Software Defined Radio as a solution to testing RF avionics

Pulsed radar is an important technology used in both commercial and military aircraft. Learn how Software Defined Instrumentation utilizing Graphical Software Design and COTS PXI RF instrumentation can be configured to simulate and test different types of pulsed radar. This paper will cover fundamentals of pulse generation and analysis as well as advanced techniques such as the simulation of secondary radars that require real time interrogation handling and response generation. Illustrating this will be a case study on TACAN (Tactical Air Navigation) beacon emulation. The TACAN beacon is implemented on generic COTS PXI RF hardware. The functionality is defined in FPGA software. The hardware is reusable by loading and executing application specific FPGA software. TACAN has been around since the late 1950s. It is a military standard that combines distance measuring with direction finding, typically for aircraft to ground station navigation. The TACAN signal is defined in MIL-STD-291C and is ~1GHz. The system is designed to utilize a PXI chassis with an RF downconverter, RF upconverter, and an IF transceiver with an onboard FPGA to receive/analyze a TACAN interrogation and generate a TACAN reply signal. There are two major software tasks for the FPGA identified as follows: TACAN interrogation signal reception with parametric analysis and TACAN ground station composite signal transmission. The receiver will perform a minimal amount of parametric testing on the received pulse pair to create a trigger for the transmission of a response signal. The transmitter is responsible for the response pulse generation that adds a delay to simulate the selected distance in nautical miles and phase relationships to simulate the selected bearing in degrees. Components of the response pulse generation include 15Hz and 135Hz sine wave generation, Morse code identification, and randomly distributed pulses known as squitter to achieve relatively uniform average power. The FPGA is programm- d with visual programming language LabVIEW FPGA from National Instruments.