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.

 

What You Need to Know about Line of Sight

August 25, 2016 at 8:00 AM


When designing a wireless network, one of the most significant factors to consider is Line of Sight (LOS) - the path between two antennas. Obstructions in the LOS path can wreak havoc on a Wi-Fi signal so determining what, if anything, is between the antennas is crucial to your network working properly. Here, we’ll examine the main concepts you need to know in order to clear the path for Line of Sight and make sure your wireless network is a success.

 

The first step in navigating Line of Sight is to determine the LOS conditions. Once the conditions are defined, the correct type of wireless system can be chosen for the network area. There are three main Line of Sight conditions:

 

1.       Full Line of Sight (LOS) – no obstacles between the two antennas

2.       Near Line of Sight (nLOS) – partial obstructions between the two antennas, such as tree tops

3.       Non Line of Sight (NLOS) – full obstructions between the two antennas, such as an entire tree  

 

Outdoor networks may encounter the largest obstacles, but Line of Sight is also important for indoor wireless networks. Obstacles like walls, ceilings and furniture have to be considered because they will also affect the wireless signal reception.                                                                                                                         

In addition to obstructions, there are three other factors to consider that can affect Line of Sight:

 

1.       Multipath and Reflections

2.       Fresnel Zone

3.       Path Loss

 

In wireless transmissions, multipath and reflections are as important as signal strength because they too can degrade the performance of the network. Multipath is when wireless signals travel in multiple paths and arrive at the receiver at different times. Reflections occur when wireless signals "bounce" off of objects. When signals are transmitted through walls and ceilings and are reflected off of metallic objects, they will also have peaks and nulls in amplitude and changes in polarization (vertical or horizontal).

 

Fresnel Zone is an electromagnetic phenomenon where light waves or radio signals get diffracted or bent by solid objects near their path. The reflected waves/signals become out-of-sync with those that traveled directly to the receiving antenna, this delay reduces the power of the received signal.

 

Path Loss is another area of concern when determining Line of Sight. Some radio frequencies travel well through certain objects while other frequencies are not able to pass through, resulting in path loss. For example, 2.4 GHz radio waves easily pass through walls but experience path loss when going through trees and leaves. This is because walls are very dry, trees contain high levels of moisture and 2.4 GHz radio waves are easily absorbed into water. On the other hand, 900 MHz radio waves are not as easily absorbed by water. In cases like this, when trees cause nLOS or NLOS conditions, 900 MHz is a better frequency to use than 2.4 GHz to avoid path loss.

 

There are many factors to consider when designing a wireless network, but with proper site evaluation and planning you can correctly navigate Line of Sight obstacles to achieve peak performance.

 

 Comments on this post? Other topics you’d like us to cover? Email us at engineeringhub@l-com.com

 

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