When is longer not better? When you start getting lobes off to sides of the main lobe! The advantages of the 44 and 88 foot doublets is that on 20 meters they radiate at 90 degrees directly off the side of the antenna. With the 88 foot being 3db stronger than the 44 foot doublet.

Aha you think I'll just make the antenna longer and I'll have even more gain. Makes sense except that now you are starting to have other lobes appearing off to the sides of your main lobe. As you don't get something for nothing the energy in those new lobes has to come from your existing lobe.

The following examples are for 20 meters at a height of 35 feet with all radiation going 90 degress off to the side of the antennas.

First there are no side lobes.

Let's lengthen the antenna to 88 feet.Here comes those lobes!

Let's lengthen the antenna to 100 feet.Here are those lobes and there goes our gain!

Now the 100 foot antenna has less gain than the 88 foot version!

The end result of all this is that as the antenna gets longer more and more lobes start to appear. Now at times having those lobes can be a good thing. However when you want most of your radiation coming directly off the sides of your antenna you don't want those lobes. Easier to aim and if you are going portable you usually have a general direction you want to face. So sticking to antenna lengths of 88 feet and below is a pretty safe bet that your radiation will be going the direction you want it to go.

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