Re: can microwaves be polarised?

Yes.

All forms of electromagnetic radiation (e.g. microwaves, light, x-rays) can be polarized. Indeed, the concept of "unpolarized" EM waves is a fairly subtle one. A good example would be a microwave oven. The microwaves are produced by a special type of device called a magnetron and are radiated into the oven through a waveguide. The radiation comes out of the waveguide fully polarized (linear polarized I would guess). After bouncing around inside the metal chamber where one puts one's leftovers (:-) the state of the polarization varies rapidly from place to place and, because there is usually a rotating part to "stir" the microwaves (what a concept), the polarization state in any one place also varies with time. That's pretty much what we call "unpolarized" EM radiation -- in reality at any given moment of time the E and B fields have a perfectly well determined direction and (hence) polzarization at each position.

You can look at an animated picture of the E and B fields of a linearly polarized EM wave at the following URL: http:// www.phy.ntnu.edu.tw/~hwang/emWave/emWave.html

You can learn more than you want to know about the tricky concept of "unpolarized" or "partially polarized" waves in any good, advanced optics or EM text. The "mother of all optics texts" is the famous text by Born and Wolf, called, if memeory serves me well, "Optics", but it's famously opaque (sorry, couldn't resist).