Computing > Networking & Wireless

USB WiFi Adapter Antenna

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David Hess:

--- Quote from: cdev on May 25, 2021, 10:53:44 am ---Such an antenna is going to have a pattern like a squished donut.

It needs to be perfectly vertical to be helpful.
--- End quote ---

I agree when the environment supports line-of-sight and is free of obstructions, but indoor WiFi applications have so much multipath that omni-directional antenna orientation is largely irrelevant.

I think both designs are attempts to be collinear antennas and likely the gains are roughly similar and perpendicular to the element.

There are dozens of good antennas for wifi. Chances are most of them would work okay for a short distance situation.

I agree that a biquad+ reflector is an excellent choice for a fairly decent directional antenna without a lot of work.

E Kafeman:

--- Quote from: cdev on July 02, 2021, 12:09:35 am ---I think both designs are attempts to be collinear antennas
--- End quote ---

Hm, hm and hm again. I am feeling I am repeating myself, trying to describe a very basic antenna structure in a simple way that all that knows anything about antennas should be able to understand.
Why not read previous antenna comments and look at available pictures before wrongly deciding which type of antenna it is? It is just too simple to identify these antennas so wrong conclusion is a bit worrying.

First antenna design, antena-1.png, is almost too easy to identify from its PCB pattern and by then exclude it as possible collinear design.
This antenna design is even more simple to identify as it also is shown in #msg3561532 that it have dual coaxial cable feeds.

It can be a good first clue to identify this antenna, why should a low cost none collinear antennas printed on a PCB have dual coaxial cables?

Antenna pattern for this antenna is very simple and very popular type of dual band dipole antenna.

Dipole antenna is basically an antenna with two arms (di-poles), commonly 0.25 lambda length for each arm.
At first picture can it be seen a second pair of arms at each dipole with slightly different length, which allows for resonance at both 2.4 GHz and 5 GHz for a single antenna structure.
This structure is repeated, there are two double band dipoles at PCB.
Collinear double band antennas at 2.4GHz and 5 GHz is not possible or very complex and do not need two coaxial cables, why we by now can be very sure that it not is a collinear design.

Hypothetical could this be an antenna array for 2.4 and 5GHz, consisting of the both visible antenna structures but as we know that most modern WiFi routers and as in this case an USB WiFi-adapter, need MIMO antennas to achieve its bandwidth according to 802.11n and above is it no hard guess that the both coaxial cables feeds separate transceiver ports. We can even read "AC" in the 2:nd picture of this antenna, if still in doubt.

Antenna shown in picture antena-2 is an wire antenna and antena-3 is a PCB pattern but both antennas are basically similar type of antenna. It is as best a single stage of a collinear antenna.

As what I now hope can be easily understandable, these both pictures, antena-1 and antena-2 are two very different animals.
Picture antena-1 is showing two antennas, each of these both antenna are designed as a double frequency band antenna. Each antenna have its own coaxial cable feed.
Picture antena-2 is just a single antenna and it is designed for just a single frequency band.

I have a collinear design Ive built now, twice, it uses a short delay segment, its been around for at least 20 yrs, I first saw it around 1999, it uses 1 mm diameter copper wire and it is end fed. The wire is attached to an bulkhead mount N-connector and it has a respectable 5 or 6 db of gain out to the horizon. It resonates exactly at 2400 MHz. I have mine in a thin piece of PVC pipe.

There is another collinear thats very similar and it looks more like the picture 2. It is usually embedded in a black plastic radome and it has the stub section at the bottom. The coil is not a loading coil, its to introduce a time delay. e can increase the gain of this type of antenna substantially by adding more sections but one reaches a point of diminishing returns at a fairly low number of sections. You dont get much more gain from more than three sections.

E Kafeman:
>its been around for at least 20 yrs,
Collinear antenna design have been around in many versions since long, much longer then 20 years.
It was patented 1924 by C. S. Franklin, almost 100 years ago. and this antenna type is also known as a Franklin antenna.

>and it has a respectable 5 or 6 db of gain
No it haven't. dBi maybe. dB is relative to something you not did specify.

What gain you achieve is roughly calculated as it is a number of stacked halfwave dipoles.
Antenna type is mostly either centerfeed or endfeed.

>It is usually embedded in a black plastic radome
What enclosure an antenna is placed within is not an antenna property. Neither color, but yes many plastic tubers contains an antenna of some kind.

An alternative and sometimes better describing name of this antenna type could be co-phasing antenna.

>The coil is not a loading coil,
If it is a coil, it is a coil even if it is placed within an antenna structure and load? No it does not load anything, it adds serial reactance.
The phasing element can be designed in many ways, open or short stub, two coils winded in opposite directions close to each other is common, and the phasing pattern can in many cases be performed at PCB as well as using heavy metal designs.

> its to introduce a time delay.
At antenna-language do we call section between the halfwave elements for phasing element, not timedelay as that is something else.

>You dont get much more gain from more than three sections.
I have no such problems with my antennas and there are a lot of other designs that not have your limitation.
This antenna structure is nothing else then a kind of antenna array and stacking a rather high number of element is possible.
As best is gain increased with 3 dB for each doubling of number of sections as for any similar array, but poor design can of course reduce that number.
In most cases is antenna efficiency reduced for each added section but that is something else then gain.

This is a (Franklin) collinear antenna in 14 sections. Measured gain above 15 dBi. It is top-terminated with a resistor.Your link to Martybugs antenna, is not a working antenna array and whatever it is is it a real poor working co-phased antenna.
You can find descriptions of co-phasing in Balanis ANTENNA THEORY ANALYSIS AND DESIGN but collinear antenna as a defined structure, its theory is described relative simple at page 134 and forward in Transmission Lines Antennas and Waveguides. The book is first printed 1945 but still relevant and where following design is explained in more detail.


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