Finite element analysis of open-ended coaxial lines

The open-ended coaxial line is used as a probe for sensing complex permittivity since the reflection coefficient varies as a function of both frequency and permittivity. Results from a finite element analysis of the open-ended coaxial line compare well with published results. The finite element simulations are useful in analyzing how well the simplifying assumptions made with a theoretical analysis match an actual structure. The agreement between an idealized probe having an infinite ground plane and a probe with a finite ground plane was quite good. The difference was less than 0.004 for air; for lossy materials (such as water), the difference would be smaller. It is concluded that finite element analysis can be used as a tool to examine the effects on model accuracy of finite ground planes as well as profiles within the ground plane.<>