This paper proposes a high-order MIMO antenna operating at 3.5 GHz for a 5G new radio. Using an eighth-mode substrate integrated waveguide (EMSIW) cavity and considering a typical smartphone scenario, a two-element MIMO antenna is developed and extended to a twelve-element MIMO. These MIMO elements are closely spaced, and by employing multiple diversity techniques, high isolation is achieved without using a decoupling network. The asymmetric EMSIW structures resulted in radiation pattern diversity, and their orthogonal placement provides polarization diversity. The radiation characteristics and diversity performance are parametrically optimized for a two-element MIMO antenna. The experimental results exhibited 6.0 dB and 10.0 dB bandwidths of 250 and 100 MHz, respectively. The measured and simulated radiation patterns are closely matched with a peak gain of 3.4 dBi and isolation ≥36 dB. Encouraged with these results, higher-order MIMO, namely, four- and twelve-element MIMO are investigated, and isolation ≥35 and ≥22 dB are achieved, respectively. The channel capacity is found equal to 56.37 bps/Hz for twelve-element MIMO, which is nearly 6.25 times higher than the two-element counterpart. The hand and head proximity analysis reveal that the proposed antenna performances are within the acceptable limit. A detailed comparison with the previous works demonstrates that the proposed antenna offers a simple, low-cost, and compact MIMO antenna design solution with a high diversity performance.
With the increasing demand for high-speed data, rapid deployments of the 5G terrestrial heterogeneous wireless networks are expected worldwide in the next decade. In such networks, sub-6 GHz macro-cells overlapped by mmWave small-cells are being used to cater to densely populated regions. As a result, several challenges arise with the antenna design technologies used at the mobile terminal, access points, or backhaul/front haul levels. These challenges are being addressed using multiple-input multipleoutput (MIMO), massive-MIMO, and phased array antenna technologies. In order to implement these antenna technologies, considering the expanding 5G scenario, substrate integrated waveguide (SIW) offers a viable solution due to its low-cost, low-profile, high-power handling, low transmission loss, and ease of integration with the radio circuits; therefore, the SIW plays a vital role in developing the modern radio systems. The proposed study aimed to provide a comprehensive overview of SIW MIMO and phased array antennas operating in the 5G sub-6 GHz and mmWave bands. It deliberates the specific issues related to the band of operations and challenges in designing different antenna structures. After careful investigation and detailed analysis, this paper identified existing research gaps and suggested possible antenna design solutions for prospective researchers who intend to explore further the aforementioned promising area and present future research directions.INDEX TERMS 5G New Radio (NR), millimeter-wave (mmWave), multiple-input multiple-output (MIMO), planar antennas, substrate integrated waveguide (SIW), sub-6 GHz. I. INTRODUCTIONThere is rapid growth in the deployments of 5G heterogeneous wireless networks to cater to the increasing demands of high-speed data communication in the modern wireless system [1,2]. In such a scenario, the microwave and mmWave networks overlap (See Fig. 1) to serve the mobile units, access points, backhaul, and fronthaul wireless links, supported by MIMO, massive MIMO, and phased array antennas [1,2]. In order to realize these antennas, substrate integrated waveguide, a well-established planar technology, is a suitable choice [3]. A. MIMO ANTENNAThe multiple-input multiple-output (MIMO) antenna is the key enabling technology for fourth-generation (4G), fifth-generation (5G), and beyond 5G (B5G) wireless communication systems. In 4G communication, MIMO primarily supports average download speeds for mobile users. Whereas, in 5G, the MIMO at the user equipment (UE) side and massive MIMO at the base station (BS) promise to deliver high data speeds for enhanced mobile broadband (eMBB) access and enable a wide range of services, including internet of thing (IoT) and critical machine-to-machine communications [1].As per Shannon's channel capacity theorem, the direct way to enhance the date rate is by increasing the bandwidth and/or signal-to-noise ratio (SNR) [4]; however, these are not under the control of the antenna designer and are fixed by the cellular operator. Therefore, multiple antenna...
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This paper analyses patch antennas operating at 16 GHz on flexible Kapton polyimide substrate in various shapes, namely rectangular, circular, pentagon, hexagon, heptagon, and octagon. Their applications in medical areas, more particularly in wearable devices for E-health, are targeted. The bending effects of these antennas are studied, more specifically on gain, return loss, radiation characteristics, bandwidth, and beamwidth. A detailed comparison results showed that the rectangular patch had better performance even under the bending when the diameter of the surface is varied from 40mm to 120mm and maintains a gain of 4.8 dB at the given frequency. Under such extreme bending, the antennas operate satisfactorily with an efficiency of 43.424% to 47.41%.
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