Medium gain antenna for radio monitoring from manned airship

In January 2007, a Zeppelin NT airship was used by NICT for a radio monitoring demonstration. A light weight, robust, 'no sharps', circularly polarised, medium gain antenna was required for handheld use within and outside the airship gondola during flight. A microstrip patch driven short backfire antenna was attractive for this application due to its enclosed nature, but suffered from a broad E-plane radiation pattern; degrading the axial ratio, radiation pattern rotational symmetry and gain level. Parasitic wires installed within the cavity of the short backfire antenna were found to narrow the main lobe of the E-plane radiation pattern, giving an S-band medium gain antenna that was well suited for hand held radio monitoring.