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Building my 4G LTE mimo antenna prototype

September 17th, 2018


You might already read that I own a Huawei router. Currently, it is installed in the attic of our house. However, it happens not so rarely that the download speed significantly drops. In some cases, it is relevant to the meteorological conditions (the rain is not so rare on the west coast of Ireland). But in others cases, it is not really related to the weather conditions.

All that brought me to the idea of testing the reception of 3G/4G signal with the external antenna. Initially, I checked eBay for such antenna (via eBay). But after reading in different places, I learnt that Chinese sellers add together both mimo antennas gains. Very creative. You have two 5dB antennas, so you put 10dB figure 🙂 Getting 5 dB gain is what you could expect from quite many 4G antennas (even including some official vendors (via eBay)). Not really much. Especially, if you have a long cable and there are losses because of its length.

Then I decided to build the antenna myself. Some years ago, I already built Bi-Quad antenna for a tv and it worked absolutely perfectly. I googled and it appeared that this type of antenna is one of the favourite type by DIY builders 🙂 There is a reason for such popularity. It is pretty easy to build Bi-Quad antenna. Secondly, such antenna has 10dB gain (real one per one antenna).

Required parts for building 4G LTE antenna

As I was not sure about the advantages of such antenna in my case, I bought only two parts.

Building my 4G LTE mimo antenna prototype Bi-Quad antenna SMA connectors

The first one was a SMA Male to SMA Male M-M Connector RF Coaxial Pigtail RG174 Extension Cable T7M4 from eBay (via eBay). It costed 3Eur including shipment. I cut this cable in half, so I got 5 meters of low quality RG174. At the same time, this ready cable took off the hassle of putting the SMA connectors on the cable itself too 🙂 Plus, it brought another advantage. As RG174 cable has high attenuation of the signal (something like 1-2dB/m), that would create at least about 5dB loses in the cable (per each antenna). So, it is a good test for the antenna’s gain. I bought also another part – 5 meters of copper 2.2mm wire (via eBay). At the end, I made a reflector from an old CD.

Calculating the dimensions for Bi-Quad antenna

The first thing, you should google and figure out what is the frequency of LTE in your country. E.g. it is 2100MHz in Ireland. Then, there are couple very nice websites for calculating the Bi-Quad antennas. One of them is here. Another is located here. In any case, you should build something like this shape:

Building 4g LTE mimo antenna prototype Bi-Quad antenna

For the frequency of 2100Mhz, the parameters are following: L1 is 34.65mm (3.5cm), L2 is 97.02mm (9.7cm) and H is 114.3mm. It took me one evening to make the antenna from the copper wire and solder the cable to it, which you can see it below.

Building my 4G LTE mimo antenna prototype Bi-Quad antenna

Testing the LTE antenna

So, the antenna is ready and the time was to test it. My attic has the roof windows. So, I tried three scenarios: 1) in front of the window, 2) outside the window (perpendicular to the room) and 3) outside the window (in parallel with the longest wall of the room). The last two tests were designed to “catch” the direction towards the base.

So, here are the results:

  1. Inside the roomBuilding my 4 LTE mimo antenna prototype Bi-Quad antenna 3 testing Inside the room
  2. Outside on the roof 0 degreesBuilding my 4 LTE mimo antenna prototype Bi-Quad antenna 3 testing On the roof 0 degrees3. Outside on the roof 90 degrees

Building my 4 LTE mimo antenna prototype Bi-Quad antenna 3 Testing On the roof 90 degrees

Let’s discuss a bit the results

In 4G signal, there are three variables describing the signal quality: RSRQ, RSRQ and SINR.

RSRP is the average power received from a single reference signal. RSRQ indicates quality of the received signal. SINR is the signal-to-noise ratio of the given signal.

Here, I found this table which explains how to should interpret RSRQ, RSRQ and SINR:

Building my 4 LTE mimo antenna prototype Bi-Quad antenna interpreting LTE signal characteristics

What I got:

inside -6dB (RSRQ), -93dB(RSRP), 17dB (SINR)

outside 0 -10dB(RSRQ), -78dB(RSRP), 17 (SINR)

outside 90 -9dB(RSRQ), -76dB(RSRP), 17dB(SINR)

As you might expect, the outside location gives 3-4dB difference in RSRQ(in received power), which is 1000 times, and even bigger difference inRSRP(in quality of the received signal). The signal noise level remains the same.

What is left?

To get a case where to install my antenna and mount the antenna externally on the wall 😉