Idea: Homemade Passive Radar System (GNU/Radar)

[Morlock Elloi]

> As an active twist, we can also use a separate unit, Illuminating
> Transceiver (IT), periodically broadcasting a pulse of known
> characteristics, easy to recognize by the LPs when it bounces from an
> aerial target. This unit has to be cheap and expendable - it's easy to
> locate and to destroy by a HARM missile. As a bonus, forcing the adversary
> to waste a $250,000+ AGM-88 missile on a sub-$100 transmitter may be quite
> demoralizing. There can be a whole hierarchy of ITs; when one of them

Microwave oven.

This has been done in recent years in various theatres.

> Even other sources can serve as involuntary ITs. The landscape is littered
> with cellular base stations and civilian TV and radio transmitters. Just
> pick the suitable frequency and listen on.

There is enough wideband power in the ether above inhabited areas to make
passive detection from reflected EM possible in theory (without any EM
emanating from the target.) The space is illuminated, but the "eyes" are not
good enough, yet. Signal levels are extremely low, but it's likely that a
flying jet reflects back enough from hundreds of cellphone/celltower
transmissions to be few dB above the background noise. However, without knowing
where to "look" the receiver cannot use typical narrow beam high-gain antennas.
What is needed is an array, like an insect's eye, and that will be a sizeable
contraption - passive, but not small. In other words, the size of a passive eye
is proportional to the wavelength. To get human eye resolution in 10cm band the
size gets to 2km across. Big eye.



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