Explanations and Descriptions - Wi-Fi Wireless LAN Antennas

ANTENNAS

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LITERATURE

JUST THE FACTS

ANTENNAS

High-Gain, Directional, and Special-Purpose
802.11 Wi-Fi Wireless LAN Antennas

An antenna both transmits and receives radio frequency (RF) energy. The physical construction of an antenna determines how the energy is "beamed out" and a law of physics (called the "Law of Reciprocity") causes an antenna to receive signals with the same ability as it can send signals. This means that a high-gain or directional antenna both transmits and receives with the same increased gain or directionality.

How Is an Antenna Manufactured to Give It "Gain"?

Most Wi-Fi wireless LAN access points are shipped from the factory with the common 5-inch long straight black antenna as standard equipment. This type of antenna is technically called a "1/2-wave dipole" and many 802.11b access points ship with two antennas (called "diversity antennas".) The standard antenna radiates RF energy around it as if a doughnut had been placed down over the stick of the antenna. This type of antenna is referred to as "omni-directional" because it radiates in all directions around the plane perpendicular to the antenna shaft. A high-gain or directional antenna is constructed in such a way that the RF energy is radiated in a differently shaped 3-dimensional volume. For example, "flattening" the doughnut would cause more energy to be directed to the sides and less towards the top and bottom - that's a "high-gain antenna". Adding elements of the antenna construction that reflect or direct the outwardly propagating RF energy predominantly in one direction creates a "directional antenna". For example, if all of the signal going out to the left of an antenna were reflected to the right then the effective net result would be that twice the RF energy would be sent out towards the right. Different types of antennas offer different ways of shaping the RF signal energy to focus it in a desired manner. The signal characteristics of an antenna are represented with a special graph called an Antenna Pattern Polar Coordinate Graph or, simply, an Antenna Pattern Graph.

RF energy radiates outward from a dipole antenna forming a 3-dimensional volume that resembles a doughnut

How is Signal Strength Increased When an Antenna Has "Gain"?

When an antenna has 'gain' or is 'directional' it doesn't make the transmitted power any greater. The way the metal elements of an antenna are constructed (their size, shape, orientation, and relationship to each other) changes the way the electromagnetic signal radiates away from the antenna. The change in the 3-dimensional shape of the propagating wave (and, consequently, the spatial volume of the resulting 3-dimensional area) changes the density of the signal. It's increased energy density in some particular direction that results in increased signal strength for an intended receiver and is the quality of an antenna called 'gain'.

We begin thinking about gain by considering a theoretical radiating point source called an 'isotropic radiator'. An isotropic antenna would radiate signal outwards equally in all directions, creating a spherical transmission volume. There is no perfect isotropic antenna. A dipole antenna (a straight 'stick') radiates RF in a manner that can be visualized by thinking about a fluorescent light bulb. Signal radiates outwards from the sides, but not from the top or bottom. This produces a torroidal (doughnut) shape signal volume around a dipole antenna. Since the signal is 'squeezed' into a transmission volume shape that is 'flatter' than the theoretical isotropic pattern the RF energy is compressed into a smaller volume. This results in the electromagnetic energy being more 'dense' in any given area inside the transmission volume than it would have been in the spherical volume of the isotropic radiator. The increased 'density' of signal is referred to as antenna gain and it's measured in decibels relative to the isotropic case (dBi, which is often simply written as 'dB' on an antenna spec sheet.)

Where Can I Find Detailed Technical Information About RF Signal Propagation?

If you want the most concise, in-depth technical document describing, in tremendous detail, the way electromagnetic energy propagates, We've Got You Covered. Our technical white paper, "I'm Going To Let My Chauffeur Answer That" (written by Connect802's Chief Scientist and President, Joseph Bardwell) delves into the math and physics that explain Maxwell's wave equations and RF signal propagation. The math is well explained and there's plenty of concept information. You can download this free engineering white paper from the Technical Documents page of the Literature section.

The Connect802 Antenna System Designer is an on-line calculator with detailed explanations of many specific aspects of link budget calculation and antenna system design. Try it out!

The Connect802
Antenna System Designer
----------------------------
An On-Line Calculator for Link Budget, Gain, and Antenna Mounting. Try it out!

