ask: matching RFID antenna 13,56 MHz?

hi all..

i design planar antenna in frequency 13,56 MHz in HFSS. it's planar spiral antenna..
its reflection coeficient still above -10dB. it's about -3 dB.
i have change the position of the antenna, but it's stil not in matching condition.
How to match this antenna?

thx..
:D

I prefer to speak of an inductive coupler rather than an "antenna", unless it has many meters diameter. I guess, it hasn't. It's radiation
resistance can be most likely neglected compared to the resistive losses. You can however match the loss resistance to the generator
by forming a resonant circuit. Depending on the intended RFID reader bandwidth, it may be necessary to add artificial losses.

The design criterion for RFID reader "antennas" is basically magnetic field strength, according to the implemented standard.

thanks for the reply..