Terahertz-bandwidth characteristics of coplanar transmission lines on low permittivity substrates

Coplanar striplines and waveguides capable of supporting ultra-high-frequency pulses over many millimeters of propagation length have been fabricated on low-permittivity substrates, including a durable 1.4-μm-thick membrane. These transmission lines were characterized using broadband pulses from a novel in situ optoelectronic test-signal generator together with an electro-optic probe tip and an optically-based sampling technique. Pulse-propagation characteristics for the coplanar lines on the low-permittivity substrates have been compared in both the time and frequency domains with the transmission behavior of lines on GaAs substrates. A semi-empirical model has also been used to simulate the experimental results with good agreement, helping to indicate the origin of the distortion mechanisms involved. In addition, for the coplanar waveguide structures, waveforms corresponding to the even and odd modes have been individually resolved in the time domain for lines fabricated on the GaAs and membrane substrates