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 /spl epsiv//sub r/=2.07 for the dielectric substrate and /spl epsiv//sub r.top/=2.60 for the top dielectric layer. The effects of the top dielectric layer thickness, B/sub top/, on the radiation characteristics are investigated using three values of the square top dielectric layer side length, L/sub top/, holding the square substrate side length at L/sub btm/=0.8 wavelength. The investigation shows that, as B/sub top/ increases, 1) the input impedance varies with a periodicity, 2) the gain is also periodic. The difference between B/sub top,max/ (at which the maximal gain is obtained) and B/sub top,min/ (at which the minimal gain is obtained) decreases as L/sub top/ increases.