FlightAware Discussions

Waveguide type directional antenna


#21

No problem. Due to very high frequency, almost the entire RF current flows in a thin layer on outer surface of wire (Skin Effect).


#22

Ductenna ™ pointed south, 5 mins to stabilize, gain -10, blue Pro Stick, no filter. Surprisingly omnidirectional:


#23

Switch to spider with no other changes.


#24

:smile: :wink: :rofl: :+1:


#25

Nice work! Looks good.

Yes, definitely. As a rule, the higher the frequency, the more reflective the signal tends to be.
The effect is more pronounced with Wi-Fi at 2.4GHz and even more so at 5 GHz.

8 inch stove pipe (the black stuff, vice galvanized) would enable you to build a longer antenna which will give you a narrower beamwidth. It’s available in 2 foot lengths. Fairly inexpensive too.

If you were to simply add a section of stovepipe to your existing setup, you should see a significant change in performance.

By using the thin wire, you’ve actually helped narrow the bandwidth of your antenna.
(the larger the diameter of an element, the wider its bandwidth becomes)
So that’ll help a bit with rejecting unwanted signals. Maybe not a lot, but anything is better than nothing.


#26

One way to get a rough idea of the beamwidth would be to use an antenna modeling program.
I don’t know if any of the freely available ones like mininec, et al, are set up to handle wavguide antennas.
As a waveguide antenna is a horn antenna without the “horn” you might find an app that is capable
of modeling horn antennas, which might be able to be configured to model a waveguide antenna.


#27

Did you use a calculator for the values?

Also you can’t really use the optimize script.
Better check signal values in the direction the antenna is pointed manually.
You could also use my html folder that colors aircraft track by signal strength. (Coloring planes according to signal level)

Using too much gain will probably get you more planes but you could be having too much gain in the direction you are trying to receive.
Also you seem to have pointed the antenna up slightly that shouldn’t be necessary (i think).
Maybe experiment with the optimum elevation above horizon.


#28

Neat idea with the color coding by signal level. I think I’ll give it a try. FTR Here’s the output of the online calculator that I used:


#29

I’ve clearly got a little bit of directional gain. There’s a pretty major air corridor going on the NE-SW diagonal so I pointed it SW. From the screenshot below, I’m picking up more planes than I usually do in the Southwesterly direction, but it is not obvious from the color coding. I’m thinking about picking up another 10" extension.


#30

FUNNEL DUCTENNA

image . image

image


#31

If the angle of the “funnel” part is 30° those should work like champs.
The “horn” serves to match the impedance of the waveguide to that of free space,
which is ~377Ω


#32

Shouldn’t that have a turtle excluder ?


#33

The Long One

image


#34

Waveguide: Modes of Transmission

One of the most important differences in the operation of waveguide compared to transmission line concerns the mode of transmission of the electromagnetic wave carrying the signal.

In a transmission line, the wave is associated with electric currents on a pair of conductors. The conductors constrain the currents to be parallel to the line, and consequently both the magnetic and electric components of the electromagnetic field are perpendicular to the direction of travel of the wave. This transverse mode is designated TEM. On the other hand, there are infinitely many modes that any completely hollow waveguide can support, but the TEM mode is not one of them. Waveguide modes are designated either TE (transverse electric) or TM (transverse magnetic), followed by a pair of suffixes identifying the precise mode.

Figure 1: The field patterns of some common waveguide modes

.
This multiplicity of modes can cause problems in waveguide when spurious modes are generated. Designs are usually based on a single mode and frequently incorporate features to suppress the unwanted modes. On the other hand, advantage can be had from choosing the right mode for the application, and even sometimes making use of more than one mode at once. Where only a single mode is in use, the waveguide can be modeled like a conducting transmission line and results from transmission line theory can be applied.

