A Broadband Multimode Circularly Polarized Stacked Antenna With Pattern Diversity

A broadband multimode circularly polarized (CP) stacked antenna with pattern diversity is proposed in this paper. The antenna consists of three layers, two substrates with annular-ring patches and a parasitic metal patch. The antenna can radiate different patterns by exciting different modes of annular-ring micro-strip antenna (ARMSA). When port 1 is excited, the antenna is excited at the second-order mode(TM21) to generate the conical radiation pattern, whereas the antenna is excited at the fundamental mode(TM11) to generate the broad beam radiation pattern when port 2 is excited. In order to generate circular polarization, ARMSAs are fed by two feeding points and both of the annular-ring patches are fed with the network in the same layer. The two-port antenna achieves the broadband property by parasitic patch. The parasitic top metal layer can broaden the impedance bandwidth of TM11 mode while the ground plane of TM11 mode can act as the parasitic patch to broaden the impedance bandwidth of TM21 mode. To verify the design, the antenna is fabricated and measured. The measured results show that the antenna proposed in this paper has an impedance bandwidth of 0.22GHz (1.92-2.14GHz) and 3dB axial ratio (AR) bandwidth of about 0.25GHz (1.90-2.15GHz).