any better antenna type with this pattern?

[DrunkBear]

the desired pattern is a monopole-like pattern, with a bi-directional main beam close to the ground plane in the vertical plane and omnidirectional radiation in the horizontal plane, shown as the following:
3D pattern:

vertical plane:

horizontal plane:

i tried a cone monopole as an initial design:


but in the vertical plane, the elevation angle is about 50 degree above the GND. That's too large for me! the closer the main beam is to the GND, the better.

anyone has some suggestions? BTW, there's not much restriction on the bandwidth(it's just OK that the antenna is working at, e.g. 2.4GHz). other antenna type is also acceptable.
many thx!

 

[vfone]

Cone antenna is very broadband. If you need an antenna just for 2.4GHz band you can use a simple λ/4 ground-plane antenna.
The take-off angle of a ground-plane antenna is less than 10 degrees (depends by ground type).
If you are looking for higher directivity (higher side lobes also), you can increase the height of the monopole element at 5λ/8 from the ground, which will give you another 3dB extra gain.

 

[shameemkabir]

but in the vertical plane, the elevation angle is about 50 degree above the GND. That's too large for me! the closer the main beam is to the GND, the better.

elevation angle of monopole largely depends on the size of the ground plane. you need large ground plane (theoretically infinite ground) to have your expected pattern direction.

 

[DrunkBear]

Cone antenna is very broadband. If you need an antenna just for 2.4GHz band you can use a simple λ/4 ground-plane antenna.
The take-off angle of a ground-plane antenna is less than 10 degrees (depends by ground type).
If you are looking for higher directivity (higher side lobes also), you can increase the height of the monopole element at 5λ/8 from the ground, which will give you another 3dB extra gain.

yes, i'll consider using a simple monopole.
BTW, "The take-off angle of a ground-plane antenna is less than 10 degrees (depends by ground type)", what ground type do u mean? could u pls give some more explanation or some reference?
thanks a lot!

 

[vfone]

Size, Shape, Conductivity and Inclination Angle are the definition terms of a perfect ground to get the minimum take-off angle of a ground-plane antenna.
Just search (or think) what these terms means and you will get the answer.

 

[DrunkBear]

to vfone:
this is a model of a simple monopole with a finite ground. monopole length:31.25mm, ground size:200mm*200mm

S11 and impedance:




3D pattern:

E plane pattern:


as u see, the elevation angle is still large. i haven't tried the influence of the monopole length yet. i'm wondering how the very small elevation angle(10 degrees u mentioned) is obtained.

to shameemkabir:
yes, as the ground plane size increases from 100mm*100mm to 200mm*200mm, the main beam direction also increased 5 degrees, but it's still far from my destination.

 

[shahid78]

hi DrunkBear

by looking at your results i think your antenna is resonating close to 1.8Ghz rather than 2.4GHz
so you need to further reduce the lenght of monopole to make it resonate att your desired 2.4ghz frequency

i think if you plot your radiation pattern for the resonating frequency you will get better results

and i agree as you increase the lenght of the monople ground you will get the pattern close to the ideal monople antenna with infinite ground plane

regards
shahid

 

[shameemkabir]

by looking at your results i think your antenna is resonating close to 1.8Ghz rather than 2.4GHz

most probably, Shahid is right. why don't you also provide the smith chart to show at which frequency your antenna is resonating?

shameem

 

[DrunkBear]

by looking at your results i think your antenna is resonating close to 1.8Ghz rather than 2.4GHz

most probably, Shahid is right. why don't you also provide the smith chart to show at which frequency your antenna is resonating?

shameem

to shameemkabir:
usually i check the Z(impedance) plot to judge at which frequency the antenna is resonating. does the antenna have a resonance where the curve forms a knot in the smith chart? i shall check it again and show the smith chart here later.

to Shahid: i suppose it does resonate at around 2.4GHz, which could be shown in the impedance plot(rather than S11). you may find a peak in the resistance plot there. i didn't care much about the accurate resonate frequency at this moment and also didn't make much effort in impedance matching because i still have the doubt whether this simple monopole is the best candidate in terms of the required radiation pattern. i think it has the similar pattern around the resonate frequency ... so i choose a somewhat random frequency to check its pattern.
Please pick out the possible mistakes if you find any in my comments above.
thank you!

 

[flatulent]

Use a 5/8 wave vertical monopole. This will have half of the vertical pattern angle. The input impedance is 50 -jX so you will have to use an inductor in series at the feed.

 

[shahid78]

hi

well if you see in the impedance plot the real part of impedance at 2.4Ghz is close to 90ohm where as the real part of the impedance at 1.8GHZ is close to 50ohm thats why i was saying your antenna is resonatng at 1.8GHZ because other than 0 ohm imaginary part at resonacne frequency we alsowant the real part to be close to 50 ohm for matching

if you plot the radiation pattern at 1.8Ghz and then show us the result that would be good to further comment on your model

regards

 

[Azulykit]

Define "better" in terms of pattern shape, gain, antenna size, set the stage with how it is going to be used, where, the environment, cost constraints etc. and you are likely to get more useful responses.

Regards,

Azulykit

 

[DrunkBear]

Use a 5/8 wave vertical monopole. This will have half of the vertical pattern angle. The input impedance is 50 -jX so you will have to use an inductor in series at the feed.

thank you for ur suggestion!
i'm now working on this 5/8 wavelength vertical monopole design, and i'll show here if i get the desired results.

Added after 58 minutes:

hi

well if you see in the impedance plot the real part of impedance at 2.4Ghz is close to 90ohm where as the real part of the impedance at 1.8GHZ is close to 50ohm thats why i was saying your antenna is resonatng at 1.8GHZ because other than 0 ohm imaginary part at resonacne frequency we alsowant the real part to be close to 50 ohm for matching

if you plot the radiation pattern at 1.8Ghz and then show us the result that would be good to further comment on your model

regards

hi shahid78,
thanks for ur comment!
i show the radiation pattern at 1.92Ghz here (not at 1.8Ghz, i suppose u are interested in the notch frequency point in S11). it is similar as that at 2.26Ghz shown in my previously reply.




also i provide smith chart for shameemkabir.


impedance matching aside, i still believe that the location of resonace should be at where the R plot shows a peak and the X part fluctuates. of course, as u said, the impedance matching depends both on the real and imaginary part of the input impedance. thus in most cases, this frequency point is not where best matching is obtained in S11 plot, but that's another story. in this example, the judgement that the monopole resonates at around 2.4Ghz is also grounded by the fact that the physical length of the monopole is 31.25mm(a quarter of the corresponding wavelength of 2.4Ghz)

 

[zfl]

According to the pattern requirement,i think microstrip antenna is a prefered solution;and add a metal plane or loop above the antenna.
Only my ideal idea,you maybe try for it,the height and dimensions of metal loop need to be optimized.
Wish you make progress.