How to reduce the material loss?

[freqzt]

I've design a monopole microstrip antenna. The range frequency is 400-406 MHz. For this bandwidth, the VSWR is 1:1.4. I think it's good enough. The problem is that the material is -24.8 dB and the directivity is 1.8 dB, so the gain is small. What should I do? Does anyone know how to reduce the material loss? Thank you.

 

[SagSag]

what material are you using?

 

[amit_8561]

Use FR4 as material.it's ε is 4.6.

 

[biff44]

Yeah, You should use "material" with at leat 50 dB, and the directivity of your monopole should be 100 dB!

What are you talking about?

 

[SagSag]

well this is your problen, the loss tan. of FR4 is very high
you should use some other material, like RO4003.
btw, a 1.8dBi for a monopole that should have 2.15dBi (with GND) is not bad.

 

[vfone]

Indeed.
- Material is -28 dB !? I don’t think is about weight
- “How to reduce the material loss?” Another similar question could be “how to reduce copper conductivity?”

 

[freqzt]

what material are you using?

I use FR4 to simulate my antenna design. The εr is 4.4, thickness is 0.8 mm, conductor is copper. Should I use another material like RO4xxx? I prefer use FR4 because it's low cost material. I must use low cost material in this project.

The next question is what is the best material to realize this antenna? Please give me complete information about this material. Thank you.

 

[SagSag]

freqzt,

as I said, FR4 is no good for antennas.
but if you got 1.8dBi for a monopole it is
a good resault.

 

[freqzt]

freqzt,

as I said, FR4 is no good for antennas.
but if you got 1.8dBi for a monopole it is
a good resault.

1.8 dBi is just directivity not antenna gain. I think material loss can cause antenna gain decrease. I worried about decreasing of antenna gain. So, what is the best material for this case?

 

[Azulykit]

What are you measuring when you say the material is -24.8 dB?

Everyone likes FR4 because of the cost. Other materials (Rogers line of PCB materials for example) are available with lower loss tangents. R4003 was mentioned and I would concur that it may be a better choice for performance but certainly not cost.

Since you are operating below 1 GHz and the antenna is a monopole I suggest that you look at your feed loss and balun/groundplane connection. Is it working as expected and can you reduce the loss there? Try building two feeds, connected where the monopole would connect and measure the insertion loss (e. g. back-to-back). If it is sound I would anticipate that loss would be around 1 dB for the pair. Much higher and you have located a component to fix.

You don't say much about the groundplane. It may be too small and that could contribute to your problem. Think of the monopole as both the quarter wave element and the groundplane, both are necessary.

Another thing to consider is the FR4 thickness. A monopole does not need a dielectric and the thinner the supporting sheet the better. Make it as thin as the mechanical stress will allow and the loss will decrease. Consider cutting any PCB material that is around the monopole and leave just enough for support. There may be a trade here with the feed design so thinner isn't necessarily better. I recently built end fed dipoles, 3-5 GHz, under marketing pressure using FR4. They worked pretty will once I really thinned the dielectric. They are also driven with a coax so I don't have excessive loss in a feedline. I wouldn't immediately assign the blame to FR4 although I would rather eat worms than use it.

Have you taken radiation patterns with a gain reference and are you seeing what you expect? There may be a clue there.

I would not suspect that the efficiency loss that you seem to have is a result of the material. I would look at the areas I suggested above first.

Another possibility for the inefficiency: Are you using a resonant length for the monopole or is it truncated How long is the element? If it is electrically short your gain will be down.


The gain of a dipole is 2.13 dBi. Since you are working with a monopole and thus radiating primarily in the upper hemisphere the gain will be about 3 dB higher. You should be able to get to around 5 dBi. Note that the maximum is slightly elevated from the azimuth plane (assuming the monopole is vertical along the z axis). The peak moves up or down a little as the groundplane radius is changed. Figure 3-34 page 3-23, Antenna Engineering Handbook, Henry Jasik illustrates this characteristic.

An HFSS model of your structure would also be helpful to diagnose the problem.

Another stab in the dark might be to increase the plating thickness. You might consider soldering a copper rod along the trace. I am not too hopeful that this would help but it is something to try if you are desperate enough.