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
· D
²
according to the Bethe's theory. Here the TCS T is defined so that the transmitted power P
t
through the aperture may be given by the multiplication of the incident power density P
inc
[W/m
²
] and T [m
²
], i.e., P
t
= P
inc
T.