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This communication presents the design of a wideband circularly polarized (CP) antenna array based on sequential rotation (SR) technique that is excited by a substrate integrated coaxial line (SICL) with mature and stable processing technology for millimeter-wave (mm-wave) applications. Initially, the influence of the amplitude and phase errors of the feeding network on the axial ratio of the CP array is analyzed, and the detailed design scheme of the wideband CP array based on SR technology is summarized, which can be used to design SR CP array with wide bandwidth and high polarization purity. Then, an SICL-fed $4 \times 4$ CP array working in the mm-wave band that is composed of two substrate layers and a bonding film layer is designed. The radiation element is processed with a larger chamfering, which can realize elliptically polarized radiation in a broadband range, and the impedance bandwidth is significantly expanded relative to the working state of linearly polarized and CP, which has a significant impact on the final array working bandwidth enhancement. The feeding network and radiation elements are directly connected in the same plane. Finally, the proposed antenna is processed and measured to verify the theory and design scheme in this communication. Over the frequency range of 25.0–34.0 GHz, the measured 1.5 dB axial ratio bandwidth of the fabricated prototype is 30.5%, and the return losses are less than −10 dB. The maximum measured peak gain is 16.5 dBi. [ABSTRACT FROM AUTHOR]

This article presents a novel triband dual-polarized shared-aperture antenna with frequency-selective function for sub-6 GHz base station applications. The proposed antenna is composed of a dual-polarized square loop antenna with two parasitic loops for 2G/3G/4G (1710–2690 MHz) and a differentially fed dual-polarized planar antenna for 5G (3300–3600 and 4800–5000 MHz) base station applications. These two antennas are placed coaxially but different altitudes for saving the installation space. In order to achieve good individual performance for these two antennas in the same aperture without interference or blocking, the lower band (LB) antenna is designed as a frequency-selective surface (FSS) for the nether mid/upper bands (M/UBs) antenna. The measured results show that the proposed antenna achieves a high port isolation (>20 dB) between LB and M/UBs and a −10-dB impedance bandwidth of 50.4% (1.60–2.70 GHz), 14.9% (3.28–3.80 GHz), and 8.6% (4.75–5.18 GHz). To further validate the design concept, an antenna array composed of four LB elements and eight M/UBs elements with the corresponding spacing is fabricated and measured, which demonstrates the application of the triband shared-aperture antenna in array form. [ABSTRACT FROM AUTHOR]

A wideband traveling-wave circularly polarized (CP) antenna printed on a single-layer PCB for millimeter-wave (MM-Wave) applications is presented in this communication. The proposed antenna radiates the CP wave on the basis of the principle similar to the classical endfire-mode helical antenna. The proposed antenna is terminated with an absorber to realize traveling-wave radiation. The traveling-wave working mechanism causes the proposed antenna to have a frequency scanning function and higher stability compared with resonant antennas. Curved microstrip transmission lines are adopted as the CP radiation elements; the whole array antenna is etched on a single-layer substrate. A prototype operating at 30 GHz is fabricated and measured. The radiation beam of the proposed antenna scans from − 14.5° (28 GHz) to +22.5° (34 GHz), the axial ratios are lower than 3 dB, and the measured gains show a maximum value of 21.9 dBi at 33 GHz and a minimum value of 20.3 dBi at 28 GHz. The measured $| \text {S}_{11} |$ and $| \text {S}_{21} |$ are lower than −10 and −16 dB, respectively, in the frequencies mentioned above. [ABSTRACT FROM AUTHOR]

This communication presents a dual-polarized series-fed array antenna with 30° beam-pointing for millimeter-wave (MM-Wave) applications. The 45° and −45° polarized subarrays share the aperture in an interdigital shape. The spacing between subarrays with the same polarization orientation is set to $0.56\lambda _{0}$ through the use of narrower T-type folded substrate integrated waveguide (TFSIW) instead of substrate integrated waveguide (SIW). The substrate integrated coaxial line (SICL) is adopted to design the array feeding network. To validate the proposed design, a $4 \times 6$ (single polarization) dual-polarized array antenna operating at 28 GHz with 30° beam-pointing is fabricated. Based on the measurement, the return losses are lower than −10 dB from 27.5 to 28.5 GHz, the isolations between the two polarization ports are higher than 30.0 dB in the frequencies mentioned above, the maximum gain at the center frequency is 15.7 dBi, and the cross-polarization levels are lower than −18.5 dB. The proposed antenna only needs one-step processing with the standard PCB technology without additional stitching assembly. Simulated and measured results of the proposed antennas were compared. [ABSTRACT FROM AUTHOR]