Tutorial: Antenna Gain and Directivity
HPBW and BWFN for an antenna. Directivity. Gain and efficiency of an antenna. Effective aperture of antenna. Relative between Directivity and effective aperture . Antenna Gain and Directivity are two terms that are sometimes not that well understood. That is, the Antenna Gain in a particular direction is equal to the Directivity and what is the relationship between directivity and gain. The concept of antenna gain is introduced. Gain is a product of the directivity and the efficiency of an antenna.
Gain and beamwidth options for Yagi antenna This means that very high gain antennas are very directive. Therefore high gain and narrow beam-width sometimes have to be balanced to provide the optimum performance. Yagi-Uda antenna gain considerations There are several features of the design of a Yagi antenna that affect its gain: Number of elements in the Yagi: The most obvious factor that affects the Yagi antenna gain is the number of elements in the antenna.
Typically a reflector is the first element added in any Yagi design as this gives the most additional gain, often around 4 to 5 dB. Directors are then added. For mid ranges of the number of directors, each director provides very roughly 1 dB of gain.
The spacing can have an impact on the Yagi gain, although not as much as the number of elements. Typically a wide-spaced beam, i. The most critical element positions are the reflector and first director, as their spacing governs that of any other elements that may be added. When computing the optimal positions for the various elements it has been shown that in a multi-element Yagi array, the gain is generally proportional to the length of the array.
There is certain amount of latitude in the element positions. Radiation Patterns, Permittivity, Directivity, and Gain October 12, by Mark Hughes In the second part of the Antenna Basics series, you will learn more about the physics behind the antennas we use every day, including information on permittivity, permeability, gain, directivity, and more.
Antennas transfer information between locations by altering electromagnetic fields in one location and detecting changes in electromagnetic fields in another location.
To understand how antennas can transfer information to increasingly remote locations, you must first understand the physics that govern their operation. This article will extend the concepts of the previous article to include near and far field radiation patterns, permittivity, directivity, and gain.
Antenna Gain and Directivity | RAYmaps
What's Happening inside an Antenna Wire? Inside the wire, charge carriers move as a result of the applied potential difference. Above is a demo of a radiating charge simulation from the University of Colorado. You can play with it here.Antenna Directivity, Antennas Parameter in Antennas & Wave Propagation by Engineering Funda
At first, the sine-wave generator moves the charges in one direction, creating electric and magnetic fields that grow as the voltage increases. The fields are constantly changing during this time, and the changes in the field propagate outwards at the speed of light—fast, but finite.
As the generator's cycle continues, the voltage decreases and the magnitude of the magnetic and electric fields also decreases. This reverses the polarity of the electric and magnetic fields. The recently emitted fields from the previous half-cycle and the fields from the current half-cycle create alternating extremes in field intensity that propagate outward from the antenna. Radiation produced by a Hertzian dipole.
- Tutorial: Antenna Gain and Directivity
- Antenna Basics: Radiation Patterns, Permittivity, Directivity, and Gain
- Antenna gain
The presence of charge carriers in the wire creates an electric field that emanates from the wire, the movement of the charge carriers creates a magnetic field that encircles the wire, and the acceleration of charge creates electromagnetic waves that propagate outward from the wire.
And, if you remember multivariable calculus, Purcell's Electricity and Magnetism presents the topic in far more detail than I provided in the preceding discussion.
Most antennas operate in the far field and transmit information over long distances through changing electric fields. Even though radio transmitters such as the nRF24 and Bluetooth devices have limited range, they still use far-field communication—the electric field is transmitting the information. Radiation Patterns The animation above shows contours of constant radiation power density, propagating outward with time, traced in a plane that passes through a vertically oriented dipole antenna.
The contour surfaces are centered around an antenna and the contour lines are centered on orthogonal planes that intersect the antenna, often around a line of symmetry. The Hertzian dipole above transmits very little to no energy in the vertical direction.
Based on a Mathematica model found here. Different antenna designs produce different radiation patterns. The complexity of the pattern depends on the antenna's design and construction. Antenna specification sheets sometimes come with three-dimensional projections. More often, we see a two-dimensional plot and must imagine the three-dimensional pattern. Polar and Cartesian representations of a radiation pattern for a Yagi antenna. This phenomenon is due to charge polarization inside the dielectric medium.
Yagi Antenna Gain & Directivity
Permittivity is a measure of how readily those charges can align themselves polarization in the presence of an electric field. Higher permittivity indicates greater resistance to forming an electric field, and also slower propagation of a disturbance through the medium.
A high-permittivity material that surrounds a low-permittivity material will not affect the frequency of oscillation, but the high-permittivity material reduces the speed of the wave's propagation.
If we recall that wave speed is equal to the product of frequency and wavelength, we can see that if frequency remains the same, the reduction in speed must come with a corresponding reduction in wavelength. When the wave exits the high-permittivity material, the wave speed and wavelength increase.