In this paper, the radiation features of indoor WiFi energy-harvesting antennas are analyzed, and the design guidelines that enhance receiving power are proposed. It is acknowledged that an RF energy-harvesting antenna is desired to depict circular polarization (CP) and omnidirectional patterns, as ambient sources are omnipresent; however, the polarization and half-power beamwidth (HPBW) of the antenna are inconclusive in earlier studies. To clarify the requirement of the radiation characteristics for indoor environments, the receiving performance of six antennas with different HPBWs and polarizations is analyzed. The research methodology is a hybrid ray tracing algorithm that integrates image and shootingand-bouncing-ray methods. These antennas are placed at different locations in a room, and the orientations are evenly and uniformly sampled. The receiving performance of each antenna is cast into cumulative density functions, which clarify the antenna that provides the maximum amount of successful receptions at specified energy-harvesting sensitivity. The simulated results are verified by performing the measurement. Surprisingly, the results indicate that CP and omnidirectional patterns cannot offer the most favorable receiving performance. In contrast, linear polarization and narrow HPBWs with high gain are desired in most of the scenarios, even though the directions of signal arrival have been uniformly sampled.INDEX TERMS Antennas, energy harvesting, ray tracing, rectennas, wireless power transmission.
A dual linearly-polarized antenna subarray that operates at 28 GHz and 38 GHz is proposed for fifth generation (5G) base stations. In contrast to earlier millimeter-wave base-station antennas that implement individual single-band antennas, simultaneous realization of dual-band operation can save space and cost. In addition, the proposed subarray depicts dual polarizations, improving signal reliability through polarization diversity. Furthermore, the proposed subarray is scalable and expandable in size and aperture. The proposed antenna subarray consists of 2 × 2 dual off-center-fed dipoles. The dual-band feature is obtained by tailoring the structure for expanding current pathways and impedance bandwidths. Accordingly, the impedance bandwidths for the lower and higher bands are 27.2-30.2 GHz and 35.7-40.3 GHz, respectively. When uniformly-distributed currents are excited, the proposed antenna shows broadside radiation with peak gain of 13.1 dBi at 28 GHz and 13.2 dBi at 38 GHz. When various current phases are excited, the subarray provides a scanning range of ±18°. The scalability is demonstrated by an example large-scale array that comprises 4 × 4 elements. The S-parameters are robust, and the gain is enhanced as 19.6 dBi at 28 GHz and 17.8 dBi at 38 GHz. Meanwhile, a broader scanning range of ±45° can be obtained. INDEX TERMS 5G mobile communication, antenna arrays, base stations, multifrequency antennas.
A compact substrate integrated waveguide (SIW) antenna array that operates at 28 GHz and 38 GHz is proposed for fifth generation (5G) applications. The proposed array consists of four SIW cavities fabricated on one single layer of substrate. Each cavity implements a rhombic slot and a triangular-split-ring slot, resonating on TE101 and TE102 modes at 28 GHz and 38 GHz, respectively. In comparison with dual-band SIW antennas in the literature, the proposed configuration depicts a miniature footprint (28.7 × 30.8 mm2) without stacking substrates. To excite the four cavities with equal power, a broadband power divider that supports the propagation of TE10 mode is designed. Accordingly, the impedance bandwidths are 26.6–28.3 GHz and 36.8–38.9 GHz. The measured realized peak gain over the lower and higher bands is 9.3–10.9 dBi and 8.7–12.1 dBi, respectively. The measured half-power beam widths (HPBWs) at 28 GHz and 38 GHz are 20.7° and 15.0°, respectively. Considering these characteristics, including dual bands, high gain, narrow beam widths, miniaturization, and single layer, the proposed antenna array is a suitable candidate for millimeter-wave 5G communication systems with the flexibility in switching operating frequency bands against channel quality variations.
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