Ground connecting system for microwave plane or helical antenna structures comprising a radiating body that is connected to a power supply source located at ground level. In a plane antenna structure the radiating body is a flat plate with a plurality of ground connecting iron strips applied within appropriate recesses at selected regions thereof, whilst in a helical antenna structure the radiating body comprises a plurality of dielectric cylinders arranged along the circumference and inwardly the radiating surface, each dielectric cylinder located at the top of a coaxial power supply cable and being helicoidally wound with a conducting wire with ground connecting iron strips at the upper and bottom ends thereof. This selective grounding system results in a magnetic field being applied in between grounded and non-grounded regions that provides improved antenna transmission performance and effective isolation of the radiating body from the power supply source.