what material reflects microwave?

Actually it is often more absorbtive than reflective.

Give that man a cigarette and a blindfold; how dare you reveal declassified Government sneakrets.

Not even aluminium dust? But that's possibly non-conductive. The conductive paints certainly come at a premium price.

My current lappy was given in return for data recovery, what had happened is that it was dropped because someone tripped over the power cord. Had been 'repaired' but was unreliable (hence the giveaway). IN servicing the thing I discovered inside plastic was sprayed with conductive silver paint for RFI reduction. A small piece of painted plastic had broken off and shorted hard drive connector pins, creating havoc. Anyway, machine has not faulted since I properly cleaned it out :) Some of that silver paint does work as advertised. It's old now, made in 1999. Win98 or Win2k era.

Now crawling along with WinXP SP3.

Grant.

Frozen vacuum, sounds almost possible ;) Probably good enough for solar

Grant.

You might want to research passive reflectors. Not my field, but I know they are used commercially. You find passive reflectors generally in rural areas when they run telecom signals over microwave. Rather than doing point to point microwave links, they put a reflector in the middle and keep the transmitter/receiver on the ground. Damn clever of these phone companies, since that saves them the hassle of driving up mountain tops to repair their gear.

Commercially, I've only seen Microflect.

If you live in the US and want a strong signal at home, go T-Mobile and get one of their wifi capable phones. They call the service UMTS. Some call it GOIP (gsm over IP). I've used the wifi phone service in locations where there is no cellular service.

Passive repeaters (either simple reflectors or directional antenna-cable-directional antenna) are useful very close to either end of the link, but at midpoint, it is usually useless.

The power captured from the transmitter by the reflector is inversely proportional to the square of distance. Also the power from the reflector to final receiver is inversely proportional to he square of the latter distance.

A reflector at the midpoint is equivalent to the situation in the radar equation, i.e. the received power is inversely proportional to the forth power of distance from the reflector to either end station. Moving the reflector closer to one end and we have the bistatic radar case.

Assuming initial condition with a total distance between end points of

Move the reflector above the receiver antenna on a mountain 3 km away. Now the distance from transmitter to reflector is doubled and hence path loss increases by 6 dB, but the path from reflector to receiver drops to 1/10 and that path loss drops by 20 dB, so the signal strength increases by 14 dB.

By putting the same reflector on a 300 m tower, the latter path loss drops with an additional 20 dB and the received power increased by 34 dB compared to the midpoint situation.

A reflector at only 30 m (assuming free path to the reflector) would give 54 dB stronger signals compared to the midpoint reflector.

Thus, if the signal is just usable with a reflector 30 m from the receiver, the link will fail, if the reflector is 300-3000 m away or even at midpoint.

Thus, in order to increase cell phone coverage e.g. in a room below ground with a passive system, a directional antenna outside on a mast aimed towards the cellular tower a low loss coaxial cable down into the room below ground and an omnidirectional antenna in that room might help.

Assuming minimal cable losses, there is one path loss from the cellular tower to the directional antenna and an other pass loss within the room from the omnidirectional antenna to the cell phone. Of course the gain of the directional antenna also helps a bit. The cell phone might be usable a few meters from the indoor antenna and there is no need to directly connect the coaxial to the phone.

You've never heard of 'Over the horizon microwave telephone relay"? Search for 'White Alice Network' which was build in the '40s

Learn something new every day!

That's funny! I was just thinking a lot of silver-plated, high-frequency RF connectors don't contain any silver either! :) I won't name them, but they hail from Belgium. Pure crap.

Likely nickel.

Not frozen vacuum, air pressure differntial foam casting.

Exactly my point, some do and some don't contain metal.

Antennas For Communications (AFC) still makes some of those microwave antennas. The last time I passed their plant, the molds were still sitting outside in their storage lot. They were owned by Microdyne at one time, and made the 3 & 5 meter dishes for Microdyne's C-band CATV and broadcast installations.