This letter presents a new directional dual-band slotted trapezoidal inverted-F antenna (IFA) for indoor Wireless Local Area Network (WLAN) applications. The dual-band performance can be obtained by tuning the lengths of the inner symmetrical trapezoidal slots and the outer trapezoidal arms in a nearly independent manner. The measured results show that the proposed antenna can provide two separate impedance bandwidths (return loss better than 10 dB) around 180 MHz and 750 MHz for 2.4/5.1-5.8GHz WLAN bands, respectively. Good radiation performance and roughly constant in-band antenna directivities are also observed.

A ternary composite, based on the M-type hexagonal barium ferrite, BaFe₁₂O₁₉, conducting polymer, polyaniline (PANI), carbon allotrope, and multi-walled carbon nanotube (MWCNT), was prepared through a facile in-situ polymerization process. The structural properties of the synthesized composite were characterized through XRD and FESEM analysis. PANI particles were found to be able to coat on BaFe₁₂O₁₉ and MWCNT surfaces. The increased MWCNT wt% loading within the composite resulted in the increase of the electrical conductivity with values as high as 2.0320 S/m for sample PBM5 (25wt% MWCNT). The composite inherited the salient properties of its respective components to achieve optimum values of shielding effectiveness. The highest value of SE_A recorded was 42.37 dB at 17.60 GHz. The significantly larger magnitudes of SE_A than SE_R suggest that the mechanism of shielding for all synthesized composites are through absorption.

Hybrid pattern recognition is used to predict the types of insulation materials used inside wall systems of building envelopes. The hybrid pattern recognition features vector is built using the characteristics of UWB signals. UWB signals can penetrate objects, resulting in scattered signals based on the object's dielectric properties. The object's dielectric properties and structure have a signature within the scattered signals. This paper demonstrates that proper hybrid pattern recognition can be used to experimentally detect the existence and the type of insulation material inside wall systems with a high success rate.

By reductio ad absurdum, we show that a perfect power combiner of single-mode waveguides is impossible for incoherent input waves of the same frequency and same polarization as it is against the law of conservation of energy. The inevitable 3 dB loss of a three-port power combiner is explained physically. An incoherent power combiner of nearly 100% efficiency can be realized only if the two input fields have different wavelengths, have different polarizations, or are of orthogonal modes.

This paper analyzes the extremely low frequency electromagnetic wave excited by a horizontal electric dipole immersed in the sea. Analytical solutions in the air from HED underwater are deduced using a three-layer model. The effect of the sea-air interface is studied along two perpendicular directions. The electric field is inversely proportional to the square of r while the magnetic field is inversely proportional to the cube of r along the interface. By decomposing the total response into direct, up-going and down-going components, contributions of each component are discussed, indicating that interference cancellation effect occurs among the arrival electromagnetic signals from multi-paths at specific offsets and frequencies.

This paper proposes a backscattering communication technique based on modulated frequency selective surfaces (FSS) for wearable applications. The FSS is composed of dipoles loaded with varactor diodes to modulate the backscatter response, in order to separate it from the clutter. The paper describes the effect in the transponder response according to the number of dipoles, the separation between them and the effect produced when FSS is placed on-body. An analysis based on simulations of several cases and experimental results is provided.

We present a novel type of pixel antennas that are suitable for fabrication in low-cost setups based on commercial inkjet printers. The proposed antennas involve hexagonal cells that can be removed in accordance with rigorous optimizations via genetic algorithms that are supported by full-wave solutions with the multilevel fast multipole algorithm. Optimal pixel configurations are determined precisely for desired electrical characteristics, such as low power-reflection values at required frequencies. Measurements on fabricated samples demonstrate the effectiveness of the optimizations, as well as the favorable characteristics of the hexagonal-cell pixel antennas that fully benefit from the advantages of low-cost inkjet printing.

A miniaturized ultra-wideband (UWB) quasi-self-complementary antenna (QSCA) with band-rejection characteristic is presented and discussed. With the tapered microstrip-fed line and flower-shaped QSC structure, a lower cut-in frequency (3.18 GHz) is obtained with a compact size (9x17.5x1 mm³). By embedding a five-star-shaped ring resonator under the radiation patch, a band-notched feature is achieved. The measured impedance bandwidth below 2:1 VSWR is from 3.18 GHz to 13.4 GHz with a rejection band from 5.45 GHz to 5.95 GHz, and the simulated and measured results of the proposed antenna are in good agreement. Thus, the antenna is suitable to be integrated with the space-limited wireless system without electromagnetic interference at the WLAN (5.47-5.825 GHz) band.

