If you are looking for a portable, relatively lightweight and easily constructed target, then you could do far worse than a tripod design.
The model I made here is constructed using relatively cheap lumber and is held together with M12 bolts and wingnuts. The end grain target is resting on two arms which are close enough together than a log round can sit in place just as easily.
An additional feature is a tip I picked up from Mike Gross of the OSM Knife and Tomahawk Throwers Academy (you can find the details in my resources section) – the target is held under tension using a bungee cord and two ring eyelets, one of which is screwed into the target’s backplate and the other into the rear leg of the structure. This is especially useful if heavier throwing weapons such as tomahawks or axes are being sent down range.