The antenna can be classified in several methods. One method is the operating frequency band. Others include physical structure and design / electromagnetic. The antenna used for LMR both in the base station and the mobile unit which only represent a small fraction of all types of antennas.
Types and functions of the antenna
The simplest is nondirectional antenna / dipole basic / monopoles. Then the more complex among other directional antenna consisting of an array of elements, such as dipole or use a passive element and some active elements, such as the Yagi antenna.
The new antenna technology is being developed that enables the antenna to rapidly changing patterns in response to changes in the direction of arrival of the received signal. Antenna and supporting technology called adaptive or "smart" antennas and can be used for higher frequency bands LMR in the future.
1. Polished and monopoles
Dipole vertical monopole antenna can be considered one of the best for LMR applications. Omnidirectional (azimuth) is a half-wave antenna length, has a gain of 1.64 (or G = 2.15 dBi) in the horizontal plane.
A monopole above a ground plain theoretically infinite same (identical gain and pattern, in the open space above the ground plane) as a dipole in free space. In practice, plain ground can not be limited, but plain ground with a radius approximately the same as the length of the active element is a practical solution that is effective. Flat surface on the vehicle trunk or roof of the house is a nice plain ground.
Types and functions of the antenna. monopole antenna specifically for
(a) base-station and (b) mobile applications.
2. Base-Station Applications
To install the base station (where the desired omnidirectional pattern), there are two practical implementation of a vertical dipole. The first type is a sleeve antenna. Sleeve dipole antenna is vertical with the feed (transmission line) entering from one end hollow element. The second type is a monopole on plain ground. Monopole in this illustration using a set of four elements to provide ground plain wire. The radiation pattern that is very similar to a simple dipole, but a higher impedance and has a wider bandwidth.
To install the base station (where the desired omnidirectional pattern), there are two practical implementation of a vertical dipole. The first type is a sleeve antenna. Sleeve dipole antenna is vertical with the feed (transmission line) entering from one end hollow element. The second type is a monopole on plain ground. Monopole in this illustration using a set of four elements to provide ground plain wire. The radiation pattern that is very similar to a simple dipole, but a higher impedance and has a wider bandwidth.
1. Mobile Applications
Almost all vehicle antenna is mounted on the top surface of the monopoles roof (relatively) flat (as described above). In this application, the monopole is often called a "whip" antenna. In frekuaensi VHF low-band, wears a quarter wavelength monopole or can 2.5 m (about 8 feet) in length. However, an inductor (coil) on the basis of electric monopole add length, so that the physical length of the antenna can be shorter. Although this kind of "loaded" with the antenna looks like a quarter wavelength antenna, it will have a gain value somewhat less than a quarter wavelength. This loss can be eliminated, but with the ability to mount a (short) antenna in the middle of the surface which will act as a ground plain (eg, roof or trunk of the vehicle).
Almost all vehicle antenna is mounted on the top surface of the monopoles roof (relatively) flat (as described above). In this application, the monopole is often called a "whip" antenna. In frekuaensi VHF low-band, wears a quarter wavelength monopole or can 2.5 m (about 8 feet) in length. However, an inductor (coil) on the basis of electric monopole add length, so that the physical length of the antenna can be shorter. Although this kind of "loaded" with the antenna looks like a quarter wavelength antenna, it will have a gain value somewhat less than a quarter wavelength. This loss can be eliminated, but with the ability to mount a (short) antenna in the middle of the surface which will act as a ground plain (eg, roof or trunk of the vehicle).
Many vehicle antenna in the high-band VHF frequency monopoles quarter wavelength. At a frequency of 150 MHz, this means called whip antenna, approximately 0.5 m (1.5 ft), is required. Half wave and 5/8 wave monopoles are also used, but it requires some kind of antenna matching elements (ie, inductors and / or capacitors) to match the antenna impedance to that of the transmission line. This antenna has a gain of about 3 dBi.