The moving chest wall imparts a delay modulation onto the reflected IR-UWB radar signal, making the radar return a nonlinear function of chest wall displacement. Existing theoretical spectral models of the IR-UWB radar reflections from the human chest wall have restrictive assumptions that preclude realistic modeling of chest wall displacement and assume an aliased version of the radar signal. This paper presents novel theoretical analysis of the un-aliased spectrum, without the restrictive assumptions. Potential applications not specifically treated in this paper, but illustrative of the novelty and broader scope of the presented analysis, include heart-induced displacements that are realistically more bursty in nature and breathing-induced displacements consistent with, for example, non-unity inspiration-to-expiration ratios characteristic of asthma; neither of these could be analyzed using previous models. As well known, the un-aliased spectrum cannot generally be recovered from the aliased spectrum. In particular, the paper shows that the clusters of the non-aliased spectrum are not just scaled versions of each other; rather they have complex variations that if measurable, could enable estimation of parameters such as displacement amplitude; such variations are not apparent in the existing aliased spectrum model, which has just one cluster. This paper analyzes the degree to which the aliased model di↵ers from the non-aliased model. The paper also addresses some practical aspects of the spectral model, such as the number of significant components in a spectral cluster and computational complexity of the theoretical model.

In this work, four types of random arrays are compared. In particular, the mean and variance of the array factor are derived. This provides a partial statistical characterisation that allows pointing out some important aspects of random arrays and link them to the number of elements and array aperture. In the absence of a simple and effective analytical apparatus, here great importance is also given to the experimental aspect, especially as far as the side-lobe level is concerned. To this end, Monte Carlo simulations are run to experimentally build the side-lobe distribution as a function of the number of radiators and the average spacing between two adjacent radiators. The obtained results show that random arrays where one is free to impose constraints on the minimum spacing between adjacent elements can obtain performance analogous to those achievable by other schemes which do not put such constraints. However, the former are preferable because they are able to zero the probability that adjacent radiators are separated with less than a certain minimum distance and this allows the mitigation of mutual coupling effects.

We present a method to improve the resolution of available hyperlenses in the literature. In this method, we combine the operation of hyperlens with the recently proposed plasmon injection scheme for loss compensation in metamaterials. Image of an object, which is otherwise not resolvable by the hyperlens alone, was reconstructed up to the minimum feature size of one seventh of the free-space wavelength.

The development of modern communication devices for the latest technologies such as 5G has brought the millimeter wave technology into the spotlight because it offers higher data rates and bandwidth. Since highly directional transmissions are necessary for communication in these frequencies due to high path loss and atmospheric absorption, the use of adaptive antennas is inevitable. Rotman lenses have long been used as analog beam forming networks to support linear array antennas for electronic scanning. Their broad bandwidth and planar structure make them ideal for a variety of applications. However, their overall dimensions can be prohibitive especially for large scan angles. In this paper, we propose a few compact configurations that reduce the overall dimensions of Rotman lens as much as 50% without degrading its performance.

A 400 GHz monolithic leaky wave antenna (LWA) is presented in this paper. The proposed LWA, constructed by the unit cell with multiple structural parameters, is regarded as the on-chip microstrip with perforation on the signal trace and the ground plane. A hybrid full-wave eigenvalue method theoretically extracts the complex propagation constants of first higher-order mode (EH1) of the perforated microstrip to improve the unit cell design. The extracted results also assist in realizing the differential feeding network to excite the leaky mode of the proposed antenna in high efficiency. A 400 GHz LWA prototype is designed and fabricated in CMOS 0.13 μm 1P8M process. The on-chip experiments show the measured input return loss including the effects of the contact pad lower than 10 dB from 380 GHz to 420 GHz. The measured antenna gain is higher than 0.8 dBi and has a maximum value of 1.3 dBi at 400 GHz. From 390 GHz to 405 GHz, the measured main beam is at 33° to 43° from broadside, indicating good agreement with the calculated results.

In this work, the dosimetry for two resonant modes of a highly resonant wireless power transfer (HR-WPT) system is investigated, and the results are compared. The physical mechanism of the two resonant modes, which occur when the two transmitting and receiving resonators are extremely close to one another, is presented with the simulated results and the equivalent circuit models for the HR-WPT system. The difference between the two resonant modes for the specific absorption rate induced in the head model is discussed by comparing the electromagnetic fields for each mode. Furthermore, the dosimetry for the four-coil HR-WPT system is also investigated under the conditions of a single resonant mode and two resonant modes. The specific absorption rates (SARs) are calculated with head-size and body-size simplified human models at various distances from the WPT system and in each mode. The electric and magnetic fields of the odd mode show stronger distribution than those of the even mode in the area near to the WPT system, while the opposite results are found in the area farther away.

