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PCB Antenna

PCB Antenna

PCB Antenna

(OP)
Hi

I am just finalising a small rf comms design and was wondering what the best way was to implement a small pcb antenna using protel dxp...?

Any advice or how to's would be greatly appreciated...

Kind regards

comsec

RE: PCB Antenna

Manual layout is about the only choice you have, paying attention to conductor cross section for impedance control purposes.  If ends need to be squared off, use polygon fills rather than standard traces.

RE: PCB Antenna

(OP)
Forgive me but I am a little new to this:


When you say the conductor cross section do you mean the size of the antenna track?

Also, what do you mean by the "ends need to be squared off"? (No idea about the polygon thing either)

Thanks for your help

RE: PCB Antenna

I've implemented PCB antennas in Protel. Usually these are constructed of several regular "Fill" type copper. After you place a antenna with a trace or fill, change the trace/fill netlist attributes to be the same as circuit it's connected to.

Fills allow you to get a square corner. Traces or polygon planes will be rounded at the corners.

The only problem I come across is that usually you have the antenna dimensions correct, you will want to make it a library item. However, many types of PCB antenna, such as loops or F antennas, have two terminals. The fills or traces used between the terminals provide a connection between the terminals which Protel will flag as a violation. The two ends represent two different nets. Same problems occurs with meander-line inductors.

RE: PCB Antenna

kid,

Consider splitting the antenna into two symmetric halves, with each end being a port.  Place two copies on the board with one copy mirrored.  When the ends touch to make the antenna whole, it should no longer be flagged as a violation (assuming you set up the schematic correctly, as well) since a port of one antenna is connected to the port of another.  I have never tried this myself, but it sounds workable.

For example, let's say the antenna is rectangular.  Split it into two equal portions, like [ and ] .  They're symmetric, so you only need one half, let's go with the [ .  Label the top half pin 'A' and the bottom half pin 'B'.  Place two copies on the schematic, and mirror one on the PCB.  When you join them on the PCB and schematic, pin 'A' of one connects to pin 'B' of the other, and vice versa.

That should remove the violation, even if it means a bit more work.

RE: PCB Antenna

(OP)
thanks for your help so far guys, its beena  real help, I'm just in the middle of using a U shaped antenna and reckoned that using fill was the best option.

Cheers

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