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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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 02 Nov 2007 2:40 broadband matching |
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Dear all,
I have a circuit block ---R---C---L---, where R (5 ohm) is small, L is large, and C is small. The total impedance Z = R at 915 MHz (L and C resonate). Since the imaginary part can be very large, how can I design a broadband matching network? I have to point out that we can't do anything to the block itself.
Best regards,
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cooleyn
Joined: 22 May 2004
Posts: 39
Helped: 5
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| 02 Nov 2007 7:35 broadband matching |
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How wide bandwidth do u want to achieve for the matching? and the S11? For achieving above 10% band width bandpass filter maybe need for the matching..
Since R is so small, it's hard to do matching..
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 02 Nov 2007 8:29 Re: broadband matching |
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Around 10% is good enough for me. S11 should be less than -10 dB. The big problem is that how to design this bandpass filter with such a load? The imaginary part can be significantly bigger than the real part.
| cooleyn wrote: |
How wide bandwidth do u want to achieve for the matching? and the S11? For achieving above 10% band width bandpass filter maybe need for the matching..
Since R is so small, it's hard to do matching.. |
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cooleyn
Joined: 22 May 2004
Posts: 39
Helped: 5
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| 03 Nov 2007 4:57 broadband matching |
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| You could refer to some filter design/synthesis book. You have to put L and C as part of bandpass filter.Since R is so small(Q valueis high), I think it's difficult.If you accept loss matching, it becomes more easy. What're the specific values for L and C?
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 05 Nov 2007 19:37 Re: broadband matching |
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Yes, I know that it can be vey difficult. L is 35 nH, and C is 0.1 pF. The problem is that we can't seperate L and C from the block.
| cooleyn wrote: |
| You could refer to some filter design/synthesis book. You have to put L and C as part of bandpass filter.Since R is so small(Q valueis high), I think it's difficult.If you accept loss matching, it becomes more easy. What're the specific values for L and C? |
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Element_115
Joined: 23 Mar 2002
Posts: 297
Helped: 19
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| 05 Nov 2007 21:41 Re: broadband matching |
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Can you put elements in parallel with the filter?
Or add a resistor in series? More BW and more
passband attenuation.
First plot you Filter out on a Smith chart then put
Q lines on the Smith Chart and add components that
1) keeps the impedance in the Low Q region and that
will bring your filter to a Zo match.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 05 Nov 2007 23:44 Re: broadband matching |
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yes, I can put elements in parallel with the filter, but I can't add a resistor.
I can't afford to lose power.
I have no problem with these principles. I need a method to design this filter. Thanks.
| Element_115 wrote: |
Can you put elements in parallel with the filter?
Or add a resistor in series? More BW and more
passband attenuation.
First plot you Filter out on a Smith chart then put
Q lines on the Smith Chart and add components that
1) keeps the impedance in the Low Q region and that
will bring your filter to a Zo match. |
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VSWR
Joined: 07 Feb 2002
Posts: 610
Helped: 50
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| 06 Nov 2007 23:09 Re: broadband matching |
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| Quote: |
| Yes, I know that it can be vey difficult. L is 35 nH, and C is 0.1 pF. The problem is that we can't seperate L and C from the block. |
L = 35 nH, C = 0.1 pF, R = 5 ohms does not resonate at 915 MHz. Resonance is at 2690 MHz.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 06 Nov 2007 23:58 Re: broadband matching |
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Sorry, I made a wrong calculation for C, it should be around 0.9 pF.
| VSWR wrote: |
| Quote: |
| Yes, I know that it can be vey difficult. L is 35 nH, and C is 0.1 pF. The problem is that we can't seperate L and C from the block. |
L = 35 nH, C = 0.1 pF, R = 5 ohms does not resonate at 915 MHz. Resonance is at 2690 MHz. |
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derek_lkm
Joined: 15 Sep 2007
Posts: 4
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| 14 Nov 2007 6:10 Re: broadband matching |
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Hi all,
Find this topic interesting, however i not really sure why the matching is diffcult. From my basic understanding, it would just be made with the movement on the smith chart and its corresponding passive values. I understand that for maximum voltage transfer, we would like a large load, but since we are mentioning about Sparameters, we are interested in power transfer. As long as the matching is done up we should get the maximum power transfer. Maybe i'm wrong or i have taken enough factors into considerations? Would like to hear the views of the gurus out there.
Thanks and wish everyone have a nice day.
