Turn off WiFi adapter

Is WiFi antenna turned off if I disable WiFi adapter in "Adapter settings"?
Why Airplane mode only disconnect WiFi from network, not disable them?

Yes. The antenna connects directly to the Wireless adapter, disabling turns it off. Most Notebooks have a switch mechanism to turn the adapter off, a physical switch or an Fn plus Fx combination or just an Fx key itself.

Airplane mode is intended for temporary use when traveling by air to comply with FAA or Airline rules and make it easier to get back to Wi-Fi. Simply put Wi-Fi is a 2-way radio and as such can interfere with an airplane's instrumentation, in extreme cases lead to a crash.