Antenna Gain: (Power Gain)

Antenna Gain: (Power Gain):

• The gain of an antenna is specified in dBi 
• Gain of the antenna compared to an isotropic antenna
• An isotropic antenna is an ideal (theoretical) antenna that spreads energy in all directions (in a sphere) with equal power, which is impossible to design in practice.
• Some antennas may have their gains expressed in dBd (though less common), (d stands for Dipole)
• Antenna can be internal or External 

What is SNR (Signal to Noise ratio)

SNR (Signal to Noise ratio) : 

• As SNR = Signal Strength (dBm)/ Noise Floor(dBm) 
• Noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals 
• Since dBm is in logarithmic scale, SNR is obtained by subtracting the noise from the signal strength i.e (SNR = Signal Strength – Noise Floor)
• The minimum required SNR for a receiver varies depending on the bit rate or modulation.
• A positive SNR is required (i.e., signal strength should be a higher than the noise) 
• E.g if a radio (client device) receives a signal of -75 dBm and the noise floor is measured at -90 dBm, the SNR is 15 dB [ -75 – (- 90) = 15 ]
• SNR value decreases if the length between receiver and Sender increases. Because of Loss / Attenuation .
• An increase in RF interference from microwave ovens and cordless phones, which increases the noise level, also decreases SNR. 
• A higher SNR value means that the signal strength is stronger in relation to the noise levels, which allows higher data rates.

What is a DB ?

What is DB ?

• The term dB is an abbreviation of decibel, which is equal to 1/10th of a Bel
• It’s a very small quantity, is a logarithmic measure of the ratio between two quantities.
• The unit dB can also be used to represent an absolute power value,
• By defining a reference and adding the corresponding suffix to dB.
• For example, dBm stands for dB with reference to 1 milliwatt (mW).
• Therefore, 1 mW = 0 dBm

 Milliwatts to dBm Conversion

mW :   0.00001

dBM: -50 

mW :   0.0001

dBM: -40

mW :   0.001

dBM: -30

mW :   0.01

dBM: -20

mW :   0.1

dBM: -10

mW :   1

dBM:  0

mW :   2

dBM:  3

 mW :   10

dBM:   10

 mW :   100

dBM:    20

 mW :   200

dBM:   23

 mW :   400

dBM:  26 

 mW :   1000

dBM:  30

Isotropic antenna and Dipole antenna

Isotropic antenna:

 An isotropic antenna is a theoretical antenna that radiates equally in all directions - horizontally and vertically with the same intensity. The antenna has a gain of 1 dB in the spherical space all around it and has an efficiency of 100%. The concept of an isotropic antenna is often used as a reference antenna for the antenna gain.

Dipole antenna basics:

• The name 'di-pole' indicates that the dipole antenna consists of two poles or items – two conductive elements or simply 2 wire with proper length.
• Dipole antennas are the most common type of antenna used and are omni-directional, propagating radio frequency (RF) energy 360 degrees in the horizontal plane
• These are normally on the same axis,
• The dipole antenna is normally split in the centre.
• Most commonly used Dipole antenna is Half wave dipole antenna
• Conducting element which is wire or metal tube which is an electrical half wavelength long. 
• The antenna consists of the feeder connected to two quarter wavelength elements in line with each other.