Types of Antennas.

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1. Bogus Antennas.
   • "Make you whole house wiring a huge TV antenna" or so say the ads for this scam device. All conductors, your body included, are antennas. An antenna designer trys to get a bunch of conductors to feed energy in sync, or constructively in phase so as to collect the energy into one spot. It is improbable random wiring will collect energy and feed it in phase into your receiver. But then you could win a million dollars on a slot machine. I never wasted my time on this scam, or on slot machines, nor should you.
     
     
   • Small Antennas can't violate the laws of Physics. Sorry. Probably an old lamp cord would do as much.
     click on images to enlarge.
   • Ditto regarding small antennas. One of our web site visitors asked about this apparently bogus $130.00 antenna that claims to violate the laws of physics by using a small antenna to get big antenna results. Be skeptical of such claims, especially when smothered in technobable.
     
     
   • This $350 wonder is, perhaps, slightly larger, and maybe of better design. It sure looks artistic. But you may as well use a Picasso for your antenna. This money sucker is small and thus cannot gather the radio signal energy of a far less expensive larger antenna.... thus I brand this one BOGUS, especially as they suck money out of wild claims about HDTV.
   • Off the subject, but of late I have seen a lot of advertising for this kind of BOGUS antenna for cellular telephone handsets. Slapping a circuit card into your cell phone ain't gonna catch nothin' but your money.

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2. The dipole is the fundamental unit of antenna design. The impedance of a dipole at its center frequency is about 70 ohms. Impedance is the ratio of voltage to Amperage combined with the "springyness" of a circuit. in the mechanical sense it is like having a number for torque plus RPM combined with a measure for how much the metal twists in a vehicle power train. In the electrical world an impedance transformer (or any transformer) is exactly like a gear box in the mechanical world. By convention transmitters and commercial receivers are designed to operate with 50 ohm systems, while consumer receivers are designed to operate with 75 ohm systems.
3. Folded dipoles are dipoles with an extra wire. The extra wire changes the dipole impedance to about 300 ohms if the extra wire and dipole wire is the same size.
4. Twin Lead Antennas are a form of folded dipole. This is a small antenna, but at a small price, so you actually get what you pay for. Not much in either case. This guy has the right ideas about how to make your own twin lead antenna.
5. Rabbit Ears.Bunnie ears are still dipoles, and small, and slightly more expensive than twin leads, though they have the advantage that you can move them around the room or outdoors in hopes of finding a better spot to get a signal. Read how I used rabbit ears on this rabbit ear link.
6. This dish clip on antenna is advertised a lot recently. Now, you should recognize this as a twisted folded dipole. Don't expect a lot of this form of dipole. It is, possibly, not better than rabbit ears, in that you cannot move it for best reception. It is outdoors, away from your TV, so maybe it could be better than an indoor antenna, if you are lucky. You will note the similarity to the twin lead type dipole, except you can't move this baby for best signal, or adjust for wavelength. If your reception is less that ideal, don't blame me! Uhg.
7. Turnstile. This is simple. The dipole has a dead spot, so set up one crosswise to the other, feed both dipoles connecting from one to the other with 1/4 wave length delay line, and you can get an omnidirectional antenna. Great if all stations, being in differing directions have perfect signals at your location. This antenna is sold as an FM Band antenna, with dipoles, usually in the "folded" form cut for the FM band. It is OK for FM, if you never have multipath (ghosting) or interference problems. Got it? Omni is almost always a bad idea, especially for TV! How many times do I have to say that? So, you might have to look elsewhere for omni TV band antennas information. Gee, you may as well use a lamp cord for an antenna. OK?. If you are going to use more antenna than lampcord, use a directional antenna, please. Why pay for something that picks up garbage you don't want as well as the fragile signal you do want? (Oh, ya, this is the basic idea behind the gigantic Batwing antennas often used to transmit TV. This antenna is great for broadcasting in all directions. It is easy to make from tubing, so it makes a good Ham antenna. As with any antenna, you can scale it it for your particular wavelength.
8. Other Omni. This antenna, sold for FM radio, is a bent folded dipole. It is advertised a an Omni, but only approximates omnidirectional reception.
9. Yagi. The Yagi antenna is narrow band, designed to work on only one channel or FM. It has the best gain for its size, and a correspondingly narrow main lobe (beam). If you need the highest gain, or to discriminate against an interfering signal 20-40 degrees azimuth off the desired signal, use a Yagi.
10. Log Periodic Logs have designed in broad bandwidth. The boom length being shared over a band of frequencies means lower gain than a Yagi, and a fatter main lobe, but far better rejection of signals off the side and rear. Logs are infrequently used except in professional settings. Usually they are expensive, large, heavy and rugged. If you have a lot of money to spend and want something that will last a very long while, check out Log periodics. These images take you to manufacturer sites.
11. Typical TV-FM VHF Only Home Antenna. If you want to get VHF channels, this is probably the type of antenna for you. If you need FM band capability, you have to look for that as well, but be careful. FM stations can easily overpower your TV. See more on that in the interference section. If an antenna is supposed to work on a range of frequencies from 50 to over 200 MHz, and still not cost much, then compromise is in order. In real life, most consumer antennas are not pure Yagi, or log-periodic, but instead are a jumble of rods designed to get the most from the limited boom space over a wide range of channels.
12. Typical UHF Only Home Antenna. Here, in South Central Alaska, there is no place where you should use a UHF only antenna. But if where you live you have no VHF choices, or if you want to use one antenna for VHF and another for UHF, (which I don't think is a good idea for home use, but might be right for professional installations) here are views of UHF only home antennas. Years ago, the FCC studied UHF antennas, and concluded the panel style was best at lowest cost, with the corner reflector being second best. Panels are the only all band transmitting antenna used in Europe, so it must be pretty good with tens of thousands transmitting multiple channels. I have had luck with the yagi-corner reflector style and parabolic style, except on the lowest channels. On the highest channels, the parabolic may be best.
13. Atypical Low Channel UHF. In the United States UHF TV channels 14-21 (470-518 MHz) are used for land mobile two way radio, making rugged, effective and inexpensive Yagi antennas commonly available in that band. You probably will need to drill holes in the boom to mount the antenna horizontally polarized. The image is my installation used to receive channel 14 for microwave relay to Kenai. The location is subject to windspeeds above 200 km/h. I used the Maxrad MYA-4903(N). The 50 ohm antenna uses an N connector. Mismatching is not critical in a broad band system like TV so long as the antenna is only used to receive a signal and the mismatch is at the antenna. Any reflected energy bounces back into space. No problem.
14. Antenna gain over a dipole goes up as directivity increases. This can be seen in polar style gain charts. Thus far, I have not found any consumer TV antenna manufacturer offering charts except Winegard . Look at their antenna data sheets in PDF form, and you will find good information.
    
