This study presents a dual polarized broadband microstrip patch antenna for a 5G mmWave antenna module on an FR4 substrate. The proposed antenna was fabricated using a standard FR4 printed circuit board (PCB) process because of its low cost and ease of mass production. The electrical properties of the FR4 substrate in the 5G mmWave frequency band were also characterized. An air cavity structure was introduced to mitigate the high loss tangent of the FR4 substrate. Capacitive elements such as proximity L-probe feedings and parasitic patches are used to improve the impedance bandwidth of the patch antenna. For the polarization diversity of the massive multiple-input multiple-output (MIMO) capability, the antenna radiator was designed with a symmetrical structure, and the relative position of the L-probes excites the orthogonal resonant modes to enable dual linear polarization. The operation principle of the proposed antenna was thoroughly analyzed by characteristic mode analysis (CMA). The measured bandwidth of a single antenna was 23.1 % (23 ~ 29 GHz) and the gain value was 5 dBi. The measured cross-polarization suppression ratio of single antenna was 15 ~ 20 dB. The measured gain value of 1×4 antenna array was 10 ~ 11 dBi and the cross-polarization suppression ratio was about 20 dB. The size of the proposed single antenna is 0.41λ ₀ ×0.41λ ₀ ×0.1λ ₀ , and that of a 1×4 antenna array is 2.78λ ₀ ×0.41λ ₀ ×0.1λ ₀ . The envelope correlation coefficient (ECC) was calculated and was lower than 0.02 in the 5G mmWave frequency band.

Inkjet‐printing is a very promising technology for the development of microwave circuits and components. Inkjet‐printing technology of conductive silver nanoparticles on an organic flexible paper substrate is introduced in this study. The paper substrate is characterised using the T‐resonator method. A variety of microwave passive and active devices, as well as complete circuits inkjet‐printed on paper substrates are introduced. This work includes inkjet‐printed artificial magnetic conductor structures, a substrate integrated waveguide, solar‐powered beacon oscillator for wireless power transfer and localisation, energy harvesting circuits and nanocarbon‐based gas‐sensing materials such as carbon nanotubes and graphene. This study presents an overview of recent advances of inkjet‐printed electronics on paper substrate.

This paper presents an antenna structure with a reconfigurable pattern and polarization for CubeSat applications. The proposed antenna is based on spatial-mapping origami theory and consists of a center-fed 4-way Gysel power divider, delay lines, inside Lamina Emergent Torsion (LET) joints, and four thick planar dipole antennas. The LET joints are used to distribute the mechanical stress of a rigid planar material to form a flexible planar spring structure. The proposed antenna has monopole-like omnidirectional linearly polarized gain patterns in planar mode. Its gain value is about 0.5 dBi at 5.8 GHz. In folded mode, the antenna has about a circularly polarized gain value of about 8.07 dBic and broadside radiation patterns. The measured crosspolarization suppression ratio is about 25 dB, and the axial ratio (AR) value is 1.13 dB at 5.8 GHz. The size of the antenna in planar mode with a cross-shape is 100 × 100 × 0.5 mm3, and its size is in folded mode is 32.5 × 32.5 × 32.5 mm3. The size of the antenna in inactive mode is 35 × 35 × 3 mm3, and its total weight is only 4.73 g.

The newly developed research area of inkjet-printed radio frequency (RF) electronics on cellulose-based and synthetic paper substrates is introduced in this paper. This review paper presents the electrical properties of the paper substrates, the printed silver nanoparticle-based thin films, the dielectric layers, and the catalyst-based metallization process. Numerous inkjet-printed microwave passive/ative systems on paper, such as a printed radio frequency identification (RFID) tag, an RFID-enabled sensor utilizing carbon nanotubes (CNTs), a substrate-integrated waveguide (SIW), fully printed vias, an autonomous solar-powered beacon oscillator (active antenna), and artificial magnetic conductors (AMC), are discussed. The reported technology could potentially act as the foundation for true “green” low-cost scalable wireless topologies for autonomous Internet-of-Things (IoT), bio-monitoring, and “smart skin” applications.

A RFID-based backscattering sensor system is low-cost and scalable wireless sensing technology. It takes advantage of RF energy harvesting technique, wireless power transfer and backscattering principle. It also has uncountable number of applications due to its versatility. In this paper, operation principle, architecture and machine learning technique for wirelessly powered RFID-based backscattering sensor system is presented. For the sensor tag-reading and power-delivering algorithm, machine learning techniques, such as support vector machine (SVM), artificial neural networks (ANN), and naive Bayes algorithm, are introduced with experimental verifications. The supervised SVM algorithm significantly improved reading accuracy of chipless RFID sensor tags due to superior signal classification performance of the SVM method. The ANN-based adaptive dynamic matching network for magnetic resonant wireless power transfer system improved wireless power transfer distance efficiently. Position estimation method based on the naive Bayes algorithm that is essential for smart wireless power transfer platform for wirelessly powered drones is also discussed in this paper.

The detailed design considerations for the printed RFID-based sensor system is presented in this paper. Starting from material selection and metallization method, this paper discusses types of RFID-based sensors (single- & dual-tag sensor topologies), design procedures, and performance evaluation methods for the wireless sensor system. The electrical properties of the paper substrates (cellulose-based and synthetic papers) and the silver nano-particle-based conductive film are thoroughly characterized for RF applications up to 8 GHz. The reported technology could potentially set the foundation for truly “green”, low-cost, scalable wireless topologies for autonomous Internet-of-Things (IoT), bio-monitoring, and “smart skin” applications.