Project Wireless - February 2009 - (Page 15) PrOjeCT SPonSor aDvertISement MeShneticS Zigbit™ KitS At Digi-Key from digi-Key, the ZigBit development Kit comes complete with one year of professional support, which provides users with continuous software updates, dedicated design-in support, and rf design assistance. this kit is ideal for customers engaged in a full cycle of developing, prototyping, and launching innovative products made possible by the meshnetics ZigBit wireless platform. they also feature early software release access, sample applications, sources for demo applications, examples of api use, integrated sensors, many interfaces for communication, and much more. clIck here for aDDItIonal InformatIon | vOLuMe 1 | nuMber 1 performance of the antenna. also, the antenna should have sufficient vsWr in the operating frequency range. typically, a 10-dB return loss (2.0:1.0 vsWr) or better is a respectable number. consider the maximum gain with efficiency or average gain in order to get a better picture of the overall performance of the antenna. Be careful not to fall into the trap of looking at just one of these properties and jumping to a conclusion. maximum or peak gain is a good gauge in evaluating directive antennas, but can be a misleading term if used as the primary criteria to determine general antenna performance. often, in more complex devices, the gain is lower so there is implementation loss when the antenna is placed and connected to the actual device. this is because high peak gain always means some level of directivity and may result in antenna gain that is much lower in some other direction due to nulls in the radiation pattern. selecting an antenna that has a margin over the recommended decibels ensures that it will meet system requirements in the real world. most wireless systems have 50-Ω impedance, which the antenna should match as closely as possible for minimum mismatch/loss in the system. other factors to consider are polarization (vertical, horizontal, or circular) and the radiating patterns (in xz, zy, and xy planes) in order to fully characterize the antenna. most handheld portable devices need a linearly polarized antenna with omnidirectional radiating patterns for 360 omnidirectional coverage. true omnidirectional radiating patterns exist only in theory. often, device mechanics affect antenna patterns, causing nulls and directivity in the patterns. in many cases, the best way to determine true antenna performance is the total 3-d Contents viewpoint Smart integration design Signal Paths in 3G and Feature / Smart Phone Apps Antennas for Handheld devices Home Page Product Training Module Online Ordering Suppliers Catalog be careFul noT To Fall InTo The Trap oF lookIng aT JuST one oF TheSe properTIeS and JumpIng To a concluSIon. 15 http://ad.doubleclick.net/clk;211088645;32661511;z?http://www.digikey.com http://ad.doubleclick.net/clk;211153865;32661511;w?http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=758-1014+|+758-1015&x=0&y=0 http://ad.doubleclick.net/clk;211088645;32661511;z?http://www.digikey.com http://ad.doubleclick.net/clk;211088750;32661511;w?http://digikey.com/PTM/PTMMaster.page?site=us&lang=en http://ad.doubleclick.net/clk;211088807;32661511;z?http://ordering.digikey.com/ordering/addpart.aspx?site=US&source=search http://ad.doubleclick.net/clk;211088983;32661511;e?http://digikey.com/Suppliers/SupplierIndex.page?site=us&lang=en http://ad.doubleclick.net/clk;211091911;32661511;p?http://dkc1.digikey.com/us/en/pdf/Current.html
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