What is a fire control radar?

The older APG-66 and APG-68 fire control radars (FCRs) have been in use on the F-16 for 20 years. The new APG-68(V)9 fire control radar is a significant improvement in both performance and reliability, and was developed to equip the latest F-16 aircraft variants.The APG-68(V)9 radar not only has a longer detection range and can track up to four targets at once, but also has synthetic aperture radar (SAR) processing capability. In addition, the radar also has automatic calibration capability and interactive interference filtering capability. The so-called auto-calibration capability means that the radar can continuously and automatically calibrate the aircraft's inertial navigation system; and the interactive interference filtering is to minimize radio frequency interference in the frequency band, thus significantly improving the radar's anti-jamming capability.

The APG-68(V)9 radar has completed flight tests at Edwards Air Force Base. Tests of the radar, which will be installed on the 50th batch of two-seat F-16D fighters (with the rear cockpit as the mission bay), began in December 2001 and were completed in October 2003.

The APG-68(V) 9 radar will be installed on the 50th batch of two-seat F-16D fighters. This report focuses on the radar's added synthetic aperture (SAR) mode of operation and summarizes the lessons learned in exploiting the radar's potential. While SAR is not a new technology, the development of the APG-68(V)9 radar marks the first application of this technology on a light fighter aircraft. The synthetic aperture mode allows the APG-68(V)9 radar to achieve a 1-meter resolution for long-range ground targets, which is significantly better than current Doppler Beam Sharpening (DBS) modes.The synthetic aperture mode of operation of the APG-68(V)9 radar is the focus of this paper, which also describes the experience gained during radar testing and the requirements for flight testing. New flight test techniques were explored and a new reflector array was constructed to test the APG-68(V)9 radar's synthetic aperture detection mode of operation.

APG-68(V)9 radar air-to-air modes of operation:

6?1 Extended Range Search (ERS) mode: This mode of operation replaces the previous APG-68 radar's Range While Searching (RWS), Upper Look Search (ULS), and Range While Searching (RWS) modes. "This mode of operation replaces the previous APG-68 Ranging While Searching (RWS), Upward Looking Search (ULS), and Velocity Sensing While Ranging (VSR) modes.

6?1 Track While Scanning (TWS): This mode of operation is capable of distinguishing and tracking 10 airborne targets while simultaneously detecting other airborne targets.

6?1 Multi-Target Resolution Cognitive Mode (MTS): This mode of operation is capable of high-quality tracking of up to four targets and has the ability to simultaneously search for other targets.

6?1 Single Target Tracking Mode (STT): This mode of operation provides high quality tracking of 1 airborne target.

6?1 Air Combat Maneuvering Mode (ACM): This mode of operation allows for the automatic capture of targets in close proximity in high ground clutter environments.

6?1 Advanced Medium-Range Air-to-Air Missile (AMAM) datalink: Provides guidance for up to six medium-range missiles in TWS, MTS, and STT modes of operation.

6?1 Attack Cluster Resolution (RCR): determines the number of real targets in the radar resolution cell.

The APG-68(V)9 radar's ground-based modes of operation:

6?1 Air-to-Ground Ranging (AGR): This mode of operation provides accurate range measurements of ground targets.

6?1 Real Beam Map Mapping Mode (RBM)/Enhanced Map Mapping Mode (EGM): This mode of operation provides a suitable radar map display for navigation and target search/tracking. br> ?6?1 Doppler Beam Sharpening Mode 1 (DBS1): This mode of operation provides 8 times higher map azimuth resolution than the RBM mode of operation.

6?1 Doppler Beam Sharpening Mode 2 (DBS2): This operating mode has 64 times higher map bearing resolution than the RBM operating mode.

6?1 Fixed Target Tracking Mode (FTT): This mode of operation maintains precise tracking and locks on to fixed targets scattered on the ground, guiding the weapon to an attack.

