4G Double Bi-Quad Antenna Separation Query

[#1]

When making Yagi antennas, and they need to be stacked, there is generally a recommended distance between them suggested in the actual calclulation details for any given frequency.

So far, despite reading many different pages about Double Bi-quad Antennas, I have been unable to find any info about the recommended distance between two Double Bi-quad Antennas. (the proposed antennas are "flat plane" and not Yagi type bi-qads)

Is there a "rule of thumb" guide to this, that anyone can impart to me, please.

Thank you.

[#2]

@shutter 

Are you intending to stack the two aerials vertically or horizontally?

In my experience from amateur radio many years ago, antenna spacings were generally multiples of a quarter wavelength.

Could you experiment with one aerial fixed and the other movable along a mast, then vary the spacing and monitor the results?

Is your primary goal to reduce the forward beamwidth or increase the gain?

[#3]

@Mr_Paul   Thanks for your interest.

Currently I have a pair of double bi-quads made up from 1.5mm copper wire from twin and earth lighting cable. Backed by an aluminium reflector cut to the size of the frequency ( as detailed in the calculations figures) this is covered in "baco-foil" which is supported by a couple of "large" box lid type constructions, and the whole is mounted on a large piece of shutter board ( leftovers) which can be made in to use as vertical or horizontal modes for the antennas.

Here is a pic !  Heath robinson will probably cry ! ! ! . (located in the upstairs bedroom, on the top of a wardrobe) !

This was really just  "trial" before considering how to make a much more "presentable" version, with possibility of being mounted outside...

They are designed for the two frequencies of Band 3 uplink and downlink, for my 4G Lte TP LINK MR 6500V ROUTER..which provides me with internet connection , and "home phone"...  ( £12 per month)  from a mobile phone mast 1.5 miles away, 

Signal strength is 100%  and the max RSRP is -80dBm according to the mastdata site. these two antennas give me a RSRP of -83 dBm....

I did make a pair of Yagi`s for Band 1 and Band 3....

The configuration of the yagi`s means that I can set the pair vertical or horizontal , and also each antenna can be set into a vertical or horizontal plane, ( or even diagonal )  in either the vertical or horizontal stacking config. 

while they did work, they were not as good for the RSRP, RSRQ, and SNR figures compared to the Double Bi-quads.

The current spacing (of the Double Bi-quad) as in the pic, was just a matter of how I could fix them to the board, !...

I have experimented with them being vertical and horizontal, at various times of day and evening, and it seems that the best position is in the vertical position, but with the actual Double Bi-Quads at 45 degrees to the vertical.  ( V formation )

Going forward, I would follow the same configuration...... "stacking" them "side by side"...

After making them "properly"... ( hence the question of spacing between them ) . I would then need to, either, A) waterproof the antenna connector(s) and spray paint all one colour ( grey probably)... or B) try to find some suitable Plastic box like protection for them as one unit, for out door installation.

Regarding "beamwidth"... not sure how that is calculated on this type of antenna...  but certainly there is a decent increased "gain" level judging by comparison to the Yagi`s .

Future plans may include trying out a single "bow-tie" (bi-quad) design made into a Yagi` configuration. to see how that works for me......

If the spacing should be a quarter wavelength, or half wavelength, would this be measured between the centre point(s) of the antennas, or from the "Inside" edges of the reflector plates.