A low-cost, professional-grade 6 GHz VNA for both lab and field use
PicoVNA 2 presents standard VNA measurement and calibration simply, intuitively and with efficient usage at its heart. The software offers a comprehensive range of measurements and plot formats in its one, two or four user-configurable measurement channels. All the standard vector network analyzer functions can be seen at a glance.
The PicoVNA 2 software supports a comprehensive range of calibration modes to address single or dual-port workload with male, female or mixed gender interfaces, all with best achievable accuracy (least uncertainty). In some instances only a single calibration kit may be required. As you would expect, the Pico calibration kits are individually serial-numbered and supplied with S-parameter data. This standard-form data is a traceable and accurate record of measured errors for the calibration kit. It can be loaded into the software, which will correct for these errors and those of the instrument during a calibration. Alternatively, you can use a third-party calibration kit and its data, or you can enter its electrical length, parasitic values and polynomial coefficients into the software if these are supplied rather than a profile data set. As for any vector network analyzer, for best accuracy a calibration is performed before a measurement with the same sweep span and frequency steps as the measurement. If, however, a change of sweep settings is necessary for a measurement, the PicoVNA 2 software will for convenience interpolate its corrections to the new sweep settings. An enhanced isolation calibration setting is available for optimum dynamic range when using resolution bandwidths below around 1 kHz.
Reference plane extension (offset) allows you to shift the measurement reference plane away from the point established during calibration. This is useful in removing the path length of assumed ideal interconnecting , connectors cables or microstrip lines from measurements. The PicoVNA 2 software allows independent reference plane extensions on each of the measurement parameters (S11, S22, S12 or S21), either as an automatic re-reference or by manual entry. Independent extensions allow, for example, different extensions on the two ports for S11 and S22 and then thru-line normalization for S21 and S12 transmission comparison with equivalent length thru-line.
When it is unsafe to assume the above ideal interconnecting connectors cables or microstrip lines; for example to achieve greater accuracy or to remove known imperfections in a test setup, we can choose instead to de-embed the interface networks on each measurement port. The PicoVNA 2 software simply requires a full Touchstone .s2p file for the embedded interfacing network on each port. Likewise, defined networks can be embedded into the measurement to achieve a desired simulated measurement. As for a calibration, best accuracy will be achieved when the embedding network is defined at the same frequency points as the intended measurement. Unusually for a vector network analyzer, the PicoVNA 2 software will interpolate where necessary and possible.
System measurement impedance (default 50 Ω) can be mathematically converted to any value between 10 Ω and 200 Ω. The PicoVNA 2 software also supports the use of external matching pads and calibration in the new impedance using a calibration kit of that impedance.
Time domain reflectometry is useful in the measurement of a transmission line; in particular the distance-to-fault location of any discontinuity due to connectors, damage or design error. To achieve this, the PicoVNA 2 software determines from its frequency domain measurements the time domain response to a step input. Using a sweep of harmonically related frequencies, an inverse fast Fourier transform of reflected frequency data (S11) gives the impulse response in the time domain. The impulse response is then integrated to give the step response. Reflected components of the step, occurring at measurable delays after excitation, indicate the type of discontinuity and (assuming a known velocity of propagation) the distance from the calibration plane. A similar technique is used to derive a TDT (time domain transmission) signal from the transmitted signal data (S21). This can be used to measure the pulse response or transition time of amplifiers, filters and other networks. The PicoVNA 2 software supports Hanning and Kaiser–Bessel lowpass filtering on its time-domain IFFT conversions, preserving magnitude and phase, and achieving best resolution. A DC-coupled DUT is essential to the method.
The 1 dB gain compression point of amplifiers and other active devices can be measured using a power sweep, either at a test frequency or over a sweep of test frequencies. The VNA determines the small-signal gain of the amplifier at low input power, and then increases the power and notes the point at which the gain has fallen by 1 dB. This utility uses a second-order curve fit to determine interpolated 1 dB compression points.
AM to PM conversion is a form of signal distortion where changes in the amplitude of a signal produce corresponding changes in the phase of the signal. This type of distortion can have serious impact in digital modulation schemes for which amplitude varies and phase accuracy is important.
The limit lines facility allows six segments to be defined for each displayed plot. These can be extended to 11 segments using an overlapping technique. Visual and audible alarms can be given when a limit line is crossed. All plot formats except Smith chart and polar support limit testing. Peak hold functions are also available.
The supplied Touchstone measurement data for a serial-numbered check standard is loaded into the PicoVNA memory trace as a ‘Reference’ measurement. With a valid, full S-parameter, full-span calibration established and the check standard connected between the test ports, the comparison utility performs a measurement. It then compares and tabulates, at each frequency point, the measurement with the stored ‘Reference’ data. Magnitude and phase difference are tabulated. The utility combines uncertainties for the instrument and test leads (respective specifications) with measurement uncertainty and stability of the check standard (also supplied). The difference between reference and measurement is then compared with total uncertainty, giving a result of ‘pass’ (within uncertainty) or ‘fail’ (outside uncertainty). You can save the comparison dataset for archive or analysis and a Microsoft Excel template (available for download) helps you visualize the comparison and its uncertainties.
This is a very demanding evaluation of an instrument, test leads and the calibration performed, very nearly, to the full specification of the instrument and leads. The test is designed to identify a weak process, or worn, contaminated or damaged system components that might lead to a compromised measurement. To gain a pass, correct calibration procedure must be followed, including the use of torque wrenches to make the connections at calibration and comparison measurements. The uncertainty data provided attempts to take into account the expected variability of your measurement setups when mating the check standard with Pico-supplied PC3.5 or SMA port connectors. There is a wide variation in the quality of commercially available test cables and SMA connectors, and contamination, damage or wear can easily occur. We guarantee that the uncertainty data provided will cover your test setups only when you use Pico-supplied calibration standards, port adaptors and test leads in new condition.
The PicoVNA 2 software provides an ActiveX server, allowing you to write your own software to communicate with the PicoVNA Vector Network Analyzer on Microsoft Windows platforms.
Example code is available via our GitHub organization page, including a toolbox for use with MathWorks MATLAB.