Types of antenna

       January 1, 0000    897


There are many types of antenna for television. The person should buy according to their need and choice of picture clarity. Among many here are the list of few antennas for a quick glance.
1. HDTV Antenna-There is zero different about an aerial for DTV or HDTV.  Dishonest people have used this as an advertising trick.  The honest antenna makers have had to re-label their products to keep away from losing sales. It increases a measure of how much signal the antenna will collect. Beam width is how directional an antenna is.  Bandwidth is how the gain varies with frequency.  A narrowband antenna will receive some channels well but other channels poor.
2. The Dipole- This is the simplest television antenna.  Variations on the dipole are the bowtie, the folded-dipole and the loop.  All four have the same gain and the same radiation field. This sounds like a transmitting antenna. An antenna will have the same gain when receiving as when transmitting and also the same wave pattern. Rotate antenna about the onward axis the signal strength will vary as the cosine of the angle.  When the antenna elements are perpendicular no signal is received because TV signals have horizontal polarization.
3. Stacked Dipoles- Two heads are superior to one and so it is with dipoles. N dipoles will take in N period as much RF control as one dipole provided they are not too secure to each other. Thus a 4-dipole antenna would have a gain of 8.15 dBi. This assumes their positions and cable lengths are in tune so that their signals add in-phase. These details of gain may seem at odds with the balloon explanation but ultimately they are equivalent
4. Reflector Antennas- Radio waves will replicate off of a large conducting plane as if it was a mirror.  A coarse screen will serve as well.  Reflector antennas are very common. The double bow tie above has an average gain of 6 dBi.  With a better screen it would have more. The parabolic reflector focuses the signal onto a single dipole but its bandwidth is a little unsatisfactory.  The corner reflector has a little less gain but much superior bandwidth.  The curve reflector has roughly the gain of three dipoles.  It is a good medium gain antenna widely used for UHF. 
5. Log-Periodic Dipole Arrays (LPDA)- The LPDA has numerous dipoles set in height and criss-cross fed from the front.  The name comes from the geometric growth that is logarithmic.
6. Yagi Antennas- A Yagi antenna has more than a few elements arranged in level.  They are connected simultaneously by a long element, called the boom.  The boom carries no current.  If the boom is an insulator, the antenna works the same way.

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