A miniaturized, unidirectional on-body antenna designed for ultra-wideband (UWB) electromagnetic (EM) medical applications is proposed. The antenna is optimized for high-permittivity human tissues, the design delivers a wide impedance bandwidth of 170 % (0.5 - 7 GHz) and unidirectional near-field radiation, making it suitable for both deep-tissue and surface-level medical applications. The proposed antenna achieves a compact size (502 mm3) by employing multiple radiating modes excited through the shorted ring and shorted parasitic patch. Comprehensive simulations and measurements, including testing on homogeneous and multi-tissue realistic human body models were performed demonstrating effective power penetration and good matching across a broad frequency range 0.5 - 7 GHz. The proposed miniaturized on-body antenna with unidirectional pattern, and UWB bandwidth underline its potential for applications such as EM biomedical diagnosis and wireless body area networks.

An optically reconfigurable metasurface antenna for Future G beam steering applications is demonstrated experimentally. Optical reconfigurability is achieved by using photodiode arrays to provide a photovoltage to varactors, which in turn provide the required phase shift to enable beam-steering. Illumination of the photodiodes is provided over free space by using a galvo scanner to deflect a laser beam which is delivered from a high-power laser via a multicore fiber. In addition to delivering power over fiber, the same multicore fiber is also used to deliver a 64-QAM 5G NR signal to the metasurface antenna unit. Measured EVM values ranging from 3% to 5.7% for a beam-steering range of 58 degrees are obtained. The use of a galvo scanner for free space illumination of the metasurface antenna not only eliminates the requirement for on-antenna DC bias networks (thus reducing the system complexity), but also allows greater control over illumination of the photodiode arrays, resulting in continuous beam-steering over 58 degrees.

Abstract A reconfigurable inductorless negative‐refractive‐index transmission‐line (NRI‐TL) metamaterial phase shifter for sub‐6 GHz 5G antenna applications is proposed. The design consists of a microstrip transmission line loaded both in series and in parallel with varactor diodes to provide continuous tuning of the phase of the transmitted signal by varying the bias voltage applied to the varactors, without the need for variable inductor components. The total measured differential phase shift is 190° at 3.2 GHz, with a measured insertion loss of 1.5–2.7 dB in the frequency range of 3.2–3.6 GHz, when the biasing voltage of the varactors is varied between 0 and 7 V. The total size of the microstrip NRI‐TL phase shifter is 19.4 mm × 24 mm. The proposed reconfigurable phase shifter has been incorporated into the feeding network of a two‐element antenna array to demonstrate its use in beam‐steering applications. The measured results for the reconfigurable array show good impedance matching between 3 and 3.35 GHz for all biasing values, allowing continuous beam steering over a scanning range of 60°.

This paper presents a modified reconfigurable cactus-shaped planar monopole Ultra-wideband (UWB) antenna with 20 x 28 mm(2) dimensions. The three legs of the monopole enable a better command over the antenna matching parameter. The antenna operates in the UWB region ranging from 3.5 to 10.6 GHz. The reconfigurability is introduced by using three PIN diodes placed at the base of each leg. These diodes are turned ON and OFF simultaneously to manage the operational frequency of the monopole. The effortless control of the return loss extends its implementations for numerous UWB applications, particularly in intelligent sensing, intelligent surfaces (e.g. RISs, STAR-RIS) and signal filtering, where accuracy, high signal quality and noise reduction are essential for accurate and efficient data processing.

An optically reconfigurable phase shifter based on negative-refractive-index transmission line (NRI-TL) metamaterials is presented; the design is suitable for 5G antenna beam steering. Continuous tuning of the transmitted signal's phase is achieved by using varactor diodes for which the biasing is provided via an array of photodiodes placed on the back of the substrate. These are illuminated by a remote optical source whose wavelength can be tuned in the visible range, thus enabling indirect control of the varactor capacitance (and hence the phase shift) while also eliminating the need for a complex biasing network. Three different phases are achieved by illuminating the photodiode array with three different wavelengths (blue, green, and red). The compact size along with simplified biasing network introduced by the inclusion of the optical wavelength tunability has numerous applications in antenna and phased array technology, making the design a suitable candidate for 5G beam steering applications.

