Microwave imaging probe using Bowtie type of optical antenna structure

When a uniform plane electromagnetic wave is incident upon the small circular aperture in an infinite conducting plane, the transmitted power t P through the aperture is very small. More specifically, the transmission cross section(TCS) T of the aperture whose diameter D is much smaller than the wavelength λ is proportional to (D/λ)⁴ · D² according to the Bethe´s theory. Here the TCS T is defined so that the transmitted power Pt through the aperture may be given by the multiplication of the incident power density Pinc [W/m²] and T [m²], i.e., Pt = PincT.