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This paper presents a wideband printed antipodal Vivaldi antenna using straight slots for UHF DVB-T/T2 applications covering a frequency range of 470–862 MHz. The proposed antenna consists of two radiation flares with straight slots and a feeding line. A wideband impedance matching was achieved by inserting the slots between the flares and the feeding line. For the experimental verification of the proposed antenna, it was fabricated on a flat circular printed circuit board (PCB) substrate with a radius of 0.25 λ0, where λ0 is the wavelength at 0.74 GHz (the center frequency of the operating band). The measured −10 dB impedance bandwidth and maximum gain were approximately 72.1% (0.47–1.00 GHz) and 2.57 dBi, respectively. Due to the addition of the slots, the impedance bandwidth of the proposed antenna was improved by approximately 212% compared with the Vivaldi antenna without slots.

This letter demonstrates, through real-world field tests, an ambient radio frequency (RF) energy-harvesting system (fabricated on low-cost FR4) capable of harvesting from all surrounding ultrahigh-frequency (UHF) TV and FM towers in all UHF-TV and FM frequencies simultaneously to perpetually power a wireless sensor node. The system achieves $-$ 10 dB matching across the entire frequency bands. The UHF-TV portion harvested as much as 231 $\mu$ W (885 $\mu$ W for FM). The alignment-free, channel-agnostic nature demonstrates potential for ambient RF harvesting's adaption by users outside of the RF community who are not expected to be familiar with antenna alignment and frequency selection.

The near-field ultrahigh-frequency (UHF) quadruple-loop antenna (QLA) with uniform field distribution for item-level tagging is proposed. The proposed antenna consists of quadruple fan-shaped small loops and the middle feeding lines of each loop located at the top and bottom of the substrate using vias. The currents flowing through feeding lines are cancelled due to opposite directional currents (ODCs), and the proposed QLA operates as one large loop electrically. From this configuration, the proposed antenna achieves more uniform field distribution and a precise interrogation zone than conventional loop antennas. Compared to the conventional loop antennas with different sizes, the proposed antenna using the uniform field distribution achieves a interrogation zone of 40 × 40 mm $^2$ at up to approximately 50 mm.

In this article, we propose a kW-level 2.45-GHz microwave applicator for improving heating uniformity. In a conventional microwave applicator, the heating material has low heating uniformity due to various hot and cold spots caused by multiple reflections in the cavity. We propose a power-controlled microwave applicator with multiple slotted waveguides to reduce the hot and cold spots and improve the heating uniformity in the microwave heating process. The proposed microwave applicator consists of three waveguides. Each waveguide consists of longitudinal or transversal slots. To improve heating uniformity in the proposed applicator, we used the power switching method. The input power applied to each waveguide is optimized according to the peak magnitude of the electric field of each waveguide. Conclusively, compared with the conventional microwave applicator, the proposed power-controlled microwave applicator with multiple slotted waveguides improves the heating uniformity up to approximately 67%.

In this paper, a lightweight printed dipole antenna array with 3 × 2 beamforming network for wide unmanned aerial vehicle (UAV) communication coverage is presented. The proposed antenna consists of an upper substrate, a lower substrate, and two supports with a microstrip feeding. The upper substrate has a two-element printed dipole antenna array, and the lower substrate includes a beamforming feeding circuit and a ground plane as a reflector of the proposed antenna array for gain improvement. For wide beam coverage, the proposed feeding network consists of three RF switches, one Wilkinson power divider, and one 90° hybrid coupler, and generates the wide beam using one broadside beam and two end-fire beams. Measured impedance bandwidth, peak gain, and half-power beamwidth (HPBW) of the proposed array operated from 5.03 to 5.15 GHz are approximately 2 GHz, 4.3 dBi, and 155°, respectively.

Unlike conventional energy harvesters that are tuned to individual frequencies and are directional, the proposed wideband (23% fractional bandwidth), omnidirectional system harvests from all FM towers in vicinity. Hence, it does not require each sensor node to be carefully aligned to any one source and makes itself suited for mass-deployment applications such as precision agriculture and structural health monitoring. It harvests as much as 923 $\mu \text{W}$ on a rooftop at 1.54 km from an FM tower while retaining omnidirectionality partly thanks to the proposed antenna, which has a wider bandwidth and a higher measured gain (2.0 dBi) than the commercial reference wideband antenna. It achieves competitive efficiency (56%) and sensitivity (−17 dBm) while retaining wideband operation rather than being specifically optimized to individual frequencies. The system (fabricated on low-cost FR4) harvested outside ambient FM energy indoors at the same 1.54-km location to power a wireless sensor node without needing to shut down periodically.

