quadrant output signal S 2 on line 62 - 2 . The antenna elements within the third quadrant are all phase shifted and summed to provide a third output quadrant signal S 3 on line 62 - 3 . The antenna elements within the fourth quadrant are all phase shifted and summed to provide a fourth quadrant output signal S 4 on line 62 - 4 .

FIG. 3 is a simplified schematic diagram of the ESA 60 . Each subarray, i.e. each quadrant in this exemplary embodiment, includes a plurality of radiating elements, a plurality of phase shifters and a subarray summing manifold. Thus, quadrant 1 includes a plurality of radiating elements 64 - 1 , a corresponding plurality of phase shifters 66 - 1 , and a quadrant summing manifold 68 - 1 for summing the respective phase shifted outputs of the radiating elements 64 - 1 , with the quadrant 1 summed and phase shifted output S 1 on line 62 - 1 . Similarly, quadrant 2 includes a plurality of radiating elements 64 - 2 , a corresponding plurality of phase shifters 66 - 2 , and a quadrant summing manifold 68 - 2 , with the quadrant 2 phase shifted and summed output S 2 on line 62 - 2 . Quadrant 3 includes a plurality of radiating elements 64 - 3 , a corresponding plurality of phase shifters 66 - 3 , and a quadrant summing manifold 68 - 3 , with the quadrant 3 phase shifted and summed output S 3 on line 62 - 3 . Quadrant 4 includes a plurality of radiating elements 64 - 4 , a corresponding plurality of phase shifters 66 - 4 , and a quadrant summing manifold 68 - 4 , with the quadrant 4 phase shifted and summed output S 4 on line 62 - 4 .

A monopulse combiner 70 is responsive to the four phase shifted and summed quadrant signals 62 - 1 to 62 - 4 to provide outputs P 1 -P 4 to respective receivers 80 - 86 . The monopulse combiner is a conventional circuit, a network of 180 hybrids that form algebraic combinations of the quadrant outputs. FIG. 4 is a simplified schematic diagram of the monopulse combiner 70 . The monopulse combiner comprises four 180 hybrid circuits 72 , 74 , 76 , 78 . Outputs S 1 and S 2 are respectfully coupled to the input ports 72 A, 72 B of hybrid 72 . Outputs S 3 and S 4 are respectfully coupled to the input ports 74 A, 74 B of hybrid 74 . The sum port 72 C of hybrid 72 is coupled to input 76 A of hybrid 76 . The difference port of hybrid 72 is coupled to an input 78 A of hybrid 78 . The sum port 74 C of hybrid 74 is coupled to input 76 B of hybrid 76 . The difference port 74 D of hybrid 74 is coupled to input 78 B of hybrid 78 .

The ESA beam steering phase shifters 66 are used to independently set the phase shift of each radiating element in order to steer the antenna beam in the desired direction. In addition to applying the beam steering phase shifts, the phase shifters 66 are also used to modulate the phase of selected quadrants. The phase shift of quadrants 2 , 3 and 4 will be set to either 0 or 180 degrees relative to quadrant 1 by adding the desired additional quadrant phase shift (0 or 180 degrees) to the beam steering phase shift provided by the beam steering controller 100 for each respective phase shifter 66 , i.e. the commanded phase shift for these quadrants can have two components, a first component for the beam steering and a second component for the dynamic signal routing function. The monopulse combiner now has the outputs shown in tabular form in FIG. 5 , as a function of the quadrant phase shift settings ( 1 , 2 , 3 , 4 ) to accomplish dynamic signal routing. Setting the quadrant phase shifts appropriately effectively steers the monopulse combiner outputs to the desired receivers. As shown in FIG. 4 , the outputs (P 1 , P 2 , P 3 , P 4 ) of the monopulse combiner are the algebraic combinations of the input signals S 1 , S 2 , S 3 , S 4 . If the quadrant outputs are left unmodulated, i.e. without introducing additional phase shifts (0 or 180 ) as described above, the combiner outputs become:

Adding a 180 phase shift to the commanded beam steering phase shift at each element in a given quadrant effectively negates the quadrant output, i.e. multiplies it by negative one. For example, if 180 is added to the phase shifts in quadrants 2 and 4 , the monopulse combiner outputs become:

While this technique provides less routing flexibility than a full 4 by 4 RF crossbar switch typically used as shown in the system of FIG. 1. , it will allow the desired signal routing around a failed receiver or allow 3 receivers to be time shared between the four monopulse outputs.

Since the signal routing approach uses the existing ESA beam steering phase shifters, it can be accomplished by simply adding a small amount of additional logic to the beam steering controller 100 to effect the quadrant by quadrant phase shifts. In essence, in accordance with one aspect of the invention, the monopulse outputs of an ESA can be dynamically routed to a bank of receivers without adding any additional RF hardware to the system and without introducing any RF signal degradation.

In an alternate architecture, the dynamic signal routing can be implemented by the addition of a phase shifter for each of the second, third, . . . nth subarrays, to selectively add the 0 or 180 phase shift to the subarrays relative to the first subarray. There would be no advantage to doing this in a fully configured ESA, which already has phase shifters at each radiating element for beam steering purposes. However, for non-ESA antennas, such as a mechanically steered array or a stationary array, the dynamic signal routing can be achieved by the use of such a phase shifter for the subarrays to introduce the 0 /180 phase shift. Such an arrangement is illustrated in FIG. 6 , which shows array 100 comprising radiating elements divided into subarrays, here quadrants Q 1 -Q 4 . The signals from radiating elements 102 - 1 of quadrant Q 1 are combined by combiner network 104 - 1 , and the summed signal provides signal S 1 to the monopulse combiner 70 . The signals from radiating elements 102 - 2 of quadrant Q 2 are combined by combiner network 104 - 2 , and the summed signal passed through the dynamic signal routing phase shifter 106 - 2 to provide signal S 2 to the monopulse combiner 70 . The signals from radiating elements 102 - 3 of quadrant Q 3 are combined by combiner network 104 - 3 , and the summed signal passed through the dynamic signal routing phase shifter 106 - 3 to provide signal S 3 to the monopulse combiner 70 . The signals from radiating elements 102 - 4 of quadrant Q 4 are combined by combiner network 104 - 4 , and the summed signal passed through the dynamic signal routing phase shifter 106 - 4 to provide signal S 4 to the monopulse combiner 70 . By selecting the 0 /180 state of the phase shifters 106 - 2 to 106 - 4 (quadrant Q 1 is the reference quandrant, and so a dynamic signal routing phase shifter is not required for quadrant Q 1 ), the monopulse outputs P 1 -P 4 can be steered to respective receivers (not shown in FIG. 6 ) in the same manner as described above with respect to FIGS. 1-5 .

While the foregoing embodiments have been described in terms of operation on receive, it is to be understood that principles of reciprocity apply to the array systems, and that the systems can also be used on transmit.

It is understood that the above-described embodiments are merely illustrative of the possible specific embodiments which may represent principles of the present invention. Other arrangements may readily be devised in accordance with these principles by those skilled in the art without departing from the scope and spirit of the invention.