Antenna Arrays – Essential part of MIMO & Beamforming
byRahul Kaundalon
Antenna Arrays – Essential part of MIMO & Beamforming
Antenna array is an aggregate of radiating elements in an electrical and geometrical arrangement that will result in a desired radiation characteristics.
An antenna array is set of antenna elements commonly organized in a structure such as an array of rows and columns. Signals are amplified (referred as gain) by transmitting different versions of the same signal from all antennas and can be steered towards particular direction.
An antenna array can be used for both transmission and reception.
Array with two elements is considered below. Antennas are converting electrical signal to electromagnetic waves. A receiving antenna will convert the sum of two incident waves into a received signal. No difference in propagation delays in two antennas are assumed.
Gain and its pattern are derived below. With increase in antenna elements, gain increased and beam width decreased. This is the basis of higher number of antenna element arrangement and beamforming.
Array factor :- The free-space array gain has its maximum value two, for angles θ that satisfy dcosθ = 0, λ, 2λ, …. For such angles, the received power is twice as high, or 3 dB higher, as compared to the case with a single element using the same total transmit power since the signals received combine constructively. dcosθ can be recognized as the propagation path length difference between the two antennas, and hence constructive addition occurs when the path length difference equals a multiple of the wavelength.
The free-space array gain attains its minimum value 0, for angles that satisfy dcosθ = λ/2, 3λ/2, … This means that when the propagation path length difference is an odd multiple of half the wavelength, the signals from the two antennas will cancel each other. For the case with d = 0.7λ, there will be zeros for θ = 90 + 45 or 90 – 45 degrees
the magnitude of the wave vector = k
Reference – Butovitsch et al. (June 2020), Advanced Antenna Systems for 5G Network Deployments
