Equivalent Circuit Representation of a Parallel Plate Waveguide Fed Connected Array

We present an analytical model to describe arrays of connected slots fed by parallel plate waveguides (PPWs). Connected slot arrays are planar ultra-wideband arrays with wide scanning capability. PPW feeds can be used to reduce the complexity of the unit cell design. However, existing analytical expressions of the active input impedance of the array cannot account for the presence of PPWs. Here, we develop a new model that includes PPW structures in the stratification, enabling the optimization of the design together with the feed. An equivalent circuit of the unit cell is derived, where the PPW sections are represented in terms of equivalent transmission lines for each Floquet mode. Closed-form expressions are also derived for the capacitance associated with step discontinuities of the PPW and the inductance associated with the feed. Full-wave simulations are used to validate the model.