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 |Eθ| 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, singlefed, and single-radiator properties.