Antenna Pattern Polar Coordinate Graphs

Understanding the Antenna Pattern Graphs
The graphs show signal field strength from a "side view" (called the Elevation view, or "E-Graph"). You're standing in a big room looking across the room at the antenna. This is as opposed to the "top view" (called an Azimuth view or Horizontal view or H-Graph). All the graphs are E-Graphs, no H-Graphs are shown. If you're an electronics engineer then you'll also appreciate that "E" and "H" have significance beyond the memory aid of Elevation and Horizontal.

The Omni-Directional Antenna
The RF energy spreads out equally in all directions, forming a doughnut shape around the antenna. This is generally consistent with what a typical 1/2-wave dipole on an 802.11b or 802.11g WLAN access point might produce.

A High-Gain Omni-Directional Antenna
The antenna has been constructed so as to radiate power in a "flatter" doughnut shape. Since the same input power is now being radiated in a "flatter" volume, the power per unit area at any given point on the plane perpendicular to the antenna is increased. This graph shows a 2dB gain relative to the omni-directional design above.

A Directional Antenna
A reflecting element has been placed to the left of the antenna's active radiating element. Signal energy that used to go out to the left now goes out to the right. The signal power per unit area on the plane perpendicular to the antenna has now been doubled to the right. The antenna is directional. It is, of course, "high gain" relative to an omni-directional antenna. The graph shows a 3dB gain relative to the original omni-directional design.

A High-Gain Directional Antenna
Now there is not only a reflecting element (as with the directional antenna) but the construction of the radiating element is such that the doughnut is "flattened". Both characteristics combine to make very high gain, directional antennas. The graph shows a 20dB gain relative to the original omni-directional design.

Examples of 802.11 High-Gain and Directional
Wi-Fi Antennas Carried By Connect802

Click on an image to go to the Connect802 vendor page for the product family

Use for point-to-point Wi-Fi links between buildings.

High-Gain Directional Yagi Antennas
A Yagi antenna creates a very narrow beam which allows it to transmit for long distances across straight paths. Use a Yagi when you need to connect two buildings together across a courtyard or street. Very high gain Wi-Fi Yagi antennas can transmit for 40 miles or more! (..if they're mounted 200 feet above the ground.)

Microcell "Hemi" Antennas
This specialized wireless LAN antenna creates a wide, flattened pattern in one direction. It's designed for mounting on a high ceiling or side wall in a large auditorium, gymnasium, or outdoor area.

Low Profile "Disk" Antenna (3 dBi Gain)
Antennas are available to meet any aesthetic or decorative requirement. This tiny low profile 802.11 antenna (compared to a dollar bill in the photo) is adhesive-backed. Just thread the cable up through a hole in ceiling tile or drywall (or in the ceiling of a commuter train car!) and you've got solid signal coverage.

An add-on wireless networking antenna - also mountable.

Indoor 8" 4dBi Omnidirectional Antenna
Easily carried for portable use with a notebook computer (compared to a pencil in the photo) this small form factor antenna style can also be ceiling mounted. The signal pattern is omni-directional with significant gain in the horizontal plane.

Specialty antenna requirements? We've Got You Covered.

Additional Antenna Options and External USB Wi-Fi Adapters
Antennas are available to meet any requirement. An antenna is selected based on the intended frequency range (2.4GHz 802.11b/g, 5.8Ghz 802.11a and WiMAX, 600Mhz WMTS, 800-900Mhz cellular), the necessary signal gain, and the desired RF pattern (sometimes specified as vertical and horizontal "beamwidth").

Connect802 works with major antenna manufacturers and Wi-Fi equipment suppliers.

Specialty Antennas Designed and Certified for ValuePoint Equipment
Vendors of various Wi-Fi access points, wireless mesh routers, and other radio equipment (both Wi-Fi, WiMAX, and more) have selected specific antenna models for use with their equipment. Connect802 will always provide the right antenna to meet the requirements.

Panel and patch antennas for indoor or outdoor wireless Ethernet LAN implementations

Wi-Fi HotSpot Directional Panel Antennas
Different wireless network applications may demand different types of antennas. In some cases it's acceptable to have a particular degree of data loss (downloading files, for example, where lost data is simply retransmitted.) In other cases it's critical to maintain an optimum connection (wireless Voice-over-IP, where data loss show up as poor call quality.