For position detection of moving vehicles using a wireless passive sensor placed in the traveling direction, a wireless power and data transfer (WPDT) system for supplying power to the sensor is required. Particularly, in the case of a high-speed vehicle with a compact sensor environment that is convenient for installation on railways or roadways, it is difficult to operate the sensor properly due to charging time and range limitations caused by the compact sensor size. In this paper, to improve a working zone of the compact sensor, this work presents a longitudinally misalignment-insensitive dual-band WPDT system with an extended working zone. The proposed system utilizes dual transmitting and receiving coils operating at different frequencies for achieving high isolation between the power and data links, which consists of a distributed antenna array with a gap between antenna elements for wireless power transfer at 27.1 MHz and an extended rectangular loop for data communications at 4.23 MHz. It achieves an extended working zone of approximately 112% at 0.25 m distance in comparison with a conventional system with dual square coils and achieves uniform received signals within a misalignment (up to 0.53 m).

For improving transfusion safety, a smart blood bag management system using a load-integrated U-shaped near-field antenna (LUNA) array is proposed in this paper. The proposed system consists of four LUNAs for ID sensing with blood information and a switching circuit for the sensing of blood bag localization. The LUNA, which is well impedance-matched within the universal ultrahigh-frequency radio frequency identification band, operates in the near-field region for precise localization, and includes a lumped Lattice-type $LC$ -balun which is exploited to cancel out currents through the ground plane of the LUNA and to obtain opposite directional currents in order to reinforce the magnetic field between two microstrip lines in the LUNA. Using a single-pole four-throw switching circuit, a centimeter-level precise localization of blood bags can be achieved. The proposed system can be used to prevent the mishandling of blood transfusions and to manage blood bags remotely and effectively.

A near-field kandonian loop antenna with small loop array and opposite directional current (ODC) for using ultra high frequency (UHF) radio frequency identification (RFID) system is proposed. The proposed antenna is constructed by array four loop antennas smaller than the wavelength of the operating frequency. The proposed antenna expands the interrogation zone at near-field and has a uniform field distribution because each straight line at the top and bottom of the substrate in the small loop utilizes ODC to canceling current and form one large loop electrically. In addition, the proposed antenna has a lower E-field compared to the conventional single loop, which prevents detection of adjacent tags outside the interrogation zone. The proposed antenna has a maximum read range of 48 mm and the detailed characteristics of the proposed antenna are verified by comparing the simulation and measurement results.

This paper proposes a novel beam reconfigurable antenna for unmanned aerial vehicle (UAV), in which beam is reconfigured by controlling Horizontal Parasitic Element Reflector (HPER) arranged around monopole antenna which operates at unmanned aerial frequency (5030–5150 MHz). The proposed method consists of monopole antenna at axis of circular substrate with distributed HPER in the form of bow-tie with pin diode in between which connects both arms. The pin diode that bonded to the center of the HPER used to control the operation of each HPER according to the ON-state and OFF-state of the pin diode. The antenna has directivity elevation in eight directions of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° through the control of HPER using pin diodes. In this method the antenna gains has 4.9 dBi during ON-state of pin diode with efficiency of 100% respectively. This designed antenna applied to UAV with features lightweight and weight balance is centered, simple structure without any complicated equipment such as converter, amplifier, phase shifter, etc and detection applications that require radio convergence.

In this paper, a near-field ultrahigh-frequency radio frequency identification (RFID) system, which has cm-level 2-D positioning precision, is proposed. The system consists of a grid-shaped microstrip traveling wave antenna (TWA) and four-port switched differential feeding networks. To selectively form tag-read sections, opposite directional currents (ODCs) are used. To introduce a microstrip TWA for cm-level 2-D positioning, the influence of $H_{z}$ fields in microstrip TWAs is theoretically analyzed. In addition, to utilize field reinforcement and achieve precise 2-D localization, a grid-shaped microstrip TWA with four-port selective switched differential feeding networks is proposed and investigated. The proposed antenna and feeding network were fabricated on FR-4 substrates. The simulated and measured results demonstrate that precise 2-D tag positioning is achieved using the proposed system utilizing ODC along two selected adjacent microstrip lines in the TWA.

