A new type of planar inverted F-antenna has been conceived and demonstrated using a fully planar structure to provide quasi-omnidirectional-type radiations over a wide operating bandwidth. Miniaturized segmented substrate integrated waveguide technology has been extended with some modifications to accommodate two distinct modal geometries in a single structure. The new approach has been systematically studied, and their equivalent circuits have been developed. A prototype has been experimentally tested in C-band revealing quasi-omnidirectional radiations with 1.3 dBi peak gain and 48.5% matching bandwidth. This miniaturized wideband omnidirectional antenna should find potential applications in compact wireless transceiver systems occupying 0.45λ0 × 0.2λ0 real estate. © 2002-2011 IEEE.