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last updated 24 Nov 2003
Many types of antennas are reasonably sized at UHF. On the whole, the bigger the better (so long is it tunes up), but the height above ground is more important. A dipole well up in the air will out perfrom a collinear or beam at ground level (don't skimp on the feeder though - buy the best coax you can afford).

Loads of good info :
http://www.cebik.com/radio.html
http://members.fortunecity.com/xe1bef/2meters-antenna.htm

Handheld/Mobile

Antennas designed to match to 50 Ohms when used on a handheld or mounted on a vehicle.

Rubber Duck
Flexible - wire coiled up with a bendy covering. An antenna much shorter than a 1/4 wave, trying to work the same way, but with anywhere from 3dB to 10dB (or even worse) less gain. Only real use is when the 1/4 wave would be too big.
Usually a wound spiral of wire operating in 'normal mode' (i.e. like a 1/4 wave squashed downwards and compressed into a smaller space, rather than the specialised circular polarised helix antenna that radiates out of its end).
http://www.cqham.ru/spiral.htm
Wanna buy one? Try www.panorama.co.uk (interesting page on band colour codes, etc.)

Quarter Wave
1/4 of a wavelength long, the standard 'resonant length' where inductive and capacitive values are equal and cancel each other, leaving only the resistive impedance of 50 Ohms (good match to standard cables then). Needs to work 'against' a groundplane, i.e. for mobile use, mounted on a car roof - or on a handheld (radio and your hand act as a relatively poor groundplane) - HF verticals mounted near ground level need a 'mat' of many radials (buried under the lawn etc). Very basic, radiates in all directions, mostly upwards. Gain similar to a dipole with an infinite ground plane, or (in the real world) practically -3dBd.

5/8 Wave
There's nothing magical about the 5/8 proportion of a wavelength (62.5%), a whip this long has no special properties - a coil is needed to bring the antenna into resonance. It just happens to be close to the limit (0.64 of a wavelength) to which you can extend a single element (1/4 wave style) antenna before the radiation pattern breaks up in undesirable ways. By making the whip as long as possible compared to a 1/4 wave, we get a lower angle of radiation and a squashed radiation pattern (less signal goes upwards) and so a higher effective gain (3dB) than a 1/4 wave. Popular for mobile use, but they can lead to worse results in hilly areas as less signal gets up into the hills. If used on a handheld, you'll need to keep it vertical - which is why manufacturers usually provide 1/4 waves instead. 7/8 waves are slightly different, they are collinears - a 1/4 wave (2/8) combined with a 5/8 section, yielding a dB or so more than a 5/8 on it's own.

Base

Antennas for pole mounting, or for stringing up in a loft space. Designed to present a 50 Ohm impedance to match standard coaxial cables.

(1/2 wave) Dipole
The most simple fundamental antenna for base use, being two quarterwaves in line, connected in the center - each half to one part of the feeder. A 'balanced' antenna that technically needs a balun (BALanced to UNbalanced transformer) to work with unbalanced coax, although it's seldom a problem in practice. Return currents on the outside of the coax can be suppressed with a 'choke balun' (as simple as coiling the coax, which presents an inductance on the outside of the cable that signals can't get past, while leaving the inside unaffected. Or a ferrite solution that performs a similar role). About 73 Ohms at resonance, which isn't a perfect match for 50 Ohm cable but 73/50 means less than 1.5:1 VSWR - acceptable enough (less than 0.2dB loss). Mounted vertically it gives good all around coverage. About 2dB gain over the mythical 'isotropic' (point source that radiates equally in all directions, impossible to make!) due to the nulls end on. Respectable performance unless weak signal working is required. If mast mounted, best results with a 1/4 wave 'stand off'.

Folded Dipole
Same performance as a normal dipole, but as it's a direct short at DC you get the benefit of a path to ground for static or nearby lightning effects - so it's popular for professional use. The 300 Ohms impedance means that a 4:1 balun gives a good match to 75 Ohm feeders.

