Dual circularly polarized spiral and loop antennas backed by a conducting plane reflector

Using the moment method, an asymmetrical two-wire spiral antenna has been analyzed in the presence of a conducting plane reflector. The spiral outer circumference is appropriately chosen for dual CP radiation. It is found that dual operation for a 3-dB axial-ratio criterion is obtained in a frequency bandwidth of 3%. Dual operation is also attained for a reflector-backed loop antenna with perturbation segments. Calculations reveal that the loop height above the reflector is one of the key parameters for dual operation. Once the loop height is properly selected, the loop configuration can be optimized as in the case of the dual spiral antenna.