how to design antenna and filter together??

hi,

i have designed an antenna on hfss and its return loss is good with fine impedance matching with 50 ohm. Now i have to attach an simple filter with that antenna to remove its harmonics. I have designed an microstrip stepped impedance filter in ADS. Now i need to combine the filter of ADS and antenna of HFSS to get an improved antenna. Where ( in hfss or ADS) and how should i combine these two component. Please someone shed light on this.

Sika said:

hi,

i have designed an antenna on hfss and its return loss is good with fine impedance matching with 50 ohm. Now i have to attach an simple filter with that antenna to remove its harmonics.

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Except in rare circumstances, the antenna and matching network can be considered passive linear devices, so it will not produce any harmonics. There are a small number of applications where the intermodulation performance of antennas is important, but these since HFSS is a linear EM simulator, it would be unable to determine the level of those IM products anyway. (At least that is my understanding. An HFSS expert might know different).

Sika said:

I have designed an microstrip stepped impedance filter in ADS. Now i need to combine the filter of ADS and antenna of HFSS to get an improved antenna. Where ( in hfss or ADS) and how should i combine these two component. Please someone shed light on this.

Click to expand...

You should not be considering the filter as part of the antenna, but build it into the amplifier which drives the antenna.

However, if you want to combine the filter and antenna you have designed, I would have thought you needed to do this in HFSS, not ADS, unless you have the EMPro option for ADS. EMPro is a stand-alone 3D EM simulator like HFSS, but is sold by Agilent and is an option for ADS. They integrate with each other. But it would mean buying EMPro (unless your ADS license includes this option), and learning EMPro. The time to learn EMPro will far exceed what it will take you to move the filter from ADS to HFSS.

I'm not sure if there is any way of exporting something from ADS into HFSS. It might be necessary to draw the structure manually in HFSS, but I don't know. Someone else might be able to tell you that.

Dave

Sika said:

Now i need to combine the filter of ADS and antenna of HFSS to get an improved antenna.

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There are very few cases where it makes sense to EM-simulate filter and antenna together in one model.
In most cases, it is more efficient to simulate them in separate EM models, and cascade the S-parameters at schematic level (S-parameters).

In most cases, separate EM simulation will also be more accurate because filter and antenna can be meshed separately, and each EM Model can use the best possible mesh for this devive. Bringing everything together into one EM Model gives some false sense of accuracy, but is often troubled by mesh related inaccuracies.

thank you dave and volker for your response. If we don't combine antenna and filter into one EM Model then how can we show removal of harmonics in S11 curve after adding filter to the antenna.

Sika said:

If we don't combine antenna and filter into one EM Model then how can we show removal of harmonics in S11 curve after adding filter to the antenna.

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How do you you want to get the filter response from S11 only? This doesn't work. You need to simulate the filter separately, and look at S21 of the filter.

The other method, to simulate them together, does not make sense. But if you really want to do that, you could compare the antenna gain including mismatch (radiated power / incident power) with and without filter. If you compare the standard gain definition (radiated power/accepted power)you will not see the full effect of the filter.

Did I mention that your idea to simulate them together is really bad, and you should simulate them separately.

Sika said:

thank you dave and volker for your response. If we don't combine antenna and filter into one EM Model then how can we show removal of harmonics in S11 curve after adding filter to the antenna.

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Do you have a design specification you are designing to? If so, and you can share it, please do so. I've seen some pretty dumb specifications in my lifetime - one recent example being a leaky feeder antenna, where the specification stated it had to be made from a particular cable and terminated in 50 Ohm BNC connectors. That cable was a standard 75 Ohm coax, and not designed as a leaky feeder use at all!

I'm puzzled why you are concentrating on S11, which is why I'm asking what is the specification you are designing to. BTW, are you aware of constant impedance filters, where there is a good return loss both in the passband and stopband? However |S21| in the passband is very different to |S21| in the stopband.

Hi,

I have attached the antenna design in hfss and its return loss curve. My initial target is to design an filter so that the harmonics seen in the S11 curve be removed. I am trying some of the filter examples in ADS. I am learning ADS now.

- - - Updated - - -

Hi,

I have attached the antenna design in hfss and its return loss curve. My initial target is to design an filter so that the harmonics seen in the S11 curve be removed. I am trying some of the filter examples in ADS. I am learning ADS now.

https://obrazki.elektroda.pl/56_1345515485.jpg

Could anyone please help me how to proceed to remove those harmonics .. by using filter ...... My pass band should include 2.45 GHz and remove all other harmonics..

Sika said:

so that the harmonics seen in the S11 curve be removed.

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Ooops ... !

You are misunderstanding the meaning of the S11 data. Those "harmonics" have nothing to do with harmonics. Those are additional frequencies where the antenna impedance is near 50 Ohm, and they have no effect on your antenna operation.

Sika,

Multi resonance is not a issue. One thing I would like to know is what application are you targeting with this antenna, is it ISM band for Mobile Communication ?(as I can see a resonance at ~2.4 GHz). There are various factors you need to see before designing an antenna.
1) What is the application for the antenna (and hence specifies the constraints for the antenna design). In this case use resonating frequency as reason for antenna operation. Antenna Resonance below -15 dB should be considered.
2) What is the band width of the antenna (for example in Mobile communication you need a antenna with at least 8% band width. here I can see the band width is very low in your case.)
2) What is the Gain, Directivity and Efficiency of antenna in the operating reason. In a microstrip antenna the gain is near to 5-7 dB.
3) What is the Radiation Pattern of the antenna(It should not have big back lobes)
4) What is the Power Radiated by antenna.

For the discussion, I would argue that circuit + antanna is definitely useful depends on what kind of antenna you are designing. If your antenna is a pure passive transmitter or receiver. Then put it in to a pure EM model pretty much can get all you want.

However, if your antenna is complicated, such as MIMO, Smart Antenna, or even your case filter+antenna. Then circuit simulation has to be considered in the EM simulation side. Since the mutual coupling between the circuits and antenna can not be captured accurately through S-parameters (https://www.edaboard.com/threads/263775/). We have discussions here. Especially, imagine the case where you have many circuits together with many antenna elements.

The only trick that we have not mentioned is the feeding part between circuits and antennas. You can not ignore it. But EM simulation of antenna feeding is a long-last topic and might beyond this topic.