A novel approach to design of a squared cosine (Cos2) pulse modulated power amplifier used for airborne navigational applications

Abstract

A pulsed power amplifier that achieves stringent spectral requirements at RF frequencies by significantly reducing the side band radiations using a squared cosine pulse modulation scheme is proposed. The scheme compliance the requirements of MIL STD 291C, an interface standard for Tactical Air Navigation, TACAN signal. The Squared Cosine baseband is generated using an FPGA by employing a Look-Up table based method. The digitally generated samples from FPGA are passed through a DAC followed by a reconstruction filter for its smoothening. High slew rate Opamp followed by a power MOSFET further amplifies the pulse level and current drive requirements, to implement drain modulation of GaN based RF power amplifier. The designs are tested on a developed board with integrated power amplifier in the frequency band of 1025MHz to 1150MHz in step of 1MHz. The test results are matching with theoretical and simulated results.