Nothing 'new' or 'magic' in this, it's just a different 'way' of thinking about antennas and what they do.
An antenna's purpose in life is to radiate 'stuff' so that it gets from here to there. A 'perfect' antenna would do that no matter where it's mounted or how, under almost every conceivable propagation condition, as efficiently as possible. When you think about those characteristics of that 'perfect' antenna you'll realize that there just ain't no such thing. At least one of those characteristics ain't gonna be 'right' in almost every circumstance (unless you've been granted a miracle). So, the best you can reasonably expect is a less than 'perfect' antenna, just a good one for the particular circumstances you happen to be in at any particular instant. In general, that means that there are a lot of 'almost perfect' antennas around. Nothing wrong with searching for that 'perfect' antenna, just don't expect one'a them 'miracles' too often. So much for 'perfect'.
Getting a signal to go where you want it to go is the idea. Basically, that means you select a pattern of radiation that will cover the places you want to cover. Therre are a huge number of thingys that will affect that, propagation being the primary one. We have absolutely no control over that, 'Momma Nature' does and she doesn't pay much attention to what we want. So you have to live with that variable. (If you can sweet talk 'Momma Nature' into doing anything, would you PLEASE tell me how?)
There are a number of things that determine that radiation pattern for antennas. Length and height being just two of them, and probably what we have the most control over. Certain lengths radiate 'better' than others, have different shapes. Selecting the right 'shape' of that radiation pattern is a biggy! It'll put energy where you want it to go, which is the whole point, right? The 'other end' of that is also a biggy, if you can't hear'em, then you sure ain't gonna talk to them! That's called 'reciprocity', or the reciprocal. That's something else that antennas tend to have. If you get 'lucky', you can hear people unbelievably far away and talk to them, with ridiculously small amounts of power. There are two 'catches' to that happening. You have to catch 'Momma Nature' in a good mood, and everybody else in teh world has to shut up for a minute. Good luck with both!
Height. That's one of those variable thingys, depends on how 'Momma Nature' is feeling. In a very general way, higher is better. There are various limits to that height, the one that I've run into most often was that I just can't get an antenna that high for whatever rea$on. All you can do is the best that you can do, then live with it. Being able to vary height would be very nice! But, that's another one of those thingys that isn't exactly real ea$y to do. Oh well...
Back to antenna length.
There are certain antenna lengths that just have a radiation pattern that works out well. Typically, longer is better till you get to something around 5/8 wave length for a vertical. After that, the pattern sort of changes, sometimes very drastically, almost never in the way you want it to. The shortest length that's typically usable is a 1/4 wave length. That's also the length that's used as a sort of 'standard' for vertical antennas as a minimum. That's not talking about gain comparisons, just a usable length to make pattern comparisons to. The shape and size of that radiation pattern typically gets smaller as the length gets smaller. No way around that, it just is. May not be unusable, but it will never be as good as a 'full sized' antenna of whatever length.
Wave length.
It isn't a matter of inches, feet, or yards, because it depends on what frequency you're talking about. It tends to get shorter as the frequency increases, longer as the frequency decreases. So, that yardstick is frequency variable. Ain't that a fun idea??
There's a difference between wave length also because the speed of an electron is different dpending on what it's passing through, being conducted by. That difference is usually called 'velocity factor'. The distance an electron goes in one cycle in a vacuum is usually found by using the '1005' "magic" number. The distance an electron goes in one cycle in air is usually found by using the "magic" number of '984'. The 'thicker' the substance an electron is going through get's shorter as the stuff get's 'thicker', sort of. (Those "magic" numbers are not exact, but they are certainly close enough unless you wanna do some measuring. Someone has already done that measuring and you can find that information in the ARRL HandBook if you really want to know.)
Crap, gotta get ready for work... later.
- 'Doc
