Thank you for the explaination Gambit! What about ESM and detecting, or tracking aircrafts? Is that possible and in what distance could an aircraft be detected?
According to publicly available sources...
Saab 2000 Airborne Early Warning and Control Aircraft - Air Force Technology
The electronic support measures (ESM) system comprises digital narrow band and wide band receivers and associated antennae, providing close to 100 % probability of intercept (POI). The digital receiver is equipped with interferometer antenna arrays.
The ESM obtains the electronic order of battle (EOB) data and intercepts, characterises and identifies signals, defines their direction of arrival, generating and displaying warning information. The ESM system operates autonomously and allows real time ESM analysis and presentation to the ESM operator on board the aircraft. ESM data is recorded during missions for post mission tactical and technical analysis. Information is transferred to other onboard systems including the command and control system and the radio data link-controller.
The radar receivers cover low band (7GHz to 2GHz), mid band (2GHz to 18GHz) and high band (28GHz to 40GHz).
The digital RF receiver provides very high sensitivity and selectivity and uses fast Fourier transforms (FFT) and channelisation signal processing techniques. The ESM's wide band and narrow band receivers provide 360° coverage, and close to 100% probability of intercept. The system provides high sensitivity and selectivity in dense and hostile signal environments.
This sounds like a passive reception system of transmitters. If there are no transmissions from anyone from any direction, no detection. Passive receptors are easier to be 360deg coverage than an active transmitter planar array. As long as there are transmitters, their positions, ground or airborne, can be estimated. This is 'tracking' only in the indirect as you are relying upon the targets to provide you with their beacons. Ever play the swimming pool game 'Marco Polo'? For the readers who are not familiar with this children game, the person who is 'it' closes his eyes and yell 'Marco', those who are not 'it', must respond 'Polo'. The person who is 'it' must decide on which 'Polo' to pursue and 'tag' that person, if he is successful since this is play in water. The person who is 'it' can call out 'Marco' as often as he like and everyone else must respond 'Polo'.
A passive reception detection scheme is different only in the sense that the detector is totally reliant upon the transmitters. This sounds like a defensive system to help the aircraft avoid hostiles. At the same time, the direction of whatever is detected, by the target's own transmission, can be used to correlate against the active transmissions that is on going by the other side of the antenna, providing constant update to this "God's Eye" view of the scene. Normal operation would have both sides alternately transmitting. But there would be situations where it is useful to have the side of the antenna assembly that is facing a battle in active transmission to provide as real time monitoring and control as possible. The side that is not facing the battle can be in passive detection mode to alert the aircraft to any potential hostile coming from that side. Not a bad set-up. However, that claim of true 360deg active scan is still suspicious to me.
I am also interested in the Boeing 737 Wedgetail, can you say somthing about the radar performance of it, especially of the top array?
Could this plattform also be used with the Israeli Phalcon system?
The Boeing version remains faithful to the 120deg limitations created by a planar array.
Wedgetail - Australia's Pocket AWACS
The most technologically innovative proposal is that of the Boeing led team, built around an evolved variant of the now Northrop-Grumman MESA radar and the Boeing B-737-700 narrowbody airframe. The Boeing/N-G Wedgetail is "unconventional" insofar as it uses a unique antenna design. Sidelooking coverage for two 120 degree sectors is provided by the L/D-band MESA in a dorsal fin structure, while nose and tail coverage over 60 degree sectors is provided by an electronically steered "tophat" end-fire array mounted in a surfboard shaped radome above the MESA arrays. Angular resolution of the "tophat" array varies from several degrees over the nose and tail, improving by a factor of four as the beam is steered to 30 degrees off the antenna boresight. ESM is carried in wingtip pods.
Personally...I prefer to avoid butting my head against nature's limits. For any AESA antenna, the main lobe will be flanked on both sides by weaker, electronically dirtier and relatively uncontrolled side lobes at 45deg off the main lobe. Side lobes signals are most vulnerable to ECM tactics. Technically speaking, there are many side lobes with decreasing power approaching antenna's physical limits on either side, but the two side lobes at those two 45deg positions off the main lobe are the strongest and easily most problematic.
