Wireless networking antennas can be manufactured at home using simple, everyday items and a minimum of knowledge about antenna physics. Two main types of antennas, the directional and omnidirectional, relate to the direction and intensity of the transmitted wave pattern. An Easy Wifi Yagi Antenna - A 2.4 GHz WiFi antenna that can boost your WiFi signals for many miles. It's an easy to build Yagi antenna project done with some popsicle sticks, paper clips and glue. It's an easy to build Yagi antenna project done with some popsicle sticks, paper clips and glue. English Hangout 新しい時代の英語の学び方を追求する英語学習情報サイト.

• WLAN antenna 2.4 GHz Do-It-Yourself
  A simple homebrew outdoor antenna to 2.4 GHz band.
• Build a 2.4GHz Vertical antenna
  Building a 2.4GHz vertical collinear omnidirectional antenna
• 802.11b Homebrew WiFi Antenna Shootout
  Guide to homebrew your wifi antenna, using a tin can, in this cases using a pringles can. This antennas are also known as cantenna and let you spread your wifi signal.
• 13 cm Helix Antenna
  Here is the design of a 2.4 GHz antenna that is ideal for amateur satellite communications. This antenna is easy to assemble because the design itself tolerates inaccuracies in the construction without really affecting performance.
• Building a 2.4GHz 10 Element Brass Yagi
  Build this home made yagi antenna for your 2.4ghz wireless ethernet.
• A 2.4 Ghz High gain antenna
  Here is how to build a high gain antenna for 2.4 gHz wireless networks. Several hams are experimenting with these devices in an effort to build a network. It is sometimes referred to as Hinternet or HSMM.
• 43.33 Km LOS with USB WiFi stick
  Simple USB 802.11b WiFi adapter with original antenna used for this 27 miles long-range wifi connection test by adam 9A4QV.
• 2.4GHz Helix antenna
  Concise instructions on making a broadband helical antenna for 2.4GHz use, such as: 802.11b wireless networking 2.4GHz video links.
• Simple double-quad Antenna
  2.4 Ghz quad antenna
• How to build a tin can waveguide antenna
  Looking for an inexpensive way to increase the range of your wireless network? A tin can waveguide antenna, or Cantenna, may be just the ticket. This design can be built for under $5 U.S. and reuses a food, juice, or other tin can.
• 2.4GHz Cubic Quad Antenna
  The Cubic Quad antenna is a commonly homemade antenna in the range of about 150 odd MHz. Our little project was to design one of these for use in the 2.4GHz range for 802.11 wireless LANs.
• Building Helical Antennas - Seattle Wireless
  Photos and comments on building an helical antenna for wifi
• 2.4 Ghz double quad antenna
  An easy to build, compact antenna for wireless lan applications that offers a reasonable amount gain.
• 2.4GHz Short Backfire Antenna
  My short backfire antenna for 2.45ghz by carl rabe - g6nlc
• 6dbi Colinear Antenna for Wireless LAN
  This is an short description on how to make a cheap omni antenna for 802.11 wireless LAN cards.

