PicoVNA® 100 Series vector network analyzers

Reference plane extension

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

connectors, cables or microstrip lines from measurements. PicoVNA 3 software allows independent

reference plane extensions on each of the measurement parameters (S

11, 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 S

11 and S22 and then through-line normalization for S21 and S12

transmission comparison with equivalent length through-line.

After calibration

ref plane is here

For the measurement we want

the ref plane to be here

Actual device

to be tested

DUT on microstrip test jig

De-embedding embedded port interfaces

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 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 software will interpolate where necessary and possible.

Time-domain transmission and reflectometry measurements

Time-domain reflectometry is useful in the measurement of a

transmission line or component; in particular the distance-to-fault

location of any discontinuity due to connectors, damage or design error.

To achieve this, the PicoVNA 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 (S

11) 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 (S

21). This can be used to measure

the pulse response or transition time of amplifiers, filters and other

networks.

The PicoVNA software supports Hanning and Kaiser–Bessel lowpass

filtering on its time-domain IFFT conversions, preserving magnitude and

phase, and achieving best resolution. Marker readouts include magnitude, time, distance and line impedance in ohms. A DC-coupled DUT is essential to the method. The 8.5 GHz

bandwidth of the PicoVNA 108 supports time-domain pulse transition times down to 58.8 ps, with the PicoVNA 106 reaching 82.7 ps.

Time domain transmission step responses (top) and frequency responses (bottom) of two lowpass filters