A single feed broadband circularly polarized (CP) microstrip antenna operating in millimeter wave (mmWave) band is proposed. An Archimedean spiral radiator is used to realize circular polarization. By adding a special-shaped ring slot structure with two stubs connecting the inner patch to the outer ground, the radiating direction, bandwidth and axial ratio (AR) of the proposed antenna can be significantly improved. The antenna prototype is fabricated and its performance is evaluated. Measurement results show that its impedance bandwidth (IBW) is 13 GHz from 21.1 GHz to 34.1 GHz (46.43% referring to 28 GHz). The axial ratio bandwidth (ARBW) is 8.35 GHz from 23.85 GHz to 32.2 GHz (29.82% referring to 28 GHz). The gain at 28 GHz is 6.49 dBi.

A millimeter-wave (mmWave) triple-band substrate integrated waveguide (SIW) antenna with dual-sense circular polarization (CP) etched on a single substrate is proposed. A SIW cavity operating in TM210 mode is carved with a circular slot to realize upper band radiation. A circular patch is placed in the circular slot for lower band radiation. Middle band radiation is realized by the coupling between the SIW cavity and circular patch. By introducing asymmetry on both circular slot and circular patch, CP is obtained at two bands. The polarization states of the three bands are right-hand circular polarization (RHCP), linear polarization (LP) and left-hand circular polarization (LHCP). Three pairs of vias are introduced in SIW transmission line to realize good impedance matching for the three bands. A prototype is fabricated and its performances are evaluated. Simulated and measured results agree very well. Small frequency ratios are achieved and each band can be adjusted flexibly. The proposed antenna has characteristics of low-profile and simple structure which will make it easy to be applied in future mmWave wireless communication systems.

A broadband circularly polarized substrate integrated antenna with dual magnetoelectric (ME) dipoles coupled by crossing elliptical slots is proposed. The circular polarization is generated by the asymmetric crossing slots, and the parasitic dual ME dipoles are applied to improve the bandwidth and AR beamwidth. Simulation results show that the antenna obtains an impedance bandwidth of 12% over the band 27.6~31.1 GHz, a 3 dB axial-ratio (AR) bandwidth of 4.8% across the band 28.3~29.7 GHz, a 3dB AR beamwidth of 78° at the center frequency of 29 GHz, and the gain is higher than 5.1 dBic during the impedance bandwidth with the highest gain of 7.2 dBic at 30.2 GHz. Besides, the antenna based on the SIW has a low profile of 3 mm, which is attractive to array designs and integrated systems.

This work proposes a circularly polarized (CP) dielectric resonator antenna (DRA) element featured with low profile and wideband at first. A two-layer dielectric resonator (DR) with improved performance in bandwidth and gain is used as the basic resonator. On this basis, a polarization reconfigurable DRA array is further developed with three polarization states of left-handed circular polarization, right-handed circular polarization and linear polarization. PIN diodes are placed across the proposed hourglass-shaped coupling slots to reconfigure the relative length of the two arms of cross-slot and switch among the three polarization states. The measured results show that the overlapping impedance bandwidth (IBW) is 10.6% (19.6-21.8 GHz) for all the states and the axial ratio bandwidth (ARBW) is 9.7% (19.6-21.6 GHz) for the circular polarization.

A 2 × 2 wideband circularly polarized (CP) antenna array operating at millimeter wave (mmWave) band is presented. The array element is a wideband CP Archimedean spiral radiator with special-shaped ring slot. The elements are fed by an unequal amplitude (UA) feeding network based on a microstrip line (MSL) power divider. The side lobe level is improved by this UA feeding network. In addition, a cross slot is employed to isolate the elements for decoupling. A prototype is fabricated, and the measured results show that the proposed array achieves an impedance bandwidth (IBW) of 6.31 GHz (22.5% referring to 28 GHz) and an axial ratio bandwidth (ARBW) of 7.32 GHz (26.1% referring to 28 GHz). The peak gain of the proposed array is 11.3 dBic, and the gain is greater than 9.3 dBic within the whole desired band (from 25 GHz to 31 GHz). The proposed array consists of only one substrate layer and can be built by the conventional printed circuit board technology. Attributed to the characteristics of wide bandwidth, simple structure, low profile, and low cost, the proposed antenna array has a great potential in mmWave wireless communications.

A single-feed dual-band circularly polarized (CP) microstrip antenna operating in Ka-band is proposed. The lower band and the upper band are excited by Archimedean spiral radiator. The main polarization mode of two resonant frequency (29 GHz and 38 GHz) are left-hand circular polarization(LHCP). The antenna achieves a small frequency ratio(1.31). The overlaps between -10 dB impedance bandwidth and axial ratio 3-dB bandwidth are 1.3 GHz(4.5% at 29 GHz) and 2.4 GHz (6.3% at 38 GHz).