Log-Periodic Loop Antennas
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Electro-Metrics antenna kit consists of OmniDirectional and Directional antennas covering the frequency range of 10 kHz to 18 GHz. Accessories are included for use with the antennas. All antennas and accessories are placed in two carrying cases, which are provided.
Electro-Metrics Corporation is a leading designer, producer and integrator of antennas, sensors and systems for broadband RF communications and testing. The machine shop and fabrication division manufactures precision machined products and provides contract manufacturing services. The Electro-Metrics manufacturing facilities support both of our RF and Precision Fabrication divisions. Our capability to in house manufacture and fully test our products allows us to meet quality expectations and provide rapid response to urgent needs.
CISPR 25 specifies a 200 to 1000 MHz log-periodic antenna used in horizontal and vertical polarization. Rent, buy or lease CISPR 25 log-periodic antennas. The EMC Shop specializes and stock test equipment for measurements of radio frequency emissions.
A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of frequencies. It was invented by John Dunlavy in 1952.
LPDA antennas look somewhat similar to Yagi antennas, in that they both consist of dipole rod elements mounted in a line along a support boom, but they work in very different ways. Adding elements to a Yagi increases its directionality, or gain, while adding elements to a LPDA increases its frequency response, or bandwidth.
Every element in the LPDA antenna is a driven element, that is, connected electrically to the feedline. A parallel wire transmission line usually runs along the central boom, and each successive element is connected in opposite phase to it. The feedline can often be seen zig-zagging across the support boom holding the elements. Another common construction method is to use two parallel central support booms that also acts as the transmission line, mounting the dipoles on the alternate booms. Other forms of the log-periodic design replace the dipoles with the transmission line itself, forming the log-periodic zig-zag antenna. Many other forms using the transmission wire as the active element also exist.
In general terms, at any given frequency the log-periodic design operates somewhat similar to a three-element Yagi antenna; the dipole element closest to resonant at the operating frequency acts as a driven element, with the two adjacent elements on either side as director and reflector to increase the gain, the shorter element in front acting as a director and the longer element behind as a reflector. However, the system is somewhat more complex than that, and all the elements contribute to some degree, so the gain for any given frequency is higher than a Yagi of the same dimensions as any one section of the log-periodic. However, a Yagi with the same number of elements as a log-periodic would have far higher gain, as all of those elements are improving the gain of a single driven element. In its use as a television antenna, it was common to combine a log-periodic design for VHF with a Yagi for UHF, with both halves being roughly equal in size. This resulted in much higher gain for UHF, typically on the order of 10 to 14 dB on the Yagi side and 6.5 dB for the log-periodic. But this extra gain was needed anyway in order to make up for a number of problems with UHF signals.
It should be strictly noted that the log-periodic shape, according to the IEEE definition, does not align with broadband property for antennas. The broadband property of log-periodic antennas comes from its self-similarity. A planar log-periodic antenna can also be made self-complementary, such as logarithmic spiral antennas (which are not classified as log-periodic per se but among the frequency independent antennas that are also self-similar) or the log-periodic toothed design. Y. Mushiake found, for what he termed \"the simplest self-complementary planar antenna,\" a driving point impedance of η0/2=188.4 Ω at frequencies well within its bandwidth limits.
The log periodic is commonly used as a transmitting antenna in high power shortwave broadcasting stations because its broad bandwidth allows a single antenna to transmit on frequencies in multiple bands. The log-periodic zig-zag design with up to 16 sections has been used. These large antennas are typically designed to cover 6 to 26 MHz but even larger ones have been built which operate as low as 2 MHz. Power ratings are available up to 500 kW. Instead of the elements being driven in parallel, attached to a central transmission line, the elements are driven in series, adjacent elements connected at the outer edges. The antenna shown here would have about 14 dBi gain. An antenna array consisting of two such antennas, one above the other and driven in phase has a gain of up to 17 dBi. Being log-periodic, the antenna's main characteristics (radiation pattern, gain, driving point impedance) are almost constant over its entire frequency range, with the match to a 300 Ω feed line achieving a standing wave ratio of better than 2:1 over that range.
