| In recent years,with the rapid development and wide application of wireless communication technology,the spectrum resources are increasingly tense.In order to solve this problem,researchers have put forward many methods to improve the spectrum utilization.Cognitive radio technology came into being in this situation.As the transmitter and receiver of wireless communication system,antenna plays a key role.An important task in cognitive radio technology is antenna design.The difference between cognitive radio antenna and common antenna is that it can not only sense the idle situation of spectrum resources in a wide frequency range,but also adjust its communication frequency band to the idle frequency band in time for communication,which is a challenge for antenna design,especially for a single antenna to realize the broadband sensing function and the narrowband switching function at the same time.In order to solve this problem,the ultrawideband(UWB)sensing and narrowband communication functions are switched by using PIN diodes and varactor diodes,and the communication frequency can be reconfigurable in the narrowband communication state based on the UWB planer monopole antenna.The main work and innovation of this paper are as follows:(1)A novel cognitive radio antenna fed by microstrip is proposed,which has the function of UWB sensing and frequency reconfigurable narrowband communication.Based on the planar monopole UWB antenna fed by microstrip line,the UWB sensing function covering 3.3GHz-10.6GHz and the frequency reconfigurable narrowband communication function operating between 3.1GHz-8.1GHz are realized by cut an X-shaped slot on the ground and loading PIN diode and varactor diode on the slot.The design of the antenna is processed and tested to verify the effectiveness of the antenna design.In addition,based on the original structure,DC bias structure is introduced to reduce the influence of DC electric control wire on the radiation performance of the antenna.(2)A novel coplanar waveguide(CPW)fed cognitive radio antenna is proposed,which has the function of UWB sensing and frequency reconfigurable narrowband communication.Based on the planar monopole UWB antenna fed by coplanar waveguide,two symmetrical open slots are cutted on the ground near the feedline,and PIN diodes and varactor diodes are loaded on the slots.Through the on or off state of PIN diodes and different capacitance values of varactor diodes,the cognitive radio antenna with UWB sensing and frequency reconfigurable narrowband communication functions is realized.In addition,a new method of slot loaded diodes is reaserched and applied to the performance improvement of cognitive radio antenna.(3)A novel miniaturized Multiple-input-multiple-output(MIMO)cognitive radio antenna for multipath fading environment is proposed.On the basis of coplanar waveguide feed cognitive radio antenna,a miniaturized MIMO antenna structure is formed by using half cutting technology(the original antenna is cut along the symmetry line),and then the two units are combined to form a miniaturized MIMO antenna with cognitive radio function that can be applied in multipath environment.The isolation between the two elements and the influence of the isolation structure are studied. |
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