Regards
Derek
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 14 Nov 2007 21:17 Re: broadband matching |
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Because the reactive part is much bigger than the real part (i.e., Q is big), the circuit itself offers very narrow bandwidth. Theoritically, we need to cancel the reactive part all the way along the required bandwidth during the matching. It is not the problem of power matching. It is the problem that how we can remain the maximal (or reasonable) power matching within the required bandwidth.
| derek_lkm wrote: |
Hi all,
Find this topic interesting, however i not really sure why the matching is diffcult. From my basic understanding, it would just be made with the movement on the smith chart and its corresponding passive values. I understand that for maximum voltage transfer, we would like a large load, but since we are mentioning about Sparameters, we are interested in power transfer. As long as the matching is done up we should get the maximum power transfer. Maybe i'm wrong or i have taken enough factors into considerations? Would like to hear the views of the gurus out there.
Thanks and wish everyone have a nice day.
Regards
Derek |
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ND
Joined: 25 Sep 2007
Posts: 53
Helped: 11
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| 19 Nov 2007 12:07 Re: broadband matching |
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What type of circuit you are using?
If it is for example microstrip you my try design some matching network using transformer lines, rather then discreet elements.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 19 Nov 2007 18:53 Re: broadband matching |
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It is a similar antenna. However, I have no space for transformer lines. By the way, what is the advantage of transformer lines?
| ND wrote: |
What type of circuit you are using?
If it is for example microstrip you my try design some matching network using transformer lines, rather then discreet elements. |
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ND
Joined: 25 Sep 2007
Posts: 53
Helped: 11
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| 21 Nov 2007 0:55 Re: broadband matching |
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By my opinion, it is easier and cheaper (especially on higher freq.).
In your case is even more distinctive, because you will need to use elements with very high Q, although your are design circuit on very high freq.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 21 Nov 2007 1:30 Re: broadband matching |
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I have no problem for narrow band matching. How to get the broadband is my headache.
| ND wrote: |
By my opinion, it is easier and cheaper (especially on higher freq.).
In your case is even more distinctive, because you will need to use elements with very high Q, although your are design circuit on very high freq. |
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Jim cage
Joined: 02 Jul 2006
Posts: 147
Helped: 6
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| 21 Nov 2007 17:00 Re: broadband matching |
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| you can try and use double L-matching network or even triple L-matching network. this will result in lower Q and thus bigger bandwidth
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 21 Nov 2007 18:38 Re: broadband matching |
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I already tried. Because the reactive part is so large, I can't get bigger bandwidth, even with 3 L-matching network.
| Jim cage wrote: |
| you can try and use double L-matching network or even triple L-matching network. this will result in lower Q and thus bigger bandwidth |
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MW+RF=Netpig
Joined: 23 Jun 2006
Posts: 13
Helped: 1
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| 24 Nov 2007 17:58 broadband matching |
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it just like a case about DVB-S which the broadband 915MHZ--2150MHz
Added after 3 minutes:
you can simulate it with agilent ADS which include the tuning function you can get the values you need ,it's important to pay attention to the RF PCB layout. for broadband matching ,i think the PI network is the best ,you can use 2rd PI network
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 27 Nov 2007 19:17 Re: broadband matching |
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Thanks. However, I have no ADS available, 
| MW+RF=Netpig wrote: |
it just like a case about DVB-S which the broadband 915MHZ--2150MHz
Added after 3 minutes:
you can simulate it with agilent ADS which include the tuning function you can get the values you need ,it's important to pay attention to the RF PCB layout. for broadband matching ,i think the PI network is the best ,you can use 2rd PI network |
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red-sun
Joined: 13 May 2005
Posts: 56
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| 28 Nov 2007 7:58 broadband matching |
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| I you can use an additional matching network out of the block without doing any changes to the original matching circuit, and the matching circuit may be anylzed by a smith chart tool(smith.exe).
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cooleyn
Joined: 22 May 2004
Posts: 39
Helped: 5
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| 03 Dec 2007 3:36 broadband matching |
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First of all, bode-fano rule should be investigated that to what extent we can do for this broadband matching. The reflection coefficient should meet : |Tao|min=exp(-pi*Q0/Qs). In your case, assume 10%
bandwidth achieve for matching, Q0=10, For RLC series source impedance, Qs=sqrt(L/C)/R ~=40.
so |Tao|min=exp(-pi*Q0/Qs)=0.456, in log field, |Tao|(dB)>=-6.82, so for -10dB return loss task is impossible. For 5% matching bandwdith, |Tao|(dB)>=-13dB, which is reasonable for implement. For broadband matching , you can try
Genesys matching synthesis tool which is a good tool
for automatic matching.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 04 Dec 2007 1:52 Re: broadband matching |
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Yes, this is the theoritical answer that I am looking for. I totally forgot it. Thanks.
