AFRA (Antenna factor of rectangular array)
Antenna factor of rectangular array (AFRA) is a measure of the efficiency of an antenna array, specifically a rectangular array. In simpler terms, it is a measure of how well an antenna array can convert incoming electromagnetic radiation into an electrical signal.
Antenna arrays are used in a variety of applications, including radar, communication systems, and remote sensing. Rectangular arrays, in particular, are commonly used in these applications due to their ability to provide high gain and directional radiation patterns. However, the efficiency of a rectangular array can be affected by a number of factors, including the antenna element spacing, the number of elements in the array, and the antenna element geometry.
To better understand AFRA, it is important to first understand some basic concepts related to antenna arrays. An antenna array is a collection of antenna elements that are arranged in a specific pattern. The individual antenna elements are connected together in such a way that they produce a radiation pattern that is different from that of a single antenna element. This radiation pattern can be adjusted by changing the properties of the individual elements or by changing the way they are connected.
The radiation pattern produced by an antenna array is often characterized by its directivity, which is a measure of the array's ability to radiate in a specific direction. Directivity is usually expressed in terms of decibels (dB) and is defined as the ratio of the radiation intensity in a particular direction to the average radiation intensity over all directions.
The directivity of an antenna array can be calculated using the following formula:
D = 4πP/λ^2
where D is the directivity, P is the total radiated power, and λ is the wavelength of the radiation. The total radiated power can be calculated as the product of the array factor and the input power. The array factor is a function of the geometry of the array, the number of elements, and the spacing between the elements.
The antenna factor of an antenna is a measure of its efficiency in converting electromagnetic radiation into an electrical signal. The antenna factor is usually expressed in terms of decibels per meter (dB/m) and is defined as the ratio of the incident electric field strength to the voltage produced by the antenna. The antenna factor can be calculated using the following formula:
AF = 20log(E/V)
where AF is the antenna factor, E is the incident electric field strength, and V is the voltage produced by the antenna.
For a rectangular array, the antenna factor can be calculated using the following formula:
AFRA = AF + 10log(N) + 20log(cos(θ)cos(ϕ))
where AFRA is the antenna factor of the rectangular array, AF is the antenna factor of an individual element, N is the number of elements in the array, θ is the elevation angle, and ϕ is the azimuth angle.
The first term in the formula represents the antenna factor of an individual element. The second term represents the effect of increasing the number of elements in the array. As the number of elements increases, the antenna factor of the array increases due to the increased gain and directivity of the array. The third term represents the effect of the direction of the incoming radiation. The antenna factor is maximum when the incoming radiation is normal to the plane of the array and decreases as the angle of incidence deviates from normal.
In conclusion, the antenna factor of a rectangular array is a measure of its efficiency in converting electromagnetic radiation into an electrical signal. The AFRA takes into account the antenna factor of an individual element, the number of elements in the array, and the direction of the incoming radiation. By understanding the AFRA, engineers can optimize the design of rectangular arrays for various applications, such as radar, communication systems, and remote sensing.