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 multiple-output (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.

We consider a new approach for enhancing the discrimination performance of the VanderLugt correlator. Instead of trying to optimize the correlation filter, or propose a new decision correlation peak detection criterion, we propose herein to denoise the correlation plane before applying the peak-to-correlation energy (PCE) criterion. For that purpose, we use a linear functional model to express a given correlation plane as a linear combination of the correlation peak, noise, and residual components. The correlation peak is modeled using an orthonormalized function and the singular value decomposition method. A set of training correlation planes is then selected to create the correlation noise components. Finally, an optimized correlation plane is reconstructed while discarding the noise components. Independently of the filter correlation used, this technique denoises the correlation plane by lowering the correlation noise magnitude in case of true correlation and decreases the false alarm rate when the target image does not belong to the desired class. Test results are presented, using a composite filter and a face recognition application, to verify the effectiveness of the proposed technique.

Efficient wide-band transitions play a critical role in integrating substrate-integrated waveguide (SIW) and air-filled substrate-integrated waveguide (AFSIW) systems with conventional rectangular waveguide (RWG) systems in millimeter wave communication. However, existing techniques lack a systematic design approach, overlook mode purity, encounter performance issues, involve tedious optimizations, and feature complex structures. This paper presents a first-of-its-kind design technique that addresses these limitations, enabling seamless transitions from RWG to both SIW and AFSIW. For the first time, a clear and systematic design flow is introduced, covering both transition scenarios. The proposed technique eliminates the need for separate design procedures, simplifying the process, reducing complexity, and offering a cost-effective solution with state-of-the-art performance. The key innovation lies in the analytical expression for the shortest transition length, derived for both SIW and AFSIW cases, facilitating the design process and optimizing transition performance. The effectiveness of the design flow is extensively validated through four design examples, evaluating mode purity, reflection coefficient, and insertion loss. The results demonstrate excellent performances, confirming the accuracy of the approach. Furthermore, a fabricated prototype achieves remarkable results with an insertion loss of 0.35 dB and a relative bandwidth of 40%, exhibiting state-of-the-art performances when compared to reported works in the literature. In summary, the novel design technique enables seamless wide-band transitions from RWG to both SIW and AFSIW, offering a unified approach with state-of-the-art performance.

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.

Despite extensive research on integrating Substrate IntegratedWaveguide (SIW) technologies with conventional transmission technologies such as Microstrip Transmission Line (MSTL), Co-planar Waveguide (CPW), Rectangular Waveguide (RWG), and Coaxial lines, a comprehensive evaluation and design framework has yet to be explored. This review addresses this critical gap by providing a detailed examination of recent advancements in interconnect technologies at millimeter-wave (mmWave) frequencies. The paper identifies unresolved challenges and introduces a Figure-of-Merit ( FoM ) for the first time designed to evaluate and decide the state-of-the-art in interconnect technologies. Furthermore, it proposes a novel design flow that aids interconnect designers by integrating reported advances into a well-defined process. As such, the study provides a basis for further developments, leveraging existing and SIW technologies to ease mmWave system development, along with a commercial perspective.

<!----> <!----> This chapter proposes to discuss the future trends in 5G new radio (NR) antenna design, covering topics from the basics of antenna design flow to antenna integration, with their performance metrics highlighting the design and measurement challenges. In light of the new standard released by 3GPP, a joint effort by mobile service providers (MSP), and the global research community, to develop a new smart antenna is going on at a faster pace for 5G new radio. Moreover, the use of new designs for 5G technology is driven by consumer needs and business's house requirements. In order to fulfill, the increasing demand for high data rate, new radios need to be developed. They will utilize millimeter-wave (mmWave) bands, incorporating massive-MIMO (multiple input, multiple output) antennas with beamforming and beamsteering capabilities. <!----> <!---->