1/4 wave Ground Plane
Any advance over a dipole? Not really. By adding the extra radials drooping downwards, the impedance drops to 50 Ohms for a better match, but the angle of radiation may be worse (upwards). However, before taking angles of radiation for granted, be aware that it all depends very much upon height above effective ground. Usually a case of try it and see.
A 446 example is at http://www.shell.linux.se/icom2002/pmr/2/index.htm

Discone
It's a disc, with a cone underneath - which can be reduced to as few as 3 horizontal parts and three diagonals under it. Very wide bandwidth, a favourite amongst scanner users, when seen at a property it's a dead give-away that a scanner user lives there! Usually a dipole for any given frequency will outperform it - primarily because the polarisation is horizontal, but also the typical gain is only about 1dBi (-1dBd). Works OK for transmitting but beware the high bandwidth means that it may radiate your harmonics well too! A military version, quite small for it's 225-400 MHz coverage, is made from numerous dangly black rubber ducks and from its appearance it is nicknamed 'dreadlocks'.

J Pole
An end-fed halfwave with similar gain to a dipole, with a non-radiating folded quarter wave section for transforming the high impedance down to 50 Ohms. For loft use, no great advantage over a dipole. DC short for static bleed off, and better matching, but same gain and angle of radiation.
There is an example at http://www.shell.linux.se/icom2002/pmr/3/
Here is a design for a "J-Pole" antenna : http://www.qsl.net/wa3yxk/jpole.html (for 446MHz use, by amateurs in the USA of course!).
A technical examination of these kinds of antennas can be read at : http://free.prohosting.com/~w0rcy/Jpole/jpole.html

Collinears / J Pole Collinear
This page shows how to add further half-waves with folded half-wave stubs to add extra gain : http://members.tripod.com/~AMN92/antenna.htm (or also http://www.tfn.net/~gfloyd7/antenna ) - another way to arrange a collinear is with coils between each element, or reversing polarity from one tuned length of coax to another (e.g. http://www.sadona.com/news/ant_coaxcol.html - tricky to do correctly without test equipment). Basically if the radiating part of the antenna is twice as long as a 1/2 wave, you can expect 3dB gain (twice the gain), etc.
Dual band amateur collinears for 145 and 433 MHz have come to be known as 'white sticks', with 3 to 6 dB gain at VHF, up to 9dB or more at UHF - so they're a very popular effecient antenna solution. The bandwidth usually gives good results for scanner enthusiasts from at least 100-200 MHz, and 380-470 MHz, probably reasonable enough down to 70MHz - although a triple band version (50MHz ham band too) will be best.

5/8 J Pole
A version that has a 5/8 element instead of a 1/2 wave. Supposedly slightly higher gain, although one webpage I read (with LOTS of analysis) said that the 1/2 wave was optimum and 5/8 was a wasted effort! Extra 5/8 elements can be stacked on top, with 3/8 wave folded stubs. A two element has a claimed 4dB gain over a dipole or standard J pole. See http://home.comcast.net/~buck0/5-8thx2j.htm

Full wave dipole / doublet
A dipole where each side is 1/2 wave instead of 1/4 wave. The center is a folded stub 1/4 of a wavelength in size (1/2 wave of wire), with a feedpoint along the stub. Often fed at a higher impedance point using an impedance transforming stub of a 1/2 wave of coax arranged as a 4:1 balun. 3dB gain over a normal 1/2 wave dipole. See http://w1.859.telia.com/~u85920178/antennas/6dbvhf0.htm

Double Extended Zepp
A dipole where each side is 5/8 wave instead of 1/4 wave. The center is a folded stub 0.11 of a wavelength, with a feedpoint along the stub. Often fed at a higher impedance point using an impedance transforming stub of a 1/2 wave of coax arranged as a 4:1 balun. 4dB gain over a normal 1/2 wave dipole. See http://tcarc.ca/2mdez.html and http://www.qsl.net/wd8rif/text/zepp.txt

Stacked Dipoles
You can get useful extra gain by using more than 1 antenna. They need to be spaced properly, and fed correctly, but it's worth the effort. A '4 stack' made from 4 folded dipoles had wider bandwidth than a four element collinear because away from the design frequency, the wavelength errors accumulate the more collinear elements are in line. 4 stacks are popular with TETRA (the new digital UHF 'blue light' services system). Omni coverage if the dipoles are arranged around the mast, or directional if the dipoles are all directly above/below each other on one side of the mast.

