RF Antenna FAQs

June 22, 2017 at 8:00 AM

 

 

Antennas are critical components to any wireless network, so having a good grasp of antenna technology can be very important for anyone engineering, designing or managing a wireless network. With so many antenna options and so much information to digest, it’s no wonder people have a lot of questions when it comes to antennas. Here, we’ll highlight some of the questions we’re asked most frequently.

 

How do I choose the correct Wi-Fi antenna? 

There are two main types of antennas - Directional and Omni-directional:

          

-   Directional antennas emit an RF signal in a focused beam, like how a car headlight focuses light in one direction. They are great if your application is a  point-to-point Wi-Fi link. For example, if you’re transmitting a signal from one building to another, you would use a directional antenna.

 

-   Omni-directional antennas radiate an RF signal in a 360-degree pattern. These antennas are ideal if you need the Wi-Fi signal to cover a 360-degree radius.

       

-   If you have a point-to-multipoint application, such as a campus environment, using a combination of directional and Omni-directional antennas would be your best bet.

 

What is antenna polarity?

Antenna polarity is the orientation of the radio wave’s electric field with respect to the Earth's surface. Antennas can be vertically polarized, horizontally polarized or a combination of the two. For more information, check out our antenna polarization blog post.

 

What is antenna gain? 

Antenna gain is a relative measure of an antenna’s ability to direct or concentrate radio frequency energy in a particular direction or pattern. Antenna gain is typically measured in dBi or dBd. Click here for more info.

 

What is 802.11? 

802.11 is an IEEE standard for implementing wireless local area network (WLAN) communications in the 2.4, 3.6 and 5 GHz frequency bands. There are numerous 802.11 standards and new versions continue to be developed. Existing standards include 802.11a, 802.11b, 802.11g, and 802.11n, 802.11ac, 802.11ac Wave 2, 802.11ah, 802.11ax, 802.11ay and 802.11af.

 

What is a decibel (dB)? 

A decibel (dB) is a unit of measurement for the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale. Decibels are commonly used in radio and sound measurement. One decibel is 1/10 of a Bel.

 

What is dBi ? 

Decibels-isotropic (dBi) are decibels relative to an isotrope. This unit of measure defines the gain of an antenna system relative to an isotropic radiator at radio frequencies. 

 

What is an isotrope? 

A theoretical isotrope is a single point in free space that radiates energy equally in every direction, similarly to the Sun.

 

What is frequency? 

Frequency is the number of cycles of alternating current in one second. It is measured in hertz (Hz).

 

What is a microwave? 

A microwave refers to all radio frequencies above the 1 GHz range. They are shorter than normal radio waves but longer than infrared radiation. Microwaves are used in radar, communications, for heating in microwave ovens and in various industrial processes.

 

What is multipath interference? 

Multipath interference is when signal reflections and delayed signal images interfere with the desired, un-delayed, larger signal. It causes picture ghosting in over-the-air analog TV and errors in digital transmission systems.

 

What is path budget?

Path budget is a mathematical model of a wireless communications link. It takes into account a wide variety of factors that can affect operating range and performance. Path budget is sometimes referred to as "link" budget.

 

What is path loss? 

Path loss is the weakening of a signal over its path of travel. This can be caused by factors such as terrain, obstructions and environmental conditions. It is measured in decibels.

 

What is fade margin? 

Fade margin is the loss of signal along a signal path caused by environmental factors such as terrain, atmospheric conditions, etc. It is measured in decibels.

 

What is a point-to-point network? 

A point-to-point network is a communications channel architecture that runs from one point to another. Directional antennas would be used in a point-to-point wireless link.

 

What is a point-to-multipoint network? 

A point-to-multipoint network architecture runs from one point to several other points. For this type of network, you would use both Omni-directional and directional antennas.

 

What is radio frequency? 

Radio frequency (RF) is typically a frequency from 20 kHz to 100 GHZ. RF is usually referred to whenever a signal is radiated through an enclosed medium, like a transmission cable or air.

 

What is a radio wave? 

