A　compact　and　tunable　ultra-high　frequency　(UHF)　radio　frequency　identification　(RFID)　tag　antenna　is　proposed.　The　antenna　comprises　a　rectangular　ring,　two　symmetrical　radiating　arms　formed　by　multiple　L-shaped　stubs,　and　two　interdigitated　structures.　By　adjusting　the　parameters　of　double　interdigitated　structures,　the　resonant　frequency　of　the　antenna　can　be　tuned　coarsely　and　finely,　while　maintaining　a　nearly　constant　maximum　power　transmission　coefficient.　The　proposed　tag　antenna　has　a　size　of　28　mm　×　16　mm　(0.086λ×0.049λ　at　920　MHz).　Measurement　results　show　that　the　proposed　antenna　can　achieve　the　maximum　reading　distance　of　6.8　m　at　920　MHz　under　the　condition　of　3.28　W　effective　isotropic　radiated　power.　The　proposed　RFID　tag　antenna　offers　several　advantages,　including　compact　size　and　frequency　tunability,　making　it　well　suited　for　various　RFID　system　applications.　©　2024,　Electromagnetics　Academy.　All　rights　reserved.