Hi
From TI's Design Note DN024
http://www.ti.com/lit/an/swra227e/swra227e.pdf I attempting to use this concept for my own PCB antenna at 915 Mhz not 868 and definitely not the dual band version.
This is my first foray into a pcb antenna and so I was wondering if I had made any obvious mistakes. I have made a boat load of assumptions and no measurements and this I why I guess RF sometimes lies in the realm of black magic.
I basically cut down the length of L4 of the design not to 36mm from 38 and left the other measurements the same, my reasoning is I can cut the length a bit shorter if necessary in some sort of tuning process. I looked into the theory for the meandering antenna, it seems to be determined by total length but also heavily affected by the number of turns. The more turns the lower the resonant frequency.
Other queries I have an 18mm nominally 50ohm trace to the impedance matching network. I chose the "Grounded Coplanar wave guide", instead of the "microstrip line" for no good reason. In the design note they have completely different dimensions. I don't know why mine would be any worse as it should be 50 ohms.
Then I have the impedance matching network I will probably just buy a range of caps and inductors to try.
I chose 0805 for the inductor and 0603 for the caps for no good reason. Are there any dielectrics or types that I should use or avoid.
My only piece of RF test gear is my $25 TI coupon bought spectrum analyser. My grasp of Smith Charts is somewhat diminished but I am keen to use them if I can somehow produce some measurements. I haven't got any SWR meter either. So it may be just RSSI strengths I can measure.
Even though I would like to get this right, I am obviously limited in test equipment and previously I had got some good range once with the antenna pulled off the coax. So I am ok with a partially compromised antenna system.
If anyone has a suggested plan of attack it would be appreciated.
ps. Green is bottom layer, Red-Brown is top layer- used as ground, Baby shit brown is both layers.