Design and development of an omnidirectional antenna with a collinear array of slots

The design and experimental results of an ominidirectional antenna in vertical polarization, operating at a frequency centered at 1030 MHz and realized with a collinear series fed array of annular slots, are discussed. Mutual impedances between elements and leaky-wave irradiation are neglected. Three antenna design problems are considered: synthesis of the linear array to obtain the desired vertical pattern; matching of the input impedance of the antenna to that of the feeding line; and design of the radiating element as a module which fits these two constraints. A perfect omnidirectional azimuthal pattern and a cross component of zero was obtained in the limits of measurement sensitivity. A return loss below 20 dB was measured in the 1030/1060 MHz band, and the experimental and theoretical elevation radiation pattern is shown. The measured beamwidth of 35 degrees implies a gain of about 5 dB, and the antenna tilts its beam about 9 deg above the horizon and has no secondary lobes under it.