| With the development of wireless communication technology, antennas are required torealize various functions at the same time. For the purpose of the miniature design, themulti-band antenna as a good candidate is often adopted to meet the above requirements Thedemand for the design of an antenna with compact size and multiband operation has increased,because of the rapid development of high performance compact multi-band wireless terminal.Along with the up-growth of various wireless communication services and broadband dataservices, the multiple antenna technology emerges as the times require. Duo to the limitedspace of the wireless terminal device, how to reduce the mutual coupling between arrayelements is one of the core problems of multiple antenna technology. In this paper, combinedwith the scientific researches and the requirements of all kinds of wireless communicationsystem, wireless terminal antenna and its decoupling technology are researched. The author’smajor contributions are as follows:1. The wireless terminal antennas were studied.(1) For wireless devices antenna with thecharacteristics of multiple frequency band, broadband, miniaturization as so on, using thefollowing method: antenna form mainly adopts monopole antenna and PIFA antenna; resonantstrips method, multiple slit method and meander line method are adopted to achieve a goodantenna for multi-band characteristics; And mainly through improvement of the feeding mode,the common microstrip feed is modified to coupling feed and planar sleeve feed. In PIFA,probe feed is improved to a trapezoidal flat feed, to further extend antenna impedancebandwidth on the basis of the realization of multi band operating.; On this basis, the toploading and bending branches section method are employed to achieve the miniaturization ofantenna.(2) In the DVB-H monopole antenna design, the effect on the performance of theantenna carrier metal box is analyzed. According to the practical application of mobile phone,the optimum angle is fixed as150degree.(3) In the3G PIFA antenna design, the PIFAantenna excited double strips has1/8and1/4wavelength dual resonant modes, realizing thedouble broadband characteristics.2. The ground branches decoupling technique of the wireless terminal equipment formultiple antennas was investigated. Careful analysis of the coupling effect on the positionbetween the double antennas in the wireless terminal device: when the dual-antenna placed injuxtaposition, it results in strong coupling that the antenna unit in the strong near field regionof the other antenna unit,. By introducing another coupling path on the ground plane, controlling the amplitude and phase of the coupling field to offset the original field is groundbranches decoupling technique. According to the method mentioned above, a singlefrequency dual-antenna wireless device system is proposed. A coupling element of inverted Eshape ground branches structure is composed of the three vertical strips and a horizontal strip.Adjusting the longest vertical branch in the middle can control the amplitude and phase ofcoupling field; Adjusting the horizontal branch and two shorter vertical branches can changethe resonant frequency of the coupling element. The mutual coupling between antennaelements is obviously reduced, coupling coefficient S21=-46.7dB at2.45GHz, improvingabout20dB comparing with the antenna elements without the ground branches structure.Similarly, a dual-band dual-antenna system is proposed. A dual inverted E shape groundbranches structure is composed of five vertical branches and two horizontal branches. Twoupper and two lower branches effect on mutual coupling in two frequency bands (2.45/5.2GHz) respectively. In the working bands, the isolation between the two ports is less than-30dB. Ground branches structure is easy to realize. And adopting the bending technology, theground branches structure is generally small in size, suitable for decoupling between theantenna elements in small mobile terminals.3. The slot decoupling technique for wireless terminal antennas was researched. Whenslot length is about1/4wavelength at resonant frequency, the mutual coupling is theminimum. As the slot number increases, the impedance bandwidth is mismatch and themutual coupling decreases. When the slot number is reasonable, impedance characteristicsand mutual coupling characteristics are obtained better. A dual-frequency high isolation twoelements antenna is designed using the inverted T shape and double L shaped slot structures.After adding T slot structure, two antenna coupling decreases in the lower band. And afteradding a double L shaped slot, two antenna coupling is reduced in upper band. The totalfrequency range basically is less than-20dB. And compared with the1/4wavelength slot,section2resonator size decreases. The height reduced from14.6mm to4mm and reduced72.6%. Using a plurality of resonator slot structure can effectively reduce the slot size. It canalso be used for decoupling of small mobile terminal antenna element.4. The decoupling network technology for the wireless terminal device was studied. Putforward two kinds of decoupling network design method:(1) the microstrip line decouplingnetwork (2) eigenmode decoupling network. In order to avoid lumped element testingsensitivity, using microstrip decoupling network decouples two elements antenna system. Themutual coupling in the impedance bandwidth is less than-15dB. Put forward180ocoupler to work in two units loop antenna system decoupling. Mutual coupling in the impedancebandwidth is less than-20dB. Put forward four3dB bridge and shift phase composition of themixed network to work in four units antenna loop decoupling. The mutual coupling ofantenna system is less than-15dB in the impedance bandwidth. Using network decoupling,antenna unit design and network design can be done separately, which simplifies thecomplexity of joint optimization. Because of its larger size, it generally applicable tolimitation of size less rigorous multiple antenna system. |
