Design Of Miniaturized Dual-band Monopole Antenna With Defected Ground Structure

Recently,the Internet of Things（IoT）is growing vigorously.As an essential device for the IoT,antenna research applied to IoT has become an important topics in the field of antenna.For the high integration and large installation capacity of the sensor nodes in the IoT system,the antenna applied to the IoT needs to be miniaturized,low cost and easy to inte-grate.Among them,miniaturization is is particularly important.In addition,multi-band is also a requirement of todays communication systems.5.8G WiFi（5.725-5.875GHz）with low communication interference and 5G（3.4-3.6GHz）network with wide cover range will be the main transmission network for IoT applications.Hence,this paper used de-fected ground structure to design a miniaturized dual-band monopole antenna,which can operate in the 5G and 5.8G WiFi bands.The main works and results are as follows:（1）In this paper,an initial model of dual-band antenna is built in Ansoft HFSS through theoretical calculation at first.Then,the size of the antenna is adjusted so that the central resonant points of the initial antenna can locate at 3.5GHz and 5.8GHz,and the bandwidth can cover 3.25-3.65GHz and 5.0-7.0GHz.Finally,the other parameters of the initial antenna are:the size of the antenna is 30mm×30mm,the gain at 3.5GHz and 5.8GHz is 2.8 dB and 3.7 dB respectively,while the main lobe width is 210^?和140^?respectively.（2）The first optimization of the antenna through loading an L-shaped slot on the ground of the initial antenna formed a defected ground structure and reduced the antenna size.Then,the paper analyzes the effects of L-shaped slot on the resonant point,return loss,radiation current,antenna gain,and the effect of L-shaped slot size on the return loss.The size of the antenna,loaded with L-shaped slot,is 25mm×25mm,and the bandwidth is 3.3-3.8GHz and 5.12-6.32GHz,the gain at 3.5GHz and 5.8GHz is 2.2 dB and 3.5 dB respectively,while the main lobe width is 255^?和360^?respectively.（3）The second optimization of the antenna improves the structure of the antenna element and the ground plane.Different from the traditional miniaturized design,this design optimizes the antenna return loss by adjusting the location and size of the antenna ground plane,folding the antenna element simultaneously.The final optimized dual-band monopole antenna is tested after processing.The test results show that:1.The S₁₁of the antenna in the 5G and 5.8G WiFi bands are less than-10dB,means that the antenna has dual-band characteristics;2.The antenna has a miniaturized characteristic and its size is 14mm×14mm;3.The antenna performance meets the design specifications,for the gain at 3.5GHz and 5.8GHz is 2.5 dB and 3.3 dB respectively,and the main lobe width is 135^?和280^?respectively,and the minimum width of the microstrip line is 0.5mm;4.The test results are in good agreement with the simulation results,indicating that the miniaturization design is effective and feasible.