Investigation of Orthogonal Modes in a Periodic Structure and Application to Two-Separate Beams Steering Within the Same Frequency Band

This paper investigates orthogonal modes and their space harmonics in a dielectric-filled rectangular waveguide (RWG) leaky-wave structure. The dispersion analysis on orthogonal modes in periodic structures aims to determine the feasibility of two individual beams steering in different spatial regions. The Brillouin diagrams explain the basic principles of the constructed leaky-wave structure; a feeding network is developed for mode excitation. The proposed two-port prototype utilizes standard printed circuit board (PCB) and 3D printing techniques, and the dispersion properties reveal an agreement between measurements and simulations. From 19.6 to 22.2 GHz, the measurements showcase two separate beams steered for each port excitation. One excited port steers a beam in the forward quadrant, from +350 to +650, while the other port excitation results in the second beam steered in the backward quadrant, from -660 to -350. Since these two beams are produced by orthogonal modes that are independently excited from different ports, the measured in-band isolation of -20 dB between two input ports confirms that the two beams can be separately driven within the same frequency band. In addition, the two beams maintain linear polarization consistency in different spatial quadrants while scanning with frequency.