ABSTRACT
The low-pass filter is a fundamental building block from which electronic warfare systems are built. Modern warfare in the electromagnetic spectrum occurs over all timescales and frequencies, to transmit and receive very long or very short pulses of very narrow or very wide bandwidth. A fighter aircraft that only flies at a constant velocity is vulnerable to detection and destruction. So too is a user of the spectrum who chooses to only operate at a single timescale or frequency. Agility is the key in electronic warfare and low-pass filtering is one of the low-level digital mechanisms for manoeuvre in this domain. By increasing and decreasing the bandwidth of a low-pass filter, thus decreasing and increasing its pulse duration, the engineer has the ability to shift energy concentration (i.e. power) between frequency and time. The tutorial is intended to help recent engineering graduates design low-pass digital filters for this purpose. The theoretical foundations of digital low-pass filters are presented, i.e. the theory of linear time-invariant signals-and-systems. Non-recursive filters with a Finite Impulse Response (FIR) are covered first, followed by recursive filters with an Infinite Impulse Response (IIR). Simple procedures for the design of both FIR and IIR filters from first principles are described. They are then applied to the problem of radio communication and used to concentrate energy in time or frequency. Expressions to predict link quality (i.e. symbol resolvability) from the parameters of the pulse-shaping filters in a noisy channel are also derived.

BIOGRAPHY
Hugh L. Kennedy received his B.E. and Ph.D. degrees from The University of New South Wales in 1993 and 2000, respectively. Since then, he has worked for Academia, Industry and Government on the design, development and integration of software systems for sensor signal and data processing in defence applications. His research interests include detection, tracking and control.