Dear colleagues
I am not so expert for PCB antennas. So I would appreciate some advice of somebody on how to set meander monopole PCB antenna the best. My wireless network should be working in 868/915 MHz ISM band.
I have found some documents of Texas Instruments, e.g. very short document number DN024, revision E http://www.ti.com/lit/an/swra227e/swra227e.pdf and DN024. I have decided for this meander monopole PCB Antenna, because it is very recommended. I don’t have so much experiences with PCB Antenna that’s why I am inspired only from this document. I prefer mainly the 868 MHz band, but I would be happy, when the PCB Antenna will be working very good for both 868 and 915 MHz bands without changing size of the Antenna. I am able copy all dimensions of the proposed Antenna of TI (on the base of document DN024), and choose matching components Z61, Z62 and Z63. But I have Problem as follows:
I have had also very similar document DN024 revision D. In both of these documents there are written the same: “Optimum length for the last segment is dependent on the geometry of the ground plane” !! My PCB should be have fixed geometry 93,5 mm x 96,5 mm (width x height). But Ground plane (with some ICs in that) will be 93 mm x 70 mm (width x height) on the PCB. That means for PCB Antenna there is space 93 mm x 26 mm (width x height). In this space I am able to add exactly this proposed PCB meander antenna of TI with overall size 38mm x 25mm (width x height). I am going back to sentence about the effect of ground plane geometry on length the last segment. My question is, how can I find out the influence of ground plane on PCB meander antenna. I there any math´s equation to calculate it? Is it all right when I will embed such proposed PCB Antenna from document DN024 to the PCB with width of the ground plane 93 mm? Does anybody have any experiences with such PCB antenna type please?
Note: I am using CC1120 RF module.
Best regards.
Jan