Although a variety of instruments measure power, the most accurate
instrument is a power meter and a power sensor. The sensor is an RF
power-to-voltage transducer. The power meter displays the detected
voltage as a value of power in log (dBm) or linear (watts) units. Typical
power meter instrumentation accuracy will be in the order of hundredths
of a dB, while other instruments (i.e., spectrum analyzers, network
analyzers) will have power measurement accuracies in the tenths of dBs
or more. One of the main differences between the instruments is that of
frequency selective measurements. Frequency selective measurements
attempt to determine the power within a specified bandwidth. The
traditional Power Meter is not frequency selective in the sense that it
measures the average power over the full frequency range of the sensor
and will include the power of the carrier as well as any harmonics which
may be generated. A Spectrum Analyzer provides a frequency selective
measurement since it measures in a particular Resolution Bandwidth. The
lack of frequency selectivity is the main reason why Power Meters measure
down to around -70 dBm and instruments such as a Spectrum Analyzer can
measure much lower than this if narrow resolution bandwidths are used.
Average Power provides the average power delivered over several
cycles and this is the most common power measurement performed.
Average power is defined as the energy transfer rate averaged over many
periods of the lowest frequency in the signal. Average power is also
defined as the power averaged over a specified time interval. The power
meter with sensor only allow to measure the average power, while the
Spectrum Analyzer may be used also for more sophisticated power
measurements (i.e. peak and pulse power, time-gated power, etc.). We are
just interested in average power measurements in the microwave
frequency range.
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Although a variety of instruments measure power, the most accurateinstrument is a power meter and a power sensor. The sensor is an RFpower-to-voltage transducer. The power meter displays the detectedvoltage as a value of power in log (dBm) or linear (watts) units. Typicalpower meter instrumentation accuracy will be in the order of hundredthsof a dB, while other instruments (i.e., spectrum analyzers, networkanalyzers) will have power measurement accuracies in the tenths of dBsor more. One of the main differences between the instruments is that offrequency selective measurements. Frequency selective measurementsattempt to determine the power within a specified bandwidth. Thetraditional Power Meter is not frequency selective in the sense that itmeasures the average power over the full frequency range of the sensorand will include the power of the carrier as well as any harmonics whichmay be generated. A Spectrum Analyzer provides a frequency selectivemeasurement since it measures in a particular Resolution Bandwidth. Thelack of frequency selectivity is the main reason why Power Meters measuredown to around -70 dBm and instruments such as a Spectrum Analyzer canmeasure much lower than this if narrow resolution bandwidths are used.Average Power provides the average power delivered over severalcycles and this is the most common power measurement performed.Average power is defined as the energy transfer rate averaged over manyperiods of the lowest frequency in the signal. Average power is alsodefined as the power averaged over a specified time interval. The powermeter with sensor only allow to measure the average power, while theSpectrum Analyzer may be used also for more sophisticated powermeasurements (i.e. peak and pulse power, time-gated power, etc.). We arejust interested in average power measurements in the microwavefrequency range.93
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