Radiation characteristics of higher-order modes in microstrip ring antenna

The results of the theoretical analysis of modal fields and radiation characteristics of the microstrip ring antenna are presented. Radiation patterns for the different modes are derived from the fringing fields at the inner and outer peripheries of the ring. Theoretical patterns are compared with experimental results at 1.8 GHz. The analyses show that the TM 1m -modes (m = 2, 4, 6,...) are suitable for broadband boresight antennas while TM 1m -modes (m = 1,3,...) may be used for narrowband boresight antennas.