| In recent years,the market scale of intelligent wearable devices has experienced explosive growth,with the shipment volume surging from 1.91 million in 2012 to 220 million in 2019.As the main force of wearable devices,smart watch has been favored by consumers because of its powerful function and portability.However,powerful functions need to be supported by corresponding software and hardware,which means that more hardware needs to be integrated in the limited space of smart watch,which will further compress the space left for antenna design.Due to the limited design space,there are two main design ideas for the smart watch antenna: one is to design the antenna on the bottom plate or side frame of the dial,which can only cover a few frequency bands such as WiFi and Bluetooth;the other is to design the antenna on the watch band of the smart watch.Although the antenna bandwidth is wide,its size is large,and it is easy to break in use.In view of the above problems,this paper systematically studies the structure,principle and performance of the antenna used in the smart watch,and designs three miniaturized and multi-band antenna schemes.Firstly,this paper designs a seven-band bending antennas based on watch straps.As the strap antenna has two states of straightening and bending,a straight plate antenna is designed to simulate the antenna straightening state when the watch is taken off,and its performance after bending is studied;then a curved antenna is designed to simulate the antenna bending state when the watch is worn on the wrist of the consumer.The bent antennas can cover seven frequency bands of GSM850/900(824-960MHz)and GSM 1800/1900/UMTS2100/ LTE2300/LTE2500(1710-2690MHz).Secondly,a zero clearance coupled feed antenna is designed on the side wall of watch by using reconfigurable technology.The antenna is composed of a coupling ring and a coupling ground short-circuit band.Both the coupling ring and the ground shortcircuit band are fed by a T-shaped feed branch.An adjustable capacitor is respectively connected to the earth terminal of both the ring and the short-circuit band to realize reconfiguration and cover the above seven frequency bands.In order to improve the transmission rate and channel capacity of the antenna,using MIMO(multiple inputs and multiple outputs)technology,a six band 2 × 2MIMO antenna with zero clearance is designed on the side wall of the watch.The antenna can cover the GSM850(824-890MHz),GSM1800 / 1900 / UMTS2100 / LTE2300 / LTE2500(1710-2690MHz)six frequency bands.Finally,a slot antenna based on metal frame is proposed.The antenna is slotted on the metal frame,and uses the matching circuit technology to increase the bandwidth.However,due to the small floor of the watch,the impedance matching is not perfect.In order to improve the impedance matching of the antenna,two metal bands are added on the two watchbands to connect with the metal frame of the watch.Finally,it can completely cover the above seven frequency bands.In this paper,five smart watch antennas are simulated.In the required frequency band,the simulation s parameters of the antenna basically meet the corresponding requirements(S11 ≤-6dB,S12 ≤-10dB),and the antenna simulation efficiency also basically meets the corresponding requirements.In addition to the simulation,the zero clearance coupling feed antenna and the metal frame slot antenna are processed and tested.The test efficiency is higher than 20% in the working frequency band of the antenna,which has practical application value. |
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