Some thoughts on antenna choices for LTE
For the moment at least, most of us adopting LTE probably want to achieve maximum possible choice of service providers, ie you want to be able to switch easily between the likes of MTN, Vodacom and Telkom Mobile in order to get the best service and value for money from both network provider and ISP.
Arguably, you might also still want some degree of "fallback" capability so that you can continue to use 3G or even - perish the thought - EDGE and plain old GSM if the LTE wheels were really to come off. This means you want :
a) An LTE router that supports operation in both FDD (Frequency-Division Duplexing) and TDD (Time-Division Duplexing) LTE modes. The router must also support operation in the frequency band(s) used by your chosen network operator(s). For the moment at least, MTN, Vodacom and Neotel currently use FDD in Band 3 (1710-1880MHz); whereas only Telkom Mobile (so far) is using TDD in Band E (2300-2400MHz).
b) An antenna system that gives good performance and supports operation in LTE, 3G and perhaps EDGE/GSM modes at the frequencies used by your chosen network operator(s). The system should offer consistent performance to give a nice, stable internet connection - something that built-in antennas are not always that good at.
c) If you opt for a directional antenna system, the ability to orient the antennas suitably for different network operators' towers, if the need arises.
All of this is no mean feat. Fortunately, in the Huawei B593s-601 router, we have a near-perfect solution for the requirements of (a) - for South Africa, and for the present, at least.
If you have decent signal, the internal antennas in the B593 are already pretty good. In my situation, they actually seem to perform slightly better than the included "ice-cream stick" external antennas.
However, if you're in an area of marginal signal, or you want more consistent performance and higher speed, you'll want to consider a better antenna solution - either one of Poynting's "desktop" antennas, like the
XPOL-0010, or an external antenna system. While the desktop solutions are convenient and portable, almost any suitable external antenna system is going to position you well for better performance.
As regards external antennas, you may want to try one of Poynting's omnidirectional antennas like the
XPOL-0001, particularly if you seem to have reasonable signal already. The advantages would be:
- It's a self-contained antenna already including the two elements needed for LTE.
- It doesn't lock you into any one network operator as it supports all common frequency bands.
- It retains compatibility with 3G, EDGE and GSM.
- It doesn't lock you into one tower as it's not directional.
Going a little more complicated, you could try two of Poynting's
OMNI-0121's or
OMNI-0069's (watch
this video for excellent insights on this).
If you want even better performance, and you can handle a bit of schlepp if/when changing service providers, then you probably want to consider a directional antenna system. This will mean having to align the antenna when setting up and when changing network operators. In more extreme cases (like the XPOL-0006, which is completely specific to Telkom Mobile), you may limit yourself to one network operator and/or one communication system (like LTE).
If I were starting from scratch with LTE, I would probably go for the new
XPOL-0002-V2 dual-element antenna when it becomes available in SA. On paper at least, these offer a good compromise for the requirements of (b) and (c) above. They are quite directional and offer good gain and matching across all the frequency bands currently used in SA for "1G" (GSM), 2G (EDGE), 3G and "4G" (LTE).
It's important to note that Poynting are regularly updating their antenna designs to offer improved performance and to take account of frequency bands starting to be utilised in SA (and elsewhere). This results in designations like "V2" and "V3" which should be watched carefully, particularly if you're buying on the second-hand market.
A case in point was Telkom's recent allocation of spectrum at 2300-2400MHz. The technical performance of Poynting's original XPOL-0002 wideband antenna (the "V1", in retrospect) was arguably marginal in that band, with both a significant mismatch (high VSWR) and a variation of VSWR slap-bang in the middle in that band. The new "V2" version (the XPOL-0002-V2) addresses that shortcoming, so this is a good one to watch.
It so happens that I already have two Poynting LPDA-0020 antennas left over from a previous 3G project, so I'll be trying those shortly. The '0020 is an LPDA (Log-Periodic Dipole) ultra-wideband antenna intended for use across basically all common frequency bands from GSM through 3G (1700-2170MHz) and LTE, also including the 2.4GHz WLAN band. Like the XPOL-0002, it was also recently updated to "V2" (
LPDA-0020-V2), with some obvious changes to the performance curves :
At face value - given the much more variable gain and so-so VSWR curves on the V2 - you could be forgiven for wondering if it's actually an improvement. But if nothing else, V2 is at least fully characterised above 2400MHz. This could be an advantage if any operators start to utilise spectrum above 2400MHz in future.
LPDA-0020-V2 also has a slightly different mounting arrangement - the mounting bracket is now separate from the antenna back plate, whereas with V1 it was an integral part.
In terms of performance, a twin LPDA-0020 array
should be comparable to the new XPOL-0002-V2. In terms of aesthetics, it's not nearly as "pretty" as the XPOL, but not quite as industrial as a twin LPDA-0092 installation. Another downside is that you need two of everything in the signal cable path, including two surge protectors, if you go that far.
One thing that intrigues me is this : In Poynting's LTE videos, they show two LPDA-0092 antennas oriented at 0 degrees and 90 degrees relative to the vertical plane, ie vertical and horizontal. For the LPDA-0020, they show the two antennas mounted orthogonally, but at +45 and -45 to the vertical plane - see
here.
I'm curious about :
a) Why most of Poynting's LTE antennas have horizontal and vertical elements, whereas the dual LPDA-0020 array is an exception at +45/-45 degrees;
b) Whether it would be possible/advisable to mount an LPDA-0020 array in the 0/90 position (as opposed to +45/-45); and
c) What the relative advantages (if any) of a 0/90 array might be.
Intuitively, it seems that a more conventional 0/90 installation might give better fallback performance when used with 3G. So far I haven't managed to get a technical opinion out of Poynting, but I'm still hopeful! More when I know more. Anyone else with info on the subject, please share.
I'll be posting some install pics and performance tests as things progress.
