A Linear Waveguide Transverse Slot Array with Parasitic Dipole Layer and Reflection Canceling Posts for Grating Lobes Suppression

A broad-wall transverse slot array is important in that it radiates linear polarization orthogonal to that of shunt slot array. A bore-sight beam transverse slot array requires the slot spacing of a guided wavelength λg, which is always greater than the free space wavelength λo, hence the array suffers from unwanted grating beam radiations. From the design point of view, it utilizes non-resonant slots and array design taking the reflection from elements into account becomes a kind of large EM analysis which is computationally heavy. The array input reflection is also large as each slot unit, spaced at a guided wavelength λg, adds up the reflection in phase at the input. A few methods have been proposed to deal with the problem of the grating lobes of transverse slots. A baffle technique was proposed by Josefsson [1], where radiation takes place between two parallel plates to eliminate the grating lobes. A partially dielectric filled waveguide was introduced by Joubert [2] to reduce the slot spacing to less than λo. The authors proposed a new way of grating lobe suppression by installing a parasitic dipole layer over the slot array without considering the interior reflection problem of the waveguide into account [3-4]. The input reflection problem from a slot was studied by Park et al. [5], where the reflection is controlled with an inductive post. Recently the authors introduced a unit element [6] consisting of a transverse slot, a post and a pair of parasitic dipoles for an application in the bore-sight beam antenna array with suppressed grating lobes and minimized reflections. The pair dipoles are placed at a height of half free space wavelength λo/2 from the slot to generate a Dual Parasitic Beam (DPB) [4] that suppresses the radiation of the slot in the directions of the grating lobes. The post position for each unit is designed to minimize the reflection. In this paper, the authors have presented a design of transverse slot array with the element mentioned above. The design parameters for a unit radiator consisting of a single slot, an inductive post and a pair of parasitic dipoles are determined for specified excitation coefficients by the Method of Moments (MoM) analysis. A 5-element transverse slot array with uniform excitation is constructed by simply cascading units thus designed without considering mutual coupling. This is acceptable since units are largely spaced at a guided wavelength λg and reflection free. The array performance is simulated by the Ansoft HFSS. The simulated results show that input reflection of the array is less than -15 dB over 100 MHz in 11.9 GHz band while the grating beam can be suppressed by more than 15 dB at same frequency band.