无线家庭网络印制倒F型天线的分析与设计

Analysis and design of printed IFA for WHAN

从电波传播机理出发，分析室内电波的退极化现象，研究WHAN对天线的极化、辐射及阻抗匹配特性的特殊要求．从传输线理论入手，推导出印制IFA输入阻抗的解析武，并据此分析其输入阻抗随其水平分枝长度变化的规律．根据印制IFA各分枝的电流分布特性，得出其空间辐射电场的解析式，从而证明其辐射既具有等向特性又具有交叉极化特性．仿真印制IFA各尺寸参数变化对其输入阻抗和谐振频率的影响效果，给出其规律及设计方法，并设计出一例适用于蓝牙WHAN的小尺寸印制IFA．测试结果表明，在2．4GHz频率附近，电压驻波比为2．0时的带宽约为490MHz，可完全覆盖蓝牙的工作频段2．400～2．484GHz，而且所测方向图也进一步印证该天线确实具有等向辐射特性和交叉极化特性．此外，该天线可与蓝牙模块合为一体，其各种蓝牙产品均已商用，并获江苏省科技进步一等奖．

Starting with radio wave propagation mechanism, the indoor depolarization phenomenon is analyzed, and the special antenna requirements of WHAN （ wireless home area network） for polarization, radiation and impedance match are researched. Proceeding with the transmission line theory, the analytic formula of the input impedance for the printed IFA （ inverted F antenna） is educed, and the regularity of its impedance variation with its horizontal branch length is studied. Based on the current distribution characteristic of each branch of the printed IFA, the analytic formula of the radiation electric field is derived, which proves that the printed IFA has both isotropic radiation and cross polarization characteristics. The impacts of all the dimension parameters on both input impedance and resonant frequency of the printed IFA are simulated, and the impact regularity along with the antenna design method is given as well, based on which a small size printed IFA for Bluetooth WHAN is designed. The experimental results show that around 2. 4 GHz when VSWR （ voltage standing wave ratio） is below 2.0 the band width is about 490 MHz, which is enough for the 2. 400-2. 484 GHz band of Bluetooth, and the measured radiation patterns also testify further that the antenna has both isotropic radiation and cross polarization characteristics. Furthermore, the antenna can be integrated with Bluetooth module, and varieties of Bluetooth products with the antennas are already in commercial usage, which has won Science ＆ Technology Advancement Prize of Jiangsu Province.