Design Approach on the Dual-Band Circularly Polarized Stacked-Layer Strip Antenna With Wide Frequency Ratio Range and Stable In-Band Gain

In this letter, an effective approach to design a dual-band circularly polarized (CP) stacked-layer strip antenna is proposed featuring the extended frequency ratio range and relatively stable in-band gain performance. Initially, characteristic mode analysis (CMA) is utilized to the proposed antenna to get the four desired boresight radiating modes excited. Then, the equivalent circuit model is developed to clarify the mechanism on the CP generation at the two distinctive bands. After that, a simple yet effective way to reallocate the lower or higher frequency band is proposed by independently manipulating the two paired resonant modes of the antenna. In such a way, one of the widest frequency ratio ranges (from 1.19 to 2.15) can be reached compared to other related dual-band CP designs. Finally, two prototypes with the specific frequency ratios of 1.19 and 2.15 are simulated, fabricated, and measured to validate the principle. Apart from the agreements between theory and practice, relatively stable and similar CP gain values of 8.5/9.2 dBic and 8.7/8.4 dBic for the two dual-band antennas are highlighted as another merit of the design.