I am designing a PCB monopole antenna to work with a transceiver (C110L) operating at 915MHz. The manufacturer provided a reference design, however the reference design appears to be have been designed for 868MHz. It also states that this design should also work for 915MHz (due to the large bandwidth of the antenna design), however, I'd like to further tweak this antenna to make it work better at 915MHz.
I got a PCB fabricated that made an exact copy of the reference design, and got almost the same results as shown in the reference design. During my bandwidth measurement testing, the center frequency hovered around 870MHz. However, I'd like to see if I can adjust the design such that that center frequency is closer to 915MHz.
In theory, it appears that I should slightly shorten the total length of the PCB antenna trace.
If I wanted to adjust the dimensions of this antenna (i.e. total length), what is the best way of going about this to ensure I won't mess anything else up? From my calculations, I should shorten the total length of the PCB antenna trace by about 5% (870/915 = 0.95). However, I could go about doing this multiple ways:
Reduce the length of L4 only, such that the total length of the entire trace is 5% smaller.
Reduce all lenghts of all segments of the trace by 5% (including L4, L3, L2, L1).
I do not believe I need to change W, as changing that might change the impedance.
Is my understanding correct? Can I simply alter some of the dimensions of this reference design in an attempt to get the center frequency closer to 915MHz? What is the best way of going about this?