TH2025BS-1 circulator

The TH2025BS-1 circulator is tuned for a frequency range from 2.4 to 2.5 GHz and has been found on AliExpress

Measuring S parameters

The S parameters have been measured using a NanoVNA device in conjunction with the NanoVNA saver software. To measure the performance of the circulator ports 1 and 2 have been attached to a pair of ports and the third port of the circulator has been terminated with 50 Ohms. Note that when you leave the port open the circulator will not work. It only works when you have no reflections, i.e. a matched load as usual for RF systems.

For each combination (there are 6 possible combinations) the VNAs $\mid S_{11} \mid$, i.e. the reflection of the VNAs first port, and it’s $\mid S_{21} \mid$, i.e. the transmission from VNA port 2 to port 1 has been recorded. Those 12 measurements correspond to the 9 S parameters of the circulator. The desired parameters and the connections used are shown in the following table:

VNA port 1 connected to	VNA port 2 connected to	$S_{11}$ on VNA corresponds to	$S_{21}$ on VNA corresponds to
Port 1	Port 2	$S_{11}$	$S_{21}$
Port 1	Port 3	$S_{11}$	$S_{31}$
Port 2	Port 1	$S_{22}$	$S_{12}$
Port 2	Port 3	$S_{22}$	$S_{32}$
Port 3	Port 1	$S_{33}$	$S_{13}$
Port 3	Port 2	$S_{33}$	$S_{23}$

Parameter	Measurement	Estimate around 2.4 GHz
$S_{11}$		$\approx 0$
$S_{12}$		$\approx 0$
$S_{13}$		$\approx 1$
$S_{21}$		$\approx 1$
$S_{22}$		$\approx 0$
$S_{23}$		$\approx 0$
$S_{31}$		$\approx 0$
$S_{32}$		$\approx 1$
$S_{33}$		$\approx 0$

This leads to an estimate for the following S-parameter matrix:

[ \begin{pmatrix} S_{11} & S_{21} & S_{31} \\ S_{12} & S_{22} & S_{32} \\ S_{13} & S_{23} & S_{33} \end{pmatrix} \\ \begin{pmatrix} 0 & 0 & 1 \\ 1 & 0 & 0 \\ 0 & 1 & 0 \end{pmatrix} ]