Radiation efficiency and impedance bandwidth of conductor-backed CPW-fed broadside twin slot antennas on two-layer dielectric substrate

The radiation efficiency and impedance bandwidth of matched broadside twin slot dipoles, fed by a coplanar waveguide on a conductor-backed two-layer substrate, are investigated as a function of distance between the slots and height of the bottom substrate layer. It is confirmed that the low radiation efficiency associated with a single slot due to the excitation of parallel-plate modes may be greatly increased by using two slots spaced half a wavelength of the dominant two-layer parallel-plate mode apart. It is also demonstrated that the radiation efficiency of optimally spaced twin slots may be further improved by increasing the height of the bottom substrate layer, in general at the cost of decreased bandwidth. The effect of bottom substrate height on gain and directivity is investigated, and radiation patterns are provided for the case of optimally spaced twin slots. Twin slots on a conductor-backed two-layer substrate can yield high radiation efficiencies similar to those of previously reported twin slot antennas with a back plane, with the advantage of reduced overall height.