Re: what is wave guide
A waveguide is basically something that guides a wave. When a wave is received from outer space, or some other source, we need to send it in a particular direction to our circuit or other region of interest for further study. Using the boundary conditions of Electric and magnetic fields, the waveguide can be designed to break up the received wave into particular modes and polarizations for further study...
See David Cheng, "ElectroMagnetics," or Simon Ramo, "Wireless Communication" for a more mathematical derivation. If you are really feeling good about yourself, look up "Electrodynamic" by Jackson.