Study And Design Of Wideband And High Gain Microstrip Antenna

Antenna is an important part in the wireless communication system.To adapt to the rapid development of modern communication technology,antennas are developing towards the directions of miniaturization,wideband,and high gain.Microstrip antennas have been widely used in various wireless communication regions due to the advantages of compact,easy to fabricate,and easy to integrate.But the disadvantages of narrow bandwidth and low gain significantly limit microstrip antennas'further application.To widen application areas of microstrip antennas,the research works in this paper to broaden the bandwidth and improve the gain of microstrip antennas can be summarized as follows:Firstly,to broaden the bandwidth of microstrip antenna,a compact super wideband microstrip antenna is proposed.The impedance bandwidth of the microstrip antenna is gradually improved by combing the rectangular radiation patch with a ring patch,loading a parasitic patch,slotting and truncating corners of the ground plane.The overall antenna size is 120mm×150mm×1.6mm.The measured results show that the frequency range of S₁₁<-10d B is from 0.65GHz to 6.92GHz,the fractional bandwidth is 166%,the bandwidth ratio is greater than 10:1.Meanwhile,the gain of the antenna vary in the range of1.91d Bi-5.42d Bi,and the radiation patterns show nearly omni-directional characteristic.The proposed antenna is compact in size,simple in structure,and low in cost,and good omnidirectional radiation characteristic is achieved,which meets the practical needs of wireless communication.Secondly,to improve the gain of microstrip antenna,the Fabry-Perot resonant cavity antenna is studied and designed.The Fabry-Perot resonant cavity is established by placing the partially reflective surface parallelly above the microstrip patch antenna.Compared with antenna array,the Fabry-Perot cavity antenna can overcome the disadvantage of low gain for the microstrip antenna,and there is no need to establish array antennas and complex feeding networks.However,due to the narrow bandwidth of the feeding antenna and the limitation of the resonance condition,the impedance bandwidth and gain bandwidth of the Fabry-Perot antenna are inherently narrow.To improve the gain in a wide frequency band,a wideband microstrip antenna and a partially reflective surface which can resonate in a wide frequency band is designed.By combing them,a wideband Fabry-Perot cavity antenna is established.The microstrip antenna has a size of 60mm×60mm×1.6mm.The wideband characteristic of the microstrip antenna is achieved by loading H-shaped and U-shaped parasitic patches around the rectangular radiation patch.According to the simulated results,the operating frequency band of the microstrip antenna is from 5.71GHz to 8.04GHz,the fractional bandwidth is 34%,and the gain is range in 3.38d Bi to 5.30d Bi.The reflection phase of the traditional partially reflective surfaces decrease with the frequency,which makes them can only resonant in a narrow frequency band.But the reflection phase of the designed partially reflective surface increase with the frequency,that is,it has a positive reflection phase gradient,the resonance condition can be satisfied in a wider frequency range.The partially reflective surface is composed of an array of a unit cell.The unit cell consists of two square patches,a substrate,and a metal via,the positive reflection phase gradient range is between6.22GHz-7.90GHz(23.8%).The Fabry-Cavity antenna is fabricated and measured,the measured results show that the operating frequency bandwidth of the Fabry-Perot cavity antenna for S₁₁<-10d B is from 5.69GHz to 8.06GHz,the fractional bandwidth is 34.5%,with a maximum gain of 10.40d Bi.By buliding as a Fabry-Perot Cavity,the gain of the microstrip antenna is effectively enhanced,and the maximum gain enhancement is 5.32dBi at 6.2GHz.