| Normally, when directly amplifying a RF signal in the same band, the gain is less than 60dB on account of the stability design. Another side, the gain of a receiver is more than 80dB. According to this problem, down-converter is adopted to get the required high gain, by distributing a certain amount of gain in different frequency bands. In this method, it is easy to get a total gain with high level over 80dB. But it’s necessary to amplify the RF signal directly without frequency converter in the digital receiver system, because sampling technology in RF band is applied up to S band in recent years. The received signal is firstly amplified to a required level and then sampled in RF band. In this condition, the 60dB gain of the traditional microwave amplifier module will not able to meet the demand, and a higher gain should be provided.In this paper, based on basic traditional microwave amplifier circuit theories, a technique of getting ultra-high gain in amplifier module has been researched. Some new methods are brought in the paper. These ways, including reducing the working bandwidth, improving the isolation between gain blocks, the design of independent structure with small box, strengthen shielding measures, are adopted in the research. The main design steps are as follows:1, Sub-modules are designed which include the amplifier, attenuator, filter and isolator, and each device is tested to ensure the results meet the design requirements.2, Using CASCADE circuit system simulation software, system simulation is accomplished with these sub-modules and the whole amplifier chain is designed.3, Based on the design, a verifying platform is established with the modules to prove the chain.4, After that, the whole amplifier module is designed including PCB layout, mechanic drawing, system debugging and optimization.5, In a complete test environment, the amplifier module is measured and the data results are analyzed accordingly.A stable amplifier with more than 80dB gain is achieved in the end. Testing results show that the VSWR is less than 1.5, the output power at ldB compression point is more than 15dBm and the spurs rejection is better than 60dB.And also a dynamic range of 50dB is achieved. Finally the amplifier module is applied in a digital receiver project, serving with sufficiently high gain and dynamic range. |
