Dual frequency antenna for a mobile telephone

摘要

An antenna 1 comprises an elongate conducting radiator 7 and a feedline 5. The feedline is screened and has a signal conductor 5a and a screening conductor 5b. A conducting sleeve 9 surrounds both the radiator 7 and the feedline 5 at their junction. The conducting sleeve 9 may or may not be connected to the feedline screening conductor 5b. Region A forms an effective inductance and region B forms an effective capacitance; the sleeve 9 therefore constitutes an rf impedance. The antenna operates as a quarter wave monopole at one frequency band and a half wave dipole at a second band. The two frequency bands may be the GPS (global positioning system) frequency at 1575 MHz and a UHF communications band at 380 to 420 MHz. The antenna may be used in a mobile phone or similar device.