The Research Of Differential Frequency Reconfigurable Antennas

In recent years,wireless communication systems are developing rapidly toward highlyintegrated,multi-function and ultra-wide band,as an indispensable part of the wireless communication system,antennas need to develop and innovate constantly as well.Differentially-fed antenna can directly connect to the RF front-end,avoid using the intermediate section.Reconfigurable antennas have functions of many traditional antennas,thus save much space and can be used to realize diversity.Among reconfigurable antennas,frequency reconfigurable antennas can switch operating frequency according to its working environment,and ensure the stability of other performance like radiation pattern and gain.Therefore,differential frequency reconfigurable antennas finds wide applications in wireless communication systems.In this paper,we mainly study the differential frequency reconfigurable antennas,the antennas are designed according to the following three points:(1)The structure of differential antenna tends to be symmetrical.Therefore,the location of feed points and RF switches on the antenna matter.(2)The main goal of the antenna is to realize the differential feed and frequency reconfigurable,but also require the radiation pattern,polarization to be similar or identical at different work states of the antenna.(3)It is creative to let the antenna use the same feeding network at different work states,and load the PIN diodes on the radiation unit or the feeding network according to the actual situation.Based on these points,this paper proposes three differential frequency reconfigurable antennas with simple structure and good performance,the main contributions are as follows:1.A stacked differential frequency reconfigurable antenna is presented.The antenna only has two layers of substrate and adopts proximity-coupled technique,the air gap between the two substrate layers is only 2.5mm.By controlling a DC bias circuit to change the work states of the four PIN diodes loaded on the two layers of the antenna,the antenna can be switched in two frequency bands,2.37-2.67 GHz and 3.39-3.62 GHz,the experimental results show that good radiation pattern and gain are achieved.The length of the feed line depends on the work state of the antenna.The antenna covers band 2.45 GHz and 3.50 GHz,which demonstrates that the antenna achieved the expected characteristic of differential frequency reconfigurable and has good application prospects.2.A CPW differential frequency reconfigurable antenna is proposed.By designing a DC bias circuit to change the working states of the four PIN diodes,the differential frequency reconfigurable antenna can be reconfigured in two frequency bands,2.02 to 2.89GHz(35.4%)and 3.27 to 3.66GHz(11.3%),and the performance of frequency reconfiguration barely has influence on the antenna's directions,the average gain on two states can achieve 3.18 d Bi and 3.61 d Bi,respectively.This antenna has a compact structure and wide bands which own to the CPW structure,it's also the combination of differential technology and frequency reconfigurable technology,and can be applied to the 2.45 GHz band of WLAN and two bands of Wi MAX,2.45 GHz and 3.50 GHz.3.Firstly,a differential frequency reconfigurable antenna based on dipoles is proposed.The structure of the antenna is compact and symmetrical,by controlling the four PIN diodes on the four ends of the double dipoles,the antenna can change its operating frequency band between 2.31-2.51GHz(8.3%)and 3.45-3.67GHz(6.2%),the radiation patterns on two states are stable and the average gain can achieve 2.63 d Bi and 2.64 d Bi,respectively.After that,we made a lot of improvements on the first antenna and then present an improved dipoles differential frequency reconfigurable antenna,which can be reconfigured in two frequency bands,3.17-4.07GHz(24.9%)and 5.00-6.19GHz(21.3%),it can be applied to the 3.50 GHz band of Wi MAX,two bands 5.25 GHz and 5.80 GHz of WLAN.The measured and simulated results of all performances show that the radiation patterns on two states are stable and the average gain can achieve 2.81 d Bi and 2.95 d Bi,respectively.Compared with the first one,the second antenna is smaller in size and has wider bands and higher gains.Compared with the stacked differential frequency reconfigurable antenna,both of the differential frequency reconfigurable antenna based on dipoles and the improved one use four PIN diodes placed on the radiation part of the antenna to realize frequency reconfiguration,and do not need to change their feeding network on different work states of the antenna,so the structure of these two antennas are more compact which means they are easy to fabricate.These researches enrich the antenna theory and design methods of differential frequency reconfigurable antennas,and provide technical support for future applications.