electrical length

Hi,

Can anyone help me in understanding what is the significance of Electrical Length in designing a microstrip?

When I change the electrical length parameter, it doesnot effect characteristic impedance, only the physical length got changed.

Then, what is the role of this parameter and how should i take care while designing RF PCB at 2.4GHz?

Thanks,

What do you mean by saying that you are "designing RF PCB at 2.4 GHz"? If you are just laying out a board that someone else or the manufacturer gave you the artwork for the RF portion for, just do what they told you to do. If you are trying to actually design something, like filters, couplers, power splitters--i.e. anything with a specific shape required to it, then put down the mouse, step away from the keyboard, and go hire a qualified RF design consultant to tell you what to do.

I am actually designing a RF PCB.
I have to draw a 50 ohm microstrip at 2.4GHz.
I am using RF calculator for finding out the required track width with my PCB specifications.
But I am not sure about this term "Electrical Length".
Can anyone give me some idea?

Thanks,

You are not giving us sufficient information in your question for us to answer you. If you are just running a 2.4 GHz signal from point A to point B, it does not matter what the line length is. The only things that would matter are:

1) if the line length were very long, say 4 inches, the signal will loose some of its power. This is because the microstrip line is lossy.

2) if you need to bend the line, how you do it can impact if it will work well or not

3) the width is important. If you know the type of material the board is made from (specifically its dielectric constant), and how thick that material is between your 50 ohm line and the ground plane, then you can calculate the correct width for 50 ohms.

4) if you are adding any components at all to the RF portion of the circuit, such as integrated circuits, capacitors, connectors, etc, you really need to know what you are doing, so get some advice

Some simple microstrip concepts :

1)Frequency inversely propotional to Wavelength
2)Wavelength in microstrip (medium) < wavelength in air. They are related by the Dielectric constant of the medium.

3) Characteristic Impedance depends on the ratio of the Width of the line and the Height of the dielectric.

the electrical length which you are referring to is probably the wavelength in medium (Landa G)

I've always heard length doesn't matter, its the girth. If you are just running traces between matched components, keep the traces as short as possible to minimize loss, radiation, etc.

Then put down the mouse, step away from the keyboard, and go hire a qualified RF design consultant to tell you what to do.

The physical length of a trace is obviously the length you can measure directly. However, a trace on a PCB is more than just a strip of copper. It is a transmission line with resistance, capacitance and inductance.

That means a signal "looking" down the trace from the source "sees" a network of series resistance, parallel capacitance, and both serial and parallel inductance. That network will imped the progress of the signal as it tries to move from the source to the sink. The reactive elements create a difference between the signal's propagation time along the trace, and what it would be in perfect free space to go the same physical distance. That difference in propagation time defines the electrical length.

Dear vibhatomar

look also at this links
http://en.wikipedia.org/wiki/Transmission_line
http://en.wikipedia.org/wiki/Microstrip

pl

hi all

well i think vibhatomar was interested in knowing how to decide about the length of the microstrip line.

we know the width of the microstrip line is decided about the substrate height and its dielectric constant but whats the deciding factor in defining the length?

in my point of view this length should be as small as possible to minimize losses of microstrip transmission lines if we are using to connect impedance matched components

regards

hi...
I am designing RF PCB with two differential microstriplines at 5GHz.
I have calculated width and gap of two microstrip lines, substrate height using single ended impedance Zo=50Ω and differential impedance Zdiff=100Ω, dielctric constant er=4.6, 35um thickness of conductor...



I am using Ansfot 3D simulator to model microstrip lines , how to calculate the physical length of microstrip line to model it in simulator ? where and how do i know the the electrical length in degrees in general or in Ansoft simulator if i model in it?

I think electrical length is important in impedance matching especially that using quarter wave. The question is, how to know the electrical length of microstrip line using RF simulator such as CST or HFFS?