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New for November 2022. Once in a while, microwave engineers need to look outside the Smith Chart fox-hole and look at what actually goes on in a system that employs microwave hardware... this page provides one such example.
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Barker codes are named after English physicist Dr. Ronald Hugh Barker. While working with early computers and developing radar, telemetry and even digital speech systems at UK's Signals Research and Development Establishment (SRDE), Barker presented a paper titled "Group Synchronization of Binary Systems" in 1953. The basic idea is to insert a pre-planned binary sequence into a digital data stream, so that a "smart" receiver is able to correlate exactly where transmitted data starts and stops. A "Barker Code" is the key to correlating the data. Barker proposed seven different codes in lengths 2, 3, 4, 5, 7, 11 and 13 bits, each with the property that that sidelobes are all equally low (also known as "ideal auto-correlation"). You can see the codes here on Wikipedia. The greater the length of the code, the higher probability that it won't be accidentally reproduced in the data stream, which could lead to synchronization errors. In the RF world, Barker codes are typically implemented in phase modulation, where signals are either "1" (0 degree phase) or "-1" (180 degree phase). Interestingly, in the many decades following Barker's paper, no one has been able to develop a Barker Code with more than 13 bits.
While we develop a more detailed explanation of Barker Codes, here's a video that explains the concept and its use in radar pulse compression. Thanks to Rohde and Schwarz for the excellent presentation!
Understanding Barker Codes by Rohde and Schwarz
We will add to this page soon, we have been working on Excel spreadsheet of barker codes that is not ready for primetime...
While we are on the subject of "Barkers", here's a video of Vincent Price playing a carnival barker in the 1969 film "More Dead Than Alive". Don't confuse Barker codes with carnival life!
Reference
Barker, R. H., "Group Synchronizing of Binary Digital Systems". Communication Theory, 1953 London: Butterworth. pp. 273–287.