The video shows the inside of the box which, as you’d expect, is a toroid with a few turns of wire. The proposed antenna is an end-fed dipole fed with the unun. These are somewhat controversial ...

"Here, we report that microwave toroidal pulses can be launched by a transient finite-aperture broadband horn antenna emitter ...

[N2MXX] has an end fed antenna winder design that also contains the necessary matching toroid. This would be just the thing to throw in your backpack for portable operation. The end-fed ...