| In the modern society,the wireless communication rate and capacity are put forward higher requirements,and MIMO(Multiple-Input Multiple-Output)technology can meet the requirements of this application.However,MIMO technologies require the use of multiple antenna structure,which will undoubtedly increase the size and complexity of the communication system.and the use of a multi-polar antenna,can be completed in jointly acquired under the condition of multiple antennas.Nevertheless,with multi-polarized antennas,multiple antenna functions can be performed under antenna co-location conditions.In addition to the information transmission,radio waves can also be used for the transmission of power energy.MPT(microwave power transmission)is one kind of the typical applications.In the microwave frequencies,MPT performs the remote transmission of electromagnetic power in free space.Meanwhile,it can also be used to collect electromagnetic energy from the environment to converte into dc power.Rectifying antenna system is one of the key modules to realize the MPT.Usually,it consists of receiving antenna,input filter,matching circuit,diode rectifier circuit,output of dc filter and load.The input filter is mainly used to suppress second order and third order harmonics resulted from a diode rectifier.If the receiving antenna and input filter functions both are completed by the single receiving antenna to form a harmonic suppression antenna,the system size and insertion loss can be reduced under the premise of improving the system efficiency.Based on the above considerations and using printed slot antenna structure,the dual polarized antenna and harmonic suppression antenna with the planar dimension are designed and analysised.Considering the randomness of the environmental electromagnetic energy,the construction of the harmonic suppression antenna with dual polarization characteristics is also carried out.For the dual polarization MIMO antenna,it consists of the T-shaped slot fed by the coplanar waveguide(CPW)and the open-end slot fed directly by the SMA connector.The open-end slot is inserted into the CPW inner conductor of the T-shaped slot antenna from the other end.So,the symmetry of the antenna structure can be kept,and the open-end slot is located in the strongest electric field zone of the T-shaped slot.By using the polarization orthogonality,good port isolation is achieved.At the same time,the antenna structure also has a smaller size.The experimental results of the antenna prototype show that within the working frequency band the port isolation reaches more than 20 dB.Meanwhile,the antenna presents bidirectional radiation characteristics,and In the direction of the main lobe,the cross polarization level than the main polarization level 40 db,antenna has a two-way radiation characteristics.Loading small size notch in the center of narrow slot element can control the high order harmonics of slot antennas.At this time,even if the narrow slot length is larger,the high order harmonic can be effectively controlled,and the fundamental frequency showed double-frequency broadband characteristics.When the microstrip line of the terminal short circuit is loaded on the narrow slot element of the notch to couple the antenna,the inhibitory effect of the second order harmonic can be further improved.Antenna prototype experiment results show that the relative bandwidth of the work fundamental frequency can reach 38%,and the second order and third order harmonic radiation efficiency is less than 30%.Meanwhile,there are no other parasitic modes at higher frequency side.This antenna also exhibits bidirectional radiation characteristics.In order to make full use of the electromagnetic energy in the surrounding environment,a dual-polarized antenna is designed using a rectangular slot ring,and its two ports are composed of two orthogonal microstrip lines to feed two adjacent rectangular gap edges,respectively.To reduce the antenna size,a slot parallel to the ring side is added at each side.The loaded slots also utilize its band-stop resonance characteristics to achieve high-order harmonic suppression.In order to further improve the harmonic control ability,the microstrip feeds extend and intersect at the antenna center,and then the intersectionpoint is grounded.Antenna prototype results show that the high order harmonic radiation efficiency of two ports both are less than 40%,and the second order harmonic inhibition is more apparent.However,the working fundamental frequency performances the narrowband characteristic,and in this band,the isolation of two port is around 20 dB.The radiation field of each port has a high polarization purity,while the antenna is also bidirectional radiation.According to the performance and characteristics of the proposed antenna,the dual-polarized antenna is suitable for indoor MIMO small stations or MIMO mobile terminal system.On the other hand,the harmonic suppression antennas are suitable for collecting environment electromagnetic energy,,rather than for the microwave power transmission point to point.So the harmonic suppression antennas have more application value for little energy consumption node or equipment,such as the sensors..The above design of antenna in addition to the practical application value,also has the corresponding application reference value in the design of the antenna.In addition to the practical application value,the above proposed antennas also have the reference significance for the corresponding antenna design. |
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