Will a "5.8Ghz" wifi antenna work well with routers broadcasting 5.1GHz?

Question

I am looking at this antenna to purchase for outdoor wifi use:

5.8 GHz 12 dBi Professional Omnidirectional Antenna - HG5812U-PRO

http://www.l-com.com/wireless-antenna-58-ghz-12-dbi-professional-omnidirectional-antenna#

Its specifications are:

Center fed collinear array
Heavy duty industrial grade design
Fiberglass radome
All weather operation
Integral N-Female Connector

2.4/5.8 GHz IEEE 802.11a/b/g applications
5.8 GHz UNII and ISM applications
2.4GHz Wi-Fi applications
Wireless video systems
Point-to-multipoint applications

I saw that it only has "5.8GHz" listed as its frequency. Will the antenna still work well with wifi routers broadcasting 5.1GHz?

Answer 1

The answer is likely, no, it wouldn't be suitable.

According to the datasheet, the workable frequency range is:

5725 MHz to 5850 MHz

This corresponds to Wi-Fi channels 149 through 165. These are legal in several regions including the US/Canada, Russia, Australia, and others. They are not legal for high power applications in EU countries.

In any case it is highly unlikely that the antenna will provide the desired performance at 5.1GHz given that you would be operating over 600MHz outside the rated range of the antenna. The impedance this far out will not be nicely matched to its rated 50Ω impedance and so when hooked up to your Wi-Fi router will cause nasty signal reflections that will harm performance.

The same company sells antennae that are specifically designed for the 5.1GHz to 5.8GHz range, including ones with similar gain ratings (13dBi in one case). You would be much better investing in something which is rated for what you need.

Answer 2

Considering that router wifi signals bounce everywhere in the house and often have Ricean Fading issues near the extents of a house, expect high directional losses from a 10 degree beamwidth to be hit or miss solution. (**ie not recommended)

Directivity advantage is high gain vs narrow beamwidth, so unless you like to play with antenna pointing to fix deadspots in remote locations, this is a definite maybe. If this is point to point then OK just look at Return Loss issues for an antenna designed with VSWR=1.5 over a +/-1% BW and you want to operate 12% off centre frequency is begging for Return Loss issues to compromise much of the Diversity gain.

Just try a length of wire tuned to 1/4 or 3/4 wavelength, and compare RSSI signals with Netstumbler.exe (x86) or a Network Analyzer.

High gain is only under optimal conditions in an anechoic chamber. I remember designing my 1st dipole antenna that had to spin out from a Black Brandt VI rocket in a vacuum after the nose cone was ejected. I tuned the length of coiled flat braid wire using string to stretch it out as with centripetal force and got RL=-20 dB then someone walked into the lab 10m away and it started to degrade in cycles. I thought I just invented a motion sensor and then discovered Alarm companies already discovered this. This is the energy from reflections that reduce apparent signal strength and when out of phase we call it Rice Fading or Ricean. Then WiFi modems have to equalize and retrain to find a better constellation in base band signal usually hidden from the mobile user.