Tunable Compact UHF RFID Metal Tag Based on CPW Open Stub Feed PIFA Antenna

Figure 5

Antenna input impedance tuning. (a) Input resistance curves of the antenna with different inset depths 𝐿_inset (𝐿=37 mm, 𝑊=20 mm, ℎ=3 mm, 𝐿_𝑠=30 mm). (b) Input reactance curves of the antenna with different open stub length 𝐿_𝑠 (𝐿=37 mm, 𝑊=20 mm, ℎ=3 mm, 𝐿_inset=14 mm).

(a)

(b)