# Tune a microstrip notch

Channel: development; package: 2.0.0rc1; source: 2c32b7cf79b796fae825bfa08fc73d9914e61723

Page: https://remilab.ai/rfx/gallery/microstrip-notch/
Source: https://github.com/bk-squared/rfx/blob/2c32b7cf79b796fae825bfa08fc73d9914e61723/docs/public/gallery/microstrip-notch.mdx

A short open-ended branch attached to a microstrip line acts as a resonant stub.
Changing its length changes the frequencies that pass through the line. It is a
compact way to connect a geometric design variable, a frequency response and a
local field pattern.

Historical visualization. The design-path and field films use different stub lengths. They illustrate the same structure family, not one jointly reproduced result.

  ![Video poster](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_phase.jpg)

    [source](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_phase.mp4)

    [Download the field replay](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_phase.mp4).
  
  The normalized real part of the complex electric field, Ez, as its phase is advanced. The x/y axes are millimeters. This is a single-frequency DFT phasor replay: it shows relative phase and standing-wave structure, not pulse propagation or arrival time.

## Read the model

| Part | Meaning |
|---|---|
| Structure | A planar microstrip line with an open-ended side branch |
| Materials | Conducting trace and ground with a dielectric substrate |
| Design variable | The open-stub length |
| Measured response | Transmission through the line, S21, over frequency |
| Field panel | A normalized Ez slice at one frequency |

The field movie uses a 7.22 mm stub. The final spectrum associated with the
archived design path uses 7.14 mm. The field panel therefore explains the local
mechanism without certifying the final design-path spectrum.

## Follow the design path

  ![Video poster](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_path.jpg)

    [source](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_path.mp4)

    [Download the design path](https://remilab.ai/rfx/gallery/assets/showcase-20260927/notch_path.mp4).
  
  The coarse portion of this path is explanatory interpolation. Only the fine-stage sequence of 60 iterations comes from the recorded optimization history. Intermediate drawn positions do not imply additional electromagnetic solves.

## Explore the related source

The versioned [notch research example](https://github.com/bk-squared/rfx/blob/a9054338616b91bb1364699882c2530fa29a0048/validation/tmtt_paper/msl_stub_notch_tuning.py)
contains the model and design objective. It is a full multi-start research
workload: unlike the taper example, it has no short `SMOKE=1` mode.
Read its [run notes](https://github.com/bk-squared/rfx/blob/a9054338616b91bb1364699882c2530fa29a0048/validation/tmtt_paper/README.md)
before executing it from a matching source checkout:

```bash
JAX_PLATFORMS=cpu PYTHONPATH=. python validation/tmtt_paper/msl_stub_notch_tuning.py
```

For a smaller first exercise, use
[Ports and S-Parameters 101](https://github.com/bk-squared/rfx/blob/a9054338616b91bb1364699882c2530fa29a0048/examples/tutorials/ports_and_sparams_101.py).
Keep the excitation, port calculator and reference planes with any new response.

**Try changing:** the stub length. Track where the transmission minimum moves
across the band, and inspect the full curve rather than a single frequency bin.

## Evidence and provenance

These original presentation clips have not been regenerated on the documentation
revision. The exact simulation source revision and a complete raw data bundle are
not available here. The current source link identifies a related model; running
it does not promise byte-for-byte recreation of either film. No current notch-depth,
gradient-accuracy or cross-solver agreement is claimed by this page.

[Media catalog and SHA-256 hashes](https://remilab.ai/rfx/gallery/assets/showcase-20260927/media-catalog.json) ·
[Sources & ports](https://remilab.ai/rfx/api/sources-ports/) ·
[Support Boundaries](https://remilab.ai/rfx/support/) ·
[Visual manual](https://remilab.ai/rfx/gallery/visual-manual/)