Wifi client won't reconnect after channel switch

[code4sex]

INTRO:
I'm working on the custom prototype WiFi device with a reference to "esp32_hardware_design_guidelines_en.pdf" notes.
At the moment, I don't have the pcb antenna connected to the device properly (C15-L4-C14 missing) since the impendance match work is still in progress. However, I tried to go without antenna on a short distance (~20 cm) and still got the device working well.

SETUP:
ESP32 D0WD + (IDF 5.0.1) + wifi_country_t ("JP", ch1 ... ch14, tx_power 80, WIFI_COUNTRY_POLICY_MANUAL or WIFI_COUNTRY_POLICY_AUTO (both options tried)).

STEPS:
- ESP32 operates in SoftAP mode and starts "My_AP" (ch=6)
- client (Win10 laptop) joins "My_AP"
- ESP32 switches to APSTA mode
- ESP32 STA connects to "Neighbour_AP" (ch=12) run on Xiaomi 13T Pro
- naturally, channel switch takes place and ESP32 AP moves from ch=6 to ch=12
- client leaves "My_AP" and I'm always getting three WIFI_EVENT_AP_STADISCONNECTED events one by one:
>> Client left, AID=1, time connected, sec: 37
>> Client left, AID=1, time connected, sec: 37
>> Client left, AID=1, time connected, sec: 38
- ... client never returns

Everything works fine if no channel switch takes place (both channels match).
I can't figure out why my client does not get back...

TO CONSIDER:
The previous prototype run on WROVER kit on IDF 4.4.2 and I don't remember such problems. Yes, client also left after the channel switch but it reconnected back in a while.

POSSIBLE REASON:
Is it a chunked antenna or IDF 5.0.1 issue?

Any ideas to cure this issue highy appreciated!

Also, I'd like to learn how to perform a prior channel switch (before connecting to another AP) without losing a connected client...

[aliarifat794]

The missing components in your antenna circuit (C15-L4-C14) are crucial for impedance matching. It affects signal strength and stability. While your device is working at close range, the absence of a properly tuned antenna can lead to unpredictable behaviour.

[code4sex]

OK, thank you for the reply.
Impendance matching is almost done. Will keep you updated you on the test results.

[code4sex]

(1) This is the intial setup with a detached antenna and no chips (very poor SWR) - this is the version the firmware was tested with client drop off:

01.jpg (299.2 KiB) Viewed 1046 times

(2) Only C15 added (SWR much better) - firmware not tested yet:

02.jpg (298.18 KiB) Viewed 1046 times

(3) Some antenna cutting and C15 (the best SWR obtained):

03.jpg (295.84 KiB) Viewed 1046 times

In all cases L4 and C16 were removed from pcb.

[code4sex]

NEWS:

I ported my firmware to WROOM-32 dev board and run several tests. The table below shows the results:
- "NO" stands for the client leaving and not returning after channel switch
- "YES" stands for transparent channel change without getting WIFI_EVENT_AP_STADISCONNECTED event.

The laptop I used is equipped with Qualcomm QCA9377 802.11ac Wireless Adapter.

tests.jpg (173.88 KiB) Viewed 780 times

It follows that:

(a) antenna has nothing to do with the channel switching problem
(b) looks like there's smth special about IDF wifi stack internals and hardware

Espressif, please help with this issue.