One sees online discussions and videos where phase from a NanoVNA display is central to the subject, and more often than not, the use is quite confused.

Let’s look at some examples.

## Example 1

A poster advising on how to measure inductance using a NanoVNA posted a .s1p file of his measurements of a SM inductor of nominally 4.7µH from 1-5MHz and discussed the use of phase in determining the inductance.

Above is a plot of the data in the VNWA PC client. Four values are plotted:

- s11 magnitude;
- s11 phase (°);
- Z magnitude; and
- Z phase (°).

An explanatory note, the y-axis zero for the magnitude plots is the bottom of the chart, for the phase plots it is at the fifth division and the scale is 50°/div.

Since this article is about phase, lets look at the phase plots.

For an ideal inductor, the phase of Z would be 90° independent of frequency. For a good inductor, it will be close to 90° independent of frequency.

In this example, the phase of Z (red) is very close to 90° above about 250kHz, quite as expected for the SM inductor over the measured frequency range (a tribute to the measurer).

Now look at the phase of s11 (orange) over a wide range, it is clearly not the same as the phase of Z.

## Example 2

This example is measurement of a lossy ferrite inductor from 1-30MHz.

Above is a plot of the data in the VNWA PC client. Four values are plotted:

- s11 magnitude;
- s11 phase (°);
- Z magnitude; and
- Z phase (°).

An explanatory note, the y-axis zero for the magnitude plots is the bottom of the chart, for the phase plots it is at the fifth division and the scale is 50°/div.

Since this article is about phase, lets look at the phase plots.

For an ideal inductor, the phase of Z would be 90° independent of frequency. For a good inductor, it will be close to 90° independent of frequency. For a lossy inductor, it will vary from 0-90° depending on the ratio of X/R at the frequency.

In this example, the phase of Z (red) varies from about 87° to 23° over 1-30MHz, quite as might be expected from the datasheets.

Now look at the phase of s11 (orange) over a wide range, it is clearly not the same as the phase of Z.

## Example 3

This example is measurement of a nominally 50+j0Ω load.

Above is a plot of the data in the VNWA PC client. Four values are plotted:

- s11 magnitude;
- s11 phase (°);
- Z magnitude; and
- Z phase (°).

An explanatory note, the y-axis zero for the magnitude plots is the bottom of the chart, for the phase plots it is at the fifth division and the scale is 50°/div.

Since this article is about phase, lets look at the phase plots.

For an ideal 50+j0Ω, the phase of Z will be very small.

In this example, the phase of Z (red) varies and is <0.1° over 1-30MHz, quite as might be expected.

Now look at the phase of s11 (orange) over a wide range, it is clearly not the same as the phase of Z.

Some argue that phase of s11 is a good indicator of resonance or a non-reactive load. Whilst it is true that a non-reactive load has s11 phase of 0° OR 180° (depending on its magnitude) , the reality is that measurement noise makes this a pretty impractical metric for that purpose.

## Which is appropriate?

It depends on the use.

Very often, users are interested in the phase of Z and mistakenly / unknowingly use phase of s11.

Here is the catch, VNAs and PC clients may not offer a plot of phase of Z, in the plots give above, a custom function was written to plot phase of Z.