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The principal techniques of coding used for secure encrypted communications are first indicated. Then, after a brief recall of the essential points of frequency-agile filters, a second order frequency-hopping bandpass filter operating in current mode and implemented with CCCII is introduced. It necessitates six CCCII only and uses an improved multiple feedback loop connected in such a way that all of its frequency-agile filters of classes 0, 1, 2 and 3 are available. This very low consumption active filter so offers the advantage to have four central frequencies selected digitally for each value of its bias current. Validation results in 0.25 μm SiGe BiCMOS technology are given. They highlight the new perspectives for encrypted communications to be expected from this approach. [ABSTRACT FROM AUTHOR]