A horizontally polarized slot-array antenna on a coaxial cylinder

We built a circularly polarized slot-array antenna on a coaxial cylinder that is omnidirectional in the horizontal plane and can have a shaped beam in the vertical plane. Using this slot-array antenna, we were able to achieve horizontal polarization, overcoming the problem that the vertical slots corresponding to horizontal polarization would not become excited. In order to produce horizontally polarized waves in the broadside direction, we arranged the slots with lean angles alternating between 45 degrees and -45 degrees along the axis at intervals of /spl lambda/g/2, where /spl lambda/g is the wavelength in the waveguide. However, the reflected waves from each slot in the waveguide were in phase at such an interval, resulting in poor feed matching. In order to improve the matching, we arranged the axial arrays with an alternate shift of /spl lambda/g/4 along the axis. In such an arrangement, the reflected waves of neighboring slots around the axis were out of phase and were cancelled. We fabricated such a slot-array antenna on a coaxial cylinder with uniform slot sizes, and evaluated its performance.