| Low Noise Amplifier is one of the key components of the wireless Receiver, it is the first active component in the system. After several decades'research, it is still a hot topic. The Low Noise Amplifier is widely used in Universe Communication, Radars,Electronic Countermeasures, Telemetry and Remote Mapping , Radio Astronomy , Geodetic , Microwave Communications, etc. The main effect of the LNA is to amplify the weak signals received from the antenna, reduce the noise interference, so that the required information can be demodulated. The basic requirements of the LNA include: low noise figure, enough power gain, reliable work stability, sufficient bandwidth and the wide dynamic range. In addition, their volumes, weights, power consumptions, etc. may be restricted under the different applying condition. At present, the LNA is developed towards to the directions of the higher frequency, lower noise, wider bandwidth, more integration and standardization.On the basis of the linear two-port network theory, several problems in development of the cascade amplifier which include the calculating of the noise coefficient, the designing of the matching circuit and the improving method of the stability of LNA, etc. are summarized in this paper. A low noise amplifier which has a frequency range of 1.9GHz to 2.1GHz was designed by using the microwave circuit simulation software Advanced Design System ,and the Performance Indexes are shown as follows: less than 1dB noise figure, 200MHz bandwidth, more than 30dB gain and the fluctuation within 1.2dB,less than 1.5dB input and output VWSR. This amplifier carries out two-stage amplification by using P-HEMT transistor ATF-54143 and the integrated amplifier module MGA86576 which manufactured by the Agilent company. In the design process, the input and output matching circuit of the amplifier and the bias circuit was designed and optimized by using ADS commercial software. The advantages and disadvantages of several common topologies of the amplifier were analyzed in the paper. The application mode of the hybrid circuit in which microwave discrete components combined with microstrip line was established as well as the bias circuit structure with single power supply. The source-level series negative feedback was introduced during the stability designment and the stability of the amplifier is improved. Conjugate matching technique is used in matching circuit designing in order to math with standard 50?. Considering several Performance Indexes including gain, NF, VSWR, the LNA is further optimized. The simulation result shows: the noise figure is less than 0.7dB, the gain is about 36dB, the input VSWR is less than -18.5dB, the output VSWR is less than -20dB, the properties of the LNA are good .The low noise amplifier's layout is obtained with protel software finally. |
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