| In order to meet the requirements of higher speed,larger capacity and higher quality of the current communication system,the Ministry of Industry and Information Technology has released a frequency usage plan for 5G systems in the 3000-5000 MHz frequency band(midband).In the initial stage of 5G pre-commercialization,4G mobile Communication and currently widely used mobile communication methods such as Wi-Fi and Wi MAX will not exit immediately.Therefore,it is very important to develop a broadband indoor antenna that is compatible with both the 5G frequency band and the existing common communication frequency bands(Wi-Fi / Wi MAX).To meet the needs of the current indoor communication system,an indoor distributed antenna that can cover the 5G low-frequency band is designed.The main research contents of the paper include:Firstly,the basic theoretical knowledge involved in the article is explained,including the basic parameters of the antenna,the cone oscillator theory,the loop antenna theory,and the directional radiation theory involved in designing a directional antenna.Secondly,a dual-polarized omnidirectional ceiling antenna that works in multiple frequency bands is proposed by using multiple combinations of horizontal and vertical polarizers.The structure of vertically polarized oscillator is an asymmetric double cone to be placed vertically,owning a wide frequency band characteristic.The design of the horizontally polarized oscillator is based on the radiation characteristics of a magnetic dipole realized by an ideal uniform current loop.The low-frequency horizontally polarized vibrator expands the antenna bandwidth using three the structure of a regular arc symmetrical oscillator array and places it outside the double cone oscillator.The intermediate frequency horizontal polarization oscillator uses five symmetrical oscillators to simulate a current loop and is connected with a one-to-five power divider.The nested hole in the middle of the oscillator is convenient to use in combination with the vertically polarized vibrator,the high-frequency vibrator uses the conformal solution with the asymmetrical cone to fully utilize the space and simplify the antenna design.Through the above three combinations,horizontal polarization and vertical polarization have achieved the goal of working in three frequency bands of 698-960 MHz,1710-2700 MHz,and 3300-3800 MHz.Thirdly,based on the wideband characteristics of the cross dipole,a low-frequency oscillator operating in the 698-960 MHz frequency band and a medium-high-frequency oscillator operating in the 1710-3800 MHz frequency band are designed.The two types of oscillator use different feeding structures.The low-frequency oscillator is fed through a more stable structure of the microstrip balan,and the current path is extended by loading a metal pendant at the end of the dipole.The medium and high frequency oscillator improves the existing cross dipole structure to a tapered structure,and the feeding method uses Y-shaped branches coupling feed.By opening U-shaped grooves on the conical oscillator and placing a coupling unit above the radiating oscillator,two new modes are excitated in the high frequency band,and these two modes are controlled by the size of the U-shaped groove and the position and size of the coupling unit.Thereby the bandwidth of the antenna are extended.Finally,a reflecting plate suitable for the above-mentioned directional oscillator is designed,and the coupling problem caused by too close distance between the oscillators is solved.Lastly,combining the theory of antenna wideband and miniaturization,an ultra-wideband omnidirectional ceiling antenna is proposed.The antenna element adopts a monopole form.The current is prolonged by improving the ordinary cone to a stepped cone,reducing the size of the antenna.Further combining the antenna loading technology(such as loading sleeves,shorting branches,disks,etc.)to expand the antenna bandwidth,the antenna impedance bandwidth of-10 d B is 172.4%,which provides a design for this type of antenna. |
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