• 10 element Yagi WiFi Antenna- A DIY project of a WiFi 10 elements Yagi antenna
• 13 cm Helix Antenna^pop- Here is the design of a 2.4 GHz antenna that is ideal for amateur satellite communications. This antenna is easy to assemble because the design itself tolerates inaccuracies in the construction without really affecting performance.
  [ Hits: 65146 | Votes: 85 | Rating: 5.96 ]
• 2.4 GHz Collinear antenna- 2.4 GHz sleeve co-linear antenna construction details
• 2.4 Ghz double quad antenna^pop- An easy to build, compact antenna for wireless lan applications that offers a reasonable amount gain.
  [ Hits: 27784 | Votes: 83 | Rating: 5.17 ]
• 2.4 GHz Quad Antenna^updated- A 2,4 GHz 13cm band quadrible qiad antenna with reflector offering a 14dbd gain
• 2.4 GHz Sky mini-dish Antenna- How to modify a Sky mini-dish so it will work effectivly at 2.4Ghz.
  [ Hits: 671 | Votes: 4 | Rating: 4.25 ]
• 2.4GHz Colliner Antenna Design- Antenna for 802.11 applications
• 2.4GHz Cubic Quad Antenna^pop- The Cubic Quad antenna is a commonly homemade antenna in the range of about 150 odd MHz. Our little project was to design one of these for use in the 2.4GHz range for 802.11 wireless LANs.
  [ Hits: 36935 | Votes: 68 | Rating: 5.51 ]
• 2.4GHz Helix antenna^pop- Concise instructions on making a broadband helical antenna for 2.4GHz use, such as: 802.11b wireless networking 2.4GHz video links.
• 2.4GHz Short Backfire Antenna^pop- My short backfire antenna for 2.45ghz by carl rabe - g6nlc
  [ Hits: 27103 | Votes: 27 | Rating: 6.07 ]
• 2400 MHz Helix Antenna- This antenna is easy to build and suitable for broadband work, satellite work and terrestrial work.
• 43.33 Km LOS with USB WiFi stick^pop- Simple USB 802.11b WiFi adapter with original antenna used for this 27 miles long-range wifi connection test by adam 9A4QV.
  [ Hits: 50959 | Votes: 103 | Rating: 5.64 ]
• 6dbi Colinear Antenna for Wireless LAN- This is an short description on how to make a cheap omni antenna for 802.11 wireless LAN cards.
• 802.11 2.4Ghz Low-Power Vertical Antenna- A 2.4Ghz low-power 5dBi vertical collinearantenna for 802.11 applications
  [ Hits: 9059 | Votes: 8 | Rating: 4.37 ]
• 802.11b Homebrew WiFi Antenna Shootout^pop- Guide to homebrew your wifi antenna, using a tin can, in this cases using a pringles can. This antennas are also known as cantenna and let you spread your wifi signal.
• A 2.4 Ghz High gain antenna^pop- Here is how to build a high gain antenna for 2.4 gHz wireless networks. Several hams are experimenting with these devices in an effort to build a network. It is sometimes referred to as Hinternet or HSMM.
  [ Hits: 61213 | Votes: 89 | Rating: 5.53 ]
• A Short Back Fire antenna- A Short Back Fire antenna improved for Wireless-LAN applications
• A simple Wi-Fi Yagi- Add two parasitic elements to the sleeve dipole of a Netgear Router
  [ Hits: 1848 | Votes: 6 | Rating: 2 ]
• A Tincan feed for 2.45Ghz- Construction details for a simple but effective antenna for 2.45Ghz wireless lan use.
• A Tincan feed for 2.45GHz- Construction details for a simple but effective antenna for 2.45Ghz wireless lan use.
  [ Hits: 503 | Votes: 5 | Rating: 6.8 ]
• An Easy Wifi Yagi Antenna- A 2.4 GHz WiFi antenna that can boost your WiFi signals for many miles. It's an easy to build Yagi antenna project done with some popsicle sticks, paper clips and glue.
• Belkin F5D7050 External Antenna- Adding an external antenna to the Belkin F5D7050
  [ Hits: 4545 | Votes: 9 | Rating: 5.33 ]
• BiQuad 802.11b Antenna- BiQuad 802.11b Antenna 11dBi, wide band by Trevor Marshall
• BiQuad 802.11b Antenna- Home made WiFi 11dBi, wide band antenna by T. Marshall
  [ Hits: 1191 | Votes: 2 | Rating: 1 ]
• BiQuad Antenna calculator^updated- Online calculator for Bi-Quad antennas
• Biquad Antenna Construction- This page details the construction of a biquad antenna. The biquad antenna is easy to build, and provides a reliable 11dBi gain, with a fairly wide beamwidth.
  [ Hits: 9245 | Votes: 19 | Rating: 7.57 ]
