Design And Implementation Of A WLAN Band Active Antenna

With the progress of the technology and development of society,wireless communication device is developing toward miniaturization,multifunction and intelligence,which demands more for the performance of antenna.Active antenna has characteristic of higher gain for increasing the distance of signal transmission or improving output signal to noise ratio of the receiver,and it has great significance of research and important value of application in the domain of military,health care,radio astronomy,etc.In this thesis,relevant research and design of WLAN 2.45 GHz active antenna is carried out,and the main work completed is as follows:(1)A filtering power amplifier with harmonic suppression is designed.By transforming the impedance at one port of the bandpass filter directly to the optimized load impedance of the transistor,the output matching network of traditional power amplifier is replaced and co-design of filter and PA is realized.This can effectively reduce the circuit size.Based on the matchingfilter synthesis theory and anti-parallel-coupling technology,a 8.3% bandwidth(centered at 2.4GHz)three-pole bandpass filter is designed as output matching network of the power amplifier to match optimized fundamental impedances for filtering and harmonic suppression.The measured results show that the filtering power amplifier exhibits good bandpass filtering behavior in the passband with more than 35.1 dBm output power and more than 10.1 dB gain.(2)A Quasi-Yagi antenna with metamaterial is designed.The radiator of antenna is dipole which is etched on the opposite side of the substrate,and double-sided parallel-strip is used as balun to reduce the size of antenna.In order to enhance the gain of antenna,negativepermeability metamaterial was loaded in the end-fire direction of the antenna,and the distance between the metamaterial and antenna was obtained by simulation and optimization.The QuasiYagi antenna with 2 rows and 4 columns metamaterial unit cell was simulated and tested.The results show that the antenna has good directional radiation characteristics over 2.3～2.5 GHz with less than-10 dB reflection coefficient and more than 4.5 dBi gain.(3)A negative feedback common source low noise amplifier is designed.The source of transistor is in series with high impedance microstrip line in order to enhance the stability and reduce the effect on noise figure and gain.The complete circuit was simulated and tested.The results show that the low noise amplifier exhibits gain from 11.7 dB to 13.2 dB,noise figure less than 1.1 dB and reflection coefficient less than-10 dB over 2.3～2.5 GHz.