Definitions and descriptions of Antennas that you might find on the Web:

A conductive structure specifically designed to couple or radiate electromagnetic energy. In RFID systems, the antenna may be used to both transmit and receive electromagnetic energy.
A device for transmitting and/or receiving signals. The size and shape of antennas are determined, in large part, by the frequency of the signal they are receiving.
An aerial for receiving or transmitting radio signals. A high gain antenna is highly focused, whereas a low gain antenna receives or transmits over a wide angle
A conductive physical device designed to radiate RF energy from a transmitter, or to capture RF energy for application to a receiver.
A device for transmitting or receiving radio waves. Also known as aerial. In satellite communication systems the antenna usually consists of a parabolic reflector and a feed horn. In a receiving system the reflector focuses radio waves onto the feedhorn for detection and conversion into electrical signals. In a transmitting systems the reflector concentrates the radio waves emitted by the feedhorn into a narrow beam aimed towards the satellite.
The device that transmits and/or receives microwave and radio energy
The part of a radio system that is designed to radiate electromagnetic waves into free space (or to receive them). This does not include the transmission lines or waveguide to the radiator.
A conductive structure specifically designed to couple or radiate electromagnetic energy. In a driven mode the structure is a transmitter antenna. In receiver mode the structure is a receiver antenna. Antenna structures, often encountered in radio frequency identification systems, may be used to both transmit and receive electromagnetic energy, particularly data modulated electromagnetic energy.
Any system of wires, poles, rods, reflecting discs, or similar devices used for the transmission or reception of electromagnetic waves.
An Antenna is any device used for transmitting signals. Antennas come in all shapes and sizes, their size and shape depending on the frequency and use of the signal transmitted. Some antennas can broadcast signals in all directions, they are called omnidirectional antennas. Other antennas can also broadcast signals in a fine straight line - like a flashlight, they are called directional antennas. Electrical signals with frequencies higher on the spectrum, for example, are shorter and more directional. As they get higher on the spectrum, they behave more like light. These must be focused and thus, require antennas which are shaped like the mirror reflector of a focusing flashlight. This parabolic shape focuses the broad beam (of the bulb or the electrical signal), into a narrow, focused beam. The weaker the received signal the bigger the antenna must be.
An electrical device that sends or receives radio or television signals

Connect802 provides high performance 802.11b, 802.11g, 801.11b/g, and 802.11a wireless LAN antennas. In some cases a Wi-Fi booster antenna will allow your RF signal to reach out beyond the RF coverage area that a standard half-wave dipole antenna can provide. When you want to build a wireless bridge link between two buildings or across the street you need an effective directional Wi-Fi antenna. Directional Wi-Fi antennas from Connect802 are offered as 2.4 GHz Wi-Fi directional antennas and 5.8 GHz directional Wi-Fi antennas. We can also help you with Bluetooth 802.15 compatible antennas, and even 2.5G and 3G cellular antennas for CDMA/EV-DO, and other cell phone antenna design requirements. Talk to an RF engineering professional or use Connect802 as an antenna system design consultant - we have omni-directional antennas, patch antennas, panel antennas, radome-enclosed yagi antennas, parabolic grid antennas, and dish antennas. If you need Wi-Fi or other implementation of sectorial antennas or mobile mount antennas, rubber duck antennas or ceiling mount antennas, "We've got you covered." Talk to us about In-Building Wi-Fi antennas, Wi-Fi repeaters and range extenders, outdoor omnidirectional WiFi antennas, outdoor directional wireless antennas, and mobile wireless LAN antennas. "We've got you covered." Some antennas need to be mounted on antenna towers. Connect802 can consult with you and arrange installation of an antenna tower or roof mount antenna structure. We will help assure that all local building codes, FAA, and FCC rules are met for your antenna tower installation and construction. Our installation team can erect an antenna tower from over 200 locations nationwide. If you need a Wi-Fi antenna tower or antenna structure, "We've got you covered." Wireless LAN antennas can help you implement building-to-building bridges, optimize 802.11 connectivity in many environments, and Connect802's wide range of antennas and accessories will help you build your wireless network the right way the first time. How does a wireless LAN 802.11 Wi-Fi antenna affect wireless LAN security? Let our experts explain the "Law of Reciprocity" and how someone with a high-gain directional Wi-Fi wireless LAN antenna can be miles away, and still intercept your WiFi 802.11 RF signals.