1/4 wave elements and 3/4 wave loaded elements are in the main wide-banded because there are no coils or other components to lower the Q.
This is a sweep from Tom M0RMY, showing his Classic with inverted L for 80m. It covers the whole HF spectrum.
The third mild dip from the left is the harmonic for 80m which is fairly near 30m band so if you are using 80m and not 30m, you will need a quick touch of your ATU other than that, you will find that most bands will achieve better than 1.5:1 across the whole band you are interested in.
You can also see the 15m dip, this is the harmonic from 40m.
Note the 3:1 SWR horizontal line which should give you a perspective of the depth of tuning.
This is just basic physics. Always remember to connect some radials (minumum 8 really).