An alternative configuration for an infinite coaxially end-fed waveguide phased-array antenna is explored. In the proposed configuration, the integration of the end-fed launcher and the output waveguide, rather than the waveguide in itself, acts as a basic radiator. This allows the design of more compact antenna elements. In order to analyze and optimize the structure, an accurate full-wave simulation tool based on the multimode admittance matrix representation is developed. Results are validated against state-of-the-art commercial CAD software. Numerical simulations involving singly and doubly tuned configurations are presented and discussed to illustrate the potential convenience of the proposed configuration and of the CAD tool developed.