Impedance of PCB track at 433Mhz

You'll have to use antenna modeling software on it. Try MMANA, it's free.

Leon

Further to my previous post, if it is a 1/4 wavelength long at 433 MHz, you could just assume that the impedance is 50 ohms.

Leon

Thanks , I'll have a look. It's not 1/4 wavelength. That would be closer to 17.3cm

Cheers Rob

Hello Rob,

I assume that there is a return path (as one end is connected to ground). The impedance (in particular the real part of it) depends heavily on the return path and path of trace.

Maybe you can describe the geometry so that someone can do a ball park calculation or EM simulation.

Best regards,

Wim PA3DJS

One side of the track is connected to gnd(ground plane) , the other side is where the "drive " would come from.

I thought the antenna trace comes direct from the RF output and is open ended. On mine, there is a gound plane under the first part of the track ( curved) then it goes straight.( for 1/4 length). Works fine at 868 Mhz.

What happened to "there is no ground plane"?

John

I think you need to post a picture. What it's connected to is important, of course, but what it's close to is also quite important.

I'll second the "we need a picture," or even better, an accurately dimensioned drawing. It's not the impedance of "a PCB track," it's the impedance of an antenna which consists of a PCB trace, "ground" plane, dielectrics, and perhaps a bunch of other stuff.

Can't you just measure it? But of course, even there you'll find pitfalls: you need to make sure your connections between the antenna and the network analyzer don't add significantly to the antenna structure.

Cheers, Tom

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I don't have any equipment that can measure it. 60Mhz scope and 1G spectrum analyser. I'll try and get a picture.