Opinion: Don't forget your wireless LAN's antenna
 
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If you're like me, the only time you remember antennas exist is when whatever is attached to the antenna, like a TV or FM radio, starts looking - or sounding - fuzzy.
But with wireless LANs, the time to start thinking about antennas is before, not after, you buy, according to Leslie Reading, CTO at Galtronics, a Phoenix antenna and electronics manufacturer for 23 years.
Reading is not unbiased. Galtronics just recently launched a subsidiary, Pear Wireless, that will offer a line of IEEE 802.11b (and eventually '11a) wireless access points. The initial products are aimed at the so-called small-office/home-office (SOHO) market, but Pear will come out with an enterprise product in 2002. And it's exploiting its antenna expertise to deliver some intriguing features.
Antenna design can affect everything from the range of your wireless LAN, to security, to the number of access points you have to deploy.
"The networking guys [vendors] don't know from nothing about RF [radio frequency]," Reading says. "This market is really begging for someone who understands the RF side to make this thing [wireless LANs] really work."
Think of radio waves like a water-filled balloon: you press one part of it, and another part increases. Antennas do this pressing. "You want the [radio] energy to come preferentially in one specific pattern," Reading says.
Good antenna design, the quality of the cable that connects the antenna with the radio, and reflectors can "sculpt" the direction and spread of radio waves with surprising precision. Pear, for example, is creating an access point that will cover the inside of a conference room, but go no further. This kind of precision means companies can prevent RF waves from spilling outside their buildings or even between floors, an important security consideration.
One of the key measures of an antenna is "gain," in decibels (dB). An antenna with 10 dB of gain is sending out a narrower signal that's 10 times stronger than a signal simply radiating out from the antenna in all directions, Reading says.
"Here's the surprise, you increase the power sent in one direction. If the receiver [on the other end] has an antenna with the same gain, it increases the sensitivity of the receiver by 10 times. [With two 10-dB antennas] the next effect on the overall communications increases by a factor of 100," Reading says
You don't have to be an RF expert, Reading says, as long as you demand evidence to back up the vendors' claims. "Unless it's been tested, don't believe it," Reading says, citing an RF maxim. "People will sell things [with claims] that defy the law of physics. They know that the customer doesn't have the resources to check that out." That's because RF equipment testing takes complicated, specialized, and expensive gear.
"We provide full test data for all our antennas," he says. There is no independent certification, but vendors can test against a relevant IEEE specification, IEEE 149.
Higher gain makes an antenna more "directive" and can make it more sensitive. But manufacturers can ignore or sacrifice electrical efficiency, Reading warns. "You can direct twice the power in one direction, but if you lose half of it getting it there, you haven't improved anything," he says. "There are lots of ways to throw away power, but not many ways to get it back."
In this case, another important measure is "voltage standing wave ratio" (VSWR), expressed as a ratio, such as 1.5:1 or 2:1. The optimal VSWR is 1:1, according to Reading. As gain measures the energy spilling out the front of the antenna, VSWR measures the energy spilling out the back - so-called "reflective" power. The more power reflected back (the higher the ratio), the less efficient is the antenna.
You can't do the complicated RF tests yourself. But you can check the Federal Communications Commission Web site to find data about the components, including the antenna, that a given LAN manufacturer uses in its wireless LAN products. The search engine uses an FCC ID number, which typically is issued for a given product prior to marketing.
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