At UHF, quarter-wavelength whip has a length of about 15 cm (6 in). Because of this length are physically small, some design considerations can be used to increase profits. For example, as shown in Figure 6 (b), two 5/8 wave monopoles can be "coupled" with coil tapping them. It is, effectively the antenna array that provides a gain of about 5 dBi.
At a frequency of 800 MHz, a quarter wavelength monopole is not working properly, so the closer the composition of two monopoles, with a phasing coil of which needs to be done. Such as an antenna, looks like a mobile phone antenna and has a gain of about 3 dBi.
Azimuth pattern of all monopoles ideally is a circle. In other words, an advantage over the azimuthal angle in the horizontal plane is constant. In practice, the pattern in the horizontal plane is generally not omnidirectional, as part of the vehicle that is used as a ground plain is not symmetrical, and usually there are other obstructions.
3. Corner Reflector
An antenna consists of one or more elements of the dipole in front of a corner reflector, called corner-reflector antenna, illustrated in Figure 8. A photograph of a special reflector angle is shown in This antenna has a high gain, but the most important feature is the way forward, because gainya much higher than profits in the opposite direction. This is called the ratio of front-to-back and clear the pattern shown in.
4. Yagi
Antenna design using passive elements. This antenna, can be made cheaply and effectively. It can be made with one or more (usually one or two) reflector elements and one or more (usually two or more) elements of the director. Generally, the more elements Yagi has, the higher the gain, and narrow beamwidth. This antenna can be installed to support the polarization either horizontally or vertically and is often used for the application of point-to-point, such as between the base station and repeater-station.
At UHF, quarter-wavelength whip has a length of about 15 cm (6 in). Because of this length are physically small, some design considerations can be used to increase profits. For example, as shown in Figure 6 (b), two 5/8 wave monopoles can be "coupled" with coil tapping them. It is, effectively the antenna array that provides a gain of about 5 dBi.
At a frequency of 800 MHz, a quarter wavelength monopole is not working properly, so the closer the composition of two monopoles, with a phasing coil of which needs to be done. Such as an antenna, looks like a mobile phone antenna and has a gain of about 3 dBi.
Azimuth pattern of all monopoles ideally is a circle. In other words, an advantage over the azimuthal angle in the horizontal plane is constant. In practice, the pattern in the horizontal plane is generally not omnidirectional, as part of the vehicle that is used as a ground plain is not symmetrical, and usually there are other obstructions.
3. Corner Reflector
An antenna consists of one or more elements of the dipole in front of a corner reflector, called corner-reflector antenna, illustrated in Figure 8. A photograph of a special reflector angle is shown in This antenna has a high gain, but the most important feature is the way forward, because gainya much higher than profits in the opposite direction. This is called the ratio of front-to-back and clear the pattern shown in.
4. Yagi
Antenna design using passive elements. This antenna, can be made cheaply and effectively. It can be made with one or more (usually one or two) reflector elements and one or more (usually two or more) elements of the director. Generally, the more elements Yagi has, the higher the gain, and narrow beamwidth. This antenna can be installed to support the polarization either horizontally or vertically and is often used for the application of point-to-point, such as between the base station and repeater-station.
5. Log-Periodic
This is a rather new, but very useful, log-periodic antenna design. This antenna is based on the dipole elements. As shown in the illustration 14, the antenna was actually composed of a set of dipole, are all active, varying in size from the smallest in front of more memebesar on the back. Typically, this antenna is made with the antenna terminals located in the front (on the shortest dipole). The main feature of this antenna is, first of all broadband nature, and both the gain ratio of front-to-back relatively high. This last feature is apparent in particular radiation pattern shown in.
This is a rather new, but very useful, log-periodic antenna design. This antenna is based on the dipole elements. As shown in the illustration 14, the antenna was actually composed of a set of dipole, are all active, varying in size from the smallest in front of more memebesar on the back. Typically, this antenna is made with the antenna terminals located in the front (on the shortest dipole). The main feature of this antenna is, first of all broadband nature, and both the gain ratio of front-to-back relatively high. This last feature is apparent in particular radiation pattern shown in.
