Tutorial: Antenna Gain and Directivity
Feb 9, The gain is typically between 0 and 2 dBi. Figure 3 illustrates a radiation pattern of a quarter wavelength whip antenna, also known as a. Feb 8, Antenna Gain and Directivity are two terms that are sometimes not that I need difference between dirctivity, gain and efficiency of antenna. Directivity D is a quantitative measure of an antenna's ability to concentrate radiated power per unit solid gain, and relationships between them. To accomplish.
Therefore they are more useful in mountainous and metropolitan areas with tall buildings. A 3 dBd gain antenna is a good compromise for use in suburban and general settings. A 5 dBd gain antenna radiates more energy toward the horizon compared to the 0 and 3 dBd antennas. This allows the signal to reach radio communication sites further apart and less obstructed. Therefore they are best used in deserts, plains, flatlands and open farm areas.
Directional antennas are used in some base station applications where coverage over a sector by separate antennas is desired. Point-to-point links also benefit from directional antennas.
Yagi and panel antennas are directional antennas. For example, for a 0 dB gain antenna, 3 db beamwidth is the area where the gain is higher than —3 dB. The far-field is also called the radiation field, and is what is most commonly of interest.
The nearfield is called the induction field although it also has a radiation component. Ordinarily, it is the radiated power that is of interest so antenna patterns are usually measured in the far-field region.
For pattern measurement, it is important to choose a distance sufficiently large to be in the far-field, well out of the near-field. The minimum permissible distance depends on the dimensions of the antenna in relation to the wavelength.
The accepted formula for this distance is: Two often-used special cases of elliptical polarization are linear polarization and circular polarization. Initial polarization of a radio wave is determined by the antenna launching the waves into space. The environment through which the radio wave passes on its way from the transmit antenna to the receiving antenna may cause a change in polarization.
With linear polarization the electric field vector stays in the same plane. In circular polarization the electric field vector appears to be rotating with circular motion about the direction of propagation, making one full turn for each RF cycle.
The rotation may be right-hand or left-hand. Choice of polarization is one of the design choices available to the RF system designer.
Mobile radio system waves generally are vertically polarized. TV broadcasting has adopted horizontal polarization as a standard. This choice was made to maximize signal-to-noise ratios. At frequencies above 1 GHz, there is little basis for a choice of horizontal or vertical polarization, although in specific applications there may be some possible advantage in one or the other.
Circular polarization has also been found to be of advantage in satellite applications such as GPS. Circular polarization can also be used to reduce multipath.
Theoretically, a whip provides an omnidirectional pattern in the horizontal plane and a dipolar pattern in the elevation plane.
Antenna Gain and Directivity | RAYmaps
In practice, this condition is never achieved. Common effects of reduction of the size of the ground plane are: The maximum energy is not radiated in the expected direction. The aperture of the radiating element is modified, and the gain of the antenna is decreased. In conclusion, we could say the bigger the ground plane, the better the control of the electrical performance of the antenna.
Quite often this is implemented by placing a loading coil at the base of the antenna. Gain depends upon the amount of loading used. Four common styles are: Using more than three radiating elements in a base-fed collinear configuration does not significantly increase gain.
The majority of the energy is radiated by the elements close to the feed point of the collinear antenna so there is only a small amount of energy left to be radiated by the elements which are farther away from the feed point. Please note the directivity is given above for common antenna configurations.
Gain depends upon the electrical efficiency of the antenna. Here is where the real difference between antenna manufacturers is seen.
Antenna Basic Concepts – Pulse Electronics
If you cut corners in building an antenna, the gain may be significantly lower than the directivity. Larsen uses low-loss materials to minimize the difference between the gain and the directivity in our antennas. WHIP The vertical portion of the antenna assembly acting as the radiator of the radio frequency GPS Active GPS antennas include an amplifier circuit in order to provide better reception of the satellite signal. This active stage generally includes a low noise amplifier and a power amplifier.
Dipoles are the most common wire antenna. Fed by coaxial cable. Sleeve Dipoles are realized by the addition of a metallic tube on a coaxial structure. Printed Dipoles have a radiation structure supported by a printed circuit. This structure could be externally mounted ex: YAGI A directional, gain antenna utilizing one or more parasitic elements.
A yagi consists of a boom supporting a series of elements which are typically aluminum rods. PANEL Single Patch describes an elementary source obtained by means of a metallic strip printed on a microwave substrate.
These antennas are included in the radiating slot category. Patch Arrays are a combination of several elementary patches. However, the peak gain of an antenna can be arbitrarily low because of losses or low efficiency.
Electrically small antennas small relative to the wavelength of the frequency that the antenna operates at can be very inefficient, with antenna gains lower than dB even without accounting for impedance mismatch loss.
Is a High Gain Antenna Advantageous? Often manufacturers of antennas be they wifi antennas, gps antennas, or tv antennas specify the antenna gain. For instance, manufacturers of wifi antennas may market the wifi antenna as a "high gain antenna", which is more expensive than a similar low gain antenna.
If you know exactly where your desired signal is coming from, you would like to have maximum gain towards the desired direction. However, if you don't know where the desired signal will be coming from, it is better to have a low gain antenna. A couple examples will make this clear. If you mount a TV antenna on your roof, and know the tv broadcast antennas are to the south for example, on some hill south of the citythen it is preferred to have a high gain antenna.
Antennas with gain of at least dB are preferred. GPS antennas for mobile devices are receive only.
Tutorial: Antenna Gain and Directivity
The job of the gps antenna is to triangulate your position by measuring the received signal from multiple gps satellites, which are all in different directions relative to the receive antenna. For this case, a very highly directional antenna would not be preferred. The cellular antenna on your smartphone communicates with a single cellular network tower. However, the cellular antenna can be held in any orientation, and can be in any position relative to the network tower.
Hence, for your mobile device, it is preferred to have a low gain antenna.