Circular polarisation for 4G LTE router antennas?

Thread Starter

Ludens

Joined Nov 12, 2014
3
Hi all,

I need to build good antennas for a 4G LTE router that will be used in a hilly, woody location pretty far away from the cellular base stations. I do have experience building antennas, but no experience with 4G LTE, and I lack suitable test equipment for the LTE bands.

The company providing best service in the area uses both the 700MHz and 2600MHz bands for 4G LTE. It has twice as much spectrum on 2600 than on 700. The place where the router will be used gets signal, but weak. A smartphone just barely gets it. There is direct line of sight to one cell tower of this company, but at considerable distance - I can see it only with binoculars, on a clear day.

The router supports both bands and has two antenna ports. It's a Huawei B310. I understand that for best performance both ports need to be used, to provide diversity reception.

My questions are the following:

- Is it good, bad, or indifferent to use circularly polarized antennas instead of linearly polarized ones?

- If circular, would it help to make one left-hand and the other right hand polarized?

- Is it really helpful to make antennas that cover both bands, or would it suffice to make antennas optimized (higher gain) for the 2600MHz band, where greater bandwith is available and probably there are fewer competing users?

The options I see are either two axial-mode helix antennas for 2600MHz, which are easy and relatively uncritical to build, and thus suited for my situation (no test equipment for 2600MHz); or else two log periodic arrays that cover 700 to 2600MHz, installed with crossed polarization. The helices would have higher gain and circular polarization, while the log periodics would cover both bands. Which would likely be better?

I wouldn't want to try building high gain Yagi antennas, because these are too narrow-banded to get good performance without having test gear to adjust them. And they might even be too narrowbanded to accomodate the TX-RX offset, specially on the 700MHz band.

I would be grateful for any answers to my questions, and any suggestions about alternative antenna types I could built. Tried and tested designs are of course very welcome too, perhaps for PCB log periodics. Just please don't suggest to buy a factory-made antenna. I need to build and install these antennas within a few days, and anything I buy online takes months to arrive. I do have suitable materials, tools, etc, also a good sized roll of low-loss coax cable and connectors.

The antennas will be installed in an RF-transparent attic, so weather resistance isn't a factor.
 
Hi,

You need to use an antenna with the same polarization like the cell. As far as I know, the LTE cell use vertical and/or horizontal polarization antenna. So, If you use a circular polarization, you will have a loss of couplage between both polarization.

If you are far away from the cell, use the 2.6 GHz is useless because higher frequency has a lower propagation condition (I think at some trees between you and the cell). So, an 700 MHz antenna will be better.

The easy solution is to use a high gain antenna only in 700 MHz, with good connectors, good cable and especially with the shortest cable that you can, to avoid losses between the antenna and router.

If you want to build your own antenna, few basic dipoles can be coupled to increase the gain but you need to have a 3dB coupler. You can also connect an antenna on each connector if you router is compatible with MIMO.

Please, let me informed, I'm curious about your problem,
Joss
 
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