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printed antenna with lumped inductor

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Member level 4
Mar 3, 2002
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lumped inductor


Just want to ask following: I have a printed dipole on FR4 material for 868 MHz. The pb size is too short to make it without loading inductors. pb total width is about 65 mm.
So actually, I made some test with antennas I have cut on a one sided FR4 board and I introduced 2 chipcoil at about 1/3 th from both dipole ends.
If I want to simulate it, I do not know how to take into account the inductors S-parameter file and the remainder of the line. Is this possible in e.g. a planar simulator such as Momentum ? I tried already but the simulation only takes the length into account untill the position of the chipcoils and not the further length of the copper dipole ends.

I could not find hints on how to do this in the manuals ...

Do I need something else ? Please your advice....

:roll: Rgds


some thoughts

Here are some thoughts on your design. Inductively loaded antennas have most of their losses in the coils. You can try adding a capacitive hat at the end of the antenna trace with traces perpendicular to it. This will allow a smaller coil and reduce loss. Attached are three programs for loaded antennas that can get you pointed in the right direction. Also, in general putting the coil in the center of the length minimizes loss.

Hi Flatulent

Thanks for your reply. I was aware of the about middle position for the loading coils etc. I similar a a shortwave ham antenna for mobile use.
Currently I have about 5 dB loss compared to a normal wire dipole with this pb structure. I also think the Q of the coils is important... however chipcoils at 800 MHz still have quite limited Q. I heard of some new Murata types which were announced. I still need to look at them.
My frustration however is that I cannot simulte the g.d damn thing. It would give me a bit more justification in the thoughts and more peace to my mind.
I have some simulators here , @ds mom ans so*nnet but I am quite a novice in EM simulating and I could not figure out how to introduce an external component to a printed structure such as a coil or a cap. I am not sure if it possible at all since none of the supplied examples is doing such thing.

Kind regards

:? Mike

try wire antenna simulators

Try one of these wire simulators that use NEC. Yes, the coil loss is the bad part. You might try zig-zaging the antenna so that you fit the right conductor length without any coils in the board length.

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