Limitations in measurement of leaky waves on open planar transmission lines

This paper documents leakage on a slotline through simulations done in the CST Microwave Studio. This leakage effect is shown for an infinitely large slotline, and also on a line of finite dimensions. The paper shows the difference between fields of infinite dimensions and finite dimensions of the slotline and then the results of measurement of the electric field. The slotline is designed to radiate power into its substrate in the form of leaky waves in a defined frequency range. The field distribution on a fabricated slotline of finite dimensions was measured in the same way as in the case of the microstrip line that was successfully measured in our previous work. The electric field measured above the slotline substrate with the aim of experimental verification of leaky waves is figured out using 3D visualization here. The main aim of the paper is to show that measurement over the substrate is not in general a proper way to verify leaky modes in all types of open planar transmission lines.