Improved Wheeler Cap Method For Microstrip Antenna Efficiency Measurement

As an important part of wireless communication equipment,the antenna is directly related to the quality of communication.Antenna efficiency is one of the antenna performance indicators,but it is often overlooked.Most publicly published literature on antenna research does not give antenna efficiency.One of the reasons is that the measurement of antenna efficiency is difficult,and the accuracy of the measurement is not high.In fact,the antenna efficiency is very important,it directly affects the antenna gain.Therefore,this paper has practical application value to study the low-cost and high-precision antenna efficiency measurement method for microstrip antennas.Commonly used methods of antenna efficiency measurement include pattern integration method,radiometric measurement method,Q value method,reverberation chamber method and Wheeler cap method.Among them,the pattern integration method,radiometric measurement method,Q value method,and reverberation room method are more complicated,time-consuming,low repeatability,and have many limitations.The Wheeler cap method is more suitable for the measurement of the efficiency of the microstrip antenna,but the resonance mode coupling between the antenna and the Wheeler cap causing the antenna input resistance to rise sharply when the resonance is in the antenna operating frequency band,between the Wheeler cap and the ground plate the electromagnetic wave energy leakage and the surface wave generated by the microstrip antenna have an effect on the measurement of the efficiency of the microstrip antenna,which narrows the bandwidth of the antenna efficiency measurement and reduces the accuracy of the antenna efficiency measurement.Therefore,improving the traditional Wheeler cap method has important research significance.The main work of the paper is:(1)According to the dimension design principle of the Wheeler cap and the coupling resistance characteristics between the antenna and the Wheeler cap,the Wheeler cap with a size of 136 mm × 90 mm × 68 mm was designed and manufactured using 3D printing technology,and the length and height were 20 mm adjustable.By adding movable metal conductive plates on the top surface,left and right sides of the Wheeler cap,the problems of narrowing the measurement bandwidth of the antenna efficiency and reducing the measurement accuracy caused by the coupling resistance between the microstrip antenna and the Wheeler cap are overcome.Experiments show that the designed Wheeler cap can effectively reduce the influence of the coupled resonance mode on the efficiency measurement of the microstrip antenna,and improve the accuracy of the measurement of the efficiency of the microstrip antenna in the wide band of 4.8 GHz to 5.6 GHz.It has the characteristics of wide band frequency measurement,high accuracy,good repeatability,and low cost.(2)According to the characteristics of the source-stirred chamber,a source-stirred chamber with a size of 143 mm × 143 mm ×143 mm was designed and manufactured using 3D printing technology,and the electromagnetic band gap was added around the source-stirred chamber.It overcomes the influence of electromagnetic wave energy leakage between the source-stirred chamber and the ground plate and the surface wave energy generated by the microstrip antenna on the efficiency measurement of the microstrip antenna.In addition,the peak method and the modified wide band Wheeler cap method are used to overcome the influence of the coupled resonance mode between the source-stirred chamber and the microstrip antenna on the efficiency measurement of the microstrip antenna.Experiments show that the use of a source-stirred chamber with an electromagnetic band gap effectively avoids electromagnetic wave energy leakage and surface waves generated by the microstrip antenna,and the influence of the coupled resonance mode on the efficiency measurement of the microstrip antenna,improving the accuracy of the measurement of the efficiency of the microstrip antenna in the wide band of 5 GHz to 6 GHz.It has the characteristics of measurement frequency bandwidth,high accuracy,good repeatability,simplicity and convenience...