• Build a 2.4GHz Vertical antenna^updatedpop- Building a 2.4GHz vertical collinear omnidirectional antenna
• Building a 2.4GHz 10 Element Brass Yagi^pop- Build this home made yagi antenna for your 2.4ghz wireless ethernet.
  [ Hits: 64712 | Votes: 118 | Rating: 7.33 ]
• Building Helical Antennas - Seattle Wireless^pop- Photos and comments on building an helical antenna for wifi
• Building the Single Sided 8 Slot Waveguide- Online calculator and a full documented pictorial guide to build a single sided 8 slot waveguide antenna
  [ Hits: 731 | Votes: 5 | Rating: 7 ]
• Building the WiFi parabolic antenna- Building a Bell ExpressVu satellite dish with a waveguide coffee can cantenna feed, and a Netgear USB Rangemax wifi card (WPN111).
• Cantenna Calculator- Online calculator for Cantenna special antenna for 802.11 Wi-Fi bands
  [ Hits: 4253 | Votes: 113 | Rating: 5.38 ]
• CantennaCalc- Kioan's calculator for building a Cantenna , directional waveguide antenna for long-range Wi-Fi
• CD Case WI-FI antenna- A bi-quad antenna for wireless 2.4 Ghz made using a cd case
  [ Hits: 14173 | Votes: 41 | Rating: 6.08 ]
• Coffee Can WiFi Antenna- This wi-fi antenna design is a much simpler DIY project than the pringles cantenna. Basically there are 3 parts to a build-your-own 2.4 Ghz cantenna kit: a pigtail, an N-female connector and a metal coffee can.
• Cookie Cantenna Wi-Fi- Make a cheap, portable, high performance (15-18 db) directional antenna out of commonly available parts that can be purchased in most grocery and hardware stores.
  [ Hits: 6375 | Votes: 3 | Rating: 10 ]
• DirectionalWaveguide - Seattle Wireless- Waveguide antenna is a type of DirectionalAntenna and is a modified waveguide. A waveguide is simply a tube, either rectangular or cylindrical in cross-section, that will carry a microwave radio signal with very low signal loss
• Dish 802.11 Wireless Networking Antenna- This antenna modification is for the IEEE 802.11b networking protocol that operates at 2.4 GHz. It can be scaled easily to the 5 GHz frequency used by IEEE 802.11a by simply scaling the dimensions on the feed can and the excitation antenna to 2.4/5 = 48% of the dimensions shown above.
  [ Hits: 9378 | Votes: 8 | Rating: 6 ]
• DIY Wireless Antennas Update and Resource Center- Your DIY Guide to Wireless Antennas for boosting wireless signal strength. How to build a wireless antenna for little or no money.
• Do-It-Yourself Wireless Antennas- Your guide to wireless antennas, how to build a wireless antenna without spending much moneyThe Pringles Cantenna, Coffee Can Antenna, Parabolic Reflector and Antenna Designs. Combine a homemade Tripod Mount with an inexpensive Pistol Grip and go Wardriving.
  [ Hits: 10942 | Votes: 10 | Rating: 6.3 ]
• Easy 2.4 GHz Omnidirectional Antenna- A step by step guide to easily make a homemade antenna for the Wi-FI band and for a fraction of the cost of a common WIFI commercial antenna.
• Helical Antenna for 2.4 GHz and 802.11b- The following page details construction of a Helical antenna based on the superb design by Jason Hecker.
  [ Hits: 5282 | Votes: 6 | Rating: 7.17 ]
• Helical Antenna for WiFi- Improved Helical Antenna Design for 802.11b WLAN by PA0HOO
• Home-brew Compact 6dBi Collinear Antenna- This page details the construction of an easy-to-make collinear 360 degrees omni-directional, vertically polarised, antenna for 802.11b/g wireless networking.
  [ Hits: 20433 | Votes: 29 | Rating: 7.89 ]
• Homebrew WiFi Antennas- Lincomatic's Homebrew WiFi Antennae, Cantenna, Toothpick Monopole, Patch Antenna, BiQuad, collinear wifi antenna all in one page
• Horn Antenna Designer- 802.11b Horn Antenna Designer, calculate horn antenna dimension for wi-fi application
  [ Hits: 3002 | Votes: 10 | Rating: 5 ]
• Hot to test a homebrew wifi antenna- Homebrew Wifi antenna test page
• How to build a tin can waveguide antenna^pop- Looking for an inexpensive way to increase the range of your wireless network? A tin can waveguide antenna, or Cantenna, may be just the ticket. This design can be built for under $5 U.S. and reuses a food, juice, or other tin can.
