A Design of Wideband CP Antenna Based on Equivalent Circuit Analysis of Mode Decomposition

A wideband circularly polarized (CP) antenna is designed based on equivalent circuit (EC) analysis of mode decomposition. The proposed antenna adopts an inverted configuration integrating a sequential-phase (SP) feed network, ring slots of ground, two MTS rings, quarter-wavelength branches and grounded pins to produce five CP modes and those CP modes are decomposed into vertical (VP) and horizontal polarization (HP) modes. ECs of VP- and HP-modes are deducted to reveal the production mechanism of the CP modes. When the reflection coefficients of VP-EC equal to HP-EC at one frequency, implying the radiation energies of VP and HP resonant modes are equal, leading to a CP resonant mode. With eight impedance resonant modes and five CP resonant modes, a wide impedance matching bandwidth (IMBW) of 47.62% and a 3 dB axial ratio bandwidth (ARBW) of up to 35.29% are obtained. A prototype antenna was fabricated and measured.