PIFA antenna with modified resonant frequencies

摘要

A planar inverted F antenna (PIFA) is formed from a grounded conductive plane with a slot 104. The slot has an extending portion 104c that increases the perimeter of the slot as a whole. A current path (indicated by arrows) is formed between feed point 111 and ground point 108 around the perimeter of the slot. The length of the current path is influenced by the slot perimeter and the resonant frequencies of the antenna are reduced as slot perimeter increases. In the preferred embodiments the PIFA has two operating frequencies, at a quarter wavelength and at three quarter wavelength, which enables the antenna to be used in a dual band mobile phone. By varying the slot perimeter, the resonant frequencies are altered and the frequency ratio between them varies from the standard 1:3 value. Other shapes of slot may be used to influence resonant frequency (see figures 13, 17 and 22 to 26). Two of the PIFAs so formed may be combined to give an antenna with three or four resonant frequencies.