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To compare the results of an S-parameter measurement, consider the example shown in Fig. 2, which uses a 3-to-12-GHz broadband amplifier with a gain of 23 dB as the DUT. In this example, four S-parameters are measured from three different VNAs, two benchtop instruments, and one handheld instrument. All three instruments were configured with a frequency range of 100 MHz to 26.5 GHz, as well as for recording 401 measurement points and operating with an intermediate frequency (IF) bandwidth of 10 kHz. They were calibrated using a full two-port mechanical calibration.

For comparison purposes, the three sets of recorded S-parameters were ported into one of the benchtop instruments and overlaid. As can be seen from Fig. 2, the three sets of measurements are virtually identical except for a deviation in the S21 data from the benchtop instrument, which is signified by the blue trace and only at the high end of the frequency range. There is excellent correlation between the handheld (magenta trace) and the other high-performance benchtop instrument (green trace). Here again, the handheld analyzer shows itself to be ideally suited for S-parameter measurements in the field, as well as for common laboratory applications.

Correlate Handheld And Benchtop Measurements, Fig. 2

When measuring RF power for continuous wave (CW), pulsed, and complex waveforms, a variety of equipment configurations can be used, with the primary component being a power sensor. The power sensor can be configured with a separate power meter, or else connected to a personal computer (PC) or handheld/benchtop instrument through a Universal-Serial-Bus (USB) cable. The PC or handheld/benchtop instrument is then used simply to display the power measurements. Assuming the same power sensor was used for the handheld and benchtop measurement configurations, both should yield extremely close results.

While the power meter is considered the gold standard for RF power measurement, it is possible to conduct power measurements using a handheld instrument only—assuming, of course, that the handheld instrument has the capability to directly measure signal power. For comparison purposes, the table shows the measured power of a CW test signal as a function of frequency. It compares the measured power using a power sensor and meter combination to that of a measurement taken using a handheld instrument with built-in power measurement capability. While using a handheld instrument may not be as accurate as employing a power sensor, the convenience of using a single instrument to measure power in challenging environments and test conditions cannot be overstated.

As the table details, accurate power measurements are possible with a FieldFox handheld analyzer from Agilent Technologies and its Channel Power Meter (CPM) capability. The measurements with the portable instrument are very close to those made with a dedicated power meter and power sensor combination, and can be made across similar frequency ranges as needed. In making use of the CPM capability, all that is required is a short coaxial cable to connect the portable instrument to the test point and for the user to specify a bandwidth to measure the channel power.

Correlate Handheld And Benchtop Measurements, Table

The previous examples effectively demonstrate how to correlate measurement data and clearly show that a modern handheld analyzer is more than capable of performing measurements that have excellent correlation to those recorded from benchtop instruments. One reason this is possible is that modern handhelds utilize some of the same measurement science as their benchtop counterparts. Some high-performance RF and microwave benchtop instruments, for example, rely on custom monolithic microwave integrated circuits (MMICs). Those same MMIC chip designs may also be employed in handheld electronic units to integrate multiple functions into compact, high-performance chipsets.

These highly integrated circuits improve a handheld instrument’s performance and reliability, while also reducing its total power consumption. Additionally, they enable the handheld electronic unit to be configured as different instruments, such as a spectrum analyzer, VNA, power meter, or cable and antenna analyzer, to name a few.

In addition to these technological advances, modern handheld instruments now offer features like automatic alignment and built-in calibration, which enable them to maintain a high level of measurement accuracy across their full frequency range. Such capabilities are a key reason why modern handheld instruments now boast high-performance measurement capabilities consistent with those of benchtop instruments.

When using a handheld instrument for field testing, it is essential to ensure its measurement results closely agree with those recorded using benchtop instruments. Correlating the measurement results is one way technicians and engineers can be assured of their agreement. From the correlation examples provided here, it is clear that modern handheld instruments are well equipped for measurements both in the field and within common laboratory applications. For those seeking further details on correlating measurements between portable/handheld instruments and benchtop instruments, a copy of the application note, “Correlating Microwave Measurements Between Handheld and Benchtop Analyzers,” is available for free download.

Tom Hoppin, Application Consultant

Agilent Technologies, 1400 Fountaingrove Pkwy., Santa Rosa, CA 95403; (707) 528-2672

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