Phased Array Antenna (Smart Antenna) also referred to as Antenna Arrays are used in wireless communication system. It helps in achieving reliable and high-speed, high-data rate transmission. This post will discuss Phased Array Antenna (also known as Smart Antenna or Antenna Arrays), how it works in Cellular Wireless Communication, it’s types, applications, advantages and disadvantages.
What is Phased Array Antenna (in Cellular Wireless Communication)
Conventional Antenna uses limited Bandwidth and hence lot of interference issues persists in the system. The solution to this was the development of Phased Array Antenna (Smart Antenna). This type of Antenna system aptly utilizes radio spectrum in cellular wireless communication applications. It is the combination of an Antenna Array with a digital signal-processing capability to transmit and receive signals. It is typically implemented in the Base Station.
Fig. 1 – Introduction to Phased Array Antenna (Smart Antenna)
Phased Array Antenna adapts its radiation pattern with respect to its signal environment to achieve improved performance. The development of powerful low-cost Digital Signal Processors (DSP’s), ASIC’s, and software based DSP techniques using Algorithms have made Phased Array Antenna practical for wireless cellular communication systems.
Fig. 2 – Multi Beam Formation of Smart Antenna
Types of Phased Array Antenna (Smart Antenna)
Smart Antenna System is classified into two types. They are:
- Switched Beam Antenna System
- Adaptive Array Antenna System
Switched Beam Antenna System
Switched Beam Antenna System is pre-defined and has fixed number of beam patterns. It forms multiple fixed beams with intense sensitivity in specific directions. This type of antenna detects signal strength and switches from one beam to another depending upon the mobility of the mobile. The outputs of multiple antennas are combined to form a directional beam. This process is called as Spatial Filtering technique or Beam forming technique.
It is based on a switching function i.e. it selects the beam that gives strongest desired signal. Fig. 3 shows block diagram of Switched Beam type Phased Array Antenna System in which Phase Shifting Network is used to change the transmission phase angle of an input signal. Phase shifting Network provides an output signal with an equal amplitude with respect to the input signal. The direction of the combined signals from multiple antennas can then be steered by varying the phase in each element.
Fig. 3 – Block Diagram of Switched Beam Antenna System
These combined signals when radiated, forms the antenna radiation pattern. RF Switch unit consists of switches that helps in routing the signals through transmission paths. The antenna beam is adjusted in the desired direction by changing ON-OFF states of the switches. At any give instance, one RF switch is turned on while others are in ‘OFF’ state.
The output of this is connected to Power Detector. The Power Detector measures the signal strength of the incoming signal and sent to Control Logic Unit. The Control Logic controls the whole system. It compares the signals by filtering techniques and gives feedback to RF Switch to select the signal with high S/N Ratio. Thus, the desired radiation pattern is obtained.
Adaptive Array Antenna System
This type of Phased Array Antenna is the most advanced antenna available till date. This system has the ability to distinguish user signal and interference and directs the beam in the required direction using DSP techniques to maximize signal reception and minimize interference. They are capable to modify their radiation patterns by utilizing the wireless radio channel at both transmitter and receiver section with high precision using DSP.
Fig. 4 – Block Diagram of Adaptive Array Antenna System
Improved S/N Ratio and Optimal Gain is achieved by this type of Antenna. These are best employed in relatively low multipath, interference limited environments, to derive greatest system benefits.
Adaptive Array consists of N identical antenna elements. The phases and amplitudes of the signal exciting the elements determine the gain of the array in a certain direction. Phases and amplitudes are electronically adjusted to attain maximum gain. Complex weights are placed in the signal path and combined to get the output signal. This signal is fed to the control unit. Several adaptive algorithms are used to focus the array beam for transmission.
How does Phased Array Antenna (Smart Antenna) Work
Basically, Phased Array Antenna or Antenna Arrays scans the environment for the clients and interference using embedded algorithms. Based on the computation, the system selects optimal beams from over multiple pattern combinations. This is possible with Digital Signal Processing Techniques. Within a short span, an optimal beam combination is shaped for each User (Client). This cycle repeats to dynamically shape different patterns in response to changing environments.
Fig. 5 – Schematic Representation of Smart Antenna System
Applications of Smart Antenna
The applications of Phased Array Antenna (Smart Antenna) include:
- Used in UAV’s.
- Antenna Arrays are used in Radar Systems.
- They are extensively used in Wireless Cellular Systems.
- Phased Array Antennas are also used in Radio Telescopy.
- They are used in Electronic Warfare System.
Advantages of Smart Antenna
The advantages of Phased Array Antenna (Smart Antenna) are:
- Minimum Interference can be attained using Smart Antenna.
- Adaptive antenna’s Range/Coverage is high.
- Low power requirements enable greater battery life.
- Spectral efficiency can be achieved.
Disadvantages of Smart Antenna
The disadvantages Phased Array Antenna (Smart Antenna) include:
- Physical size of the antenna is a major concern.
- It is expensive.
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