The PLA is also known to be interested in bi-static radar, which uses separated transmitter and receiver, and multi-static radar, as a means to defeat stealth. The PLA is also reported to be interested in other novel counter-stealth detectors such as Passive Coherent detection.
Readers, the above paragraph implied something mysterious is afoot. Hardly...A multi-static radar and 'passive coherent location' detection techniques are at the core --
THE SAME THING.
Figure 1 illustrate the 'big picture' of what is a multi-static radar detection system
AND passive coherent location (PCL) techniques.
The 'transmitter' towers could be television, music radio, cell phone, or even a radar antenna assembly.
Passive coherent location (PCL) is called 'passive' in the sense that the operator is not in control of the medium -- EM signals. The operator is exactly that -- passive. He relies on what is called 'illuminators of opportunity', which are transmitters or sources of EM signals that are
NOT under his command, hence the word 'opportunity'.
Just in case anyone thinks am making this phrase up...
Bistatic radar using satellite-borne illuminators of opportunity
The use of satellite-borne iluminators of opportunity in various kinds of surveillance applications is examined, in particular Direct Broadcast by Satellite Television (DBS TV) transmissions. The stability of TV waveforms for radar operation is considered.
The word 'opportunity' is problematic because it clearly mean that the EM transmission source may or
MAY NOT be available. The PCL operator is totally at the mercy of others for EM sources.
Figure 1 shows that in the event where a target is bombarded with EM signals from multiple sources such as TV, radio, or cell phone towers. It is technically possible to use the echoes signals from the aircraft to locate it.
But if the Devil is in the details, then he certainly lives in Figure 2. There is something called the bi-static triangle...
Bistatic radar noncooperative illumination synchronization techniques
Synchronization techniques used in the Bistatic Alerting and Cueing (BAC) program are examined. Particular attention is given to illuminator search, target search synchronization, RF synchronization, PRF (pulse repetition frequency) synchronization, range gate synchronization, and solution of the bistatic triangle. All of the synchronization techniques have been implemented and tested during the two and a half years of field-test demonstration of the BAC system. It is concluded that feasibility testing produced excellent results.
For Figure 2, the bi-static triangle is between the transmitter, the target, and the receiver and inside this triangle are two smaller triangles.
First...The receiver should know what the transmitter is doing and when it will be transmitting. That is the line called 'Direct signal'. But as the transmitter is doing its thing, its signals are hitting the receiver and that is the line called 'Interfering signal'.
Second...As the transmitter's signals are impacting the aircraft, we have echoes and those signals are picked up by the receiver.
As the aircraft flies, the main bi-static triangle may disappear but the transmitter's signals continues to be picked up by the receiver, possibly producing false targets. The 'Direct signal' line is where the receiver can use to correlate or cancel out other signals. But should this line be hardwired or wireless? Structurally speaking, how long would this link be? Every network engineer knows that the longer the wire, the greater the data loss. Every radar engineer knows that depending on the antenna, the closer the transmitter and the receiver are the greater the contamination.
When there are more than one transmitters and receivers inside a network, we can call this a 'multi-static' setup. But at its core, it is still dependent upon individual bi-static transmitter-receiver pairing to make the network functional. A station can be in several pairings at once. But the more the pairings the greater the data processing load for obvious reason: they all talk to each other. The main problem for the PCL operator is that not only does he does not have control of the medium, he may not have that 'Direct signal' reference information to filter out false positives. A wireless link can be highly unreliable and in a combat situation, it can be jammed. Worse yet, the adversary can send in drones to saturate the network with blanket noise. What if the main electrical source is destroyed? How are those TV, radio, and cell phone towers transmit to be those 'illuminators of opportunity'?
The bi-static radar is the greatest threat to 'stealth' aircrafts but hardly the guarantor of detection and reliability.
