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A magnetodielectric substrate is firstly proposed for implantable antennas in medical implant communication service (MICS) band. Ba 3 Co 2 Fe 24 O 41 (Co 2 Z), Z-type hexaferrite flakes synthesized by molten-salt method were incorporated with a polymer matrix, having a real permeability of 2.88 and a magnetic loss of 0.029 at 402 MHz. A spiral antenna with the magnetodielectric substrate has a bandwidth 70% and 50% broader than that with a commercial dielectric substrate, Rogers 3210, in a 2/3-phantom model and a multi-layered body model, respectively. The band broadening retains the bandwidth to be overlapped after implant positions change, leading to an enhancement in insensitivity to the implant position.

A broadband radar absorbing structure (RAS) covering both X and Ku bands (8.2–18.0 GHz) was designed by integrating an inductive frequency-selective carbon fiber fabric composite (FSFC) and multiwalled carbon nanotube (MWCNT)-loaded glass fabrics which can modulate EMI characteristics of the FSFC. All the layers of the structure consisted of fiber-reinforced fabrics, and thus general composite fabrication processes can be easily applied. An existing scaling law based on the percolation theory was modified to replicate permittivity of the MWCNT-loaded fabrics. Coefficients and exponents of the power law were expressed by frequency and MWCNT concentration. The modified model provides a good description of the dielectric property of MWCNT fabric composites, and thus paves the way for parametric evaluation of reflection loss of the FSFC-embedded double-layered RAS regarding the permittivity of the lossy dielectric composites, as well as thickness of each layer and the total thickness of the RAS. The reflection loss of the RAS, drawn from the parametric study, can cover 10 dB in the whole X and Ku bands with two separated absorption peaks, while its thickness was 3.63 mm only.

In this paper, we propose a novel method realizing multi-input–multi-output (MIMO) transmission in near-field magnetic induction (NFMI) communication for increasing channel capacity where limited capacity is a major bottleneck problem in magnetic communication systems. Since conventional magnetic communication systems using the same antenna patterns cannot easily implement MIMO transmission due to strong crosstalk between transmitters, we propose heterogeneous antenna arrays with multipole antennas, enabling crosstalk cancellation. We confirm the crosstalk cancellation of the proposed antenna array through numerical simulations and experiments, and verify the capacity enhancement of the proposed NFMI communication system over conventional NFMI communication schemes.

Among electromagnetic compatibility considerations, radiated emissions constitute one of the areas of highest concern because wireless power and communications systems operate by emitting magnetic fields. In this letter, the radiated field of the antiparallel loop is theoretically analyzed and experimentally verified at distances in the near- and far-field regions. A reduced magnetic field strength of approximately 6 dB is obtained with the proposed antiparallel loop when compared to a conventional loop at the measuring distance up to 10 m. Furthermore, since portable devices with an NFC function require the configuration of simple structures for wireless charging, the proposed design concept for antiparallel resonant loops offers considerable benefits as it suppresses the generation of electromagnetic interference noise.

In this paper, an analysis of the effect of time-variant reflected impedance and its detection method on wireless power transfer(WPT) systems are presented. The reflected resistance at WPT systems is very important parameter as it indicates how well matched antenna is and will exhibit high efficiency. Proposed detection method is based on transmitter current variation analysis with respect to frequency sweep. Using the proposed design method, a wireless power transfer system operating at the frequency of 125 kHz, is design and detect reflected impedance variation. The proposed design method provides good agreements between measured and simulated results. Therefore, The proposed detecting method provides a nonintrusive method to detect harmful object in WPT system.

Using a current-controlled loop with a loaded capacitance, we experimentally demonstrated distance-insensitive wireless power transfer (WPT) and near-field communication (NFC) without additional tuning network and algorithms. The proposed loop can achieve the uniform mutual inductance within the operating distance by controlling the ratio of the current flowing through the forward and reverse loops according to the loaded capacitance. By reducing the impedance mismatch within the operating distance ranging from 0 to 7 cm, the proposed loop can provide the transfer efficiency over approximately 60% for WPT and a stable channel bandwidth for NFC operating modes. In particular, when the receiving antenna is close proximity to the transmitting antenna, the transfer efficiency of the proposed loop is up to nearly six times higher than that of conventional loop.

In this letter, a frequency selective loop isolator using dual resonance for a mobile wireless charging system is presented. Resonance of the proposed frequency selective loop isolates a transmitting loop from a receiving loop at one frequency whereas it transfers wireless power between them at the second harmonic frequency. Simple arrangement of lumped elements changes operation of the proposed frequency selective loop to a series resonator at 6.78 MHz and a parallel resonator at 13.56 MHz. Experimental results show the difference in the transmission coefficient between with/without the frequency selective loop is approximately 21 dB at 6.78 MHz whereas it is about 2 dB at 13.56 MHz, without degradation of efficiency. Moreover, this approach suggests how to transfer wireless power based on frequency selection.

