Hi,

TRY THESE:

1. Having a finite thickness of metal for conductor strips tends to increase the capacitance of the lines, which effects the εeff and Z0 calculations. Metal thickness is also important, especially when metal thickness t >0.1w or t >0.1g; w = width of microstrip line and g = width of the gap).

2. Wave Port Size:

The standard recommendation for most CPW wave ports is a rectangular aperture.

Port width should be no less than 3 x the overall CPW width, or 3 x (2g + w) = 3 x (2*0.25 + 3) = 10.5mm (in your case).

Port height should be no less than 4 x the dielectric height, or 4h = 4*1.57 > 6.3 mm.

3. Wave Port Location:

The wave port should be centered horizontally on the CPW trace.

If the port is on GCPW, the port bottom edge should lie on the substrate bottom ground plane.

If the port is on ungrounded CPW, the port height should be roughly centered on the CPW metal layer.

4. Wave Port Restrictions:

As with all wave ports, there must be only one surface normal exposed to the field volume.

Port should be on exterior model face, or capped by a perfect conductor block if internal.

The wave port outline must contact the side grounds (all CPWs) and bottom ground (GCPW).

The wave port size should not exceed lambda/2 in any dimension, to avoid permitting a rectangular waveguide modal excitation.

4. Radiation Boundary Size Conditions:

a. HFSS needs airbox to model free space radiation. A radiation boundary is used to emulate free space by truncating infinite free space to finite calculation domain. This minimize reflections from outer surfaces and ensures maximum absorption. This is very similar to an anechoic chamber.

b. For this, the distance from the radiator must be a minimum of λ/4 (or λ/2) for strong radiating surfaces. Here λ represents the wavelength for the minimum frequency used.

c. A distance of λ/4 from the radiating surface is taken for the reason that similar impedance mismatches can be cancelled at quarter wavelengths. This ensures that there are no reflected waves and thus the radiation boundary absorbs all the radiation.

d. Maximum absorption of energy occurs when the fields are perpendicular to the boundary.

These are for HFSS.

I. Also, try to find out the input impedance of the antenna. The S11 from the results appears too high compared to the results in the paper. Maybe, this is because, the port impedance and the input impedance don't matching properly.

II. Adjust the width of the microstrip line in between the slot antennas connected to the exciting port for 50 Ohms. This might ensure proper matching. TRY IT!

Regards,

Suhas. D.

@suhan

thank you. it is helpful. i try it. 

best regards

Thanks @suhan

@ Azita

The .hfss file is of no use for me. Thus I have to resort to your description. Looking into the .pdf, one question rose:

Are you aware that the antenna described is not a bowtie antenna but a bowtie slot antenna ?

Basically the negative of a bowtie antenna! With some more limitations regarding the ground plane dimensions. And they are also not too clear about the ground plane underneath (on the bottom side of the substrate). See fig. 11!

As dipole and dipole slot antennae in this paper do not have the same geometric dimensions (and different characteristics even in the final state), I would expect the same for bowtie vs. bowtie slot antenna. Could this be (one of) the reason(s) for your differences?

Hope this helps

1) There is no such thing as the negative of an antenna, Dreher.

2) It is so obvious to our fellow antenna engineers, that there is no ground plane on the other side of the photograph, so to speak, that this is not even mentioned in the paper.

@ Denis Jaisson

I had my doubts first. Fortunately there is a photo of the bowtie slot antenna where you can clearly see the bowtie etched into the top copper. IMO "negative" is not the worst of all descriptions you could think of. As well as how this antenna is connected (on top). Regarding the backplane: it is not mentioned consistently, but defining a board thickness together with epsilon makes little sense without. And there are more slot variants - together with the 'positive' variants.

Careful reading of the pdf attached is necessary as eg. the 'slot' attribute is missing in some places.

Hello Azita,

 I found the mistake about your design, you have to remove the ground plane in your design, is not necessary in Co-planar bow tie antenna. The ground is already on top.

B.regards

attached are the simulations results S11, 3D radiation pattern, after removing the ground plane of substrate,.

Regards

1) You are playing on words, Dreher; that one may come up with a nonsense that be worse* than your «negative antenna», fails to makes your concept useful.

* pray give us an example, as we are all curious

2) Defining board's thickness implies by no means that there be a ground plane on the other side of the board.

Dear Suhas,

What about integration line and position for the CPW fed designs?

If you have any design like this please send me............

@ Chaouki Hannachi

thank you dear. i try it too. in this paper it isn't mentioned about the ground plane. so, i think your idea is true. thank you

@ U. Dreher 

yes. i think i should delete the ground plane. and do according to the SUHAN and CHAOUKI answers.

thank you

@ Azita

Seems you were assuming a backside ground plane as well. Turns out the assumption was wrong. Chouaki Hannachi did a great job.

Regards

it works, i try your advice and finally my result is similar to the paper.

i delete the ground and excite the antenna according to the SUHAN answer.

thank you all.

@ U.Dreher

thank you dear. i delete gnd plane and i get the true answers. 

Hello Azita,

GOOD NEWS, I'm glad that it can work

Regards

Chaouki Hannachi Dear Sir, I know this is from two years ago but I am working on a similar antenna. Thanks to your answer I managed to get my simulation showing the desired result. But the problem is, I can't find the theory about CPW-fed Bow-ties which states that it doesn't need ground plane. Could you please help me on that? Can you recommend some literature on that matter?

Thanks and regards.