This article provides a summary of recent microwave antenna sensor technologies published in peer-reviewed journals. This study is primarily focuses on the resonator-based microwave sensor, microwave wearable textile antenna sensors, and resonator-based flexible metamaterial devices along with their possible industrial applications. The survey emphasizes on both the possible disadvantages and advantages of employing this technology. Furthermore, it provides an overview of the key issues addressed in the context of antenna sensors, starting with material selection and finishing with the antenna’s frame, as well as the numerous case applications. This article, in particular, offers a description of the various types of textile materials used in the creation of wearable antenna sensors. This article provides various instances of antenna sensor applications in the human body, including the detection of NaCl and sugar solutions, blood, and other biological variables like strain, finger positions, and temperature. In addition, suggestions are made regarding the potential industry and scientific obstructions, as well as future directions for the study.

This letter presents a technique for size reduction of wideband multiple-input-multiple-output (MIMO) antennas. Our approach is a two-stage procedure. At the first stage, the antenna structure is modified to improve its impedance matching. This is achieved through incorporation of an n-section tapered feedline, followed by reoptimization of geometry parameters. Reducing the maximum in-band reflection well beyond the acceptance level of -10 dB creates room for size reduction, realized in the second stage as explicit footprint area minimization with the constraints imposed on the maximum in-band reflection level (|S ₁₁ | ≤ -10 dB) and element isolation (|Sε| ≤ -20 dB). The technique is generic and can be applied to various monopole-based MIMO structures. It is validated using two antenna structures operating from 2.8 to 20 GHz. Various complexities of the tapered lines are also investigated, from n = 1 to 5. To the best of the authors' knowledge, the obtained footprints (452 and 546 mm ² , respectively) are the smallest to date while ensuring acceptable performance, specifically impedance matching, isolation, envelope correlation coefficient (<;0.005), and diversity gain (>9.99 dB).

Internet of Things (IoT) will play an important role in modern communication systems. Thousands of devices will talk to each other at the same time. Clearly, smart and efficient hardware will play a vital role in the development of IoT. In this context, the importance of antennas increases due to them being essential parts of communication networks. For IoT applications, a small size with good matching and over a wide frequency range is preferred to ensure reduced size of communication devices. In this paper, we propose a structure and discuss design optimization of a wideband antenna for IoT applications. The antenna consists of a stepped-impedance feed line, a rectangular radiator and a ground plane. The objective is to minimize the antenna footprint by simultaneously adjusting all geometry parameters and to maintain the electrical characteristic of antenna at an acceptable level. The obtained design exhibits dimensions of only 3.7 mm × 11.8 mm and a footprint of 44 mm², an omnidirectional radiation pattern, and an excellent pattern stability. The proposed antenna can be easily handled within compact communication devices. The simulation results are validated through measurements of the fabricated antenna prototype.