This study verifies close proximity effects of metallic environments on the antiparallel resonant coil for near-field powering based on the theoretical analysis and experimental measurements. Compared to the conventional coil with a forward loop, frequency shifting of the antiparallel resonant coil which consists of forward and reverse loops with opposite-direction currents is unchanged regardless of the proximity of metallic plates. Furthermore, highly efficient near-field powering for metallic objects can be achieved with the antiparallel resonant coil because of the added magnetic field caused by the image current of the metallic plates.

In this communication, a compact dual-band quadruple inverted-F/L antenna (QIFLA), with right-hand circular polarization (RHCP) for global positioning system (GPS) L1/L2 band, is presented. The proposed antenna is composed of four spiral-shaped dual-band antennas. For good radiation efficiency at two nearby frequencies, a branched dual resonant inverted-F/L structure is employed and analyzed. The size of the proposed dual-band QIFLA is 35 $\, \times \,$ 35 $\, \times \,$ 10 mm $^{{{3}}}$ and experimental results show a peak gain of 0.5/2 dBic and the axial ratio under 1.5 dB in the two target frequencies.

This paper describes the development and performance of a 2 by 4 element suspended microstrip patch antenna array with linear polarization. The proposed structure with a new geometrical composition of entire array possesses the advantages of being wide bandwidth, high gain, precise side lobe level control and low cross-polarization level. The measured antenna has the peak gain 14.12 dBi and the cross-polarization is lower than −16 dBi within the impedance bandwidth. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:825–829, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27423

A wideband circularly polarized pinwheel-shaped planar monopole antenna fed by a wideband feeding network is presented in this paper. The proposed antenna is formed by four wideband planar monopole antenna elements with aquadruple feeding network in order to improve the performance of circular polarization. Additionally, the antenna, which is introduced here, has a high gain in the z axis direction because of its folded antenna structure. The attractive characteristics of the proposed antenna are the wide impedance bandwidth of 87.3 % (1 GHz to 2.55 GHz), the 3 dB axial ratio (AR) bandwidth of 92.3 % (1.05 GHz to 2.85 GHz), and the maximum gain within the 3 dB AR bandwidth is about 8.24 dBic.

In this paper, new beam-forming array antenna is proposed. The proposed beam-forming array antenna has control ability for beam-direction/width by employing low loss reconfigurable power divide and three-dimensional array structure. The reconfigurable power divider is key idea in the proposed antenna, because it has reconfigurable RF power distribution ability to each antenna. And, for research and verification of the proposed antenna, 3-dimensional beam-forming array antenna is implemented, and the experimental results show that the proposed antenna has various radiation modes from 1:1 to 1:N by adjusting RF power distribution.

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power e-ciency and reading range at speciflc distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power e-ciency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the flxed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near fleld communication (NFC), radio frequency identiflcation (RFID), or wireless power transfer (WPT) devices.

The analysis of an antenna mutual coupling is a signiflcant issue for designing the wireless communication system especially includesan array mutual coupling problem. The accurate analysis of the mutual coupling between antennas is needed. Accordingly, several methods for the mutual impedance calculation of dipoles have been studied in cases of coplanar-skew and nonplanar-skew. This paper proposes an exact and simple method for analyzing the mutual impedance between two arbitrarily located and slanted dipoles using the modifled induced EMF method; their expressions and the exact analytic solution. The proposed formula and their closed-form solutions are verifled by numerical solution using HFSS and give good agreement.

A wideband circular polarized planar monopole antenna array (PMAA) that employs dual band-notched characteristics is presented in this paper. The proposed antenna array is formed by four pinwheel-shaped folded planar monopole antennas (PMAs) in order to improve the performance of circular polarization and high directivity. Also, it achieves low-proflle, small-sized structure. The attractive characteristics of the proposed PMAA are a wide impedance bandwidth of 87.3% (1GHz to 2.55GHz), the 3dB axial-ratio (AR) bandwidth of 92.3% (1.05GHz to 2.85GHz) excluding dual notch bands, the total bandwidth of 35% (1.8GHz to 2.55GHz), and the maximum gain of 8.24dBic within the total bandwidh. Moreover, in order to generate dual band-notched characteristics in a circular polarized antenna, a folded PMAA with multiple U radiators and inverted W slots is proposed.