  [ Hits: 37502 | Votes: 44 | Rating: 7.42 ]
• How to extend your Wireless Network- How to extend your Wireless Network by building a 2.4 gHz wifi cantenna
• Laptop Mini Wireless Antenna- A small antenna to improve signal reception of a laptop wireless card. This will boost the gain of your wi-fi card and will increase network speed and bandwidth.
  [ Hits: 1239 | Votes: 7 | Rating: 3.29 ]
• Linear Focus Parabolic Wifi Antenna- This antenna can be made in a couple of hours and involves a fair amount of measuring, cutting, bending, and bolting metal.
• Long Range Wi-fi Dish Antenna- Build parabolic WLAN antenna adapted from a small satellite dish. It provides high gain and long range connections.
  [ Hits: 5174 | Votes: 9 | Rating: 5.22 ]
• Making an 802.11 antenna from a tin can- How to make a wifi cantenna using a mini ravioli can
• Mobile 2.45Ghz antenna- A prototype 2.45ghz antenna for mobile use. This antenna has been u sed for surveying signal strength using a variety of free wlan tools.
  [ Hits: 6044 | Votes: 9 | Rating: 5.33 ]
• Portable Dish Antenna- Homemade portable dish antenna for 13 cm band
• Practical Wifi Antenna Measurement- This page describes a simple way to determine the main RF characteristics of a Wifi (IEEE802.11b/g wireless LAN) antenna.
  [ Hits: 2912 | Votes: 3 | Rating: 4 ]
• Pringles WiFi Antenna- DIY Wifi Antenna with a pringles can and extend your wifi signal, also known as cantenna.
• PringlesCantenna - Seattle Wireless- The PringlesCantenna is an ultracheap Yagi-type directional antenna that can be built for under $10. The original Pringles Yagi was designed by Andrew Clap.
  [ Hits: 9317 | Votes: 4 | Rating: 6 ]
• Prototype SWR meter for 2.45Ghz- Testing antenna's is a lot easier if you have a good swr meter this is a prototype of a design by g7eyt.
• SardineCanAntenna - Seattle Wireless- Sardine Can Antenna. is a BiQuad or Bi circle - wire length each side (8 x 1/4 waves ) 31 mm
  [ Hits: 10131 | Votes: 13 | Rating: 4.61 ]
• Sector Antenna for Wifi- Homebrew Sector Antenna for Wifi ISM band (2,4GHz)
• Sector Antenna for Wifi- DIY a sector antenna for de Wifi 2,4GHz ISM band.
  [ Hits: 1611 | Votes: 13 | Rating: 7.54 ]
• Selecting a WiFi antenna- What is the best WiFi antenna for me?Looking for a range extender antenna for your WiFi system. This article will help in choosing the correct antenna for your system
• Simple double-quad Antenna^pop- 2.4 Ghz quad antenna
  [ Hits: 43942 | Votes: 26 | Rating: 6.2 ]
• Slotted Waveguide 802.11b WLAN antennas- 802.11b WLAN Waveguide Antennas Unidirectional &Omnidirectional. High gain, Simple construction by Trevor Marshall
• Uni-Directional WIFI Range Extender- Requires no modifications to a USB WIFI adaptor or your computer.
  [ Hits: 4757 | Votes: 1 | Rating: 10 ]
• WiFI Collinear antenna- Pictures and homebrew instructions for this collinear 2.4 Ghz antenna
• WiFi Helical Antenna Design- DIY a Wi-FI Helical Antenna for better performances, a project by PA0HOO i Dutch end English
  [ Hits: 1395 | Votes: 4 | Rating: 4.5 ]
• WiFi Long Range Helical Antenna- High Gain Wi-fi Helical Antenna by AB9IL
• WiFi Spider Antenna- Quarter wave omni-directional spider antenna for 2.4GHz 802.11b
  [ Hits: 949 | Votes: 6 | Rating: 7.33 ]
• WiFi Yagi Antenna- Long Range Wi Fi Antenna by AB9IL
• WK8L's ATV Page- Includes links and documentation on wifi antennas, 2.4 GHz Coffee Can Feed Antennas
  [ Hits: 3514 | Votes: 4 | Rating: 5 ]
• WLAN 802.11b/g Bi-quad antenna- Building and testing a WLAN 802.11b/g Bi-quad antenna
• WLAN antenna 2.4 GHz Do-It-Yourself^pop- A simple homebrew outdoor antenna to 2.4 GHz band.
  [ Hits: 138323 | Votes: 182 | Rating: 5.52 ]
• Woktenna- A woktenna. The collector and stand collapses in seconds, is aimable, portable, and gave terrific gain. This is a great little setup for a laptop on the go trying to get the distant wifi access.
• Yagi-16DBI for 2.4 GHz- Wifi yagi antenna with 16 Dbi (in French)
  [ Hits: 12040 | Votes: 34 | Rating: 6.05 ]

