Radiation characteristics of a patch antenna with a top dielectric layer

A patch antenna (printed on a dielectric substrate) with a top dielectric layer is analyzed using the FDTD method. The relative permittivity is chosen to be ε_r=2.07 for the dielectric substrate and ε_r.top=2.60 for the top dielectric layer. The effects of the top dielectric layer thickness, B_top, on the radiation characteristics are investigated using three values of the square top dielectric layer side length, L_top, holding the square substrate side length at L_btm=0.8 wavelength. The investigation shows that, as B_top increases, 1) the input impedance varies with a periodicity, 2) the gain is also periodic. The difference between B_top,max (at which the maximal gain is obtained) and B_top,min (at which the minimal gain is obtained) decreases as L_top increases.