Short helical antenna array fed from a waveguide

An array consisting of short helical antennas is fed from a single rectangular waveguide. Stubs are introduced near the array elements in order to make a matching condition between the array elements and the waveguide. On the basis of a transmission line theory, a coupling phase and a coupling factor are determined. The mechanical rotation is applied to each array element so that in-phase condition at the aperture may be formed. Excellent agreement between the calculated and experimental results is demonstrated in the arrays of five, seven, and nine helical antennas.