Alaris Antennas manufactures naval monitoring antennas.
There are 2 approaches: Omni directional vs rotating high gain directional antennas.
OMNI-A0205 Product Description:
This vertically polarised omni-directional antenna consists of an active antenna array, covering 20 MHz to 6000 MHz. The antennas are combined under one compact radome and output in either a single (OMNI-A0205-01) or two connectors (OMNI-A0205-02). The active part of the antenna protects the system from excessive field strengths and boosts low level signals.
SYST-A0005 Product Description:
The SYST-A0005 is a shipborne rotatable antenna system used for wideband detection and monitoring of communication signals. It consists of two LPDA antennas fitted to a single vertical mast, mounted on a rotator. The rotator can be aimed at all angles and is controlled via software.