Antennas

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Antennas : WiFi

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WiFi Lab (also known as Radio Lab) is a Division C that was a trial event at the 2017Ohio state tournament, the 2017 Boyceville Invitational, the 2018Texas state tournament, the 2017 and 2018Virginia state tournaments and the 2018 National Tournament. Competitors are asked to build an antenna that transmits a signal at 2.4 GHz and complete a written test about electromagnetic waves. Teams may bring a three ring binder and two computational calculators, and are required to provide graphs and tables showing the relationship between power and distance for different configurations of the antenna.

Building an Antenna

Electromagnetic Spectrum

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation, including radio waves. The frequencies of these waves are measured in hertz (Hz). The frequency range is divided into separate bands, and the waves within these bands have different names. From the largest wavelength to the shortest wavelength these bands are radio waves, microwaves, infrared and visible light, ultraviolet, x-rays, and gamma rays.

X-rays and gamma rays are known as ionizing radiation and can be dangerous if an organism is exposed to them for too long. X-rays are defined as electronic transitions and gamma rays are generated from nuclear processes such as decay. Both gamma and X-rays have many uses in medicine and occasionally gamma rays are used in the sterilization of foods and seeds. Ultraviolet (UV) rays are not ionizing, but can still break chemical bonds causing sunburn and even potentially skin cancer. Some UV rays in the middle of the range also have a strong potential to cause mutation. Most damaging UV rays emitted by the sun are absorbed by the atmosphere, being blocked by the ozone layer or being absorbed by oxygen or nitrogen in the air.

Visible light occupies a very small portion of the electromagnetic spectrum. Different visible colors are the result of differing electromagnetic wavelengths, with red having the longest wavelength and purple the shortest. Electromagnetic radiation between 400–790 terahertz (THz) is visible to the human eye, but sometimes infrared and ultraviolet rays can be referred to as light. Infrared rays are useful in thermal imaging and occasionally in data transmission. Television remotes transmit signals using infrared light, which is why if the front of the remote is blocked the signal will not be received. Some infrared light can also be detected by photograph film.

Microwaves and radio waves have the lowest frequency of the electromagnetic spectrum, and are most well known for their use in microwave ovens. They can also be used in industrial heating and radar systems, as well as transmitting information. However, at that intensity microwaves do not have the same heating effects.

Radio Waves

Radio waves are the focus of the event, as WiFi is transmitted over radio waves. Radio waves are transmitted and received by antennas and are widely used to transmit information. They are also used for GPS systems and locating distant objects with radars. To generate radio waves, a transmitter generates an AC current which is applied to the antenna and generates an electric and magnetic field.

WiFi is most commonly transmitted over the 2.4 GHz and 5.8 GHz bands which are divided into multiple channels. These channels can be shared by multiple networks, making WiFi much more vulnerable to attack than wired connections. Security protocols have been created so that WiFi access is secure as possible, including the WEP and WPA protocols.

Antennas

An antenna is an instrument that can be used for transmitting and/or receiving electromagnetic waves (usually radio waves). Transmission antennas work by emitting energy as electromagnetic radiation. Reception antennas absorb energy and use it to generate an electric current.

Radiation Patterns

An antenna's radiation pattern is a plot that represents the strength of radiation output or input in any direction.

Build Wifi Antenna For Laptop

Radiation patterns like the one above are usually graphed in polar (2-dimensional) or spherical (3-dimensional) coordinates. This allows one to define the strength of the emission in terms of the direction (angle). Polar coordinates are plotted in terms of radius [math]displaystyle{ r }[/math] (distance from the origin) and angle [math]displaystyle{ theta }[/math] (theta, angle from the usual [math]displaystyle{ x }[/math]-axis, known as the polar axis). Spherical coordinates are plotted in terms of radius [math]displaystyle{ r }[/math] (distance from the origin), azimuthal angle [math]displaystyle{ phi }[/math] (phi, angle from the usual [math]displaystyle{ x }[/math]-axis), and polar angle [math]displaystyle{ theta }[/math] (theta, angle from the usual [math]displaystyle{ z }[/math]-axis).

One significant property that all antennas have is that their transmission and reception radiation patterns are always the same. This fact is known as reciprocity.