This paper presents a design for compact bandpass filters (BPFs) that feature high selectivity. This high selectivity is achieved through the use of open-/short-circuited coupled-line segments at the filter’s input and output and a pair of symmetrical parallel-coupled lines connected to a pair of open stepped-impedance resonators (SIRs) introducing three transmission zeros (TZs) on either side of the passband. In addition, two different designs for these BPFs, one with a fixed bandwidth and one with a tunable bandwidth are also presented. The characteristics of the proposed structure are analyzed using even-, odd-mode and ABCD analyses. To enable bandwidth tuning, two varactor diodes are added to the edges of the open SIRs, allowing the TZs to be adjusted around the upper band edge. The paper includes details of two prototypes that were designed, fabricated, and tested: Filter A with a constant bandwidth that covers the entire S-band (2-4 GHz) and a 3-dB fractional bandwidth (FBW) of 60%, and Filter B with a tunable bandwidth and a 3-dB FBW that varies from 12% to 60%. The filters have been measured to have insertion loss of less than 0.8 dB for Filter A and less than 1.1 dB for Filter B throughout the passband, and return loss of greater than 16 dB and 15 dB for Filter A and B, respectively. These filters have a compact size of less than $0.113\lambda _{g}^{2}$ , and feature high selectivity with a wide 3-dB bandwidth tuning range ratio, as well as an upper stopband suppression level of more than 40 dB.

A 1-bit reconfigurable phase shifter for 28 GHz mm-wave beam steering antennas is proposed. The design uses two beam-lead GaAs PIN diodes loaded on a microstrip transmission line in parallel, to provide two discrete phases for the transmitted signal. When the diodes are switched OFF, no shift in the phase of the transmitted signal is observed while a phase shift of ~90° is achieved when the diodes are switched ON. The total length of the phase shifter is $\sim\lambda /2$ . The compact size, low cost, reduced complexity and easy adaptation in antenna and phased array technology makes it a suitable candidate for 5G mm-wave beam steering applications.

A 5G-NR radio-over-fiber system (RoF) that also incorporates power-over-fiber (PoF) via a multicore fiber (MCF) link is used to support a reconfigurable metasurface (MSF) antenna for rapid beam steering. Optical signals for RoF-PoF are generated in a central office (CO), and transmitted to the remote antenna unit (RAU) via MCF. A reconfigurable MSF antenna has been designed to perform continuous steering of the radiated beam using indirect optical control of varactor diodes. Subsequently, a proof-of-concept 5G-NR system has been demonstrated for the sub-6 GHz band. The PoF part of the system was able to provide 0–5 V to reconfigure the MSF antenna and thus achieve total beam steering of 66°. For the RoF segment, the measured EVM values for a 64-QAM scheme vary between 2.6%–6.9% for all states.

A fixed-length arbitrary-phase tunable phase shifter, based on the concept of negative-refractive-index transmission-line (NRI-TL) metamaterials for sub-6 GHz antenna beam steering applications is proposed. The design consists of a fixed microstrip transmission line which is reconfigured by loading varactor diodes in both the series and shunt branches. A continuously tunable phase of 210° at 3.2 GHz for the transmitted signal is achieved at the output by varying the biasing voltage from 0 – 7 V for the varactor diodes. The insertion loss varies from 0.9 – 2.5 dB for the design in the frequency range of 3.2 – 3.6 GHz. The total length of the tunable NRI-TL metamaterial phase shifter is λg/4.

A head wearable antenna array embedded on a multilayer substrate to enable unidirectional radiation pattern, broad bandwidth and compact size for trans cranial radiofrequency stimulation is proposed. The top layer consists of $4\mathrm{x}4$ radiating patches, an EBG array and feeding network while the bottom layer consists of $4\mathrm{x}4$ MTM reflectors. The EBG array consists of 9-unit cells arranged near the feeding network to reduce the surface waves while the MTM reflectors compel the antenna to radiate towards the broadside thus achieving a unidirectional radiation pattern for the complete structure. A broad impedance bandwidth and compact size are achieved by using the DNG properties of the meta material. The unidirectional pattern along with compact size and broad bandwidth enable the proposed design to be used for transcranial radiof-requency stimulation and other biomedical applications.

