For people who want as much DAB signal as possible (and most people don’t need a high gain DAB aerial) we stock a 5 element DAB aerial. There are even larger DAB aerial available with even more elements, but, bearing in mind DAB aerials would usually have to be end mounted* I really don’t think any marginal increase in gain (and it would be marginal due to the law of diminishing returns….) is worthwhile for the resulting even larger wind load.
I would estimate that the 5 element DAB aerial would give about 2dB more gain than a 3 element, i.e. about 5dBd.
* In the case of this aerial we would recommend end mounting it because mid mounting would put the pole between the (vertically polarised) elements thus negatively affecting the gain.