Performance of standard aperture shielding techniques at microwave frequencies

The theory and measurement of microwave coupling through circular apertures is discussed. Experimental results show that the effective areas of untreated apertures increase rapidly with increasing frequency up to about the first resonant frequency of the aperture. Above resonance, the effective area tends toward the geometrical optics limit (i.e. the physical area of the aperture). Below the resonant frequency of the aperture, aperture polarizability theory provides an accurate estimation of the effective area of the aperture. Treating an aperture with a metal screen significantly reduces its effective area. A waveguide below cutoff reduced the effective area to the noise floor of the measurement system for frequencies below the cutoff frequency of the waveguide. For high frequencies, however, the effective area was about the same as for an untreated aperture.<>