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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 cavity serving as a magnetic dipole (M-dipole) is devised for the dual-band vertical polarizations, and four slots are etched on the M-dipole to adjust the frequency ratio reasonably. Two independent electric dipoles (E-dipoles) are introduced for the dual-band horizontal polarizations. Then, the M-dipole and the E-dipoles are connected by the parallel double-side compensate lines to adjust their amplitudes and phase differences, 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 simulated and measured results is obtained. Measured FBRs of the propose antenna at 2.42 GHz and 5.02 GHz are 15 dB and 14.2 dB, respectively.

Ideal dipole antennas are desirable for antenna calibration. However, real-world implementation issues introduce inevitable non-ideal effects that can significantly affect the quality of calibration. In this communication, a 2-GHz standard dipole (SD) antenna is presented with an excellent overall performance. This result is achieved by an innovative design with an optimized element shape and an embedded (shielded) balun. The designed feeding structure is a balanced structure that transitions from parallel strip lines to coaxial lines. The feeding method avoids the impact of electromagnetic environment asymmetry while achieving an appropriate balance. The measured relative bandwidth of the dipole exceeds 15%, and the antenna gain is approximately 2 dBi. The cross-polarization ratio is greater than 27 dB in the horizontal plane, and the horizontal gain variation is less than 0.2 dB. The dipole has a symmetrical vertical plane pattern, and the maximum gain point does not deviate from the horizontal plane. The high performance of this SD makes it suitable for antenna calibration.