Radiated spurious emission reduction using parasitic element for mobile applications

In this paper, a quarter wavelength open stub as a parasitic element has been proposed to reduce radiated spurious emissions (RSE) in GSM 1800/1900 networks caused by non-linear devices at the amplifying stage of radio frequency (RF) systems. As the proposed structure is located in a signal line between a front-end module (FEM) and an antenna, it is possible to effectively and additionally suppress harmonic signals below RSE certification test limit. To verify the effect of the proposed structure, the proposed open stub is combined to a planar inverted-F antenna (PIFA) and a low pass filter of the FEM which they are fabricated and measured. The measurement result shows that the radiated powers at 2nd and 3rd harmonic frequency are reduced about 6 to 13 dB while having a reasonable insertion loss of 0.7 dB in a carrier frequency band.