6?1 Enhanced Sea Surface Search Mode (ESEA): This mode of operation enables detection of surface targets in adverse sea conditions.

6?1 Synthetic Aperture (SAR) mode of operation: This mode of operation allows for high azimuthal resolution mapping in adverse weather conditions and improves target identification and precise target indication.

6?1 Ground Moving Target Indication (GMTI) mode: This mode of operation searches for multiple moving targets on the ground or at sea and displays them on a background radar map.

6?1 Ground Moving Target Tracking Mode (GMTT): This mode of operation continuously and accurately tracks a single moving target on the ground or at sea, guiding the weapon to an attack.

6?1 Beacon Mode (*N): this mode of operation interrogates and receives ground replies and airborne beacons.

What is synthetic aperture radar (SAR)

Synthetic aperture radar (SAR) can draw high-resolution maps, the principle is to let the pulse radar to a certain direction of movement, and radiation and receive electromagnetic waves, will receive all the signals through the information stored and processed, with the phase of the same phase, the effect of which is equivalent to a large radar antenna to radiate and receive electromagnetic waves. Because the synthetic aperture radar can receive the real radar antenna from different angles of the electromagnetic wave, so the synthetic aperture technology can greatly improve the radar's azimuthal resolution.

Synthetic aperture radar's imaging performance is closely related to the size of the onboard radar, so the APG-68(V)9 radar has a larger size antenna compared to the older APG-68 radar.

The advantage of modern synthetic aperture radars is that their resolution is not limited by their detection range. The azimuthal resolution of a synthetic aperture radar is related to the size of its synthetic aperture and, furthermore, its resolution is related to the aircraft's navigational capabilities, the radar's bandwidth, and the radar antenna's ability to accurately locate the aircraft. At a range of 4 nautical miles, the resolution of a synthetic aperture radar is two orders of magnitude higher than that of a Doppler beam sharpening (DBS) radar. And Doppler Beam Sharpening (DBS) mode is the best map mapping mode of operation for the older APG-68 radar.

To illustrate the technical advantages of SAR, let's use an analogy: if we were to map an area 40 nautical miles away with a SAR radar and a conventional radar, we would need at least a conventional radar with a radar antenna 2,000 feet long to get a high-resolution map from the SAR mode of the APG-68(V)9 (the antenna is obviously that large). Obviously, a radar antenna of that size cannot be mounted on an airplane).

When mapping targets using SAR technology, the SAR is required to be constantly moving to keep detecting the target from different directions, so the target cannot be directly in front of the nose of the aircraft when mapping with SAR. Figure 0 shows the operating range limitations of the synthetic aperture radar on the F-16 aircraft. Its maximum detection angle is limited by the radar's field of view (LOS), and its minimum detection angle is limited by the range of rotation of the radar's antenna rotation mechanism.

Operating range of synthetic aperture radar on the F-16 aircraft envelope synthetic aperture radar's advantages are obvious, it draws a map is not only high resolution, but also has the advantages of all-weather, all-weather, not subject to atmospheric propagation and climatic influences, and strong penetration, etc., and it also enables combat aircraft in the airspace away from the dangerous battlefield mapping of the battlefield.

Additionally, SAR can plot very precise target coordinates on a map, which not only aids in precise aircraft navigation, but is theoretically accurate enough to be used to guide J-band inertial-guided weapons (AIMs) to directly attack a target.

While SAR is still in the developmental stage, the theory of its use has already been developed, allowing pilots to map a large, low-resolution map when the aircraft is still 100 nautical miles from the target. And when the aircraft gradually close to the target, synthetic aperture radar can redraw a higher resolution map, for example, when the distance from the target of 40 nautical miles, synthetic aperture radar can be mapped with a resolution of 1-meter scale maps, so as to accurately locate the target of the strike.

When the pilot has identified the strike target on a precise map, the pilot will use the precise coordinates of the target provided by SAR to unleash an inertially guided weapon at maximum range, while the aircraft can move away from the dangerous battle zone. The SAR's high resolution and precise targeting capabilities will greatly enhance the F-16's all-weather strike capability.

