Classification of Transmission Modes through a Narrow Slot in a Thick Conducting Screen

This paper examines electromagnetic energy transmission through a narrow slot in a thick conducting plate when a plane wave is incident to the slot. The slot in the thick plate creates a waveguide structure. From the perspective of cutoff frequency, the transmission characteristics are classified into three modes. The transmission cavity resonance (TCR) mode in the range above the cutoff depends on the plate thickness, and peak transmission cross-sections (TCSs) appear periodically along the plate thickness, known as Fabry-Perot resonance. The near-cutoff resonance transmission (NCRT) mode depends on the slot length and plate thickness, and the maximum TCS appears only once as a slot length resonance (or transverse resonance). The peak TCS for the NCRT mode occurs with a thin plate thickness, which produces slot length resonance. The non-transmission cavity (NTC) mode is a non-transmission and non-resonance mode and is not propagated. All the maximum TCSs for the TCR and NCRT modes occur in parallel resonance. The analysis results show that the classification of the three transmission modes through the thick plate slot is effectively explained by the TCS and aperture impedance.