Ground-based Passive Radar and On-board Beacon for Airborne Target Tracking with GPS based Time Synchronization

Abstract

To achieve the mission objectives of range safety, it is crucial to track the flight trajectory of an airborne target during its flight. Flight instrumentation systems like ground-based radar and on-board transponders are used to track the trajectory of airborne targets. In general, radar transmits a microwave signal to the target, and the transponder in the airborne targets retransmits an encoded microwave signal towards the radar and obtain the range using the round-trip radar range equation. However, this technique involves high-power microwave transmitters that use a large amount of electrical power from hundred kilowatts to few megawatts at peak to meet the link margin requirement. The transmitter deals with very high voltages and tubes, so they often become vulnerable to electrical and microwave damages to the system as well as the environment. It also reduces the reliability and increases the operation and maintenance cost of the radar. In this article, we propose a method using ground-based passive radar and transmitter-enabled onboard radio beacon. In the proposed approach, the airborne targets and passive radars are equipped with dual-band GPS receivers being synchronized with the GPS time to determine the timestamp of transmission and reception of radio pulses at the radar end. The beacon transmits a time-synchronized pulse width modulated signal from the on-board of a target to the passive radar to determine the range using a one-way radar range equation. The proposed method overcomes the requirement of huge electrical power and related issues in the radar. It also optimizes power usage and improves the power security of airborne targets by eliminating the involvement of high-power radio transponders. It also enhances the payload capacity of the airborne target with low weight and compact beacons instead of bulky and heavy transponders. An experimental prototype has been implemented using a drone as the airborne target to evaluate the feasibility and accuracy of the proposed method.