6. Arrays
An antenna array (or antenna arrays) is as it sounds, the antenna which has some elements that are interconnected and arranged in a regular structure to form a single antenna. The purpose of the antenna array is to produce a radiation pattern that has certain desirable characteristics as a single element. A stacked dipole array, consists of a vertical dipole elements.
Dipole array has an omnidirectional pattern as elements instead of a dipole; but has a higher gain and beamwidth of the main lobe narrow in the vertical plane.
-plain vertical radiation pattern for
(a) a single half-wave dipole,
(b) two-element array, and
(c) three-element array
This is called a binomial or collinear arrays. Because the number of elements increases, the gain and beamwidth decreases.
The omnidirectional antenna coaxial collinear (often referred to as "omni") is a very popular design array for BTS. The antenna consists of a quarter-wavelength part coaxial with the inner and outer conductors routed at each connection. Although it is more complex than the illustration, this array antenna behaves like a series of vertical dipole are stacked one above the other. The lower part, the greater the gain and narrow vertical beamwidth. Variations in the electrical design can produce a downward slope from the vertical-plane pattern. This antenna is often covered in fiberglass sheath, called radome, and with a simple pole at the support that can be mounted on the side or on top of a pole or tower.
As in all the antennas, antenna arrays depending on the frequency. Gain, directivity, and radiation pattern of each function of frequency. Some antenna will work well only for a certain frequency, and their performance will decline in other operating frequency of the design frequency.
7. Unusual Antennas
Although not as common, wire or rod antenna, the antenna aperture by no means unusual. This antenna works openly in a relatively large, conductive (metal) surface. The simplest aperture antenna is a slot antenna, which is equivalent to a dipole. Slot simple and more complex version suitable for covert operations. They may be on the surface of the vehicle and hidden behind the cover of a thin insulating material. Slot antennas are common on aircraft and missiles. Not so much the type of antenna as an antenna antenna features, broadband and multiband design is the result of an effort to make the antenna performs well over a wide band channel. There may be trade-offs in making broadband antenna, such as a decrease or increase the size of the physical strengthening. The design goal of the usual for this type of antenna that makes the gain and radiation patterns, as well as terminal impedance, relatively constant over the frequency range of operation. Log-periodic antenna array broadband examples.
Multiband antenna is designed to operate on multiple bands, for example, on both VHF high-band and UHF. These antennas are often involves intelligent design in which one part of the active antenna for a band, and other parts for a different band. Once again, there will be a compromise. The antenna may have a gain on average lower or may be physically larger than an equivalent single-band antenna.
8. Active Antennas
An active antenna is one that contains several electronic circuits which can amplify the signal received at the antenna and thus avoiding interference that may enter the system in the transmission line. Antenna "element" is connected to the input of an amplifier. Amplifier output terminal is a terminal antenna for this active antenna. Antenna element and amplifier included in the "active antenna," is shown as the dashed box in the figure.
Another goal of the active antenna unusual to change the impedance of the antenna terminal to a constant value that matches the characteristic impedance of the transmission line. This function is useful for some antenna design where the desired features of a particular pattern, but can not be achieved without causing the antenna terminal impedance unusual. An active antenna nonreciprocal and can not be used for transmission.
9. Diversity Antennas
Diversity is a technique that improves the reception of radio waves by taking advantage of the fact that the signals that vary with time (eg, fading) is not the same in a separate location. In other words, a decrease in the strength of the signal may be very different for the two locations separated by as little as a single wavelength. To take advantage of this, two antennas, separated by a certain distance, which is used to receive the same signal. Of the two signals, one with the highest signal level, at a particular time, is automatically sent to the recipient. This process is only useful for acceptance. Electronic needed for the type of signal processing is sometimes part of the antenna system.
