Shaping of flat-topped element patterns in an array of slow-wave strip structures excited by parallel-plate waveguides

A two-dimensional (2-D) model of a corrugated-rod antenna array in the form of an infinite periodic array of finite slow-wave strip structures arranged above the apertures of two-or three-mode parallel-plate waveguides excited by TEM modes is analyzed. The formulated problem is solved by the method of matching the waveguide and Floquet modes on the waveguide apertures in combination with the Galerkin method for calculation of the currents on the strips. The geometrical parameters of the strip structures are optimized for shaping the flat-topped element patterns. It is shown that high quality of the flat-topped patterns in the element spacing range from 0.65 to 1.3 of wavelength is achieved if the excitation of the optimized structures is performed using the second and third reflected waveguide modes returned back to the apertures with the corresponding optimum phases. The presented examples also show that the shape of the obtained patterns keeps well at least in a 10% frequency band.