A quarter-wavelength shorted microstrip antenna with a slot for dual-frequency operation

A novel dual-band internal antenna similar in size to the single-band internal antenna for cellular handsets is proposed. Our approach to realize a small and low-profile dual-band internal antenna is to use the dominant mode (TM₁₀ mode) and the higher-order mode (TM₃₀ mode). In order to use this approach for recent dual-band cellular systems it is necessary to lower the resonant frequency of the higher-order mode (TMao mode). This motivated our development of a new antenna configuration with a slot on the radiation element of a quarter-wavelength shorted microstrip antenna to lower the resonant frequency of the TM₃₀ mode. In this paper, the experimental and the analytical results for this antenna are presented. In the results, by adjusting the location and the length of the slot, the dual-frequency operation can be achieved with the frequency ratio (TM₃₀ modc/TM₁₀ mode) from 2 to 3. In addition, the enhancement of bandwidth is presented.