Investigation on the Radiation Efficiency Local Minimum in Open-Slot and T-Shaped Antennas

The mechanism for the radiation efficiency local minimum in antennas, especially for open-slot antennas and T-shaped antennas, has been investigated. It is found that the local minimum in those antennas always corresponds to an ideal differential mode. Furthermore, the frequency position of the ideal differential mode is decided by the parasitic parts of the antennas. Simple methods for estimating the local minimum position are proposed based on the mechanism we have found. In addition, the duality relation between those two types of antennas is also discussed. Our findings provide a guideline for designing mobile phone antennas with improved efficiency.