8.8.2 Mobile Communications Base Stations
Mobile communications base stations vary their transmitted power with traffic and may use several frequency bands, multiple-input multiple-output antennas, and time-varying beam steering. A field measurement made at one moment is therefore not necessarily representative of the exposure under the defined maximum operating condition.
A base-station assessment should use a standardized method appropriate to the evaluation purpose. Depending on that method, the result may combine in-situ measurements with network or control-channel information and a defined extrapolation to an actual-maximum condition. The operating state, traffic loading, measurement duration, and extrapolation factors should be recorded. For adaptive or beam-steered antennas, sampling must be sufficient to represent the relevant variation in beam direction and power rather than relying on a single short observation.
The assessment should include relevant ambient sources and accessible locations at antenna level as well as at ground level. Close to a large array, measurements may be in the radiating near field and may require spatial sampling or a source-specific computational method in addition to a conventional field survey.
8.8.3 Radar Systems
Radar systems commonly combine high peak-envelope power, short pulses, low duty factor, and a narrow beam that scans or rotates. The assessment must distinguish time-averaged exposure from any applicable brief-exposure requirement. Under RPS S-1, microwave radar is evaluated against the relevant time-averaged restrictions and, where applicable, brief local-exposure provisions expressed through integrated quantities. The instantaneous temporal peak field-strength reference levels apply only within their specified 100 kHz to 10 MHz range; another applicable standard may provide additional pulse provisions. A peak reading alone can greatly overstate average exposure, while an instrument that averages too slowly or cannot respond to the pulse waveform may fail to characterize the quantities required by the exposure standard.
Instrument bandwidth, detector mode, crest-factor capability, dynamic range, triggering, and sampling rate should be suitable for the waveform. Pulse width, pulse repetition frequency, duty factor, scan angle, rotation rate, beamwidth, and dwell time at the measurement position should be obtained from equipment data or verified where necessary. Measurements may need synchronization with the antenna scan, time-domain capture, or a documented calculation that relates peak-envelope power and antenna motion to the relevant averaged or integrated exposure quantity.
The final result should state which quantity and averaging interval it represents. Where both longer-term and short-duration restrictions apply, compliance with one does not remove the need to evaluate the other.