A conformal rat head wearable antenna has been designed to provide unidirectional radiation to expose the head and brain for transcranial RF stimulation at 2.45 GHz (ISM band). The compactness of the microstrip patch has been achieved by using vertical slots in its orientation that increase its electrical length, without increasing the physical size of the antenna. The antenna layer is sandwiched between biocompatible and non-toxic layers of parylene-C. The antenna has been conformed and optimized for transcranial stimulation with a model of rat phantom that includes the properties of different layers of the rat's head (e.g. brain, skull, skin). Precise and controlled delivery of RF energy to specific brain regions is enabled by virtue of the compact size, conformal nature, and optimized design of the antenna. The proposed antenna demonstrates a unidirectional pattern, crucial for achieving reliable and effective stimulation outcomes and can be used in various biomedical applications, including trans cranial RF stimulation.

Beamsteering of a sub-6 GHz 5G metasurface antenna is achieved via free space optical control. A scanning angle of 66 ° is demonstrated at 3.25 GHz. The antenna consists of varactor-based phase shifters, whose voltage is controlled by photodiodes that are illuminated over free space.

In this work, a wirelessly enabled beam steering metasurface (MSF) antenna for bio-imaging is proposed. The design consists of multiple layers, the top layer consists of an MSF layer, while the bottom layer consists of two layers, one that contains the feeding antennas and the second consists of the feeding network. In the feeding network of the MSF antenna, an RF energy harvesting (EH) system has been incorporated that allows dynamic switching to achieve the desired beam steering required for torso scanning. In the designed EH system, a receiving antenna and rectifying circuit harvests the low power received RF signal at three different frequencies in the 2.4 GHz ISM band. In order to avoid coupling between the EH system and MSF antenna, the former operates in the 2.4 GHz ISM band, while the latter operates in the 900 MHz ISM band. The proposed approach has potential to be used in biomedical imaging applications and to provide an alternative to complex biasing networks required to reconfigure devices.

This manuscript presents a novel UHF IoT humidity and temperature sensor module that is powered from an integrated energy harvesting (EH) system. The module is intended for smart agriculture applications. The sensing module is powered from the collected RF energy that is harvested by a meander monopole antenna operating at 915 MHz (US UHF band) and therefore the use of a battery is not required. The rectifying voltage doubler converts the received RF energy into DC while the Power Management Unit (PMU) boosts-up and stores the rectified voltage providing a regulated output voltage of 1.8V to the RFID tag IC (ROCKY100) and 3.3V to the microcontroller unit (MCU) and the humidity and temperature sensor IC. The communication RFID antenna uses the European UHF frequency band centered at 868 MHz. When the RFID tag IC is supplied with 1.8 V from the PMU it operates in semi-passive mode and it effectively increases its communication range. The ROCKY100 is EPC C1G2 compliant and is compatible with power harvesting modules and SPI communication to support external low-power sensors and actuators. In addition, a capacitive digital humidity and temperature sensor (HTS221) is used as the sensing module for soil measurements. The process of measuring the relative humidity and temperature of the soil is controlled with a Texas Instrument mixed signal microcontroller that possesses two SPI interfaces that allows it to communicate with the RFID IC and the sensor in parallel. Upon receiving a SPI directed read request from the RFID reader, the ROCKY100 SPI bridge requests the value of the last measurement from the microcontroller and the humidity and temperature measurements taken by the HTS221 IC are sent to the RFID reader. The use of harvested wireless energy as a power source makes the demonstrated module a potentially batteryless and thus a “Green” sensor.

This paper discusses a dual-layer metasurface (MSF) superstrate, consisting of double split-ring resonator cells in the 28 GHz 5G mm-wave frequency band. The MSF superstrate is added above a conventional patch antenna, and an enhancement in the performance of the patch antenna in terms of bandwidth and gain is achieved. This is due to the negative index metamaterial (NIM) properties of the designed MSF superstrate. In this design, the impedance bandwidth is improved from 2.6 GHz to 3.6 GHz, while the gain of the patch antenna is increased from 6.59 dBi to 12.9 dBi. The simplicity of the design to achieve a higher gain and broader bandwidth makes it a suitable candidate for applications in 5G mm-wave communications.

