Increasing the Voltage Modulation Depth of the RF Produced by NLTL

Lumped nonlinear transmission lines (NLTLs) have been studied for the generation of radio frequency (RF) signals in the range of the order of tens of megahertz (MHz) up to a few hundreds of MHz depending on the nonlinear element used in the LC line. The oscillations obtained at the output of these lines are applied in defense mobile platforms and communications systems. Low power NLTLs use varactor diodes as nonlinear elements, which show a strong nonlinear effect with capacitance variation of the order of 90% at their p-n junction with the applied voltage, which is an excellent performance to obtain oscillations at the line output. However, these semiconductor devices operate at low voltage, producing small voltage modulation depth (VMD), low power, and consequently reduced signal range. Looking for increasing the VMD of the signal generated with NLTLs, this work developed a RF amplifier using a metal–oxide–semiconductor field-effect transistor (MOSFET) model RD06HVF1. A 30-section line using varactor diodes MV209 as nonlinear elements can work as an RF source to obtain oscillations with a frequency of 33.3 MHz at the line output. Using SPICE simulations, it has been demonstrated that an amplifier circuit connected to the output of this varactor diode transmission line can produce an increase of the VMD produced at line output from 10.7 to 40 V approximately, thus allowing higher level power to electromagnetic wave propagation and consequently higher signal range. Experimental comparison using a printed circuit board (PCB) prototype with the corresponding simulation will be also shown.