s2psee

Open a Touchstone .s2p file and see S11 / S21 in your terminal.

打开 VNA 导出的 .s2p，不用 ADS、不用 MATLAB，一条命令看 S11 / S21。

$ pip install "git+https://github.com/CAOShurong/s2psee.git"
$ s2psee --demo

demo: series 100 nH in 50 ohm   2-port  S  RI  Z0=50 ohm   61 pts   1 MHz - 1 GHz
S11  max -0.11 dB @ 1 GHz   min -44.04 dB @ 1 MHz
S21  max -0.00 dB @ 1 MHz   min -16.07 dB @ 1 GHz   -3 dB @ 159 MHz

S21  (dB)
  -0.0 ██████████████████████████████████│
  -1.8                                   ██████│
  -3.6                                         ███│
  -5.4                                            ██│
  -7.1                                              ██│
  -8.9                                                ██│
 -10.7                                                  ██│
 -12.5                                                    ██│
 -14.3                                                      ██│
 -16.1                                                        █
       1 MHz                                              1 GHz  (log f)

--demo is a series 100 nH inductor between 50 ohm ports. Theory puts |S21| = -3 dB at 159 MHz (wL = 2 Z0); the interpolated crossing in that plot is 159 MHz.

Point it at a real file from a VNA or simulator:

$ s2psee filter.s2p
$ s2psee antenna.s1p --trace S11
$ s2psee antenna.s1p --smith
$ s2psee filter.s2p --phase --trace S21
$ s2psee after.s2p --compare before.s2p

--compare interpolates the second file onto this file's frequency grid and plots ΔdB (this minus the other). Use it after a matching tweak: max |ΔS11| says whether the smith chart actually moved. Different Z0 is noted; different port counts are rejected.

No dependencies. Python 3.9+. The parser is Touchstone v1 (RI / MA / DB, Hz–THz). Two-port data uses the v1 column-major order N11 N21 N12 N22.

$ pipx run --spec git+https://github.com/CAOShurong/s2psee.git s2psee --demo

What it will not do

This is a viewer, not a VNA, not ADS, and not scikit-rf.

• It plots S-parameters only. A file whose option line says Y, Z, H or G is rejected with that reason — convert or re-export as S.
• Touchstone v2 keywords other than [Number of Ports] are skipped; noise blocks stop the parse. If your file is a v2 .ts with mixed networks, use a full RF library.
• The default picture is a log-frequency terminal sketch of magnitude, phase, or VSWR. --smith is an ASCII Γ-plane sketch of S11 (unit circle + r=1). It is not a calibrated Smith chart and it does not de-embed, gate, or calibrate.
• --compare is a magnitude-dB difference after linear Re/Im interpolation. It is not a vector-calibrated delta, and it does not resample onto a new VNA sweep grid beyond this file's points.
• The −3 dB marker is linear interpolation between two samples of |Sij|. It is not a fitted pole.

License

MIT. Touchstone is a trademark of the relevant standards body; this project is not affiliated with them.