Directivity

An antenna's directivity describes how concentrated the power output of the antenna is in any direction. An isotropic antenna, one that has a perfectly spherical radiation pattern, radiates equally in all directions (since the radius is the same in all directions), so it would have a directivity of 1. Although directivity is technically a function that outputs the directivity at any given angle, it is commonly defined as a constant in terms of the direction of greatest radiation (which is the definition used in this page).

In the image above, the directivity could be given in terms of the angle [math]displaystyle{ theta = frac{pi}{2} }[/math]. However, you could also define a function [math]displaystyle{ Dleft(thetaright) }[/math] which outputs the directivity at an angle [math]displaystyle{ theta }[/math].

Directivity is proportional to ratio of the maximum radiation intensity to the average radiation intensity. If these two values are not given, it is very difficult to calculate the directivity. If they are given, however, then the formula is simply [math]displaystyle{ D = 4pi cdot frac{text{Maximum radiation intensity}}{text{Average radiation intensity}} }[/math]. For this formula, the value of the directivity is unitless. However, directivity is often represented in terms of decibels, using the formula [math]displaystyle{ D_{text{dB}} = 10log{frac{D}{D_{text{reference antenna}}}} }[/math]. Since decibels are a relative unit, you must choose a reference antenna to compare the directivity. This is often an isotropic antenna with a unitless directivity of 1, which gives the final value of the directivity in terms of a special unit called decibels isotropic ([math]displaystyle{ text{dBi} }[/math]).

Gain

The gain of an antenna refers to how much power is emitted in the direction of greatest radiation. The difference between gain and directivity is that gain is calculated by multiplying the directivity of an antenna by its efficiency, meaning it takes into account power loss.

The formula for gain is [math]displaystyle{ G = eta D }[/math], where [math]displaystyle{ eta }[/math] is the efficiency. This, in turn, is calculated as [math]displaystyle{ eta = frac{P_{out}}{P_{in}} }[/math], where [math]displaystyle{ P_{out} }[/math] and [math]displaystyle{ P_{in} }[/math] are the total power output and power input of the antenna, respectively. Efficiency essentially measures how much of the input power is actually emitted by an antenna. For an antenna that outputs all of the power put into it, the efficiency would be equal to 1 and the gain would be equal to the directivity. Such an antenna is often referred to as an isotropic antenna.

If the value of directivity used in the formula is unitless, then the gain is in decibels ([math]displaystyle{ text{dB} }[/math]). If the directivity is in terms of decibels isotropic ([math]displaystyle{ text{dBi} }[/math]), then the gain is also in decibels isotropic. Gain can also be given in comparison to a perfect dipole antenna with no loss, which has a gain of [math]displaystyle{ 2.15 text{dBi} }[/math], a unit called decibels dipole ([math]displaystyle{ text{dBd} }[/math]). To convert to and from [math]displaystyle{ text{dBd} }[/math], use the formula [math]displaystyle{ G_{text{dBd}} = G_{text{dBi}} - 2.15 }[/math]. An important thing to realize here is that an antenna with a gain of [math]displaystyle{ 2.15 text{dBi} }[/math] would have a gain in decibels dipole of [math]displaystyle{ 0 text{dBd} }[/math]. This does not mean that the antenna has no gain, but rather that its gain is the exact same as a perfect dipole antenna with no loss. This same idea applies for any values, including gain, which are represented in decibels relative to another antenna.

Impedance

Impedance is a measure of opposition against an antenna's transmission. The idea of impedance is related to that of resistance in a circuit. Impedance is measured in ohms, with the symbol [math]displaystyle{ Omega }[/math] (uppercase omega). The actual impedance of an antenna is difficult to determine since it depends on the antenna, operating wavelength, and especially the environment.

Types

There are numerous types of antennas and countless ways to classify them. Of these, the simplest type is technically the isotropic antenna, although it is purely theoretical and cannot be constructed. Instead, the isotropic antenna is mainly used as reference for properties of real antennas, such as efficiency, directivity, and gain. However, it is possible to construct a nearly-isotropic antenna by making it smaller than the wavelength it emits. This is the principle applied in half-wave dipoles, discussed below.