I can't go with the automatic matching. It is too expensive for me to implement.
| cooleyn wrote: |
First of all, bode-fano rule should be investigated that to what extent we can do for this broadband matching. The reflection coefficient should meet : |Tao|min=exp(-pi*Q0/Qs). In your case, assume 10%
bandwidth achieve for matching, Q0=10, For RLC series source impedance, Qs=sqrt(L/C)/R ~=40.
so |Tao|min=exp(-pi*Q0/Qs)=0.456, in log field, |Tao|(dB)>=-6.82, so for -10dB return loss task is impossible. For 5% matching bandwdith, |Tao|(dB)>=-13dB, which is reasonable for implement. For broadband matching , you can try
Genesys matching synthesis tool which is a good tool
for automatic matching. |
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VSWR
Joined: 07 Feb 2002
Posts: 610
Helped: 50
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| 04 Dec 2007 22:15 Re: broadband matching |
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The Bode-Fano Criterion
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luqing
Joined: 23 Aug 2007
Posts: 11
Helped: 2
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| 14 Dec 2007 9:57 broadband matching |
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There are many methods for broadband match,such as RFM.Recently I have been designed an matching network with that method.But I must say that we cannot get very satisfying results ,which depends on the impendance data.
BTW,cooleyn,can you tell me what is Genesys matching synthesis tool,can you send me some materials about that tool.And do you use tool Mosaic for matching network.what about this tool?
hope your reply, thank you in advance!
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 15 Dec 2007 2:33 Re: broadband matching |
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luqing,
do you have articles about RFM? I would like to give it a shot.
Thanks,
| luqing wrote: |
There are many methods for broadband match,such as RFM.Recently I have been designed an matching network with that method.But I must say that we cannot get very satisfying results ,which depends on the impendance data.
BTW,cooleyn,can you tell me what is Genesys matching synthesis tool,can you send me some materials about that tool.And do you use tool Mosaic for matching network.what about this tool?
hope your reply, thank you in advance! |
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VSWR
Joined: 07 Feb 2002
Posts: 610
Helped: 50
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| 15 Dec 2007 12:12 Re: broadband matching |
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Title: Design of a Matching Network for Dipole Antennas
Abstract: The input impedance of an antenna is highly dependent on the frequency range in which it operates. For an electrically small antenna to operate in a broad frequency range, the antenna must be properly matched. This thesis presents the design of a matching network for a 1-meter monopole antenna, operating over 30-90 MHz using the real frequency method (RFM). It outlines the mathematical steps needed to determine the equalizer function, which ultimately leads to the circuit design. The goal of the RFM, given the real frequency data, is to optimize the Transducer Power Gain (TPG), and minimize the reflection coefficient or power lost due to the impedance mismatch. Complete design including network realization is given.
http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA265115&Location=U2&doc=GetTRDoc.pdf
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
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| 17 Dec 2007 20:47 Re: broadband matching |
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VSWR,
thank you very much.
| VSWR wrote: |
Title: Design of a Matching Network for Dipole Antennas
Abstract: The input impedance of an antenna is highly dependent on the frequency range in which it operates. For an electrically small antenna to operate in a broad frequency range, the antenna must be properly matched. This thesis presents the design of a matching network for a 1-meter monopole antenna, operating over 30-90 MHz using the real frequency method (RFM). It outlines the mathematical steps needed to determine the equalizer function, which ultimately leads to the circuit design. The goal of the RFM, given the real frequency data, is to optimize the Transducer Power Gain (TPG), and minimize the reflection coefficient or power lost due to the impedance mismatch. Complete design including network realization is given.
http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA265115&Location=U2&doc=GetTRDoc.pdf |
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Jim cage
Joined: 02 Jul 2006
Posts: 147
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| 18 Dec 2007 11:50 Re: broadband matching |
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| The problem with using double L matching network is that it is hard to tune it. since Cap and Inductors doesnt acts as true capacitors and inductors this task will be very difficult. It will be advised to use transmission lines or paralell stubs to tune your circuit.
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luqing
Joined: 23 Aug 2007
Posts: 11
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| 20 Dec 2007 13:58 Re: broadband matching |
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hi,VSWR
can you tell me how to download the article"Design of a Matching Network for Dipole Antennas"
Thanks a lot!
Added after 5 minutes:
To:bingjiang99
I am sorry for my late reply and I have no articles about RFM.Here I just have a book in which there is a chapter mentioned that.
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bingjiang99
Joined: 27 Apr 2005
Posts: 112
Helped: 4
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| 09 Jan 2008 0:19 Re: broadband matching |
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Thank you luqing. I found some papers from IEEE.
| luqing wrote: |
hi,VSWR
can you tell me how to download the article"Design of a Matching Network for Dipole Antennas"
Thanks a lot!
Added after 5 minutes:
To:bingjiang99
I am sorry for my late reply and I have no articles about RFM.Here I just have a book in which there is a chapter mentioned that. |
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