A radio wave is an electromagnetic wave of a frequency used for long-distance communication. It is a combination of electric and magnetic fields varying at a radio frequency and traveling through space at the speed of light.

 

What is very-high frequency? 

Very high frequency (VHF) is the designation for radio waves in the range of 30 to 300 MHz.

 

What is ultra-high frequency? 

Ultra-high frequency (UHF) designates radio waves that are in the 300 to 3,000 MHz range.

 

Antenna Gain for Dummies

July 14, 2016 at 8:00 AM

 

Many customers ask us to explain antenna gain, but it can be a little tricky to wrap your mind around. So, here we’ll break it down for you in our version of Antenna Gain for Dummies.

 

Antenna gain is the relative measure of an antenna’s ability to direct or concentrate radio frequency (RF) energy in a specific direction or pattern. Typically measured in decibels relative to an isotropic radiator (dBi) or decibels relative to a dipole radiator (dBd).

 

An Isotropic Radiator radiates energy equally in every direction, similar to a light bulb. The isotropic radiator antenna radiates uniformly and exhibits the same magnitude or properties when measured in all directions.

 

Why Antenna Gain Is Important:

 

One of the major factors used to analyze the performance of radio frequency (RF) communications links is the amount of transmitter power directed toward an RF receiver.


This power is derived from a combination of:

  1. 1.Transmitter power
  2. 2.The ability of the antenna(s) to direct that power toward an RF receiver(s)

 

Typically, antennas with higher gain will perform more efficiently and operate with a farther range distance.

  

How It’s Measured:

 

To determine the directivity of an antenna, a reference antenna is needed in order to compare performance. An isotropic radiator is the preferred antenna for comparison because it transmits equal amounts of power in all directions - like a light bulb.

 

To increase the directivity of the isotropic radiator, an antenna is added behind it to act like a reflector and direct the antenna’s energy - just like a reflector behind the bulb of a flashlight.

 

With the reflector, the flashlight will now appear much brighter, as will the energy of the antenna being pointed in one direction. Now the directivity can be calculated by measuring the difference between the antenna’s energy before and after the addition of the reflector. 

 

The directivity is then converted into decibels to determine the antenna gain relative to an isotropic source (dBi). For every 6 dBi in gain, you double the range of the antenna.

 

Now that you have a better understanding of antenna gain, there are still many factors to consider when selecting the right antenna for your application. In certain instances, too much gain can be a bad thing. 

 

For more information about antenna gain and other common wireless terms, check out our wireless glossary

 

Antenna Arrays 101

April 7, 2016 at 8:00 AM

 

Not sure what an antenna array is? Want to brush-up on the subject? We’ve got everything you need to know right here with this week’s post… Antenna Arrays 101.

 

What it is:

An antenna array is a set of two or more antennas working together to form a single Omni-directional signal.

 

How it works:

When two or more directional Wi-Fi antennas are grouped together, the signals combine and are able to work as a single antenna with improved directional characteristics.  This is usually done with panel-style antennas connected by an RF splitter to a single access point or Wi-Fi amplifier. The number of antennas in an array can be as few as two or as many as four.

 

Why it‘s used:

An antenna array provides better performance and coverage than a single Omni-directional antenna

Additional benefits include:
    • o   Increased overall gain
    • o   Diversity reception
    • o   Cancellation of interference from specific directions
    • o   Sensitivity toward certain directions
    • o   Ability to determine the arrival direction of incoming signals
    • o   Maximizes the Signal to Interference Plus Noise Ratio (SINR)

 

Applications:

Antenna arrays are used in outdoor point-to-multipoint applications.
   
L-com offers three configurations: 4 - 90° panels, 3 - 120° panels and 2 - 180° panels. To ensure maximum wireless signal coverage, these antenna arrays feature 0°-20° down-tilt capability to compensate for the installation location geography.
 

There you have it, the basics of an antenna array - antennas working together to achieve better coverage than a single Omni-directional antenna.

 

Gain Gone Wild: How Too Much Antenna Gain Can Be A Bad Thing

March 24, 2016 at 8:00 AM

 

When designing a wireless network, one way to improve the strength and range of your Wi-Fi signal is to increase the antenna gain. This is a perfect solution for many applications.  But in certain situations, a high gain antenna stretches the wireless signal too far.