Dipole antennas are the simplest and most common viable antennas, and serve as the foundation for most complex antennas. They antennas consist of two wires or rods pointing out in different directions (usually opposite of each other but sometimes at an angle). Of the dipole antennas, the half-wave dipole is the most common. Half-wave dipole antennas are characterized by having a total length nearly equal to half the wavelength they operate at. The advantage of this design is that the radiation being transmitted lines up with each monopole (the wires or rods pointing out, a property known as resonance. This results in an omnidirectional antenna with optimal impedance, making it very useful for various applications such as communication and, in the past, television.

Although dipole antennas are useful, a single dipole antenna is not very powerful. Instead, the most common antennas consist of multiple dipoles, such as the Yagi-Uda antenna. A Yagi-Uda antenna is constructed from multiple dipole elements systematically placed together at different distances. As a result of the numerous dipole elements, Yagi-Uda antennas have higher directivity and gain (shown below).

However, Yagi-Uda antennas can be noisy and can only operate from around 30 MHz to 3 GHz. In addition, since the design of the antenna depends on the wavelength (and thus, the frequency) at which the antenna operates, a single antenna cannot be used for multiple frequencies. Yagi-Uda antennas are most commonly used as receptors for television.

In general, antennas made up of a system of multiple antennas are referred to as array antennas. The main advantage of array antennas is the ability to increase directivity by having signals interfere constructively and destructively to boost the power in certain directions and cancel it out in other directions. This is done by adding different phase shifts to the signals of each antenna. Phase shifts are essentially shifts in the position of a wave that are used to create interference. Because of their high directivity, array antennas are used for everything from broadcasting to astronomy.

Radio Wave Propagation

There are three main ways in which radio waves can be sent from a transmitter to a receiver. The simplest method is line-of-sight (LOS) propagation. LOS propagation occurs when the signal is sent straight from the transmitter to the receiver through the shortest possible straight line path. This method is primarily used for shorter distances as the signal can be affected by any obstacles in the way and can only be used when the transmitter and receiver are in view of each other. A slightly better method is ground wave propagation, where the signal travels in a curved path around the Earth, allowing it to travel farther. Sky wave propagation is the final method, which utilizes a layer of the atmosphere known as the ionosphere to bounce the signal to the receiver. The signal is sent up to the ionosphere, when it is reflected, hits the ground, and continues this cycle until it reaches the destination. Sky wave propagation is more difficult to conduct and can only be used within the frequency range from 2 to 30 MHz.

Long Range Wifi Receiver Antenna

Information

Information is a very abstract concept but can be defined as any form of uncertainty or randomness in a system that allows it to store meaning. As a counterexample, a piece of paper with nothing on it contains no information at the macroscopic level. However, once one begins to write or draw on it, it now stores information, even if the writing or drawing is meaningless scribbling. As a result, the string 'qwerty' contains information, as does the word 'radio'. This is important because, when information is stored and transmitted, it is usually not transmitted in a human-readable form. Instead, it may be represented using the binary system transmitted as voltage by computers or using the amplitudes and frequencies of radio waves transmitted by an antenna. Although neither of these forms make sense (or are even perceivable) to a person, they still store information that can be understood and decoded into something like music or text.

Information is typically measured using entropy, which measures the unexpectedness or 'surprise factor' associated with an event. For example, a single fair coin with two sides carries one bit of information on average, either heads or tails (where bit refers to the fact that there are two outcomes with equal probabilities). If the coin were unfair, such that one of the outcomes is more likely than the other, then it would contain less than one bit of information on average, since one outcome would be more expected.

As another example of entropy, if you were given the letter 'q' as the first letter in a word and asked what letter will come next, the letter 'u' would contain very little information since, knowing the general rules of English, you can almost always assume that the letter 'u' follows the letter 'q'. However, if the next letter turned out to be 'i', this would be very surprising. As a result, the letter 'i' coming after the letter 'q' has higher entropy and thus contains more information. If the next letter were 'u', this would not be very informative since you could easily predict it, thus the letter 'u' coming after the letter 'q' contains very little information.

Using entropy, engineers can determine a way to code (or translate) messages into a signal. For example, the bigram 'qu' can be treated like a single letter since after a 'q' is almost always a 'u'. This is much simpler and more cost-efficient than sending the letters 'q' and 'u' separately when they appear together. Message coding is a very important topic in communication theory, since sending large amounts of long and inefficient messages can cost a lot of energy.

Resources

Wifi Receiver Booster Antenna

Build Yagi Antenna Wifi Receiver Manual