Adaptive antenna extending the concept of diversity that a step further. These antennas are usually incorporate more than just two elements (ie, the individual antennas) in the array. An adaptive antenna can modify the radiation pattern (within limits) in real time to ensure that the main lobe points in the direction of the largest signal level. Alternatively (or, perhaps, at the same time), the same technique can be used to designate a null in the direction of the unwanted interfering signals.
The omnidirectional antenna coaxial collinear (often referred to as "omni") is a very popular design array for BTS. The antenna consists of a quarter-wavelength part coaxial with the inner and outer conductors routed at each connection. Although it is more complex than the illustration, this array antenna behaves like a series of vertical dipole are stacked one above the other. The lower part, the greater the gain and narrow vertical beamwidth. Variations in the electrical design can produce a downward slope from the vertical-plane pattern. This antenna is often covered in fiberglass sheath, called radome, and with a simple pole at the support that can be mounted on the side or on top of a pole or tower.
As in all the antennas, antenna arrays depending on the frequency. Gain, directivity, and radiation pattern of each function of frequency. Some antenna will work well only for a certain frequency, and their performance will decline in other operating frequency of the design frequency.
7. Unusual Antennas
Although not as common, wire or rod antenna, the antenna aperture by no means unusual. This antenna works openly in a relatively large, conductive (metal) surface. The simplest aperture antenna is a slot antenna, which is equivalent to a dipole. Slot simple and more complex version suitable for covert operations. They may be on the surface of the vehicle and hidden behind the cover of a thin insulating material. Slot antennas are common on aircraft and missiles. Not so much the type of antenna as an antenna antenna features, broadband and multiband design is the result of an effort to make the antenna performs well over a wide band channel. There may be trade-offs in making broadband antenna, such as a decrease or increase the size of the physical strengthening. The design goal of the usual for this type of antenna that makes the gain and radiation patterns, as well as terminal impedance, relatively constant over the frequency range of operation. Log-periodic antenna array broadband examples.
Multiband antenna is designed to operate on multiple bands, for example, on both VHF high-band and UHF. These antennas are often involves intelligent design in which one part of the active antenna for a band, and other parts for a different band. Once again, there will be a compromise. The antenna may have a gain on average lower or may be physically larger than an equivalent single-band antenna.
8. Active Antennas
An active antenna is one that contains several electronic circuits which can amplify the signal received at the antenna and thus avoiding interference that may enter the system in the transmission line. Antenna "element" is connected to the input of an amplifier. Amplifier output terminal is a terminal antenna for this active antenna. Antenna element and amplifier included in the "active antenna," is shown as the dashed box in the figure.
Another goal of the active antenna unusual to change the impedance of the antenna terminal to a constant value that matches the characteristic impedance of the transmission line. This function is useful for some antenna design where the desired features of a particular pattern, but can not be achieved without causing the antenna terminal impedance unusual. An active antenna nonreciprocal and can not be used for transmission.
9. Diversity Antennas
Diversity is a technique that improves the reception of radio waves by taking advantage of the fact that the signals that vary with time (eg, fading) is not the same in a separate location. In other words, a decrease in the strength of the signal may be very different for the two locations separated by as little as a single wavelength. To take advantage of this, two antennas, separated by a certain distance, which is used to receive the same signal. Of the two signals, one with the highest signal level, at a particular time, is automatically sent to the recipient. This process is only useful for acceptance. Electronic needed for the type of signal processing is sometimes part of the antenna system.
Adaptive antenna extending the concept of diversity that a step further. These antennas are usually incorporate more than just two elements (ie, the individual antennas) in the array. An adaptive antenna can modify the radiation pattern (within limits) in real time to ensure that the main lobe points in the direction of the largest signal level. Alternatively (or, perhaps, at the same time), the same technique can be used to designate a null in the direction of the unwanted interfering signals.
KELOMPOK:
HAYU ZARWANI
I MADE BAYU WIRAWAN
IQBAL ZULFIKAR
M. DIMAS NUGROHO
M. RIFQI MAULANA
Tidak ada komentar:
Posting Komentar