 

To put this into perspective, let’s look at an example of when too much gain becomes a bad thing:

 

You own a restaurant and want to set up a wireless network in an outdoor courtyard area. You choose an Omni-directional antenna to provide full 360° wireless coverage for your customers. For extra assurance that your Wi-Fi signal will reach everyone in the courtyard, you choose an antenna that also has a high gain rating of 15 dBi. Here is an illustration:

It seems logical that the high gain antenna would be able to connect the customers in your courtyard to your Wi-Fi network. But in actuality, your wireless signal is being projected far beyond the 300-foot coverage area that you’re aiming for. With the high gain antenna, the strongest Wi-Fi signal is outside of the courtyard space, leaving your patrons with slow speeds and poor signal quality. Weak vertical coverage from the high gain antenna also means the Wi-Fi signal won’t reach customers who are closer to the ground, sitting in chairs.

 

In this situation, your best option is an antenna with a lower gain, such as 5 dBi or 8 dBi.  This concentrates the Wi-Fi signal within a smaller area to better serve the customers within the courtyard. A lower gain antenna also has a stronger vertical reach to project the Wi-Fi signal lower to the ground for everyone seated. Here is a diagram:

The moral of the story is to proceed with caution when ramping up your Wi-Fi signal with a high gain antenna. It is possible to have too much of a good thing and ,depending on your wireless application, a high gain antenna might not be the best solution.

 

Can You Define Antenna Gain?

July 24, 2014 at 10:00 AM

 

"What is gain?" 

 

Many of our customers ask us this question. 

 

In fact, it has become so common that we created a Wireless Glossary to explain “gain” along with other common wireless terms.

 

But, the term “gain” is tricky to define, so we're going to dig into it a bit more here.

 

One of the major parameters used in analyzing the performance of radio frequency (RF) communication is the amount of transmitter power directed toward an RF receiver.

 

This power is derived from a combination of:

 

1.Transmitter power

2.The ability of the antenna(s) to direct that power toward an RF receiver(s)

 

 

 

Directivity

 

The directivity of the antenna is determined by the antenna design. Directivity is the ability of an antenna to focus energy in a particular direction when transmitting or to receive energy better from a particular direction when receiving. To determine the directivity of an antenna, we need a reference antenna with which to compare our antenna's performance.

 

Omni Directional:
360° Coverage

Directional:
Focused Coverage

 

 

Over the years there have been several different reference antennas used to determine directivity; however, today an isotropic radiator is preferred as the standard antenna for comparison. The isotropic antenna transmits equal amounts of power in all directions (like a light bulb).

 

To increase the directivity of a bulb's light (or the antenna's energy)- similar to a flash light or automobile head lamp in this example- a reflector (antenna) is added behind the bulb. At a distance the light bulb now appears to be much brighter in the light beam. The amount that the bulb appears brighter compared to the bulb without a reflector is the directivity of the reflector (antenna).

 

When directivity is converted to decibels we call it the “antenna gain” relative to an isotropic source (dBi). Typically the higher the gain, the more efficient the antenna's performance, and the farther the range of the antenna will operate. For every 6 dBi in gain, you double the range of the antenna.

 

It should also be noted that many factors need to be considered when selecting the "best" antenna for the desired application, and it’s best to discuss any antenna selection with someone knowledgeable in RF radiation and antenna performance. L-com has experts to help you make the best selection for performance and price to fit your application.

 


 

Helpful definitions to summarize our topic:

 


Antenna Gain: A relative measurement of an antenna's ability to direct or concentrate radio frequency energy in a particular direction or pattern. This measurement is typically measured in dBi (Decibels relative to an isotropic radiator) or in dBd (Decibels relative to a dipole radiator).

 

Isotropic Radiator: is a theoretical single point in space that radiates energy equally in every direction similar to the Sun radiating its light. The isotropic radiator exhibits the same magnitude or properties when measured in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centered on the source.

 

 

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