Waveguide Slot Array Design With Compensation for Higher Order Mode Coupling Between Inclined Coupling Slots and Neighboring Radiating Slots

Existing design equations do not include higher order coupling effects between inclined coupling slots and longitudinal radiating slots of planar arrays. Several studies have shown that higher order mode coupling in the waveguide junctions causes errors in the excitation of radiating slots, which in turn result in antenna performance degradation. Efforts to compensate for these effects have to date been restricted to trial-and-error or applying full-wave analysis to an existing design and perturbing the slot dimensions to improve the array performance. In this paper, we present an efficient design approach that accounts for the higher order coupling in the waveguide junctions. Compensation is achieved with the addition of closed-form terms in the expression for the active admittance of the radiating slots straddling the coupling slot in each branch. In addition, we propose amendments to the method for calculation of coupling slot dimensions that accounts for phase differences between scattering parameters of coupling junctions. The effectiveness of the proposed procedure is demonstrated by means of two illustrative design examples.