Boonton 4500B Peak Power Meter - Manual (Page 314)

Boonton 4500B RF Peak Power Analyzer
Application Notes 6-4
Frequency Response. The carrier frequency response of a diode detector is determined
mostly by the diode junction capacitance and the device lead inductances. Accordingly,
the frequency response will vary from detector to detector and cannot be compensated
readily. Power measurements must be corrected by constructing a frequency response
calibration table for each detector.
Mismatch. Sensor impedance matching errors can contribute significantly to
measurement uncertainty, depending on the mismatch between the device under test
(DUT) and the sensor input. This error cannot be easily calibrated out, but can be
minimized by employing an optimum matching circuit at the sensor input.
Signal Harmonics. Measurement errors resulting from harmonics of the carrier
frequency are level-dependent and cannot be calibrated out. In the square-law region of
the detector response (Region A, Figure 6-3), the signal and second harmonic combine on
a root mean square basis. The effects of harmonics on measurement accuracy in this
region are relatively insignificant. However, in the linear region (Region C, Figure 6-3),
the detector responds to the vector sum of the signal and harmonics. Depending on the
relative amplitude and phase relationships between the harmonics and the fundamental,
measurement accuracy may be significantly degraded. Errors caused by even-order
harmonics can be reduced by using balanced diode detectors for the power sensor. This
design responds to the peak-to-peak amplitude of the signal, which remains constant for
any phase relationship between fundamental and even-order harmonics. Unfortunately,
for odd-order harmonics, the peak-to-peak signal amplitude is sensitive to phasing, and
balanced detectors provide no harmonic error improvement.
Noise. For low-level signals, detector noise contributes to measurement uncertainty and
cannot be calibrated out. Balanced detector sensors improve the signal-to-noise ratio by 3
dB, because the signal is twice as large.
Model 4500B FEATURES
The Model 4500B design incorporates several significant features to reduce measurement
error, simplify operation, and speed internal processing. These features include:
Balanced diode sensors enhance error performance by increasing signal-to-noise
and suppressing even-order signal harmonics.
Random sampling achieves wide measurement bandwidth at moderately high
sampling speeds. Waveforms can be displayed for repetitive signals when the
trigger event is stable.
Smart Sensors (sensor-mounted EEPROM) store sensor frequency calibration
and temperature compensation data, eliminating operator entry.
Floating Point Digital Signal Processors for each channel provide high speed
processing for near real-time measurements.
A built-in programmable calibrator which creates a unique calibration table for
each sensor as well as pulsed RF test signals.