Antennas

Now that we have covered cellular and other wireless standards. Lets move to the hardware side of it.. We will be discussing the antennas. 

Lets start with the basic definition of what an antenna is.. "An antenna is a transducer that converts the electrical power into radio waves or vice versa.." This Wikipedia definition says it all..I hope it answers the question of "How exactly does the transmission happen?"...Most importantly I do not claim that this post can be used as a comprehensive guide for antennas. I am trying to catch a glimpse of the wide subject.

In this post , lets understand the following details about antennas.

1. Fundamentals
2. Types
3. Antenna Design Concepts


1. Fundamentals 

The antenna has certain characteristics.. Here are some important parameters related to antennas.

• Frequency : Any antenna is designed for a range of frequencies. 
• Reciprocity : For any antenna, the characteristics when it sending the data and receving the data remain same. This is a fundamental property of any antenna.
• Gain : Antenna gain is a measure of how the antenna focuses available power away from a spherical wavefront to a limited number of directions
• Polarization : It is the orientation of the Electric field. An antenna can have linear/circular or elliptical polarization.
• Densitization/Desense  : Degradation of the sensitivity of an antenna due to noise.
• Effective Isotropic Sensitivity : Sensitivity of antenna in a single direction.
• Effective Isotropic Radiated Power : It is calculated as (Power - Loss + Gain)
• Radiation Patterns : This is a relative pattern in 3D. This depicts the relative strength of radiated field in various directions from antenna at const distance.

2. Types of Antennas : 

The antennas can be categorized depending on the frequency ranges they support , the directional properties or application.

a. Depending upon Directional properties

• Omni directional : These antennas transmit in all directions. (Its not isotropic!!)
• Semi directional : These have a broad sense of direction and accordingly the radiation pattern.
• Highly directional : This antennas are most widely used antennas , they propagate in a very specific direction.  Examples include Yagi antenna , Dish antenna , Patch antenna etc

b. Depending on the Application

There are antennas used for point to point or point to multi point communication.

3. Antenna Design Concepts

Here is the basic list of parameters one should keep in mind while designing/selecting antennas.

• Frequency Requirements
• Conductor Types
• Dimensions
• Placement 
• Regulations

In the next post , lets look at the Smart Antennas. Propagation Engineering and Practical Antenna Handbook are "MUST" reads on this topic.