Research On Wideband Antenna With Filtering Characteristics

With the rapid development of modern wireless communication technology and the rapid growth of various electronic devices,more and more communication frequency bands are occupied,which makes the limited spectrum resources even more strained.In order to meet the needs of more users,it is necessary to pursue higher spectrum efficiency,which will increase the signal interference between adjacent frequency bands.By adding filters to the system,the interference of unwanted signals to the communication system can be eliminated with expense of the increase of system size and loss.In addition,due to the extensive application of MIMO(multiple input,multiple output)technology in 5G mobile communication system,the number of antennas and filters will also show an explosive increase,which will increase the size and loss of the system even more seriously.In order to realize the miniaturization and low consumption of the communication system,the concept of the filtering antenna was proposed.Filtering antenna integrates the filter into the antenna,with filtering and radiating functions simultaneously,which not only saves space and cost,but also helps to reduce the interference between the antennas working in adjacent frequency bands.In this thesis,the wideband filtering antenna is studied deeply,and several different types of filtering antenna were designed.The research content of this paper mainly includes the following parts:1.A broadband magnetoelectric dipole antenna with approximate elliptical filter response was designed.Different from the traditional magnetoelectric dipole antenna,a forked microstrip line coupled feed was utilized,which extends the antenna's bandwidth.Reasonable use of the intrinsic zero of the lower edge of the magnetoelectric dipole antenna can reduce the complexity of the antenna without introducing other filtering structures.Moreover,a mathematical model was proposed to explain its generating principle.The four driving branches were directly connected to the short-circuited wall of the magnetoelectric dipole,which is used to excite the plane dipole.Its working principle can be explained by equivalent circuit.In order to further suppress the out-of-band radiation in the lower stopband,the antenna introduced two short-circuited symmetrical u-shaped branches with a length of0.25 wavelength,and another radiation null was generated in the lower stopband.In order to verify the correctness of the analysis,an antenna prototype was fabricated and measured.The measured results showed that the antenna achieved an operating bandwidth of 53.5%(2.95-5.1 GHz),and the out-of-band suppression level was greater than 17.9 d B.In addition,the antenna obtained a radiation gain of 8 d Bi and a good radiation pattern over the entire operating bandwidth.2.A broadband dual-polarization magnetoelectric dipole filtering antenna was designed.The antenna was composed of radiation patches,a short-circuited wall,a ground plane and feed structure.The antenna's bandwidth was greatly expanded by means of microstrip-slot coupled feed.By using the inherent characteristics of the magnetoelectric dipole antenna,a radiation null can be achieved at the lower edge of the passband without introducing a filtering structure,which reduces the complexity of the design.A parasitic patch is nested inside the radiation patch and thus a radiation null was successfully introduced to the upper edge of the passband,resulting in a good filtering response.The simulated results showed that the antenna achieved a relative bandwidth of 78%(2.65-5.69 GHz).The out-of-band suppression level was higher than 18 d B.In the whole operating band,the antenna obtained a radiation gain of 8 d Bi and good radiation patterns.3.A wideband high gain triple-slot bidirectional filtering antenna was designed.Based on the theory of radiation cancellation,two parasitic radiation slots with different lengths were introduced into a traditional slot antenna and thus two radiation nulls are introduced beside the upper and lower passband edges,achieving a good filtering selectivity.In addition,the important parameters that affect the antenna performance were analyzed.The measured results showed that the antenna obtained an operating bandwidth of 56.8%(2.9-5.2 GHz).The out-of-band suppression level at lower stopband is greater than 10 d Bi and more than15 d B for upper stopband.Over the whole passband,the antenna realized a high gain of 5d Bi and stable radiation patterns.Furthermore,a broadband high gain triple-slot unidirectional antenna was designed.A metal reflector was introduced at about a quarter wavelength below the antenna to achieve unidirectional radiation.At the same time,four copper stubs were introduced at the four corners of the antenna.On the one hand,the spurious radiation at 1.6 GHz was suppressed;On the other hand,the antenna structure was well supported.In addition,an equivalent model was established to explain the principle of spurious radiation suppression.For verification,an antenna prototype was fabricated and measured.The measured results agreed well with the simulated results.The antenna achieved a wide impedance bandwidth of 56.8%(2.9-5.2 GHz).The measured results showed that the antenna obtained an operating bandwidth of 56.8%(2.9-5.2 GHz).The out-of-band suppression level at lower stopband is greater than 28 d Bi and more than 23 d B for upper stopband,showing a good filtering characteristic.Meanwhile,the antenna also achieved a high antenna gain of 10 d Bi and stable radiation patterns in the whole operating bandwidth.