Primary Metrology covers RF and Microwave measurement standards in transmission media such as hollow waveguides, coaxial lines, dielectric waveguides and planar lines in high frequency integrated circuits.
The four main measurement parameters, power, attenuation, impedance and noise, are highly interdependent, and progress in the development of measurement standards in this field requires a predominantly integrated approach. The main application areas for guided-wave standards are broadly those served by the free field RF and Microwave standards, i.e. telecommunications, aerospace, defence, radar, EMC issues and health and safety, and free-field standards depend strongly on guided-wave standards for traceability.
The function of the Power Section is to research, develop and disseminate standards of microwave power. The work is directed at supplying traceability to UKAS and other-accredited laboratories.
Attenuation is a measure of the reduction in power level experienced by a signal as it passes through a circuit. Being a power ratio, attenuation can be directly measured as such over small dynamic ranges. For high dynamic ranges, and high resolution, it is necessary to use systems specifically designed for attenuation measurement.
The impedance of any transmission medium can be stated in a number of ways depending upon the requirement. For standards purposes it is most useful to give the scattering parameters or voltage reflection coefficient that would apply if an item were connected to the ideal of the medium of interest.
Noise measurements at NPL encompass noise sources, amplifier noise and oscillator noise. The commonest of these is measurement of a noise source. Noise sources are usually used to measure the noise of a receiver or amplifier although full characterisation of amplifier noise is a more complex process. Oscillator noise measurement is the measurement of the phase and amplitude noise on a notionally pure signal.