Experience with Low Noise Amplifiers
Chris has several years' experience with low noise amplifiers (LNAs) covering a range of frequencies from VHF to SHF. He has designed and developed various types including GaAs FETs at UHF (~ 800 MHz), bipolar devices at VHF and PHEMT technology types at VHF and SHF. He has performed many noise figure measurements in the past using the legendary HP/Agilent 8972A with the 346A/B noise source and, more recently, the Agilent N8973A noise figure analyzer.
He has a good understanding of noise figure theory and extensive hands-on experience with equipment and components where there has been a tight noise figure requirement. He is familiar with ways of getting reliable results from the HP 8972A with secondary amplifiers, mixers and filters and various down-conversion setups as well as obtaining equivalent results via indirect routes calculated from spectrum analyzer measurements.
He has designed LNAs using noise figure circles helped up by his deep understanding of S-parameters and Smith Chart techniques. In some cases, where data sheet information was limited/unreliable he has generated noise figure circle data manually using a stub tuner setup and a network analyzer, then using this going on to design optimum input match for noise figure.
He has made many measurements of devices and systems with and without frequency conversion and understands the other parameters associated with thermal noise including: single and double sideband measurements, excess noise power and temperature, ENR and noise power density approaches.