PicoVNA™ 106 vector network analyzer

Quad RX four-receiver architecture

In a VNA a swept sine-wave signal source is used to sequentially stimulate the ports

of the interconnect or device under test. The amplitude and phase of the resultant

transmitted and reflected signals appearing at both VNA ports are then received

and measured. To wholly characterize a 2-port device under test (DUT), six pairs of

measurements need to be made: the amplitude and phase of the signal that was emitted

from both ports, and the amplitude and phase of the signal that was received at both

ports for each source. In practice this can be achieved with a reasonable degree of

accuracy with a single source, a transfer switch and two receivers; the latter inputs being

switched through a further pair of transfer switches. Alternatively three receivers can be

used with an additional input transfer switch or, as in the PicoVNA, four receivers can

be used. Using four receivers eliminates the receiver input transfer switch errors (chiefly

leakage and crosstalk) that cannot be corrected. These residual errors are always

present in two- and three-receiver architectures and lead to lower accuracy than that of

the Quad RX design.

Support for 8 and 12-term calibration and the unknown thru

Almost all vector network analyzers are calibrated for twelve error sources (six for each

signal direction). This is the so-called 12-term calibration, which experienced VNA users

are used to performing fairly regularly. In a four-receiver design some error sources

are so reduced that 8-term calibration becomes possible, along with an important

and efficient calibration technique known as the unknown thru. This gives the ability

to use any thru interconnect (including the DUT) during the calibration process, vastly

simplifying the procedure and reducing the number of costly calibration standards that

need to be maintained.

Other I/O

Power (12 to 15 V DC @ 22 W) and USB 2.0 control are located on the rear panel. Trigger

I/O for sweep synchronization and 10 MHz I/O for reference clock synchronization are

available on four BNC sockets.

Bias-Ts

Bias-Ts are often not provided, or

available as costly extras, on other

VNAs. Use the PicoVNA 106’s built-in

bias-Ts to provide a DC bias or test

stimulus to active devices without

the complexity and cost of external

DC-blocks. The bias is supplied from

external power supplies or test sources

routed to the SMB connectors adjacent

to each VNA port.

Use bias-Ts to power an active DUT

DUT

DC pwr

DC pwr

b1

a1

a2

b2

Receivers

Transfer switch

Source

Port 1

Port 2

DUT

Port 2

Port 1

10 MHz reference in /out

USB host connection

+12 V to +15 V DC power

Power on/off switch

Sweep trigger in/out