Thank you for your replies.
The antenna is a senor that its resonant frequency would change in the range of 1GHz-5GHz. For example, if the environemnet pH value changes, the resonant frequency of the antenna changes.
The goal is to build a readout chip to wirelessly sense the resonant frequency of the antenna so that the pH value can be wirelessly read.
The coupler idea is good, but it requires the readout circuit close to the antenna. Is it possible to wirelessly read the resonant frequency of the antenna with a longer distance? For example, 10m.