    
15. Typical All Band Home Antenna. This is what I use at home. See more about this on the next page.

Keep in mind that antennas are reciprocal, i. e. transmitting and receiving characteristics are identical. Also, they scale with wave length. If the wave is ten times larger, an antenna 10 times larger will be identical in all respects except effective area. (see Antenna Formulas). However, in real life, with real materials, we must change things depending upon use and wavelength.

1. HF-Shortwave Dipoles: Dipoles take many forms, but are still dipoles.
2. Slot: A conducting sheet (metal) with a slot is equivalent to empty space with a wire. Excite the slot with radio frequency electricity, and it acts like a dipole, except the polarization is opposite of that of a solid antenna. Note that a slot can be cut into the skin of a vehicle, such an an airplane or automobile.
3. Slotted Cylinder: Wrap the sheet with a slot into a 1/10 wave length diameter cylinder and you get an almost omnidirectional antenna. Make the cylinder larger and you get interesting directional effects.
4. Medium Wave Antenna: Take half a dipole (1/4 wave wire) and use the earth as the other half, and you get the antenna usually found at a medium wave (AM) broadcast station. Here radial wires, hundreds under ground, provide a mirror image of the part above ground to equal a whole dipole. The wire need not be exactly 1/4 wave.
5. Long Wire:A long piece of wire will collect energy (have gain) in some directions.
6. Beverage:This long wire is used used to receive medium wave.
7. Rohmbic:Wire in the shape of a rhomboid makes a long wire into a high gain precision antenna.
8. Ground Plane: Move the 1/4 wave wire above ground, and make the wave length shorter, and you get an antenna common to two way radio. Usually 3-4 wires comprise the ground plane.
9. Superturnstile: Take the turnstile used for omnidirectional reception, stretch the wires into vertical sheets, and nick the middle of the sheet into a sort of vertical bow tie, and you get the broad band antenna common to VHF TV broadcasting. O, yes, you can think of these things as slot type antenas also, since they have a vertical slot between the two batwings.
10. Arrays: All the above may be combined into arrays of various sorts. Here you can see what happens in an array of omni radiators. or find this software by Karl L. Barrus.
11. FM VHF Broadcast Horizontally Polarized Antenna: Bend the dipole into a loop, shorten it a tad, load the ends with capacitance and you get a narrow bandwidth omni directional antenna.
12. FM VHF Broadcast Circular Polarized Antenna: Attach a vertical dipole to the ends of the loop, and you get a "mixed" polarization antenna common in FM Broadcast.
13. Helical: A helical wire can have axial or broadside to axis radiation. Helix antennas are used for every VHF, UHF and microwave purpose from point to point to TV broadcast.
14. Frequency Independent: If an antenna characteristics are periodic with the logarithm of the frequency, an antenna can be made that is independent of frequency. The log preriodic mentioned above is only one type of frequency independent antenna. The idea is to have a working area appear as a constant structure regardless of wavelength. As the wave grows shorter, the larger part of the antenna is inactive. Look for conical and planar spirals and other log periodic designs.
15. Discone: A disk connected to the center conductor and cone connected to the shield comprise a type of frequency independent antenna.
16. Microwave: As wave lengths shortens, optical style antennas become more practical. Parabolic prime focus, Gregorian feed, and other types are common. You can learn about these types reading about telescopes. Also very large arrays of dipoles or slots can be arranged, often on printed circuit cards.
17. Low Frequency: To receive, inefficient antennas are fine, and very small (relative to wave length) loops of wire will do. Transmitting with electrically short antennas always means dealing with lost efficiency, and one must expend great effort to minimize loss. For example see this.
18. Crossed Field: Claims for this electrically small antenna are controversial. The linked paper supports the idea that you can not get something for nothing. In other words, antennas cannot be way small and still be efficient radiators or gatherers of radio energy. The claims can be seen at this link.

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