Synthesis of CSC2 θ type antenna patterns using two-dimensional surface wave arrays

The development and design principles for pattern synthesis with a unique flat array (0.032 inch thick atK_{a}band) of non resonant slot radiators are described. A surface wave of the dielectric image line type is used as a transmission mode to excite a two dimensional traveling wave array of slot radiators. The beam maximum in the longitudinal (narrow beam) plane is designed to be approximately normal to the plane of the array. A dielectric image line of the appropriate size has a field in the transverse direction that decays almost identically as the amplitudes of the Fourier coefficients of typical ground mapping shaped beam patterns. Thus, in the transverse plane an array of identical slots provides the proper excitation amplitudes. Displacing the slots in the longitudinal plane provides the required transverse plane phase excitations. For a 25-1/2 wavelength transverse array, a specific\csc^{2}\thetatype pattern normalized to about 3 degrees theoretically can be approximated with a 0.4 db ripple. Measured patterns for an array designed neglecting mutual impedances are within 2 db of the desired pattern over a 20 db range. Theoretical ripple as a function of the number of Fourier terms is shown for illumination functions yielding\csc^{2}\thetatype patterns whose maxima are at 3 degrees and 15 degrees below the horizon. The curves show that it is theoretically possible to synthesize a typical\csc^{2}\thetapattern to a tolerance of 0.4 db with an aperture efficiency corresponding toHPBW = 90 \lambda/D.