Imagine the horizontal for now. As the main lobe, or beam if some prefer, is swept from side to side, the sidelobes will also move in keeping with that nature imposed structure. When a sidelobe begins to approach that 180deg position, the wave superposition principle begins to manifest in an adverse condition. Remember that there are many sidelobes and despite whoever said what, even AESA antennas produces multiple sidelobes. So what happens, if you can imagine, is those smaller and weaker sidelobes begins to build upon each other as they have nowhere else to go. This is antenna physical limit. This electronic mess begins to contaminate the main sidelobe, the one that is at the 45deg position off the main lobe, and if the main lobe is continuously pushed towards that antenna physical limit, any target information derived past the 120deg position becomes suspect. Already systems are programmed to filter out sidelobes on hostile environments...
Sidelobe Blanking
Jamming through a sidelobe. If jamming starts to come in through one of the radar antenna's sidelobes, the omnidirectional antenna receives a stronger signal than the main radar antenna. In this case, the summing point detects the unusual situation and feeds into the switch to stop momentarily the main radar antenna signal from passing to the processor and display. This continues until the situation returns to normal (main radar antenna signal strength is greater than omnidirectional antenna signal strength). The receiver may not receive a signal for some time in this case, especially if the jammer can maintain jamming throughout the scan of the radar. In this case, the switch is "off" until either the jamming stops, or passes through the antenna’s main beam.
Just so the readers can have a better visualization of the relationships of these three lobes produced from an AESA antenna, an example from an old mentor back in the business came to memory...I need to implant some FLASH into my brain as I age...
Anyway...The reader should take a hand, any hand, and splay out three -- only three -- fingers: the thumb, index and pinkie. Keep them rigidly splayed out. The index finger pointing straight ahead would be the main lobe. The thumb and pinkie on either sides would be the two main sidelobes. Now imagine many more but invisible sidelobes. As the reader sweep this hand 'antenna' from side to side while keeping the finger 'lobes' rigid, it is easier to see how one lobe will meet antenna physical limit and as power is being continuously applied in transmission, the main index finger 'lobe' will begin to meet a sidelobe. Then problems could occur past that 120deg point. So while it is technically possible to sweep past those two 120deg points on either side, because of the existence of sidelobes, even as small as AESA antennas produces, it is not desirable to do so due to contamination and increased vulnerability to ECM tactics at those two points and more.
With modern day fighters small enough as is and with the advent of very low observables like the F-22, this dancing around those two 120deg points through creative filtering algorithms to reach 150deg (or higher) marketing claims is playing with pilots' lives. In my opinion, of course.
especially of the top array?
The top array is to compensate for the sort of 'missing' coverage area. Caution: I said that currently conformal or shaped arrays are still experimental and that still stands. The Kopp article above has an image of that Boeing and the 'surfboard' antenna have curved ends. Those ends are
NOT shaped arrays but only radomes for the flat planar antennas inside them. This is strictly for aerodynamics. They are smaller than the main side antennas and keep in mind that output power is heavily dependent upon antenna physical dimensions. Less power equal to less effective detection distance but not necessarily target resolutions as target resolutions are more dependent upon freqs and pulse manipulations techniques. That is a can of worms beyond the scope of this discussion. That mean the Boeing version will have less effective
DISTANCE coverage in front and rear than on either sides.
I am certain much discussions occurred among Boeing designers and the military as to the importance of this deficiency. In a normal AWACS mission, the aircraft would be in an 'orbit' flight pattern around a target area facing an antenna side anyway so it must have been determined this deficiency is not a 'killer' for the design.
Could this plattform also be used with the Israeli Phalcon system?
Money talks but I think it would be more like a complete redesign rather than an adaptation.