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The dimensions of a microstrip line depend on reletive permaebility Er , substrate thickness H , conductor thickness t .
Regarding to Zo ; dimensions are defined.
You can find lots of information about microstrip lines at Internet but you can also use a simple program that can be downloaded from www.appwave.com called as TXline which is free.
It depends on your system impedance. When you know what would be the impedance and electrical length of your transmission line, you can easily tramsform in microstrip with the TXLINE mentioned by BigBoss, or there are more free transmission line calculator programs on the web:
AppCad at www.hp.woodshot.com
RFCalc at the Milmega website www.milmega.co.uk (you have to register). And many others.
And first of all, search elektroda, there are a lot of topics with microstrip subject.
It's depends on system Z as AL0117 say but if You means the circuit like power supply curcuit in Rf-amp, the impedance can be another to reduce the parasitic effects in Your lumped element. In this case the length of the line (between resistor and shunt capasitance) usually equal the quarterwavelength on central freq and Z is hight to reduce the affects of this circuit to micrwave part of device. But really it's not always can be achieved due to dimention limitations (especially on high freqs.).
I am working at about 8 GHz. What about T-connectors. How their dimensions are calculated or if want to connect a 100 ohm resistor to 2nH inductor in series what will be the dimensions of the microstrip line.
If you make the connections very short, it does not really matter what the transmission line impedance is. I suspect that you are connecting these parts to an IC pin or a pre-made transmission line component like a directional coupler.
At 8 GHz (and even on lower freq's) they are a lot of things to take into account: every change in width of your transmission line (microstrip) is a discontinuity, so when you connect the pads of your smd components to the microstrip line, you introduce parasitic elements in your circuit. The parameters (R,L,C) of your components are no more concentrated, they are distributed.
You can simulate this by a few free programs ( Ansoft designer student version for circuit simulation, Maxwell SV for planar EM or Sonnet Lite from Sonnet) and you can see the impact of the distributed transmission lines on the overall performance of your circuit.
At 8 GHz also be aware of the passive you are using: the resistor (with its case parasitics) can be very different from 100 Ohm and self resonance frequency of 2 nH inductor should be much larger than operanting frequency. Very small and high quality components should be used (SMT 0402 or 0201 !!).
Consider to use microstrip to make your network, if possible.
Mazz
try with Agilent's Appcad (free download from www.agilent.com and followin semiconductors, RF and Microwave and appcad 3.0) it's very simple and useful
The company called Modelitics created some models for inductors and capacitors that are substrate dependent. It is the best thing to have as you can see what you will get from the circuit. Accuracy is quite amazing! The models are availble for Genesys 2003 and MWO 2003.
hi,fasha.im also doing the design of microstrip filter and will use the microstrip line but im a new one coming to this field of filter.after the design and simulation analysis ,which fadamental parameters shall we take close attention to??
Preferably the line is 50 ohm (depend on application). To calculate the width for 50 ohm line, most of the members already recommended some free software for you. Since it is lumped element, try to make the connection between them as short as possible (<1mm) and use 0402 size lumped element as your operating frequency is about 8GHz...
In order to coupling a resistor an capacitor, you may follow some theory about transmission waveguide. When one works at wavelength related to cm or mm, short-cut can work like inductance, and open circuit as capacitance. So, regardless losses in waveguide, you can aproximate inductance nearby to j*Zo*tan(B*l) and capacitances as -j*Zo*ctg(B*l), where Zo is the intrinsical impedance, B is 2*pi/lambda, and l is the longitude across the line.
If you want a coupling, you may put a short-circuit across calculated distance away capacitance, in order to achieve reactive impedance equal to zero, and coupling, for example, 50 ohm antenna with the resistor.
Also, you may review a lambda-quarter transformator to shit impedance phase about -180 degrees.
Finally, you must review related documents. I suggest you:
Filters for RF/Microwave Applications. Jia-Sheng Hong, M. J. Lancaster
Introduction to wave propagation,transmission lines,antennas
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