Rohde - Schwarz HE200 is an Active Directional Antenna
Used conjunction with a compact, portable mini-receiver (eg EB200) the HE200 is ideal for tracing signal sources and interfering sources.
The direction is found by pointing the antenna towards the direction of maximum signal voltage.
The overall frequency range from 20 MHz is covered by three exchangeable antenna modules, which handle both vertically and horizontally polarized signals and have almost identical cardioid patterns in both planes.