The simple facts behind antenna basics

No matter how expensive your wireless system may be, its performance depends on the strength of its antennas.

Editor's note: In the second of a three-part series, analyst Craig Mathias details the science behind the technology

that underscores today's wireless networks. Part one examined the basic fundamentals; this installment discusses the role antennas play.

The antenna, which anchors both the transmitter and the receiver, is the most important part of a radio system. But wait, you say: Isn't the antenna just a simple piece of metal that typically costs a few cents? How can a little piece of metal be more valuable than all of the sophisticated processing that's engineered in integrated-circuit chips? Well it is, and with this simple analogy, I can break down antenna basics for you. Anyone who is an avid fan of motorsports or who just likes driving a car knows one simple truth – tires are critical. Why? Because even with all of the other sophisticated technology and luxury in engines, drivetrains, suspensions, entertainment and communication systems, tires are the only part of the machine that actually touches the medium upon which the vehicle operates.

So it is with antennas, which again are the only part of the radio to actually touch the radio's medium – in this case, the air. Picking the right antenna and using it optimally are the keys to success in any wireless application. Remember, the baseline operational parameters of any radio system are specified in regulation. Radio system designers do their best to balance a huge number of variables – among them size, weight, power consumption, data rate, desired range, cost and environmental characteristics. Antennas compensate and optimize to a very great degree as required, which helps improve both their value and performance.

Design helps bridge performance gap

Before examining the different types of antennas, remember that radio waves propagate through space in a very non-linear fashion. It's in fact impossible to tell exactly how, or even if, a given radio signal will propagate from the transmitter to the desired receiver: The only way to know for sure is to try it. Appropriate antennas can be used to address any shortcomings in more cases than not.

This capability is important because a mobile device usually doesn't know the location of the other end of the connection.

First, antennas can be directional or omnidirectional . In general, mobile devices use antennas that are omnidirectional, meaning that they can receive and transmit in every direction -- generally a 360-degree arc around the antenna. This capability is important because a mobile device usually doesn't know the location of the other end of the connection. Fixed infrastructure, like cellular base stations, can use directional antennas because these systems know, at least relatively, where their clients are. Directional antennas focus energy in a particular direction, improving range, reliability and throughput. Omnidirectional antennas waste energy when transmitting and are suboptimal when receiving, but clever technology helps offset those shortcomings.

Omnis can also be adjusted to improve results in certain installations. For example, some Wi-Fi access points (APs) have external antennas that can be oriented to different angles. While there's often more art than science in performing this optimization, results can be improved—occasionally, dramatically.

Optimize to improve performance

Next, antennas can be tuned to specific frequencies and even act like amplifiers -- a property referred to as "antenna gain." The tuning part can be accomplished by designing the physical size and structure of the antenna so it's optimized for a particular range of frequencies. In general, the higher the frequencies, the smaller the antenna can be. Antenna gain can be realized even in completely passive antennas (the kind that are really just small pieces of metal), and is an important element in optimizing performance. Think of this as a high-performance tire.

More from this series

The magic behind the technology

There’s another clever optimization, and that's by focusing the energy in a particular direction via multiple omnidirectional antennas. This is called beamforming, and it has become increasingly popular in Wi-Fi implementations. Beamforming is a standard feature in the new 802.11ac standard, and it is essential in improving both throughput and distance – what we call "rate-versus-range" performance. Many 802.11ac APs will be purchased not because they offer 1.3 Gbps, but rather because they can reliably reach the back conference room upstairs.

Finally, we can even apply electronic or smart antennas to the problem. As implied, these antennas go well beyond simple metal strips – they contain active circuitry that optimizes and enhances performance. Yes, they are more expensive, but only by a little, and require electrical power. But the improvement in performance (again, "gain") can be dramatic.

Part three of this series will discuss advanced wireless systems, protocols and architectures.

This was first published in June 2014

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