A low-profile, compact, four-element, eight-port multiple-input--multiple-output and diversity antenna for 5G Internet of Things and cellular handheld applications is presented in this letter. This antenna structure contains four antenna elements, which are same in its configuration. The antenna ground dimensions are taken similar to a modern mobile handset, i.e., 60 mm × 120 mm. The four antenna elements are situated at four corners of antenna ground structure. Each antenna element has two feeding ports, thus making a total of eight-port antenna. A single antenna element has two feeding plates, which are placed perpendicular to one another so that they become cross polarized, thus exploiting polarization diversity, whereas spatial diversity also exists between different antenna elements. For reducing mutual coupling between different antenna ports, slots are cut in ground plane, including a small strip etched along the entire length of ground plane and rectangular slots cut in ground plane under every antenna element. The minimum bandwidth attained by all eight ports for S ₁₁ < –10 dB is more than 1.4 GHz from 2.4 GHz to more than 3.8 GHz, which testify that it covers majority of frequency bands allocated for 5G sub-6 GHz spectrum. The isolation obtained between different ports has a minimum value of –13 dB, and the maximum value goes below –30 dB. For the covered frequency bands by this antenna structure, the correlation coefficient is found to be below 0.03, whereas the measured peak gain is in the range of 3.2--5 dB.

In response to the increasing demand for voice, data, and multimedia applications, the next generation of wireless communication systems is projected to provide faster data rates and better service quality to customers. Techniques such as Multiple-Input–Multiple-Output (MIMO) and diversity are being studied and implemented to meet the needs of next-generation wireless communication systems. Embedding multiple antennas into the same antenna system is seen as a promising solution, which can improve both the system’s channel capacity and the communication link’s quality. However, for small handheld and portable devices, embedding many antennas into a single device in a small area and at the same time providing good isolation becomes a challenge. Hence, designing a shared antenna system with multiple feed ports with equivalent or better performance characteristics as compared to the approach of multiple antennas with multiple feed ports is a promising advantage which can reduce the size and cost of manufacturing. This paper intends to provide an in-depth review of different MIMO antenna designs with common radiators covering various antenna design aspects such as isolation techniques, gain, efficiency, envelope correlation coefficient, and size, etc. There is also a discussion of the mathematical concepts of MIMO and different isolation techniques, as well as a comparative analysis of different shared radiator antenna designs. The literature review shows that only very few antennas’ design with common radiator have been suggested in the available literature at present. Therefore, in this review paper, we have endeavored to study different antennas’ designs with common radiator. A comparison is provided of their performance improvement techniques in a holistic way so that it can lead to further develop the common radiator multiport antenna systems and realize the promising advantages they offer.

A compact four-port multi-input, multi-output (MIMO) antenna with good isolation is proposed for sub-6 GHz and Internet of Things (IoT) applications. Four similar L-shaped antennae are placed orthogonally at 7.6 mm distance from the corner of the FR4 substrate. The wideband characteristics and the required frequency band are achieved through the L-shaped structure and with proper placement of the slots on the substrate. To obtain good isolation between the ports, rectangular slots are etched in the bottom layer and are interconnected. The proposed antenna has total dimensions of 40 mm × 40 mm × 1.6 mm. The interconnected ground plane provides good isolation of less than −17 dB between the ports, and the impedance bandwidth obtained by the proposed four-port antenna is about 54% between the frequency range of 3.2 GHz to 5.6 GHz, thus providing a wideband antenna characteristic covering sub-6 GHz 5G bands (from 3.4 to 3.6 GHz and 4.8 to 5 GHz) and the WLAN band (5.2 GHz). The proposed design antenna is fabricated and tested. Good experimental results are achieved when compared with the simulation results. As the proposed design is compact and low profile, this antenna could be a suitable candidate for 5G and IoT devices.

In today’s world, the increasing cost of healthcare and tremendous growth of elderly population introduced a major issue for medical monitoring and healthcare applications. A tiny sensor attached outside/inside the human body in Wireless Body Area Sensor Network (WBASN) monitors the surrounding environment and function of human body. Meanwhile, the heat dissipated from antenna and sensor node’s circuitry and antenna deteriorates human tissue. Thus it is very important to design a routing protocol in WBASN by incorporating the effect of temperature into routing metrics. A WBASN consists of heterogeneous nodes; therefore, the routing protocols must be designed to balance traffic among these sensor nodes. Vital signals of human body require different quality of service for different data types. Thus designing QoS aware routing protocols is a challenging task. In this paper, conventional temperature and QoS aware routing protocols are compared and open issues in routing protocol design are discussed.

In this paper, a novel coplanar waveguide (CPW) structure featuring top-layer geometry invariant capabilities, loaded with a defected ground structure (DGS) that serves as a CPW impedance regulator, is presented. The proposed CPW transmission line (t_x line) keeps the 50 Ω impedance stable across micron-thick films of various thicknesses without requiring changes to the CPW dimensions. This CPW model obviates the need for repetitive CPW structure design over different film thicknesses for impedance tuning while simultaneously offering manufacturing standardisation. A critical limitation in conventional CPW and Grounded CPW (GCPW) is the significant dependence of impedance on substrate thickness, requiring re-optimisation of t_x line width (S) and slot gap width (W_s) for each substrate variation. Both conventional CPW and GCPW need concurrent modification of S and W_s to reach 50 Ω impedance. In contrast, the proposed CPW model can match the 50 Ω impedance by tuning only a single parameter, the DGS width, R_sw (range between 3.08 mm - 3.16 mm). At a fixed CPW geometry, this model exhibits low characteristic impedance sensitivity to substrate variations, averaging 0.003 Ω/μm, which is 23 times lower than conventional CPW and GCPW (0.07 Ω/μm). When embedded into an antenna system, it has demonstrated an excellent S11 response, with simulation and measurement results showing a close match, with only a 1.44% frequency shift and a 2.98% S11 magnitude deviation.