Improved Model for Inclined Coupling Slots in the Feed of a Planar Slot Array

The conventional design equations for centered-inclined slots of a planar array feed network rely on certain assumptions regarding the phase relationship between the elements of the scattering parameters of coupling junctions, and do not account for higher-order coupling between tilted slots. Phase variations between S-parameters give rise to excitation errors in the radiating branches, and discounting the effects of higher-order coupling causes the input reflection coefficient minimum to deviate from the design frequency. In this communication, we derive new design relations which accommodate phase differences between individual scattering parameters and compensate for higher-order coupling. Compensation is achieved with the addition of closed-form terms in the expression for the equivalent impedance of the coupling slots. The effectiveness of the proposed procedure is demonstrated by means of an illustrative design example.