In this paper, a miniaturised multi-beam-controlled circular eight-port beamforming network for long-range ultra-high-frequency radio-frequency identification (UHF RFID) hemispheric beam-coverage systems (e.g. unmanned aircraft systems) is proposed. For multi-beam control and compact implementation, the proposed eight-port feeding network consists of an integrated beam-control block with a two-stage RF switch block, 12 quadrature hybrid couplers, and 12 90° phase shifters, and was designed and fabricated on a circular three-layer 1.2 mm FR-4 substrate. The diameter of the fabricated network is ~0.47 λ 0 at 915 MHz. The measured maximum insertion loss, and amplitude and phase imbalances of the fabricated network at the authorised UHF RFID frequency band (902-928 MHz) are ~4.5 dB, ± 1.3 dB, and ± 17.5°, respectively. An eight-element dipole antenna array with the proposed feeding network shows feasibility of hemispheric beam coverage by generating multiple beams simultaneously regarding port controls. Beam coverages, where the simulated realised gain is higher than 3 dBi, are ~180° and 130° at φ = 90 and 0°, respectively.

For homogeneous microwave heating in a microwave cavity with multiple 2.45 GHz microwave generators, power-controlled phase-shifting mode is proposed in this Letter. The proposed microwave heating system consists of a multimode microwave cavity in which dielectric materials are placed to be heated, four phase-shifting WR-340 waveguides for different phase excitation, four 1 kW magnetrons that produce microwave power at 2.45 GHz, and a power supply with a system controller for the magnetron output power controls. Using the proposed power-controlled phase-shifting mode, uniform heating distribution is achieved by reducing the hot and cold spots in the microwave cavity. The proposed experiments demonstrated that in comparison to a conventional mode with simultaneous multiple inputs, the proposed mode can achieve an improved heating uniformity of 64.4 .

A quadruple-polarization reconfigurable feeding network for an unmanned aerial vehicle (UAV) RF sensing antenna operating at 915 MHz is presented. It consists of one single-pole four-throw (SP4T) switch, one 90° hybrid coupler, two 180° hybrid couplers, and two single-pole double-throw (SPDT) switches. By controlling the SP4T and SPDT switches, quadruple polarizations with two linear polarizations (vertical and horizontal) and two circular polarizations (right-hand and left-hand) were obtained. The proposed reconfigurable feeding network with quadruple polarization modes in the 902–928-MHz range has an insertion loss of approximately 2.5 dB including switch loss, and it achieves amplitude and phase variations of up to approximately 0.5 dB without divided power or switch loss, and 3°, respectively. Using the proposed feeding network, a circular low-profile UAV RF sensing antenna with quadruple polarizations was designed. Its electrical size, 10-dB impedance bandwidths, and a peak gain are approximately $0.57\lambda _{0} \times 0.57\lambda _{0} \times 0.08\lambda _{0}$ at 915 MHz, 16%, and 6 dBi(c), respectively.

The design of a half-elliptic hoof antenna for a femto-cell network in a multi-input multioutput system is proposed. The proposed half-elliptic hoof antenna incorporates half-elliptic surfaces, and has multiresonance frequencies in its TM modes. The half-elliptic design of the proposed antenna resonates with two main current paths, and the resonant frequency of each mode can be calculated using the Mathieu function. Moreover, an additional resonator is inserted between the half-elliptic patch and a ground to obtain additional resonance frequency and a wider bandwidth on the high band. The proposed antenna covers the frequency bands from 880 to 960 MHz and from 1710 to 2170 MHz for Global System for Mobile Communications (GSM)/Digital Cellular System (DCS)/Personal Communications Service (PCS)/International Mobile Telecommunications (IMT) with a peak gain of 6.8 dBi. To validate the design of the proposed antenna, the analysis of the antenna using the simulated and measured results is presented and discussed.

This letter presents a printed fan-shaped meandered dipole antenna with mutual-coupled dual resonance for enhancing impedance bandwidth in a compact antenna size. The proposed antenna consists of a printed dipole antenna mutually coupled to an antenna parasitic element of a different size for dual resonance and microstrip feeding. By applying a fan-shaped meander-line structure, the proposed antenna occupies a low-profile miniaturized electrical size of 0.21 $\lambda _0\times 0.21\lambda _0\times 0.08\lambda _0$ at 920 MHz. The proposed antenna, which was implemented and fabricated on an FR-4 substrate, achieved a wide 10 dB impedance bandwidth of approximately 12% and a peak gain of 3.2 dBi. Depending on the antenna length at the two resonant frequencies, the impedance bandwidth in the proposed antenna can be controlled.