Baseband: A Breakthrough in Precision Navigation

Abstract

Recent advancements in transponders have made it possible to measure ownship's position to within one or two feet. These transponders make use of a new technology called baseband. By baseband we refer to the generation of an energy pulse function which can be obtained, for example, when a very fast switch is momentarily connected to a direct current electrical power source. When such a pulse function is applied to a microwave antenna, a very short damped oscillation of microwave energy is propagated. This propagation is characterized by extremely short duration (order of nanoseconds), very low average power (order of microwatts, and very broad bandwidth (order of gigahertz). The broad bandwidth of baseband techniques is limited principally by the speed of the switch that generates the step function and by the antenna bandwidth. Baseband contrasts to orthodox pulsed microwave generators that usually modulate a carrier wave with a pulsed modulating wave. The principal advantages of baseband systems are reviewed and discussed in the text, specifically low interference, simplicity, light weight, low power consumption, high ranging accuracy, and relative freedom from multipath and clutter interference effects. The light weight and low power consumption of baseband systems make them ideal for handcarried instruments that can be used for trilateration measurements between moving ships, shorelines, and fixed structures such as offshore drilling platforms. A baseband system has been recently developed and has undergone sea trials for the offshore mooring of 45K TON ships in severe environments. This paper discusses the theory of baseband signaling and describes a system that can be used for offshore exploration, mooring, and docking.