Tag Archives: APG-68

Agile Beams: Active Electronically Scanned Array Radars

AESAs aim their "beam" by broadcasting radio energy that interfere constructively at certain angles in front of the antenna. They improve on the older passive electronically scanned radars by spreading their broadcasts out across a band of frequencies, which makes it very difficult to detect over background noise. AESAs allow ships and aircraft to broadcast powerful radar signals while still remaining stealthy. Above is AESA on F22

The AN/APG-77 is a multifunction radar installed on the F-22 Raptor fighter aircraft. It is one of the most advanced radar today. More than 100 APG-77 AESA radars have been produced to date by Northrop Grumman, and much of the technology developed for the APG-77 is being used in the APG-81 radar for the F-35 Lightning II. The APG-77v1 was installed on F-22 Raptors from Lot 5 and on. This provided full air-to-ground functionality (high-resolution synthetic aperture radar mapping, ground moving target indication and track (GMTI/GMTT), automatic cueing and recognition, combat identification, and many other advanced features).

APG-77 is based on Active Electronically Steered Array (AESA) technology. The AESA includes multiple individual active transmit/receive (T/R) elements within the antenna. Depending upon the precise implementation, there may be anywhere between 1000 and 2000 of these individual T/R elements which, together with the RF feed, comprise the AESA antenna. As for the passive ESA, these elements are highly redundant and the radar can continue to operate with a sizeable percentage of the devices inoperative. This graceful redundancy feature means that the radar antenna is extremely reliable; it has been claimed that an AESA antenna will outlast the host aircraft. The fact that the transmitter elements reside in the antenna itself means there is no standalone transmitter – there is an exciter but that is all. As before, there is clearly a need for a receiver as well as an RDP and signal processor. The active T/R elements are controlled in the same way as the phase shifters on the passive ESA, either by using a beam-steering computer (BSC) or by embedding the beam-steering function in the RDP.

The ability to control many individual T/R modules by software means confers the AESA with immense flexibility of which only a few examples are: First each radiating element may be controlled in terms of amplitude and phase, and this provides superior beam-shaping capabilities for advanced radar modes such as terrainfollowing, synthetic aperture radar (SAR) and inverse SAR (ISAR) modes. Secondly Multiple independently steered beams may be configured using partitioned parts of the multidevice array. Thirdly If suitable care is taken in the design of the T/R module, independent steerable beams operating on different frequencies may be accommodated and Finally The signal losses experienced by the individual T/R cell approach used in the AESA also bring considerable advantages in noise reduction, and this is reflected in improved radar performance.

The AN/APG-80 system is described as "agile beam", and can perform air-to-air, search-and-track, air-to-ground targeting and aircraft terrain-following functions simultaneously and for multiple targets. As a SAR system utilizing NG's fourth-generation transmitter/receiver technologies, it has a higher reliability and twice the range of older, mechanically-scanned AN/APG-68 radar systems. Above is F-16 APG-80 Radar

One dramatic improvement is the noise figure; it is especially significant achieving such an improvement so early in the RF front end. This results in a remarkable range improvement for the AESA radar. A number of US fighter aircraft are being fitted or retrofitted with AESA radars, these are F-22 Raptor, F-18E/F (Upgrade version) fitted with AN/APG-79, F-16E/F (Block 60) fitted with AN/APG-80, F-15 and F-35 fitted with AN/APG-81. Taking for example F-16, it is interesting to see a dofference in performance between two batches (Block 50) and Block 60. Former had target detection radar range of 50 miles, which was improved to 70 miles with AESA radards (for reference F-22 covers 125miles range). The F-16 Block 60 (now the F-16E/F) shows an improvement from 45 to 70 nm (þ55%), while the F-15C range has increased from 60 to 90 nm (þ50%). Apart from the obvious improvement in range, it has been stated by a highly authentic source that AESA radar confers 10–30 times more in radar operational capability compared with a conventional radar (Report of the Defense Science Board Task Force, 2001).

The F-16E (single seat) and F-16F (two seat) are newer F-16 variants. The Block 60 version is based on the F-16C/D Block 50/52 and has been developed especially for the United Arab Emirates (UAE). It features improved AN/APG-80 Active Electronically Scanned Array (AESA) radar, avionics, conformal fuel tanks (CFTs), and the more powerful GE F110-132 engine. However the batch bought by Pakistan Air Force (F-16C/D) is equipped with AN/APG-68 (V)9 Radar Systems. Only the Block 60 aircraft, destined for the UAE, are to be equipped with a more advanced version – the Active Electronically Scanned Array (AESA) radar. The APG-68(V)9 offers 30 percent increase in detection range, improved search-while-track mode (four vs. two tracked targets) and larger search volume and improved track while scan performance. Its single target track performance has also been improved. On air/ground missions, the new radar becomes an effective sensor, utilizing its high-resolution synthetic aperture radar mode, which allows the pilot to locate and recognize tactical ground targets from considerable distances. Although previous radars had some Synthetic Aperture Radar (SAR) capabilities, the new version generates imagery-class (2 feet resolution) high resolutions pictures, comparable to pictures delivered by the most modern commercial satellites. These pictures can be acquired from very long range, at all weather conditions and provide an effective, real-time source for the targeting of long range, precision guided weapons. The radar also has increased detection range in sea surveillance mode, and enhanced ground moving target identification and mappinc capability. The radar features an inertial measurement unit that improves dynamic tracking performance and provides an auto-boresight capability, which increases accuracy.

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