Cutoff

Another feature peculiar to waveguide is that there is a definite frequency, the cutoff frequency, below which no transmission can take place. This means that in theory low-pass filters cannot be made in waveguides. The waveguide cutoff frequency is a function of transmission mode, so at a given frequency, the waveguide may be usable in some modes but not others. Likewise, the guide wavelength (λg) and characteristic impedance of the guide at a given frequency also depend on mode.

Dominant mode

The mode with the lowest cutoff frequency of all the modes is called the dominant mode. Between cutoff and the next highest mode, this is the only mode it is possible to transmit, which is why it is described as dominant. Any spurious modes generated are rapidly attenuated along the length of the guide and soon disappear. Practical designs are frequently made to operate in the dominant mode

In rectangular waveguide, the TE10 mode (shown in above figure) is the dominant mode. There is a band of frequencies between the dominant mode cutoff and the next highest mode cutoff in which the waveguide can be operated without any possibility of generating spurious modes. The next highest cutoff modes are TE20, at exactly twice the TE10 mode, and TE01 which is also twice TE10 if the waveguide used has the commonly used aspect ratio of 2:1. The lowest cutoff TM mode is TM11 (shown in above figure) which is √5 times the dominant mode in 2:1 waveguide. Thus, there is an octave over which the dominant mode is free of spurious modes, although operating too close to cutoff is usually avoided because of phase distortion.

In circular waveguide, the dominant mode is TE11 and is shown in above figure. The next highest mode is TM01. The range over which the dominant mode is guaranteed to be spurious-mode free is less than that in rectangular waveguide; the ratio of highest to lowest frequency is approximately 1.3 in circular waveguide, compared to 2.0 in rectangular guide.

.

SOURCE: https://en.wikipedia.org/wiki/Waveguide_filter

.


#35

WiFi Measurements:

SOURCE: http://www.antennamagus.com/blog/593/pringles-cantenna-measured-in-an-anechoic-chamber

.
Pringles and copper
Pringles and Copper

.
S11 simulated vs measured
S11 simulated vs measured

.

pattern comparisons
pattern comparisons

.


#36

Not too surprising, given the inside of a Pringles can isn’t metallic although it appears to be.

From: http://www.turnpoint.net/wireless/has.html

There seems to be quite a bit of confusion on how the Pringles antenna works and what design category it falls under. The inner lining of a Pringles can looks metallic, but my tests show it not to be. The Pringles Antenna design, and some designs that pre-date it, seem to treat it as though it were metallic.

But… It was the one that started the DIY waveguide antenna thing.

The Copper one will kick some serious butt.
But a piece of Copper that size… let’s just say “it aint cheap!”


#37

It looks like it is made of cardboard coated by aluminum foil on one side. When they make the can, they keep the foil coating on the inner side of the can.

I have once tested a similar can by a multitester, and it showed continuity between two ends of the can.


#38

I don’t know what tests he used to make his determination, but the traces on the graphs you posted
bear out the fact it doesnt perform quite the same as the copper example, as well as the simulation
being different from the measurement by quite a bit. But, no simulation is perfect, so some of that’s to
be expected.


#39

I still can’t get my head around what would cause the back lobe. Part of what makes RF so interesting to me is that I might think I understand waves but then I see this stuff and it’s just not intuitive to me.


#40

Not being a math type, I can’t explain why it happens, but it does happen with any antenna.
One of the specifications - front to back ratio - is a measure of the phenomenon you’ve observed.

Antenna design is a tradeoff between forward gain and F/B ratio. An antenna with a high forward
gain won’t have the highest F/B ratio possible. Conversely an antenna with a high F/B ratio won’t
have the max forward gain possible.

Exactly the sentiment of many when it comes to RF in general.

Here’s a link with info on antenna theory: http://www.antenna-theory.com/

The author says this about himself:

I am a practicing antenna engineer, with a PhD in antennas and I have worked for many years in defense, university and the consumer electronics field as an antenna engineer.

but he’s kept the material to an easily “digestible” level.