A new balanced Doppler radar front-end architecture with Tx leakage canceller for antenna impedance variation and antenna mutual coupling is proposed. Consisting of two quadrature hybrids, two ring hybrids and 4-port feed antenna system, the proposed balanced structure achieves high transmit/receive (Tx/Rx) isolation stable to antenna impedance variation and antenna mutual coupling. The proposed 4-port feed antenna is configured by dual fed 2 × 1 patch array having 6.97 dBi and 5.65 dBi of measured Tx and Rx peak gain, respectively. In addition, the proposed architecture undergoes no power loss in both transmit and receive paths, and obtains the measured Tx/Rx isolation of more than 45 dB stable at 24 GHz regardless of the load variation. The proposed architecture that can determine the speed as low as 0.5 mm/s (0.078 Hz Doppler shift) is theoretically and experimentally analyzed for high isolation despite of antenna mismatch.

In this article, a novel six-port modulator is proposed and experimentally verified.The six-port modulator circuit is realized by using power dividers/combiners and polyphase networks for the first time. A prototype operating in 2.4-GHz instruments, scientifice and measurement (ISM) band has been fabricated and experimentally verified, to show its performance as vector modulator. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2321–2324, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26288

This letter presents a simple and innovative method for designing and optimizing two circularly polarized printed quadrifilar antennas (PQAs). The PQAs are operated at UHF RFID (902-908 MHz) and GPS (1575 MHz) and intended for use at a portable terminal. This new antenna system comprises two PQAs concentrically arranged, but electrically isolated. Each PQA comprises four inverted-F monopoles arranged orthogonally and excited with a phase difference of 90°.

Fabrics that allow selected microwave frequencies to pass through, called frequency selective fabric composites (FSFCs), were fabricated by weaving carbon fibers and dielectric fibers in periodic patterns. Design parameters affecting the electromagnetic characteristics (EM) of the FSFCs were widely discussed with respect to electrical conductivity of carbon fibers, the type of dielectric fiber and matrix, and weaving patterns. Transmission coefficients of square FSFCs with the aperture sizes of 10 mm and 20 mm were investigated considering electrical conductivity of carbon rovings, fiber undulation, and aperture-to-cell ratio. Compared with metallic frequency selective surfaces (FSSs), lower electrical conductivity of the carbon rovings caused a partial transmission near resonance frequency. The fiber undulation made little effect on the electromagnetic property of FSFCs. In addition, as the aperture-to-cell ratio decreased, the transmission of microwaves through FSFCs substantially decreased around resonance frequencies. The distinct difference in the microwave property of FSFC and FSS near resonance frequency shows that FSFCs can be new candidates as impedance modifier for microwave devices, such as microwave absorbers.

Presented is a new compact dual-band quadruple planar inverted-F antenna (QPIFA) radiating right-hand circular polarisation characteristics. The size of the proposed dual-band QPIFA is 35 × 35 × 10 mm 3 and the experimental results exhibit a peak gain of 2.5/4.5 dBic and an axial ratio under 1.5 dB in two target frequencies.

This letter presents a reconfigurable 1 × 4 power divider operated at 2.45 GHz. The proposed circuit has four power transmission states and is designed mathematically to satisfy matching conditions for each state. The experimental results for the transmission losses for each state are 1.2 dB ~ 1.9 dB while the isolations for non-path ports are greater than 25 dB and the reflection coefficients for each power transmission state are less than -20 dB at the target frequency.

In this letter, a printable chipless tag with electromagnetic code using split ring resonators is proposed. A 4 b chipless tag that can be applied to paper/plastic-based items such as ID cards, tickets, banknotes and security documents is designed. The chipless tag generates distinct electromagnetic characteristics by various combinations of a split ring resonator. Furthermore, a reader system is proposed to digitize electromagnetic characteristics and convert chipless tag to electromagnetic code.

A passive UHF radio frequency identification (RFID) reader antenna with high transmit/receive isolation, which consists of two quadrifilar spiral antennas (QSAs) and the feeding networks, is proposed. The high isolation can be achieved by two concentric, circularly polarized antennas and 4-point feed circuits, which make the same circular polarization. The simulated and experimental results show that the transmit/receive isolation is more than 40 dB and the gains of two QSAs are 1.0 dBi for the inner QSA and 0.7 dBi for the outer QSA at the 910 MHz, respectively.

In this paper, a quadruple linear polarization (LP) and circular polarization (CP) diversity antenna with a reconfigurable coupler is presented. The proposed antenna has two linear (vertical and horizontal) and two circular (right-handed and left-handed) polarizations. In order to implement real-time polarization diversity antenna, the electrical switches are used in the proposed antenna feeding network which is four mode reconfigurable coupler. The measured gains and the axial ratios of the proposed antenna are 5.6 ~ 6 dBi and 0.5 ~ 1.5 dB in four operation modes and two CP modes.

