No name antenna 27+ dbi

[clanon 246]

2 hours ago, Mishka said:

 

Does CST, or HFSS, or FEKO, or anything else besides the cocoaNEC support a programming language, or maybe have a built-in gradient descent or something like that to do the job?

CST is GUI intuitive...fast and efficient...

(no need for code or commands)

[Mishka 10]

1 hour ago, clanon said:

CST is GUI intuitive...fast and efficient...

(no need for code or commands)

Although the NEC itself is pretty old piece of software, the cocoaNEC has its C-alike programming language so it's possible to calculate parameter values using a custom optimization algorithm. This is especially useful when there is no strong antenna theory behind the model and there are a lot of parameters to tweak so a simple sweep won't work well. As another example, someone could mention fractal antennas where the antenna itself can be generated.

Therefore I'm expecting the CST (or any other modern toolkit) can automatically perform many parameters adjustment in order to minimize VSWR, return loss, etc. Can it?

P.S. I'm on a Mac, and it seems any modern antenna software requires Windows nowadays. I'll be happy to know if the CST can run gradient descent or something similar over a set of parameters, or if it has a scripting interface.

[Mishka 10]

3 hours ago, Admin said:

,,, okay, it's enough to just give the dimensions...!!!

I can easily do it for a wire wound antenna. Is this what you meant?

Or I could model a non-MIMO LPDA similar to the KNA-27. The optimized model will give starting values for dimensions to play with.

[clanon 246]

yep , is called optimization...but you could do it by hand if you know your stuff (right now i'm short on RAM and cores) so the closer y draw  and scale the sooner i get to optimal...(but JOMY is the most experienced) if you could use 2d or 3d drawing ...it would be easier to share

Edited November 20, 2020 by clanon

[Admin 2545]

[Mishka 10]

Hey, the KNA-27 is built of six dipoles, not five as I counted initially!

But there's more! When I entered its parameters - 1700-2700 MHz bandwidth, 5 dipoles - into my NEC script, it resulted in a model where the third dipole is clearly missing. Interesting.

Of course, the model is optimized (Smith chart inside the spoiler):

Spoiler

I'll re-run for 6 dipoles now.

[Admin 2545]

,,, dimensions, please ... !!!
,,, or, I may need to install the NEC program again...!!!

[Mishka 10]

1 hour ago, Admin said:

,,, dimensions, please ... !!!
,,, or, I may need to install the NEC program again...!!!

No need to bother, please just wait for a while - the SGD is not fast because it's running on top of interpreted language. I'm calculating now.

[clanon 246]

[clanon 246]

it looks like 5 ...but maybe 1 more really small close to the boom...

[Mishka 10]

7 hours ago, Admin said:

,,, dimensions, please ... !!!
,,, or, I may need to install the NEC program again...!!!

Here we go. LPDA 1700-2700 MHz, it's made of 2.5 sq.mm copper wire and has 6 dipoles in total. All dimension in mm. Antenna is [loosely] matched to 50 Ohm, but looking at the Smith chart it seem behaves closer to a dipole. Antenna fed with a symmetrical source.

Of course, a tin-plated version will have different dimensions. As I mentioned earlier, to simulate it there's must be function for a wire mesh. Not too complicated to write though, but I'll be happy if you guys could do it in the CST.

Simulation data:

Spoiler

Smith chart:

VSWR:

Return loss:

Azimuth (horizontal - solid, vertical - dashed):

Elevation (horizonal - solid, vertical - dashed):

 

[Mishka 10]

3 hours ago, Mishka said:

Here we go. LPDA 1700-2700 MHz, it's made of 2.5 sq.mm copper wire and has 6 dipoles in total.

 

OOPS!

On the antenna drawing the distance between wires in the boom is 2.6 * 2 = 5.2 mm!

The NEC model is symmetrical, so 2.6 is the distance from the axis (zero) to each wire.

Edited November 21, 2020 by Mishka

[Admin 2545]

OOPS,,, this antenna does not work...

 

[Mishka 10]

11 hours ago, Admin said:

OOPS,,, this antenna does not work...

Please hold on, an LPDA works by shifting phase across the boom. Every dipole must be fed with phase rotated 180º so it should look like this:

[Admin 2545]

,,,to see this...

 

[clanon 246]

[Mishka 10]

3 hours ago, Admin said:

,,,to see this...

 

Very interesting video. The impedance stub is a nice finish.

But I had difficulties to read cursor values on the network analyzer screen. It seem about to measure antenna return loss, but it's around 50dBm and changes insignificantly - the chart is 0.5dB/.

[clanon 246]

always TWO PEAKS of resonance (1ghz-  2,5ghz )

NO S11 though...

tubing should be better than flat plate... (i guess)

[Mishka 10]

For curiosity I've built the cocoaNEC generated dual-band LPDA. Well, the good news is that the VSWR and return loss are close to what was predicted by the NEC. Please note, the antenna was calculated for 2.4GHz and 5GHz WiFi ranges only and should not be expected to work outside of the bands. Also, my VNA can't see above 4.4GHz so unortunately I was unable to test it at 5 to 6 GHz range.

On the other side, antenna is out of impedance (which is sort of okay for LPDA). This may happen due to improper connection or other assembly issues. Such, for simpler assembly I've soldered a PCB edge SMA connector to the boom - this way the connector will fix the boom distance, but it appears to introduce phase shift between ground and the feed point. Also, the antenna assumes balanced input and this may also put it out of impedance. I'm thinking about adding the impedance matching stub like it was done by Andrew McNeil in the video above. Any thoughts on how to bring it to 50Ω will be highly appreciated.

 

Measurements:

Spoiler

Edited December 17, 2020 by Mishka

[Admin 2545]

,,,interesting...!!!

,,, can you give the dimensions ... ??

[Mishka 10]

2 hours ago, Admin said:

,,,interesting...!!!

,,, can you give the dimensions ... ??

Sure!

[Admin 2545]

,,,thanks,I"ll make a cst-simulation...!!!

[Mishka 10]

1 hour ago, Admin said:

,,,thanks,I"ll make a cst-simulation...!!!

Thank you! That would be very cool indeed! I still haven't found a Windows computer for that :-(

[Admin 2545]

,,, and here is the situation with this log-per...

I think there is still work to be done on this antenna ... !!!

[Mishka 10]

1 hour ago, Admin said:

,,, and here is the situation with this log-per...

I think there is still work to be done on this antenna ... !!!

Wow! Nice!

Please note, in the NEC model it's fed by a balanced source, and for my assembly I've rotated the SMA connector by 90 degrees (unbalanced feeding).

Well, as for ultra-wide band (2.4 - 7GHz) it looks not too bad. It seems all LPDAs are sort of compromise between bandwidth and quality. At least the model and implementation proves the gain is at about 7dB. Assuming a nice and big reflector which may add up to 20dB, should we consider the Kroks KNA+27 antenna in the subject may virtually go up to +27dBi?

Edited December 19, 2020 by Mishka