Platform based antenna design methodology for mobile devices

Abstract

This work presents a platform based design methodology to widen bandwidth of 4G LTE or later generation mobile devices. The platform based mobile antenna design methodology is an revolutionary approaches based on antenna platform composed of the antenna aperture and the impedance matching network (IMN), which is a systematic engineering method. Based on an equivalent RLC circuit model of antennas on a small chassis, this thesis proposes a dual-frequency antenna with a simultaneous dual-frequency bandwidth widening method. Moreover, the proposed method is applicable to a triple-frequency antenna.

For a given chassis dimension, it provides the optimized antenna aperture which can potentially be wideband tuned by IMN. For a systematical design, a semi-empirical modeling of an inverted-L antenna (ILA) on a small chassis is proposed. The ILA is the best antenna aperture platform due to its lowest quality factor for a given antenna area. The chassis and antenna radiators can be expressed in the form of an equivalent RLC circuit. The equivalent RLC circuit provides a means of understanding the physical operation of antennas and enables the design of an appropriate impedance matching network systematically. Moreover, it is possible to understand the physical behavior of an antenna and the physical limitations of bandwidth widening methods. The small chassis model provides physical insight into the contributions of the CR and the AR on the overall antenna characteristics. As a result, the RLC model enables a platform-based design methodology for mobile antennas without annoying trial and error methods that require considerable amounts of time and effort.

The proposed antenna consists of two ILAs (inverted-L antenna) and an IMN (impedance matching network). The bandwidth widening method based on the IMN design enables the multiple-frequency bandwidths to be simultaneously widened for the purpose of supporting the carrier aggregation technology. The proposed IMN consists of an L-section transformer and a multiple-frequency series-parallel resonators. The L-section transformer facilitates the impedance of an arbitrary load to increase with a constant transforming factor with respect to the frequency through the exact equivalent RLC circuit of an L-section transformer. After the impedance transforming, the multiplenot-frequency series-parallel resonators can simultaneously widen the bandwidths in each band. For arbitrary input impedance of ILA, bandwidths in each of the low-band (0.7 - 1 GHz) / high-band (1.6 - 2.3 GHz) or the low-band (0.7 - 1 GHz) / middle-band (1.5 - 2.1 GHz) / high-band (2.6 - 2.8 GHz) can be simultaneously widened with the proposed impedance matching network (IMN), and the corresponding design is quite systematical. Therefore, the IMN can be designed for ILAs with various form factors. For an ILA with a height of 8 mm, the measured bandwidths of the dual-frequency antenna ensuring that the total efficiency Etot is greater than -3 dB are 365 MHz and 715 MHz in the low- and high-bands, respectively, with implementation of up to Lv. 2.