Spiral antennas are inherently circularly polarized radiators and have a relatively constant radiation profile and input impedance over a wide frequency range. The upper cut-off frequency of spiral antennas is determined by the feeding area (inner radius of the antenna) and the size of the spiral antenna’s output aperture determines its lower cut-off frequency; Therefore, the bandwidth of the spiral antenna is determined with good accuracy by these two criteria. Usually, the balloon feed limits the performance of the antenna, unless very wide band feeds are considered for the antenna.