This paper presents the design of an energy autonomous radiofrequency identification (RFID) tag for communication and/or indoor localization. It makes use of the energy harvesting (EH) technique in the 915 MHz ultra-high frequency (UHF) band for the feeding of a system-on-a-chip (SoC), working also as a radio transceiver, in order to communicate data to a reader, or a gateway, at 2.4 GHz. First, the design of a multiple-input multiple-output (MIMO) antenna is described, with the dimensions of the whole tag limited to 47 × 100 mm 2 . Subsequently, the description and the performance of the UHF rectifier are reported, with its connection to the related power management unit (PMU). The PMU is then connected to a transceiver that can send information about its identification number (ID) and the received signal strength indicator (RSSI) without the need of a battery.

This paper presents the design of a dual-port MIMO antenna that consists of two probe-fed radiating elements. One compact folded monopole for the UHF band matched from 840 to 945 MHz covering a bandwidth of 105 MHz, and a fully grounded patch antenna for the ISM band operating from 2.40 to 2.48 GHz, covering a bandwidth of 80 MHz. The isolation between the two ports of the MIMO antenna is better than –20 dB. The proposed MIMO antenna is a suitable candidate for an energy-autonomous SWIPT system.

A fluidically reconfigurable metasurface (MSF) is presented in this paper in order to achieve radiation beam steering with enhanced gain. A simple square ring resonator structure is used as the unit cell for the superstrate layer and a probe-fed microstrip patch antenna is used as the radiator. The microfluidic channels are implemented inside a 3D printed polylactic acid (PLA) substrate and gallium liquid metal alloy (LMA) is injected in the microfluidic channels to switch the radiation pattern in the elevation plane from broadside to ± 20°. The proposed metasurface antenna exhibits a constant fractional bandwidth greater than 7.5% in all states of reconfiguration. The maximum realized gain remains greater than 7.2 dBi. The simulated gain and bandwidth of the proposed structure are greater than those of a conventional patch antenna, making it a good candidate for certain 5G, cellular base station, and satellite communication applications.

A dual-frequency (433 MHz and 2.45 GHz) circularly polarized MIMO rectenna with dual-branch rectifier and a common power management unit is presented. For the lower frequency a dual-layer, four-element, monopole antenna array is implemented. The four monopoles are oriented along the perimeter of a square and are fed with 90° phase difference resulting in a circularly polarized antenna array. The total covered area is $80\times 80\ \text{mm}^{2}$ , and the maximum gain is 2.45 dBi. For the 2.45 GHz antenna, an elliptical patch is used implementing it in the middle of the square substrate that is used for the 433 MHz monopoles. As a result of the close proximity of the two radiating elements, the gain of the patch is enhanced to 6.2 dBi. Both antennas are probe-fed with two coaxial cables that pass through the antenna substrates. The coaxial cables are connected on the dual-branch, dual-frequency rectifiers. For the matching networks of the rectifiers, lumped elements are used for the 433 MHz rectifier, and hybrid, distributed and lumped elements, are used for the ISM band voltage-doubler. The combined use of both frequencies results in RF-to-dc efficiency up to 70% for input power close to 0 dBm. The dual rectifiers have a common load since they are terminated with a common power management unit circuit. The commercially available e-peas AEM30940 RF is considered as the PMU circuit. It presents cold start-up from 380 mV and $3\ \mu\mathrm{W}$ , and is able to supply low-voltages (from 1.2 to 1.8 V) suitable for most microcontrollers and also “high” voltages ranging from 1.8 V up to 4.1 V.

This paper presents a battery-less single pole triple throw (SP3T) switch enabled through wireless power transfer (WPT) for a frequency range of 0.5 - 6 GHz. A set of three rectifying circuits, each connected to their independent antenna elements (rectennas) were designed. These rectennas were designed to operate at 2.3 GHz, 2.45 GHz, and 2.6 GHz, respectively. Different frequencies were used to avoid any interference between received signals. The three RF output ports of the switch were biased using each rectenna. A minimum of 1.8 V is required to actuate each RF port that was rectified when the input power ranges from 0-2 dBm with RF-to-DC power conversion efficiency (PCE) which is around 50% for each rectifier. The proposed battery-less SP3T switch paves the way to reconfigure microwave devices and antennas for a broad range of applications.