Wireless communication was a revolutionary technology that changed the way we share information. Wireless communication means transfer of information from one object to another that are not physically connected to each other by means of an electrical conductor. In 1880, photophone was invented by Alexander Graham Bell and Charles Sumner which uses modulated light beams to send voice signals from one place to another.
This event kick started a chain of events that lead to the discovery of current world wireless technologies like WiFi, Bluetooth etc. Before going further, lets see how wireless communication looks like.
What is wireless communication?
Consider a basic wireless communication system that is used for transmitting audio from one place to another.
In this model, the sound is captured and converted electrical signals using microphone, which is amplified and modulated using a transmitter circuit. This electrical signal is sent to antenna and these antennas convert these signals to EM waves and is radiated into the atmosphere. The receiving antenna captures these signals and is converted back to electrical signal. These modulated signals are demodulated using demodulation circuit, amplified and is fed to loudspeaker which will convert it to sound.
What is Antenna?
Simply speaking, Antenna is a device which converts electrical signals to EM waves or vice versa. In the case of a transmitting antenna, the electrical signal from the transmitting circuit is converted to EM waves and is radiated into the atmosphere. In the case of a receiving antenna, the EM waves in the atmosphere is captured and is converted back to electrical signals for further processing. The dimensions of various parts of antenna depends up on the frequency of the EM waves that are being transmitted. The dimensions of components of the antennas will vary to match the frequency or wavelength of the signal to be transmitted
Almost all of the wireless communication devices that are separated by a considerable distance requires antenna of some kind. Some times this antennas will be external and can be observed easily, like routers, while some are etched in the PCB of the module itself.
Types Of Antennas
There are mainly three types of Antennas
Omni Directional Antenna
Semi Directional Antenna
Omni Directional Antennas are antennas that radiates EM waves equally in all direction. Semi directional antennas transmits radio waves in particular patter depending up on the design where as direction antennas transmits energy in a particular Direction only.
WiFis Wireless Networks works the same as the above mentioned communication block diagram but instead of the voice, we will be transmitting network data packets. The Wireless Router/Access Point converts these data packets to EM waves, radiated out through the transmitting antenna and the antenna in the Client device (mobile device) converts the EM waves back to electrical signals for data processing.
WiFi uses a frequency of 2.4 GHz or 5 GHz. Wavelength of 2,4 GHz is nearly 12,5 cm and for 5 Ghz is 5-6 cm. As mentioned above, the antennas are designed depending up on the frequency of the signals to be transmitted/received, which means, we cannot use 2.4 GHz antenna in the place of 5 GHz antenna and vice versa.
WiFi Antenna Power Gain
The signal range of an antenna is measured using a parameter called Power Gain which tells us about the effectiveness of an antenna when compared to that of any standard reference antenna. It is measured in decibels (dB).
Most of manufacturers use a value called dBi value for measuring the strength of an antenna. dBi is the gain of an antenna compared to that of an Isotropic radiator. The higher the dBi value, greater will be the area of coverage.
Omni-Directional WiFi Antennas
Omni Directional Antennas are antennas that can radiate power equally in all direction in a uniform plane.
Radiation pattern of omni directional antenna is doughnut shaped. Omni directional antennas are commonly used for indoor purposes such as WiFi Routers and wifi chpsets of mobile phone, laptop, television etc.
Directional WiFi Antennas
Mini panel antennas are directional antennas that are designed to transmit power in a particular direction. Which means you will have to point this antenna to the place where you want to receive this signal. These are generally long ranged, low profile antennas that are mostly designed for indoor purposes.
These mini panel antennas have a 60 degree spread angle and it can punch through normal walls and the radiations can reach hard to reach area.
Panel antennas are enhanced versions of mini panel antenna that can that can transmit power over a larger distance. They are very strong and sleak antennas that are specifically designed for outdoor uses. These antennas are very focussed and have a 32 degree spread which less when compared to that of a mini panel antenna but, it can travel a long distance with this angle of radiation.
You can connect this to a wifi router and point it out through your window, or fix it on a pole on the roof of your house, to a building where you want to receive this signal at a distance very far away from the source.
Cantenna is one of the most popular antenna among hobbyists and pentesters. They are also highly directional and compact antennas which can radiate power at an angle of around 36 degrees.
This one focussing its energy on a narrow beam making it highly directional but the radiations are so powerful that it can travel more than 3 miles line of sight under ideal conditions. We can connect USB adapters and WiFi Routers with removable antennas directly into this, Adding this antenna will significantly improve the range of transmission as well as reception.
This one is the best long range antenna that can provide point to point link between the source and the receiver. These antennas have an ultra strong gain but a very thin beam width which makes it highly directional with a radiating angle between 3 degree and 12 degree.
These antennas are designed to withstand extreme weather conditions.