Corner Reflectors
There is scope for experimentation with metal sheets folded once into a V shape, which works like a dish if the antenna is placed in the center of the V at the right point. Might be best to use a speaker-mic, or your head will be in the way :o)

Bobtail Curtain
Vertical polarisation, with forward gain at the expense of side nulls - a 2 element array with 6 verticals gives 13.4dBi : http://www.cebik.com/hs3.html (design for 146MHz - resize by dividing by 446/146)

Beams (Yagi-Uda)
The typical TV antenna. Gains range from a few dB more than a dipole, to 20dB or more - depending primarily upon the 'boom' length (as opposed to the number of elements). The 'directors' bend signal towards the fed element, and a reflector (maybe a mesh sheet even) bounces signal back, focussing yet more power to the fed element (which is often a folded dipole - the 300 Ohms impedance is lowered considerably by the nearby other elements. Technically a balanced antenna requiring a balun - but a good match (when designed well) makes this usually unnecessary. A two element 'beam' designed by HB9CV is popular for 2m use.
When you've got the longest practical beam, the only way to improve matters is to stack several of them together.
A TV antenna can often be pressed into effective service at 446MHz, as the lowest limit of the TV band is nearby at 470MHz - even if a few tweaks are needed it still may be worth playing with. "Yagis have been described as twenty variables suspended in space" - LOL
A page about 400MHz interference to TV reception says "TV aerials designed to work right down to the bottom of the UHF TV band (470MHz) seem to work surprisingly well on 400MHz, even exhibiting some directional properties and gain! If possible avoid the use of wideband aerials." - which suggests that a wideband TV antenna could well give useful results at 446 or even 433 MHz. Considering how cheap some TV antennas are, it may well be worth experimenting.

Log Periodic
A type of beam with a tapered shape. Very wide bandwidth, determined by the length of the longest and shortest elements. Popular for scanner use. Sometimes used for TV antennas.

Dish
A dish focuses the signal onto the feedpoint, because of the parabolic shape. 'Prime focus' means the feedpoint is in the center, 'offset' means it's at the side (as with satellite TV) and is actually a segment of a larger prime focus dish. A typical satellite TV dish can have 30dB gain, but bear in mind its 60cm diameter with the 3cm wavelength of 11000 MHz satellite TV. To be worth considering, the diameter of the dish has to be many times the wavelength, so a dish for 446 MHz (with a wavelength 24 times larger than 11GHz) would have to be rather huge!

Hybrid Quad
4 dB gain over a dipole, if you fancy experimenting...

It should be obvious that for omni-directional use (all directions) there is about a 20dB range of gains from -10dBi for a typical rubber duck on the radio itself, to somewhere around +10dBi as a practical limit on effective collinears. For antennas on the end of a run of coaxial cable, the difference between the simplest dipole and a typical 'white stick' would seldom exceed 10dB, a ratio of 10:1, less than 2 'S-points' on a proper S-meter (there is 78dB between S1 and S9+30). The difference between a signal strength indoors at ground level on a handheld, and on an external antenna outdoors up at roof level with can be a LOT MORE than this (especially in built up areas) - so it's clear that putting an antenna as simple as a dipole up on the chimney is the best thing to do, better to just get one up instead of worrying about what sort of antenna to use, or how to modify your radio for a bit more power. Once you have an aerial up there, you can judge whether a better antenna is worth the trouble - it will give another improvement, but it really is mostly the usual case of location, location, location!

True, the DX and the signals you really want are often 'down in the noise', so every dB of gain helps, but take it one step at a time. From an indoors handheld to a high external antenna makes a MASSIVE difference. Plus, you'll be well placed to take advantage of tropo 'lifts' when they occur. Consider that with just a simple dipole on the amateur 70cm band, there are distant FM repeaters that I cannot normally hear whatsoever, that are S9 or more in good conditions - at least 50dB improvement!

For some interesting insight on the range that can be achieved on the amateur 2m band, I recommend the article "How Far Can I Talk on 2 Meters" by K4MSG (numerous locations on the web, try http://www.k4lrg.org/Training/2M_Talk.html ). This shows how a really dedicated VHF/UHF enthusiast really wants to use SSB or CW with stacked beams on a tower, a masthead preamp and loads of power to get the best results. But this doesn't mean that we can't have fun with low powered FM from a simple antenna on the chimney and a run of moderate quality coax. The fun comes from achieving good results despite the limitations. Nobody really bats an eyelid when Mr. Large-Tower works 1500km, but if we manage half of that with 5W FM it's great, and on straight 446 it would really be something!