| Summary: | A low-profile (0.21<inline-formula> <math display="inline"> <semantics> <msub> <mi>λ</mi> <mi>g</mi> </msub> </semantics> </math> </inline-formula> × 0.35<inline-formula> <math display="inline"> <semantics> <msub> <mi>λ</mi> <mi>g</mi> </msub> </semantics> </math> </inline-formula> × 0.02<inline-formula> <math display="inline"> <semantics> <msub> <mi>λ</mi> <mi>g</mi> </msub> </semantics> </math> </inline-formula>) and a simply-structured frequency-switchable antenna with eight frequency choices is presented in this paper. The radiating structure (monopole) is printed on a 1.6-mm thicker, commercially-available substrate of FR-4 (<inline-formula> <math display="inline"> <semantics> <msub> <mi>ϵ</mi> <mi>r</mi> </msub> </semantics> </math> </inline-formula> = 4.4, tan<inline-formula> <math display="inline"> <semantics> <mi>δ</mi> </semantics> </math> </inline-formula> = 0.020). Specifically, it uses three PIN diodes in the designated places to shift the resonant bands of the antenna. The antenna operates at four different modes depending on the ON and OFF states of the PIN diodes. While in each mode, the antenna covers two unique frequencies (Mode 1 = 1.8 and 3.29 GHz, Mode 2 = 2.23 and 3.9 GHz, Mode 3 = 2.4 and 4.55 GHz, and Mode 4 = 2.78 and 5.54 GHz). The performance results show that the proposed antenna scheme explores significant gain (>1.5 dBi in all modes) and reasonable efficiency (>82% in all modes) for each mode. Using a high-frequency structure simulator (HFSS), the switchable antenna is designed and optimized. The fabricated model along with the PIN diode and biasing network is tested experimentally to validate the simulation results. The proposed antenna may also be combined in compact and heterogeneous radio frequency (RF) front-ends because of its small geometry and efficient utilization of the frequency spectrum.
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