Compact PCB delay line for six-port based instantaneous frequency measurement

The six-port interferometer is well known for its high phase resolution and is therefor used in a wide range of applications like network analysis, displacement sensors and communication systems. In addition, six-port based instantaneous frequency measurement has recently emerged as a promising alternative for instrumentation of wireless resonant sensors, such as surface acoustic wave (SAW) resonators. This paper discusses the specific requirements and design criteria for a compact and cost-effective radio frequency printed circuit board delay line, which is a core component in the overall measurement system for instantaneous frequency measurement. Finally, a compact realization for the 2.4 GHz frequency band is shown and two different surface finishes, electroless nickel immersion gold as well as immersion silver, are experimentally compared.