Novel Dual-Band Circularly Polarized Planar Endfire Antenna With Enhanced Front-to-Back Ratios

A novel dual-band circularly polarized (CP) planar endfire antenna with the front-to-back ratio (FBR) enhancement is proposed. First, a half-mode substrate integrated waveguide (HMSIW) cavity serving as a magnetic dipole (M-dipole) is devised for the dual-band vertical polarizations (VPs), and four slots are etched on the M-dipole to adjust the frequency ratio (FR) reasonably. Two independent electric dipoles (E-dipoles) are introduced for the dual-band horizontal polarizations (HPs). Then, the M-dipole and E-dipoles are connected by the parallel double-side compensate lines to adjust their amplitudes and phase differences, and thus, dual-band CP waves are radiated. A two-stage reflector is also loaded behind the M-dipole, which improves FBRs of the antenna in two bands. Finally, a 2.4/5 GHz prototype antenna is designed, fabricated, and measured to validate our design idea. A reasonable agreement between the simulated and measured results is obtained. Measured FBRs of the proposed antenna at 2.42 and 5.02 GHz are 15 and 14.2 dB, respectively.