Evidence of Mode Coupling on Periodic Traveling‐Wave Dipole Arrays

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Abstract
Measurements of the distribution of electric field intensity along a periodic radiating structure consisting of a dipole array coupled to a balanced transmission line reveal a standing‐wave pattern that is formed at the driven end of the structure. We propose that this standing wave is formed by the interference of two normal modes of the coupled structure. These modes are found to possess conjugate wave functions exp [−αx±jβx], and to carry energy in opposite directions on the transmission line. They are identified with transmitting and receiving modes of the infinite, periodic structure; both are excited on a finite model to satisfy boundary conditions on both the transmission line and the dipole array at its driven end.These conjugate normal modes arise from coupling of the TEM mode of the unloaded transmission line with the complex, radiating mode of an undriven, periodic array of dipoles. The determinantal equation of the coupled array can be cast in a form that displays the mode coupling.

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