I built a Biquad based on the dimensions of the article featured below, and indeed I can get 4 – 5 bars strength from a base station over a hill and 8 km away.
I found this article somewhere on the internet:

NextG_bi-quad_antenna

Some photos of my Bi-Quad:

A friend who works with metal cut this sheet to size for me.

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I cut a spare 3g modem antenna in half. Careful not to break the thin shielded wire inside. 

I then soldered the wire and the shielding to the respective sides of the BiQuad.

– Securing the soldering with a blob of  expoxy resin on top, and then screwed the antenna into low loss cable.

And Pesto: plug unto a 3G modem ,  job done!