An Ultraminiature Circularly Polarized Microstrip Patch Antenna With MIM Capacitors

In this letter, an ultraminiature circularly polarized micostrip patch antenna is designed using four metal-insulator-metal (MIM) capacitors. First, four lumped capacitors are added to the edge of the conventional microstrip patch antenna to conduct the simulation of the theoretical model for brevity. It is found that the micostrip patch antenna achieves electrically small (
ka
< 1) when the capacitors are selected carefully. In addition, the axial ratio and the resonance of the antenna can be optimized by the capacitors, which derive an effective method for designing a compact circularly polarized antenna. Thus, four MIM capacitors are applied to replace the lumped capacitors to make the antenna physically realizable. A circularly polarized (CP) electrically small mictostrip patch antenna is designed, fabricated, and measured to justify the effectiveness of the proposed method. The axial ratio bandwidth and the peak gain of the CP (
ka
= 0.495) prototype achieves 0.88% and 4.25 dBiC, respectively. The size of the proposed antenna is only 0.104λ
₀
× 0.104λ
₀
.