A surface field diagnostic technique for printed antennas

The new detection system employs a novel automated homodyne phase and amplitude detector operating over the frequency range 26.5-40 GHz. In addition to providing phase and amplitude information, the homodyne detector is extremely linear and also provides a dynamic range in excess of 80 dB. The scanning network probe technique was originally intended for use as a printed circuit diagnostic at high frequencies above the normal working range of commercially available network analysers. However, it was soon realised that the technique effectively complemented the information provided by network analysers and was more likely to find scientific applications at the lower microwave frequencies rather than at high frequencies above 40 GHz. Conventional network analyser techniques can only be applied to the device ports, hence the designer has no way of accessing the performance of individual internal elements in a large printed circuit. The authors describe a noncontacting scanning probe technique which essentially measures the surface charge density over any planar network, the only requirement being that the substrate can be held flat to better than 1% of the wavelength, and normally a vacuum chuck is used for this purpose. The technique is particularly applicable to fault diagnosis and the optimization of open structures employing the microstrip, slotline and coplanar strip geometries