UFOs are 3D radio frequency transmissions that work similarly to regular RF transmissions, just much more advanced.
Saucers get thier shapes from the shape of their antennea - some saucer shaped, some rod shaped - or cigar shaped, ect. We see certain frequencies on a graph as a wave that goes up and down, but in a 3D depiction, it would be saucer shaped, ergo saucer shaped craft.
They create a inverse signal to the desired bandwidth thereby creating a field about them and once the field is created, propulsion is enguaged by tuning or surfing along a desired frequency.
The fabric of this reality is used as a medium for sending/receiving signal in the same way a tv or radio does through its screen or speaker.
So, most UFO sightings are man caused, but man got the tech from real aliens. They're in the reverse engineering stages of the development, and what we see in the skies are radio projections of these scientists trying to surf the bandwidths in a stable way. So they bob back and forth, and often dissapear very fast, and are often associated with military bases. Of course they are, because they are military projects. And the UFO culture that is predominant is mostly smoke screen to totally keep humanity at-large off-track in reguard to UFOs.
UFO tech is easy to understand, unlike human tech, which is coveted and proprietary. Perhaps, it is an oversight that the aliens never considered when encountering other intelligences - that they'd be like us. So, I think they've wised up to our threat, and when we get too dangerous, they'll have to take us back to the stone ages. Perhaps they'll give us the tech to destroy ourselves with.