×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Why twin antennas on wireless routers?

Why twin antennas on wireless routers?

Why twin antennas on wireless routers?

(OP)
Most wireless access points and routers have twin antennas on the rear.  What's the reason behind this?  And if you're trying to extend the range of the wireless link by using an external directional antenna, which antenna port do you use, or does it matter?

RE: Why twin antennas on wireless routers?

Same reason as for the receivers used with professional quality wireless microphones - their receivers typically have twin antennas.

I'm sure you've noticed that when listening to FM in your car, there will be locations where you need to pull ahead a few inches to have good reception. In fact, the process becomes nearly automatic where you always leave a slightly larger space in front of your car at those intersections in case you need to roll forward a quarter wavelength.

Twin antennas provides similar 'space diversity' to avoid nulls.  If one antenna is in a null, then the other won;t be.

RE: Why twin antennas on wireless routers?

(OP)
Thanks for the info.  I understand.  But does that mean I can use either port for the external directional antenna?

RE: Why twin antennas on wireless routers?

If everything is as I think it is, then you should be able to use either port.

Leave a whip antenna on the second port just in case it helps.  In any case, it would likely be better than leaving the second port open circuit.

If you run into any difficulties, then swap ports (directional <-> whip).

I wonder how much antenna gain I would need to tap into the free WAN that is about 10km up the road...

RE: Why twin antennas on wireless routers?

It is for receiver diversity--Most of the systems will have two little antennas on the mobile device and two on the wireless router.  The simplest use is to sample the signal from each receiver antenna and then quickly decide which antenna has a stronger signal before data comes in the packet structure.  The high frequencies (2.4 or 5.8 Ghz) indoors will allow a lot of multipath and the desired signal may be accompanied by a bounced signal that partially cancels the desired by adding out of phase with the carrier (a fade).  Having two antennas separated helps because both antennas being in a fade will be less likely.

RE: Why twin antennas on wireless routers?

Regarding Antenna gain for reception 10 km away.
Wireless communication range/distance is reduced often by a factor of 2-6 due to multipath and normal range calculations get difficult/impossible.

Assuming that your wireless communication doesn't have multipath and is 500 feet with normal zero dBi antenna gains, everytime you double your distance you need 6 dB (factor of 4) more antenna gain in your receiver to keep the same signal strength. 10 km is 6 miles = approx. 30,000 feet. So to see how much extra gain you need, here is some basic math.

dist (feet) vs. antenna gain (dBi)
500   = zero (original antenna having 500 foot range)
1000  = +6
2000  = +12
4000  = +18
8000  = +24
16000 = +30
32000 = +36 dBi gain or 4000 gain.
Gain = 40,000/[(beamwidth azimuth) x (beamwidth elevation)]
or beamwidth = sqrt(40,000/4000)= sqrt(10)= 3.3 degrees.
at 2.4 ghz wavelength = 11.803"/2.4 = 5 inches.
3.3 degree beamwidth is approx. 20 wavelengths, so your antenna would be about (20x5")or 100" x 100" in size. That's pretty big.
KCH.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close