Antenna design - sanity checking

AirBiscuit

Hi folks, this might be a bit off topic but I figure this would be a better fit than the midband forums for this type of thing

I'm planning to make 2 Yagi antennae to increase the reception on my 4G router. I had some success with this a few years ago using an old TV antenna from the 80s that didn't have filtering like most of the ones in shops seem to have now which seemed to play nicely with the 800MHz 4G band in the area, but this won't work for me in this case because the 4G band where I am now is 1800MHz.

I can see the phone mast from my window but there's either a lot of intereference because my router is on the other side of the house with only small stock antennae or the mast is oversubscribed. Either way I am hopeful that using DIY antennae will give me the boost I need to make things usable.

The plan is to use my 3D printer to make a part which fits over an aluminium boom to both isolate the elements from the boom and space everything out correctly as per the online calculator I used.

6mmØ aluminium rods for the reflector, dipole and parasitic elements, 20x20mm aluminium square tube for the boom.

Design shown is for the 1855MHz antenna, the receiver. Is there anything obviously wrong with the design visible more professional sets of eyes than mine?

Calculator used for this one:

https://www.changpuak.ch/electronics/yagi_uda_antenna.php

Javascript Version 12.01.2014, based on Rothammel / DL6WU

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Frequency    : 1855 MHz

Wavelength   : 162 mm

Rod Diameter : 6 mm

Boom Diameter : 20 mm

Boom Length  : 167 mm

d/lambda     : 0.037   ( min.: 0.002 , max.: 0.01 )

D/lambda     : 0.050   ( min.: 0.01 , max.: 0.05 )

Elements     : 6

Gain         : 9.01 dBd (approx.)

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Reflector Length  : 78 mm

Reflector Position : 0 mm

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Dipole Position   : 39 mm

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Director #1 Position : 51 mm , Length : 73 mm

Distance Dipole - Dir. #1 : 12 mm

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Director #2 Position : 80 mm , Length : 73 mm

Distance Dir. #1 - Dir. #2 : 29 mm

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Director #3 Position : 115 mm , Length : 72 mm

Distance Dir. #2 - Dir. #3 : 35 mm

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Director #4 Position : 155 mm , Length : 71 mm

Distance Dir. #3 - Dir. #4 : 40 mm

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Directors / Parasitics are isolated.

Please choose an isolater thicker than : 4 mm

martinedwards

way out of my league, sorry!

4dxc

Looks good to me. However what`s you plan on feeding the dipole? Considering using 50Ohm cable you would need to match this.

Most likely the impedance would be around 20-30Ohms depending on your set-up. The solutions below are some of the main solutions used and applicable to many types of antenna. :

• Element spacing:  There is a level of impedance variation that can be provided by altering the spacing between the elements. However it is not possible to bring the feed impedance back up to 50Ω needed for most feed applications. .
• Balun:  A balun is an impedance matching transformer and can be used to match a great variety of impedance ratios, provided the impedance is known when the balun is designed.
• Folded dipole:  One method which can effectively be implemented to increase the feed impedance is to use a folder dipole. In its basic form it raises the impedance four fold, although by changing various parameters it is possible to raise the impedance by different factors.
• Delta match:  This method of Yagi impedance matching involves "fanning out" the feed connection to the driven element.
• Gamma match:  The gamma match solution to Yagi matching involves connecting the out of the coax braid to the centre of the driven element, and the centre via a capacitor to a point away from the centre, dependent upon the impedance increase required.

It might be a bit hard for you to measure those things without the necessary equipment. Maybe worthwhile modelling it in EZNEC and design the feeding according to those results.