This paper presents a compact frequency reconfigurable antenna for flexible devices and conformal surfaces. The antenna consists of a simple easy to fabricate structure consisting of a stub loaded circular radiator, designed on commercially available RT5880 flexible substrate (εr = 2.2) with a thickness of 0.254 mm. The combination of stub loading and slot etching techniques are utilized to achieve the advantages of compactness, frequency reconfigurability, wide impedance bandwidth, and stable radiation pattern with structural conformability. The frequency reconfigurability is achieved by employing two p-i-n diodes. Simulated and experimental results showed that the antenna operates in various important commercial bands, such as S-band (2 GHz– 4 GHz), Wi-Max (3.5 GHz and 5.8 GHz), Wi-Fi (3.6 GHz, 5 GHz, and 5.9 GHz), 5G sub-6-GHz (3.5 GHz and 4.4 GHz – 5 GHz), and ITU-band (7.725 GHz – 8.5 GHz) with the additional advantages of structural conformability. Furthermore, the performance comparison of the proposed flexible antenna with the state-of-the-art flexible antennas in terms of compactness, frequency reconfigurability, and number of operating bands demonstrates the novelty of the proposed antenna and its potential application in heterogeneous applications.

The ever-growing demand for low power, high performance, cost-effective, low-profile, and highly integrated wireless systems for emerging applications has triggered the need for the enormous innovations in wireless transceiver systems, components, architectures and technologies. This is especially valid for the antenna which is an integral component of the wireless transceiver systems and contributes significantly in determining their overall performance. Antenna-on-Chip (AoC) is an alternative antenna technology, which has drawn a substantial attention in recent days because of its various benefits over off-chip antenna technology. A few of these benefits include miniaturization, low power, low cost, and high integration of the wireless modules. Motivated by these valuable advantages and to unveil the true potential of the AoCs, this article presents, for the first time, a comprehensive survey of the suitability, advantages, and challenges of the AoCs for the emerging wireless applications such as 5th generation (5G) Wireless Systems, Internet-of-Things (IoT) Wireless Devices and Systems, Wireless Sensor Networks (WSNs), Wireless Interconnects, Wireless Energy Transfer, Radio Frequency (RF) Energy Harvesting, Biomedical Implants, Unmanned Aerial Vehicles (UAVs), Autonomous vehicles, Innovative characterization methods for Integrated Circuits (ICs) and Antennas, and Smart City. In addition, this article presents the current state-of-the-art of the AoC’s applications by classifying their applications in Millimeter-Wave (MM-Wave) band, Terahertz (THz) band, and low-frequency bands. The article also investigates and describes some useful methods for the mitigation of the challenges and issues posed by the emerging applications for the realization of the AoCs in a systematic manner. A concise description of the future directions of the AoCs with respect to each emerging application is also a part of this article. It is expected that this well-structured and organized survey will not only act as an excellent source of scholarship for the relevant research community, but also open up a world of novel research opportunities.

A compact flexible multi-frequency antenna for smart portable and flexible devices is presented. The antenna consists of a coplanar waveguide-fed slotted circular patch connected to a rectangular secondary resonator (stub). A thin low-loss substrate is used for flexibility, and a rectangular stub in the feedline is deployed to attain wide operational bandwidth. A rectangular slot is etched in the middle of the circular patch, and a p-i-n diode is placed at its center. The frequency reconfigurability is achieved through switching the diode that distributes the current by changing the antenna’s electrical length. For the ON state, the antenna operates in the UWB region for −10 dB impedance bandwidth from 2.76 to 8.21 GHz. For the OFF state of the diode, the antenna operates at the ISM band (2.45/5.8 GHz), WLAN band (5.2 GHz), and lower X-band (8 GHz) with a minimum gain of 2.49 dBi and a maximum gain of 5.8 dBi at the 8 GHz band. Moreover, the antenna retains its performance in various bending conditions. The proposed antenna is suitable for modern miniaturized wireless electronic devices such as wearables, health monitoring sensors, mobile Internet devices, and laptops that operate at multiple frequency bands.

This paper reports a multiband Yagi-Uda shaped metamaterial absorber (YUMA) operating in X- and Ku-band of the microwave regime with the added functionalities of miniaturization, polarization controllability and wide incidence angle stability. The proposed YUMA shows three distinctive near-unity absorption peaks corresponding to 10.64 GHz, 12.08 GHz, and 14.09 GHz frequencies. The YUMA was analyzed under different oblique incidence angles for transverse electric (TE)-mode and different rotation angles of the top metasurface. The results showed that the proposed YUMA possesses multifunctional characteristics such as polarization controllability, and wide incidence angle stability. The comparison of simulated and measured results further demonstrates that the proposed absorber can be a potential candidate in polarization detection systems and transmissive polarizers. The proposed YUMA operating in the X- and Ku-band can have potential uses in several other applications, such as air traffic control, weather monitoring, military radar, and satellite communication.