Synthetic Aperture Radar Capability Analysis

Examining the map mapping capability of the APG-68(V)9 synthetic aperture radar is the main purpose of this test, therefore, the Air Force Flight Test Center Museum located at Edwards Air Force Base, California, has been selected as the target area, and the APG-68(V)9 will use different synthetic aperture radar operating modes to map the museum. The museum will be mapped and the test flight engineers will analyze and compare the map results.

Flight Test Experience

The optimal scenario for the APG-68(V)9 radar development test flight would have been to flight test the radar mounted on a proven avionics system platform in order to identify problems. However, the radar system was instead installed on two avionics platforms/software that were still undergoing testing, thus placing three immature systems/software together for testing caused considerable problems for the test team.

This type of test was a challenge for the test crew because whenever a problem arose in the test, we had to differentiate which of the three systems was actually failing. A problem with any one of the three systems would affect the other two. Each time there was a problem with a system, we had to wait patiently for one or both systems to restart, so the efficiency of each test sortie was reduced by the increased workload of the pilots.

Bad test conditions often led to situations where we had to deal with delays in the test schedule. The lesson we have learned from this is that it is important to allow for the selection of system platforms, especially a series of interdependent systems, to increase the efficiency of the test program.

The final lesson is how to deal with the relationship between quantitative and qualitative data. All APG-68(V)9 radar performance test requirements were developed for our purpose-built reflector arrays. In order to realistically test the radar's performance, strict control of the reflector array's spacing scale was required. Because mapping was not very helpful in collecting test data, the original test plan did not call for mapping representative tactical targets using the SAR.

Fortunately, the test pilots convinced the program office to conduct some trials of SAR map mapping, which revealed the differences between SAR for array testing and reconnaissance of typical military targets. Even so, the overemphasis on quantitative data made it difficult to reconcile the qualitative tests, on which the radar's test reports were ultimately based.

Mapping the Air Force Test Museum helps point out differences in radar operating modes. Conducting map mapping tests is best done using the Brightness Transformation Method (BTF), but the BTF method does not work in all cases.

Qualitative tests also reveal differences in SAR when mapping the same area due to different radar wave reflection strengths. As you can see in Figures 10 and 11, areas with high radar wave reflection intensity are noticeably brighter in the map, while areas with low radar wave reflection intensity are noticeably dimmer.

The original mapping image basically meets the design metrics, but the quality of the image is not as good as we would like. Although we can improve the system by improving the output method of the pictures for better military applications, the test contract only requires that the test results meet the design specifications, but does not require us to improve the system. In addition, because the system still has a series of problems, so the development time is longer than planned, we should be step by step to improve the system, first to make it meet the design specifications, and then improve it to meet the level of practical applications.

The U.S. Air Force is currently proposing a new concept of equipment testing, that is, in the weapon system test cycle as early as possible to use the test, the U.S. Air Force believes that qualitative assessment of the effectiveness of the system in the real use of the conditions of the test carried out the earlier, then the development of the system cycle will be the shorter the system to equip the forces of the time can be correspondingly early.

The goal of any test program is to get the system up to the level of practical application. For test flight engineers, the most important thing is not how to collect test data, but how users can effectively and easily use the system.

Summary

The APG-68(V)9 fire-control radar (FCR) has dramatically improved the detection capability of the F-16 aircraft. With the increased radar detection range, F-16 pilots can achieve "first-to-find," "first-to-lock," and "first-to-fire" in air combat. The SAR's all-weather high-resolution mapping capability significantly enhances the F-16's target identification, target pinpointing, and all-weather target search/detection capabilities. An increase in radar operating modes means an increase in operational modalities. And increased radar reliability means higher fielding rates and less maintenance time. However, testing SAR radars places special demands on flight test technology.