Home-brew Compact 6dBi Collinear Antenna

completed collinear antenna
This page details the construction of an easy-to-make collinear 360 degrees omni-directional, vertically polarised, antenna for 802.11b/g wireless networking. The antenna is very robust and compact, and has a gain of approximately 5-6dBi.


Various websites detail the construction of a collinear antenna suitable for 2.4GHz wireless networking. However, these antennas are quite complex to build, being made up of numerous short lengths of coax which must be accurately cut to length. You also need to know the velocity factor of the coax that is being used, as most of the measurements are based on it.
A variation of the coax collinear is constructed from brass rod and brass tubing, but is still just as fiddly to construct.

Some time ago, I made an 8-element coax collinear.
However, it took many hours to construct, and the antenna has very little physical strength. I resorted to cable-tying a length of dowel to the coax, and then encasing it all inside some 25mm electrical conduit.

I was particularly intrigued when a friend pointed out a much simpler collinear, consisting of just a length of copper wire appropriately bent, as detailed here, with a claimed gain of about 6dBi.

This version provides a number of benefits over the coax construction, requiring far less effort to construct, and providing a smaller and more robust antenna.
While the 6dBi gain is less than that of an 8 element coax collinear, the gain can be improved by increasing the number of elements. Doubling the number of elements will increase the gain by almost 3dBi, ie, double the gain.

Parts Required

The materials required:
  • approx 300mm 2.5mm2 copper wire
  • panel-mount female N-connector
  • 250mm length of 20mm light-duty electrical conduit
  • 2 end-caps to suit 20mm conduit
and optionally, for mounting of the completed collinear antenna:
  • 2 clamps to suit 20mm conduit
  • metal bracket
I used a length of copper wire from some scraps of 2.5mm2 electrical cable I had lying around. This cable has a diameter of approximately 1.6mm, and is flexible enough to bend into the required shape without too much effort or specialised tools.

electrical cable
2.5mm2 3-core electrical cable

A panel-mount female N-type connector is also required, to allow the antenna to be connected to a wireless device. Note that other connectors (ie, TNC, SMA, etc) can also be used, depending on the connectors on your pigtails.

I used a panel-mount female N-type connector, as shown in the photos below.

panel mount female N-type connector
panel mount female N-type connector
panel-mount female N-type connector

Design Details

This collinear simply consists of a length of copper wire with some loops located at specific locations. The dimensions of the sections of the antenna are important, and are shown in the diagram below.

dimensions of the collinear
dimensions of the collinear

The length of the bottom section is 1/2 wavelength (the left section in the diagram above), the centre section is 3/4 wavelength, and whip section on the top is slightly less than 3/4 wavelength, apparently to reduce the capacitance effect.

The 802.11b standard uses 2.412GHz to 2.484GHz frequency range, so at the centre of that frequency range, 1/2 wavelength is 61mm, and 3/4 wavelength is 91.5mm.

These dimensions appear to be consistent with similar commercial antennas.


Start construction of the antenna from the bottom end, and solder one length of the copper wire into the N connector. Measure 1/2 wavelength from the top of the N connector, and create the first loop.

loop detail
completed bare collinear
loop detail
loop detail, and completed bare antenna

Note that the loops are offset from the wire which makes the vertical section of the antenna.

Then measure an additional 3/4 wavelength, and create the second loop. Trim the whip section on the top so it's the correct length.

If you are intending to use a length of 20mm conduit to house your antenna, be sure to keep the diameter of the coils to approximately 15mm or less, to ensure they will fit inside the conduit (20mm light-duty electrical conduit has an internal diameter of 16mm).

completed collinear
completed collinear

However, a length of copper wire isn't particularly robust. One of the easier ways to address this shortcoming is to enclose the antenna inside a radome.

Note that you need to use something that's transparent to 2.4GHz, else it will adversely affect the performance and operation of your antenna.

I used a 250mm length of 20mm light-duty electrical conduit, with some end caps to suit. The 20mm light-duty conduit has an internal diameter of 16mm, and the loops bent in the copper were a snug fit inside the conduit.

If you need something a little more roomy, then 25mm light-duty conduit can be used.

Two small bends are required in the wire near the base of the antenna, to ensure that the loops are centrally located above the N connector, thus allowing the entire antenna to be inserted into the conduit.
Testing indicates these bends to not have any noticable impact on the performance of the antenna.

20mm conduit and end caps
20mm conduit and end caps

To mount the antenna, a suitably sized hole was drilled in one of the end caps, and after discarding the N connector's nut and washer, the N connector was screwed into the end cap from the outside.

N connector in end cap
N-type connector screwed into an end cap

The antenna can now be inserted into the conduit, and the other end cap can be installed.

enclosed collinear
enclosed collinear

If the antenna is to be used outdoors, the end caps should be glued on with appropriate conduit glue, to ensure a weather-proof seal.
Note that the antenna should be tested before gluing the end caps in place.


The collinear antenna is designed to be mounted vertically.

The conduit radome provides a robust and sturdy enclosure for the antenna, and if required, it can be mounted outside in the weather. If mounting it outside, be sure to wrap the N-connector appropriately in self-amalgamating tape to prevent any moisture ingress.

Plastic clamps made specifically for conduit can be used to attach the antenna to a vertical surface. As these clamps are plastic, they will not interfere with the operation of the antenna, while all-metal mounts placed in the radiation pattern could affect the operation of the antenna.

20mm conduit clamps
20mm conduit clamps

After attaching the clamps to the surface where the antenna is to be mounted, the antenna can easily be clipped into the clamps, and can also be easily removed.

sample mounting using clamps
sample mounting using clamps

An alternative method of mounting the antenna is with a short length of right-angle galvanised steel. A suitable hole needs to be drilled in one side, and the antenna can be attached to the galvanised steel by removing the N-connector and attached copper antenna, and passing it through the hole in the galvanised steel. The antenna will be firmly attached between the N-connector and the end cap.

using a metal bracket
using a metal bracket

If you just want to use the antenna for casual stumbling or wardriving, there is no need to mount it, and it can just be used as a handheld antenna.

demonstrating just how small it is
demonstrating just how small it is


When building my first collinear using this design, I made the loops in a similar way to those seen on many commercial antennas which have multi-loop coils, with the wire above and below the coil being centrally located with regards to the loop.

how NOT to do the loops
first attempt at the loops

However, after doing some further research, I realised this was incorrect, and made another collinear using the loops as per the approach described above.
Some quick comparison testing indicates the collinear with the offset loops performs much better than the collinear with the centered loops.

Need More Gain?

More gain can be achieved by adding additional segments to the middle of the collinear, as shown in the diagram below.

dimensions of a longer variation of the collinear
dimensions of a longer variation of the collinear

Some quick comparison testing indicates this longer collinear has approximately 2dBi more gain than the 6dBi version, with a gain of about 8dBi.

Note that lengthening the collinear antenna in this way will reduce the vertical beamwidth of the radiation pattern.

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