Mobile device multiband antenna design optimization and performance tuning in the presence of active components
The latest trend in handset design is slim smart phones that require small, thin, light weight and wideband multiband internal antennas. This trend poses two major challenges in designing a mobile device antenna: how to use a single antenna to cover all the required frequency bands and then how to make the same antenna small enough so that multiple antennas can be deployed within the same device. Although a printed Inverted-F antenna (PIFA) has been a suitable candidate due to its simple modeling and easier fabrication using a printed circuit board (PCB), it has a limitation of a narrow bandwidth characteristic. To address this issue and yet obtain multiband operations for GSM applications, this research presents the structural optimization of a PIFA antenna which is capacitively loaded with an inverted-L element. The antenna covers GSM-900 and GSM-1800.The results obtained show that the PIFL antenna lower and upper bandwidths determined at -10dB is over 110MHz and 500MHz respectively which covers the above mentioned bands very well with very low return losses of -30dB and -30dB at resonant frequencies 925MHz and 1.795GHz respectively. In addition to this, a ground plane forms the other half for quarter wave PCB antennas. Integration of these type of antennas with other components within the same PCB of a mobile device compromise the uniformity and continuity of the ground plane due to the requirement for dense routing and component mounting to optimize the use of the limited PCB space available. This will not only detune the matching and introduce losses to the antenna, but also degrade the antenna‟s performance in terms of gain, bandwidth, efficiency and radiation pattern. Again, this research presents a case study of an optimized components placement and stacking, effective PCB partitioning, routing discipline combined with right selection of antenna location to achieve a successful integration of a PCB-PIFL antenna into a mixed multilayer PCB design, which provides improved continuity and uniformity of the antenna‟s co-planar ground plane, and the antenna‟s and improves the overall performance. The results obtained show that the lower and upper bandwidths determined at -10dB is over 60MHz and 130MHz with return losses of -30dB and -14dB at resonant frequencies 915MHz and 1.931GHz.