Development Of Switch Circuit In802.11n Smart Antenna

As the rapid development of wireless LAN applications,802.11n wireless LAN,which can supply high-quality and high-bandwidth transmission, will be widely applied.802.11n wireless access point uses beam switching smart antenna, combining the hotcommunication technology MIMO and OFDM. The access point can achieve theintelligent adjustment beam, to make sure the user steadily achieve data fast transmission.Switch circuit is an important part of beam switching smart antenna.The dissertation is on the basic of RF circuit design theory and the key switch circuitperformance indicators. Comparing with many switch devices and switch circuit, the PINdiode switch has the advantage of good performance, small size, low cost; it is very fit for802.11n access point.Focus on the key technologies of PIN switch design, the dissertation first researchesthe broadband single-pole multi-throw switch, the structure of which is the PIN of everyswitch leg connecting with the public node. In order to improve the PIN workingfrequency range, the dissertation researches some methods to improve switch isolation. Asto the actual switch design, the dissertation researches microstrip line impedancecontinuity design through reducing mutation. Through adding ground holes next to thesignal hole, it can improve signal hole performance. The dissertation research alsoincludes the good performance of microstrip line to coaxial line transition structure designand actual PCB simulation.On the basis of these key technologies, according to the frequency range of802.11n,we achieved a single-pole three-throw switch used in the2.4-2.484GHz band and asingle-pole four-throw switch used in the5.15-5.85GHz band. Though debug and actualtest, when the switches are ‘ON’, the insert loss is less than1dB and the voltage standingwave ratio of common port is less than1.7. When the switches are ‘OFF’, the isolation ismore than15dB. So the switches have good switch performance, and they can satisfy theuse requirement of802.11n wireless access point. But there is also some differencebetween some simulation data and test data; it needs to be improved in future.