Extraction of Optimum PWM Levels in LORAN Switching Transmitter for Ground-Based Positioning System

Long-Range-Navigation (LORAN) pulse generator is an essential part of ground-based Local Positioning System (LPS) that provide a specific standard waveform. There are several solutions for design and implementation of the pulse generator. Switching amplifiers using Pulse-Width-Modulation (PWM) technique is one of the solutions that can be used for this purpose. In this paper, the simple PWMwas modified to a multi-level PWM and its optimum levels are extracted to provide a high power LORAN transmitter.  Multi-level PWM provides essential standards of LORAN pulse waveform. In order to provide a transmitter with 1MW power, three- to- eleven levels of PWM using 16 Class D amplifiers has been considered. At constant conditions, such as power and number of amplifier modules, the requirements and specifications of transmitter have been simulated. Simulation results show that in the best case, using eleven levels for PWM,the maximum zero crossing error in the 4th to 12th half-cycle is 16.6 ns and the bandwidth of provided pulse is 5 kHz. Moreover, MMSE and maximum error of peak points in the first eight half-cycles are 0.009 and 0.021 respectively, which are appropriate standards of a LORAN transmitter.