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[[File:VSWR.JPG|center|frame]]
Lower the VSWR, better is the antenna impedance matched. VSWR can be easily found out using Vector Network Analyser (VNA).
=== Antenna Gain ===
Antenna gain describes the power in the direction of peak power of any antenna with respect to an lossless isotropic antenna (100% efficiency and 1 directivity) when both are excited with same power. Simply speaking antenna gain takes into account both directivity and antenna efficiency and mathematically it is product of those two. <br \>
'''Antenna Gain = Antenna Efficiency x Directivity''' <br \>
Similar to directivity, antenna gain can vary considerably with type of antenna and hence the type of antenna to be selected is highly application specific
===Polarization ===
Polarization is very easily visualised as pattern traced out by the E-field in any electromagnetic wave.
[[File:Polarization1.png|center|frame]]
For example in the the above figure, when only E-field component of the electromagnetic wave is traced out on screen perpendicular to the direction of propagation of the electromagnetic wave, we get a straight line. Hence the polarization of this kind of electromagnetic wave is called linear. <br \>
Based on polarization there are three major types of waves:
* '''Linearly polarized:''' The above wave is a example of linearly polarised wave. In linear polarization, the line traced by E-field can be in any orientation.
* '''Circularly polarized:''' Consider two linearly polarised waves of equal magnitude perpendicular to each other. If we create a phase difference of 90° between them and add them, we will get a circular polarized wave. i.e. the E-field of the wave will trace out a circle. The circle can right handed (Right Hand Circular Polarization or RHCP) or left handed (Left Hand Circular Polarization or LHCP) depending on which wave is leading or lagging.
*'''Elliptically polarized:''' If the two linearly polarized waves used for circular polarization have unequal magnitude or are added with phase difference not 90° or 0° or integral multiple of 90°, then the resulting polarization will be elliptical. The ellipse, again, can be right handed or left handed.
[[File:Polarization2.png|center|frame]]
[[File:LHCP.gif|center|Left Hand Circularly Polarized Signal]]
[[File:RHCP.gif|center|Right Hand Circularly Polarized Signal]]
Now, the polarization of any antenna is simple the polarization of electromagnetic waves radiated by that antenna. The reason why polarisation of antenna is so important is it is useful in determining the losses while making the link budget.
