Design considerations in lossy dieletric nonlinear transmission lines

Summary form only given. Nowadays research on nonlinear element transmission lines (NLTLs) is an area of intense study for replacing electronic tubes in compact high power microwave devices in military applications, surveillance and monitoring systems, ultra-wide band radars, etc. Although, great success was achieved using based ferrite inductive element lines up to 1 GHz, attempts to operate at higher frequencies above 100 MHz using capacitive element lines has been described as unpractical due to the capacitor dielectric losses that damp significantly the amplitudes of the RF output oscillations (i.e. negligible voltage modulation depth-VMD). In order to address that, in this paper by means of LT-Spice simulations it will be shown the possibility of producing higher VMD using conventional dielectrics of higher losses at frequencies around 300-400 MHz (with loss tangent > 0.1 and equivalent series resistance-ESR on the order of 1-2 Ω) such as barium titanate (BT) based tiles or lead-manganese-niobate piezoelectric (PMN) ceramics, described so far in the literature in NLTL experiments [1, 2]. Basically, this can be made in simulations by increasing the mismatch at the load (with acceptable decreased RF peak power) and at generator side as well as reducing the number of line sections since attenuation increases for long lines. Other important parameter to be considered in the design of dielectric nonlinear lines is the reduction of the 3 dB down cutoff line frequency, which is much less than the line Bragg frequency calculated, as attenuation constant increases with frequency. Other alternative to be demonstrated by simulations, but at the cost of less number of RF cycles, is the use of a stronger nonlinearity dielectric to reduce the required number of sections (usually 50 or more) and, thus, to minimize the oscillations damping even for high ESRs, although according to our knowledge this material has not been tailored yet.