Could a pinhole microwave camera be made?

Question

Could a pinhole microwave camera be made? I'm talking about a camera to see the wavelengths used by cell phone. If I remember right, they're a maximum of a few inches in size. Is there an easy way to focus microwaves like a camera focuses visible light, or would it have to work like a pinhole camera? Would mirrors work, like a reflective telescope? How much "brighter" is a cell phone than background microwave radiation on the earth?

Answer 1

Cell phone wavelengths are about one foot. Your "pinhole" would need to be wider than the wavelength. It would have to be made of an electrical conductor, and it's resolution would be the distance from the hole to the sensor divided by the diameter of the hole. The sensor would be an array of cell phone receivers.

Microwaves can be focused by a conductive reflector like the big horn antenna used to discover the cosmic microwave background ratiation. (See picture of antenna at link below.)

Answer 2

The 'pinhole' would have to be larger than the wavelength or it might as well not be there. Not sure what the freq is. If 3GHz, wavelength would be 100 cm = 25 inches. One inch would be 75 GHz.

Focus by parabolic dish - think radio telescope, or radar system. Or satellite dish. I think you might need to ensure that the dish to waveguide [the thing in the center that collects the signal] distance is not an integral number of half wavelengths, but I am a ChE, not an EE or physicist.

It IS possible to make "lens-like" elements out of arrays of carefully bent wire bits, and some such arrays have a *negative* index of refraction, and other such advanced physics weirdness [I remember something about some preserving the 'evanescent wave' so that they could resolve *better* than the Rayleigh criterion allows, but not much more than that about it]. But dishes are the standard technology.

I am told that microwave motion sensors work by essentially taking radar stills and comparing them with the current scene.

Cell phones use various frequency sharing tricks, eg, spread spectrum, code division multiple access, time div MA, and more, so if you plan to use a cell phone, unless you have a pretty special multichannel receiver, you may have a problem. Of course, depending on how much of a solder jockey you are you might be able to cannibalize a cell phone.... That might give you the equivalent of color vision.....

Not sure what resolution you would need on your 'camera', ie, how many pixels, but unless you can sample and hold at well over the carrier frequency [or modulation frequency] you are going to need an array of receivers. Multifrequency operation makes it tougher.
But hey, radio astronomers have solved all of these problems, so some radio astronomy site could probably tell you all about it. They may have bigger budgets, though.

I do know that military radars use amazing amounts of computing power - it is joked that the Air Force used to buy planes and put computers in them, but now they buy computers and strap wings onto them. Then again, with luck nobody will be shooting at your camera. The Air Force would probably NOT be willing to share techniques with you.

Answer 3

Sure, most of that stuff would work. But best idea, get a parabolic microwave receiver (also called a satellite dish). Works great. A lot like a camera and a mirror.

A simple antenna works pretty well around town.

Answer 4

Real microwave cameras work with computers or optical processors to form the image.

Answer 5

that didn't make any sense to me, explain better.

Answer 6

possably it would take a longggg time!!!!!