© D.V. Tatarnikov, A.V. Astakhov, A.P. Stepanenko

Frequency bandwidth enhancement with low directivity multy-patch antenna designs has been treated. With the help of two dimensional model it has been shown that if patch antenna element is capacitively coupled to the walls of the parallel-plate waveguide then such an optimal distance in between the element and the ground plane exists so that a null of derivative of reactive part of antenna impedance frequency response within the desired frequency band will occur. Such distance is shown to be of 1/8 of the wavelength. Same result is shown for 3-D multy-patch structure consisting of angular segments mounted over semi-spherical plastic carrier. Each segment current was approximated by the lowest resonant mode. It is shown that under strong capacitive mutual coupling in between the segments and the ground plane with the radii of the semi-sphere to be of 0.3 of the wavelength the derivative of reactive part of antenna impedance frequency response has a null within the desired frequency band. This leads to significant frequency bandwidth enhancement. For azimuth antenna pattern inconsistency not to exceed ½ dB the structure has to have 8 elements. The sample of circular polarized antenna element with the overall dimensions not exceeding 0.3 of the wavelength and frequency bandwidth of 41% has been shown.