Revise GCSE Physics

Question:Are there any conditions on the size of emitters of electromagnetic radiation?

An emitter and the receiver (antenna) needs to be approximately the same size as the wavelength of the radiation it is trying to emit or receive.

So a microwave emitter will be millimeters long because microwaves are millimeter wavelength EM waves, but radio antennae must be tens of meters high to produce waves that are tens of meters in wavelength.

If the antenna is too small it does not detect the waves.