Antenna mutual coupling is a significant issue for the mobile communications system, near field communications system, to improve communication capacity and so on. Therefore, the accurate analysis of the mutual coupling between antennas is very important. Accordingly, calculating the mutual impedance of dipoles has been studied in cases of co- and non-planar skew. This paper proposes an exact and simple method for analyzing the mutual impedance between two arbitrarily located and slanted dipoles using the effective length vector (ELV) and derives its closed form solution as well. The proposed formula is verified by numerical tool and gives good agreement.

A balanced-fed dual inverted-F antenna with reduced human body effects for WLAN applications at 2.45 GHz is presented. In order to reduce the influence by a close proximity or a touch of a human body, the proposed antenna employs an impedance matching using a lumped LC-balun which has the simple and compact structure applying for mobile handsets. The resonant frequency of the proposed antenna is fixed at 2.45 GHz regardless of the close proximity of a human body. By applying for the L-shape ground plane, the proposed antenna has the wide impedance bandwidth of about 150 MHz and the peak realized gain of about 4 dBi.

In this paper, impedance tuning algorithm is proposed. To improve antenna radiation performance, antennas have high radiation efficiency and mismatched efficiency. The mismatched efficiency can be improved by the impedance matching circuit and matching algorithm. The proposed algorithm uses only standing wave ratio (SWR) information. The proposed algorithm is high-speed predicting antenna impedance algorithm. The algorithm running time is less than 25 ms.

This paper presents a dual-frequency (HF and UHF) antenna for handheld radio frequency identification (RFID) reader to embrace the benefits offered by both the UHF and HF RFID systems. In the HF (13.56 MHz) band, a spiral-shaped loop antenna is used and placed at the outmost region of the available space. In the UHF (915 MHz) band, a quadrifilar spiral antenna (QSA) is used because it is electrically small and features a low frequency shift by platform size and is placed in the center of the HF antenna. Measurements revealed that the antenna provides a quality factor of 56.5 in the 13.56 MHz and a gain of 2.5 dBic in the 920 MHz band.

A type of ultra-high frequency (UHF, 840–960MHz) band near-field antenna for RFID applications is proposed. The proposed near-field reader antenna consists of two spiral-shaped transmission lines and lines are parallel to each other. By adjusting the distance between two lines of the reader antenna, the strength of the field between two transmission lines and the recognition distance are able to be controlled. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 150 × 150 × 1 mm. The proposed near-field reader antenna satisfactorily operates in UHF band, and the measurements show that the proposed antenna has bandwidth of about 350MHz and is capable of detecting UHF RFID tags in 11cm distance for 10 dBm incident power.

A novel helical reflector antenna is presented to cover the whole UHF RFID band (860∼960MHz). The proposed antenna has a ground reflector and is composed of two antenna layers which are connected by via to form a helical structure. The total length of the proposed antenna is 1∼1.3 λ to have the higher antenna impedance. And the antenna gain is increased by using a ground reflector. The size of the proposed antenna is 200 × 200 × 35 mm3 similar to commercial RFID patch antenna with a high gain. It satisfies −10dB return loss and 3dB axial ratio in the RFID band. The measured antenna gain is approximately 6.5∼9dBic.

The frequency band for T-DMB (terrestrial digital multimedia broadcasting) system in Korea is assigned to the VHF channel 7~13 (174 MHz~216 MHz) and channel 8 and channel 12 are used in Seoul. The length of the lambda/4 monopole with an infinite ground is about 38 cm to make a resonance at 200 MHz. Generally, meander line, high dielectric constant material and parasitic elements have been used to reduce the large size of a T-DMB antenna. But, as the effective size of an antenna is reduced, the bandwidth is getting narrower. So, these passive small antennas can not cover the wideband of T-DMB. In this work, the wideband active small antenna is proposed. We integrated the lambda/32 (4.75 cm) short monopole with LNA (low noise amplifier) for the mobile application. To obtain the wideband characteristic, we used the dummy antenna, which is the 2-port equivalent circuit of real antenna.

A capacitor-loaded cylindrical resonant coil with parallel connection for high effective wireless power transfer is presented. The characteristics of the proposed resonant coil are verified by the comparisons among the theoretical analysis, simulation results, and experimental measurements. By controlling the current in the capacitor-loaded resonant coil, the non-degraded overall transfer efficiency between the transmitting and receiving resonant coils can be improved up to 43% compared to the cylindrical coil regardless of the locations of the receiving coil at the transfer distance.

A spatially structured resonant coil with uniform magnetic field distribution for wireless power transfer is presented. The characteristics of the proposed resonant coil are verified by the theoretical analysis, simulation results, and experimental measurements. Due to the uniform magnetic field distribution, the overall transfer efficiency between the transmitting and receiving resonant coils can be improved up to 44% compared to the conventional coil regardless of the location of the receiving coil at the transfer distance.