An original and flexible pyramidal antenna for satellite or terrestrial application services is presented. The ground plane of the antenna is perforated and loaded with a cutoff open-ended waveguide: this original configuration leads to a good tradeoff between rear radiation and impedance matching. Trap-loads are used to achieve multiband operation while frequency agility may be simply obtained by loading the radiating element by radio-frequency switches. The antenna radiates linearly or circularly polarized electromagnetic fields with quasi-hemispheric radiation patterns at multiple operating frequencies. Several prototypes have been simulated, manufactured, and finally measured. A specific application is given in this paper for a triband GPS/Galileo/MicroSat Telemetry antenna to combine positioning and telemetry applications. The experimental results confirm the good performances observed with the electromagnetic simulations.