Frequency-Ratio Reduction of a Low-Profile Dual-Band Dual-Circularly Polarized Patch Antenna Under Triple Resonance

A novel design concept to reduce the frequency ratio of a dual-band dual-circularly polarized (CP) microstrip patch antenna (MPA) is presented by using its reshaped TM 10 , TM 01 , and TM 20 modes. First, the far-zone radiated fields of the traditional MPA are theoretically investigated. It demonstrates that the normal | E θ | and | E ϕ | fields at xoz plane are orthogonally generated under its TM 10 and TM 01 modes, respectively. Unfortunately, its TM 20 mode radiates the nonbroadside | E θ | fields at xoz plane. Then, an open-ended stub is loaded around the edge of the radiator, aiming to reshape the TM 20 mode as the broadside radiation. After that, the patch width is decreased with the loading of two shorting pins. The main target is to move the TM 01 mode resonating between TM 10 and TM 20 modes. Finally, the proposed antenna is fabricated and tested. The results illustrate that its left-hand CP and right-hand CP radiation patterns are satisfactorily acquired at around 2.134 and 2.223 GHz, respectively, thus gaining a small frequency ratio of around 1.04. Meanwhile, the antenna holds the low-profile (0.02 free-space wavelength), small-backlobe, single-layer, single-fed, and single-radiator properties.