Scientists at NPL have made significant advancements in metrological traceability for the impedance of coaxial devices operating in the kHz to MHz frequency range.
Coaxial lines are integral to global telecommunications networks, and ensuring metrological traceability for these systems is crucial for their maintenance and development, particularly as they operate at frequencies ranging from DC to hundreds of GHz. Impedance, a key measurement quantity, describes the total opposition a device or circuit presents to the flow of alternating current (AC) at a specific frequency.
Historically, achieving traceability for the impedance of coaxial devices at low frequencies, specifically between 1 kHz and 1 MHz, has posed challenges. The difficulties in obtaining and characterising reference standards at these frequencies have led to the adoption of alternative methods, such as interpolation, which can result in higher uncertainties in measurement outcomes.
Recently, NPL's AC and RF metrologists have developed a novel method for performing traceable measurements of the impedance of coaxial connectorised devices using an LCR meter. This instrument, typically used for measuring low-frequency standards like capacitors, resistors, and inductors, has been adapted to interface with Type-N coaxial devices. A calibration method utilising traceably characterised Short- and Open-circuit standards has been successfully applied to enable traceable impedance measurements of these devices. Compared with established vector network analyser (VNA) methods, this new measurement technique provides impedance and reflection coefficient measurements with significantly lower uncertainties- in some cases, up to ten times lower.
Bridging this gap between AC and RF traceability has the potential to provide benefits to the telecommunications, quantum and energy sectors through increased measurement accuracy at these widely used frequencies.
James Skinner, Higher Scientist, said: Using existing technology in a novel way has achieved a significant improvement in measurement capability. This work is a real breakthrough in an area of RF metrology that has presented challenges for decades.
Murat Celep, Principal Scientist and Science Area Leader, said: This innovative capability has broad applicability across the field of RF metrology and has been documented in a recent publication in the IEEE Transactions on Instrumentation and Measurement.
Find out more here: Metrological Traceability for the Impedance of Coaxial Devices Using an LCR Meter | IEEE Journals & Magazine | IEEE Xplore
07 Jul 2025