Long-range wireless power transmission (WPT) is implemented with the phased array transmitter technology, which has been extensively applied in the field of the radar systems. The cost of a conventional phased array transmitter module scales up in proportion to the number of antenna elements, as the massive number of transmit channels results in the increasing complexity of hardware and feeding antenna elements. Besides, the conventional phase-shifting transmitter architecture has lower DC to RF power conversion efficiency due to the insertion loss of power combining network at microwave frequency. In this paper, the concept of spatial power combining transmitter is utilized, and the upconversion circuit is greatly simplified to an injection locked oscillator. Our WPT system is implemented with the technology of oscillator array antenna at 2.4 GHz, which converts DC power to RF power and radiates into the air directly. The feedback voltage controlled oscillator (VCO) is implemented as the microwave source using a off-the-shelf bandpass filter, and the external signal is injected to the oscillator via a microstrip coupler. {The oscillator core shows the DC-to-RF conversion efficiency of 45.87% with the injected power of 0 dBm at 2.4 GHz. Then the digital phase shifter is used to phase shifting the injected signal to extend the beam coverage. From the link budget analysis, the overall DC-to-DC efficiency of our highly-integrated system shows 1.5 times (0.22%) of the conventional phased array (0.15%) when the separation between the transmit array and the receive horn antenna is 1.2 meter. Therefore, as an modularized array, the proposed system demonstrates the promising capability of upscaling to an efficient massive array with greatly reduced bill-of-materials (BOM).

The long-term meteorological data of Era-interim from 1979 to 2014 covering the observation at 00, 06, 12 and 18 have been used to derive vertical refractivity gradient in the lowest 100. Diurnal, seasonal and annual variations of refractivity gradient and its component are analyzed for coastal and plateau areas of Nigeria. The relative frequency of the occurrence of gradient below -100 N-units/km used in clear air propagation study is derived from cumulative distribution of the gradient. Occurrence of anomalous propagation in each region is also estimated. The result will help in the effective wireless link planning and design.

This paper presents the analytical design and numerical performance evaluation of novel V-band millimetre-wave (mm-wave) beamforming networks (BFNs), based on the Rotman lens array feeding concept. The devices are intended for operation in the unlicensed 60-GHz frequency band. The primary objective of this work is to study the feasibility of designing flexible V-band beamformers, based on liquid-crystal polymer (LCP) substrates. The planar Rotman lens device has been initially developed, and the output performances, in terms of the scattering parameters and accuracy, have been analysed. This is further continued with the detailed designs of the Rotman lens BFNs based on the four different proposed flexural cases, namely the concave-axial bending, the convex-axial bending, the concave-circumferential bending, and the convex-circumferential bending. Each of the flexures has been analysed, and the performance in terms of the surface currents and phase distributions, as the primary functionality indicators, has been presented. The presented flexible beamformers exhibit significant characteristics to be potentially employed as low-cost and efficient units of the mm-wave transceivers with the in-built beam steering capabilities for the conformal wireless subsystems.

A beam-reconfigurable printed antenna on an Artificial Magnetic Conductor (AMC) is proposed for navigation and radiolocation applications at a frequency of 9.41 GHz. The AMC is formed based on a periodic Jerusalem cross shaped slot structure and is located in between two substrate layers, close to the radiator. The AMC plane has a bandwidth of 1.95 GHz around the targeted frequency of 9.41 GHz. By integrating micro-electro-mechanical system (MEMS) switches on the folded patches in combination with parasitic elements, a beam steering capability of up to ±58° is achieved with a rear full ground plane. This eliminates the need for a mechanical steering system, which is traditional in the applications targeted. The antenna achieves a high gain of 8.08 dB and 90% efficiency. A good agreement between simulated and measured results is obtained.

A topology, equations and design methodology for complex impedance-transforming branch-line hybrid couplers are presented. This method also allows the realization of real impedance-transforming to higher impedances. Limitations for real, imaginary and complex impedances are discussed. Test results are shown for a 3 dB 50 to 450 Ω hybrid coupler, at a 2 GHz center frequency, with a 21% bandwidth, an amplitude balance of 4.35±1 dB and a phase balance of 92.16°±8.8°. To showcase the complex impedance scenario, two 3 dB 50 Ω to 70-200j Ω are measured at a 2 GHz center frequency. One of these couplers uses a technique for reducing the chip size, yielding a 22.5% bandwith, 4-0.9 dB amplitude balance and 93.22°-6.74° phase balance, while acomplishing a 25% size reduction.

In this paper, a compact circularly polarized antenna based on a resonant quadrifilar spiral structure for the application of UHF RFID handheld reader is proposed and demonstrated experimentally. To reduce antenna size and improve impedance matching, the original resonant arms are revised by bending inverted-F structures and printing them on dielectric substrate, and the four arms are fed by a four-way phase shift network. Such an antenna indicates stable circular polarization performance and wide beam-width. The gain bandwidth (>2 dBi) can cover the frequency band from 902 MHz to 928 MHz, which is suitable for most of the popular UHF RFID system in the world. Moreover, the 1×4 array and 2×2 array based on previously demonstrated antenna unit are numerically investigated. The array performances, including the gain, beam scanning and low side-lobe are discussed.