Non-contacting near-field mapping of planar circuits in microwave frequency band

An ultra-wideband near-field mapping system has been setup to scan the electromagnetic (EM) surface field above planar/PCB circuits. A semi-rigid coaxial electric probe is employed to measure the electric field up to 18 GHz and an improved CPW loop-type magnetic probe with self-resonance-suppression characteristics is used to measure the magnetic field up to more than 10 GHz. In order to verify the performance of our new system, EM surface field measurement were conducted for a short-circuited microstrip line, and a UWB (3.1 GHz - 10.6 GHz) filter using broadside-coupled structure, etc. The results demonstrate that the presented new measurement system is a powerful tool to accurately characterize the behavior of planar circuits in very wide frequency bands. The comparison between the measured results and the reference data validate the good performance of our system. In addition, a further study on extracting the effective dielectric constant of the PCB substrate is also demonstrated with the experimental validation by our system.