Millimeter Wave Planar Wideband Circularly Polarized Antenna Loaded Triangular Patch for End-Fire Radiation

A planar wideband circularly polarized (CP) end-fire antenna is presented for millimeter-wave (mm-wave) applications. First, the antenna consists of an open-ended substrate integrated waveguide (SIW) feeding line in the middle, a pair of stacked substrates with shorted triangular patches on both upper and lower sides, and an offset parallel strip. The shorted triangular patch is viewed as a horizontally polarized electric dipole, while the open-ended SIW is equivalent to an enhanced magnetic dipole due to the stacked substrates. Wide axial ratio (AR) performance is achieved by simultaneously exciting the two dipoles with orthogonal phase supplied by the offset parallel strip. Then, working principle and parameter analysis are explained and discussed for a further understanding. Finally, a prototype is fabricated and measured to verify the design scheme, which demonstrates wide AR bandwidth performance of 38.6%, novel and efficient radiating structure, simple and compact antenna size, and easy fabrication and integration. This indicates that the proposed antenna is a promising candidate to design wideband end-fire CP antenna in the mm-wave frequency band.