We have two Creative Design CLP5130-1N log periodic antennas in service, one north and one south. The south antenna is dedicated to thee-CALLISTO solar spectrometer described here. The north antenna is used with various receivers for detection of meteor trail reflections and radar echos from the Moon, among other projects.
The loop antenna is another popular indoor TV antenna. A loop antenna is a modification of the dipole in which the two poles are folded back to meet one another. A loop antenna is often configured in a circle but can also form a square or even a series of circles or squares. Loop antennas are especially good for receiving ultrahigh frequency, or UHF, channels (channels higher than 13). The flat, rectangular indoor antennas that have become quite common since broadcasters switched from analog to digital signals are made with a metal loop antenna embedded in conductive plastic.
Yagi antennas receive VHF and UHF channels well. A Yagi antenna is an outdoor directional antenna that concentrates signal reception in a single direction at the expense of all others. They are known for high gain, which means that they are capable of receiving low-strength signals far better than other types of antennas. A Yagi antenna can be a good option if you live in a rural area where maximum gain is required to pick up a faint signal.
A log-periodic (LP) antenna, or log-periodic dipole array (LPDA), is a multielement attic or outdoor directional antenna that is built to operate over a wide band of frequencies. It works like a series of linked Yagi antennas, each tuned to different frequencies. The difference is the Yagi has a single driven element whereas the LP has multiple driven elements. While the Yagi provides more gain for a single frequency, the LP handles a range of frequencies more efficiently. LP antennas are a good choice for suburban and rural areas where the signal is weak.
Directional antennas receive signals only from the direction in which they are aimed. Omnidirectional antennas receive signals from all directions. In suburban and rural locations, or where the signal is weak, choose a directional antenna that will boost the weak signal. In areas where there are multiple towers located in different directions nearby, consider using an omnidirectional antenna.
Different kinds of antennas are used to receive these signals. Dipole antennas pick up VHF signals, while loop antennas capture UHF signals. Many antennas are constructed with multiple technologies to receive both VHF and UHF frequencies. Outdoor antennas are capable of picking up both VHF and UHF signals.
Within 20 miles of the broadcast tower, most indoor omnidirectional antennas provide good reception. The farther you are from the broadcast tower, the weaker the signal becomes. This is where you may benefit from an outdoor or amplified antenna. Outdoor antennas use a variety of technologies, such as directional reception and reflective arrays, to improve signal gain and make the most of a weak signal.
It is important to know that antenna amplifiers do not filter out noise; whatever the antenna picks up gets amplified. In some instances, amplified antennas may work better with the amplifier turned off.
TV antennas receive a spectrum of electromagnetic radio wavelengths from broadcast towers, typically within a distance of 35 miles. Signals are most effectively delivered in a line of sight, with obstacles such as mountains, large buildings, and even dense foliage depleting or blocking the signal. Viewers who are farther away, and those who are not within a line of sight of the broadcast tower, need more powerful equipment to receive these signals. By researching the location and frequencies of your local broadcasts, you will get the information required to choose the best antenna for your TV.
Indoor antennas are inexpensive, easy to set up, and work best for areas with strong broadcast signals, typically within 20 or 30 miles of the broadcast tower. Outdoor antennas are significantly more expensive, more complicated to install, and powerful enough to capture weak signals in areas farther from the broadcast source.
While antenna marketers claim that their antennas capture signals from 200 miles away or farther, the truth is less exciting. Because TV broadcast signals require line of sight reception, the maximum range for an antenna is about 70 miles. After that point, the curvature of the earth blocks the signal.
It varies with the type and model. Omnidirectional antennas do not need to be aimed, although they may need to be mounted on a vertical surface such as a wall or window. Directional antennas should be pointed in the direction of the broadcast tower. Use a tool like the one on AntennaWeb to learn which direction that is. 59ce067264