Nonlinear Transmission Lines Using Substrate Integrated Waveguides in LTCC

The generation and transmission of relatively short duration, broadband, peak pulse power bursts has numerous applications in the communications and defense sectors. In the past, nonlinear transmission lines (NLTLs) have been used to create such broadband pulses. While most NLTL designs are based on nonlinear capacitors or inductors arranged in a ladder network, the method presented here replaces the transmission line with a novel ferroelectric filled waveguide. When a large transient voltage is input to the guide the resulting electric field will cause the polarization field to move into the saturation region. This reduces the effective dielectric permittivity and thus the group velocity of the peak power portion of the wave is faster than all other portions of the pulse. This results in the middle portion of the pulse overtaking the leading edge and “piling-up” energy at the front edge of the pulse, creating what appears to be a temporal compression of the leading edge. The temporal compression results in increased harmonic spectral content. The simulated NLTLs can be fabricated using Substrate Integrated Waveguides (SIW) in low temperature cofired ceramics (LTCC). Closely spaced vias form trenches in the waveguide that are used to create space for the nonlinear dielectric and the trenches are filled with ferroelectric materials using a sol-gel method. The trench dimensions and type of ferroelectric fill material for each layer are determined using a genetic algorithm optimization routine that produces a maximum rise time compression of the input pulse.