This paper presents a compact wideband circularly‐polarized square slot antenna (CPSSA). The antenna is a coplanar waveguide feed structure with three T‐stubs toward the slot center and one semi‐circle tuning stub was etched to the feed line and modified inverted L‐shaped strips around the corners of the ground. Moreover, two spiral slots were loaded in the ground plane for exciting currents in a different direction. A prototype of the designed antenna is fabricated and measured to confirm the simulation results. A reasonably good agreement between the measured and simulated results in terms of the reflection coefficient <−10 dB and axial ratio are achieved. The 3‐dB axial ratio bandwidth achieved by the combination is from 4.35 to 8.15 GHz (60%, measured). The designed CPSSA has a compact size of 0.57λₒ × 0.57λₒ × 0.0116λₒ at the center frequency and fabricated on the FR4 substrate.
Metallic structures with periodic array of slits are well-known to lead to extraordinary power transmission, when slits have dimensions much less than the wavelength of incident optical wave. Excellent power transmission originates from surface waves excited by incident transverse magnetic wave. Here we show that metallic structure with array of steppedslits can transmit power of incident wave into the substrate at desired optical frequency entirely and simultaneously in terahertz frequency band by 70%, for In0.53Ga0.47As substrate. Transmitted power of the proposed structure is studied both in a closed-form by an analytical model as well as numerically by finite element method. It is found that with the increase of field intensity in the substrate, structure with array of stepped-slits (as opposed to uniform-slits) favorably has no reduction of frequency range at maximum transmitted power.Index Terms-stepped-slits, transmitted power, periodic array, optical wave, terahertz wave.
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