The TM/sub 11/ and TM/sub 12/ modes of open- and closed-ring microstrip antenna

Analytical and experimental studies of the radiation characteristics of open- and closed-ring structures indicate that the TM/sub 12/ mode can offer superior radiation properties compared to the TM/sub 11/ mode and the ideal-gap open ring is superior to a closed-ring when excited in the TM/sub 12/ mode. An extended analysis of these properties is presented, and the results indicate that the radiation patterns of the TM/sub 12/ mode can possess nulls in the normal direction whereas the TM/sub 11/ can offer superior radiation performance with increased substrate thickness.<>