Design improvement of vector network analyzer for high dynamic range measurement

Vector network analyzers (VNAs) are widely used in RF and microwave labs and factories. Almost all modern network analysers suffer from high dynamic range mesurement to some degree. Some have channel crosstalk problems, such as incident source channel crosstalk or receiver channel crosstalk. Others have receiver LO leakage problems, Known as “mixer bounce”. In this paper, a novel vector network analyzer protype is developed, and used for high dynamic range band pass filters measurement. The stopband of the filter appears not as good as it really is. In order to inspect the reasons of this not so good measurement result, we designed and performed a series experiments. With these experiments we prove that the VNA has the “mixer bounce” problem, but not the crosstalk problem. Finally, with proper hardware design improvement by inserting additional amplify and attenuation chain in receiver channel of the VNA, increasing the receivers' reverse isolation and preventing the VNA's LO leakage signal to go out to the VNA's test ports. At the end of the paper, we give the new test results using the VNA being improved, which indicates that the design improvement is successful and the VNA is now fully qualified for high dynamic range measurement applications.