What is measured at the point in the beam where the power has dropped to half transmitted power?

The point in the beam where the power has dropped to half of the transmitted power is known as the beamwidth. This concept is critical in radar and antenna design, as it characterizes the angular extent of the beam emitted or received by an antenna. The beamwidth is defined at the half-power points, which are often referred to as the -3 dB points in terms of power, meaning that at these angles the signal strength is half (or 3 dB down) of the maximum signal strength at the peak of the beam.

By measuring the beamwidth, engineers can assess how focused or wide the antenna beam is, which directly relates to the performance and directional capability of the radar system. A narrower beamwidth typically leads to improved resolution and range but may cover less area, while a wider beamwidth offers broader coverage but reduced resolution.

The other options do not align with the definition of the point where the power drops to half. Spread refers to how a signal disperses or scatters, wavelength is the distance between successive peaks of a wave, and frequency indicates how often the wave cycles per second. None of these concepts specifically relate to the measurement of power at the half-power points within the context of beamwidth.