A novel compact and multiband dipole antenna with a planar fractal-inspired configuration is presented. Several series capacitances and a parasitic element are employed as loading. Results show that the loading improves the impedance matching and enables the proposed antenna to radiate at multiple frequency bands. In addition, the proposed loaded dipole antenna offers a high degree of miniaturization in comparing with the unloaded host dipole antenna. The simulated |S₁₁| response of the proposed loaded dipole antenna shows five distinct resonant bands with the center resonant frequencies of 1.52 GHz, 3.62 GHz, 4.6 GHz, 6.9 GHz, and 9.43 GHz. A fabricated prototype has compact dimensions of the 37 mm × 14 mm × 1.6 mm, and exhibits good agreement between the measured and simulated S-parameters.

A low-profile broadband dual-polarized antenna with high isolation and low cross polarization is presented in this letter. The proposed antenna employs two different feeding mechanisms. On one hand, two out-of-phase probes loaded with two small circular patches make the proposed antenna operate in horizontal mode. On the other hand, two pins connecting two eyebrow-shaped patches and the ground form a magnetic loop which enables the proposed antenna to achieve vertical polarization. By elaborately adjusting the feeding structures, measurements demonstrate that the proposed antenna not only achieves 10-dB return loss bandwidths of 49% (1.7-2.8 GHz) and 28% (2-2.65 GHz) for Port 1 and Port 2, respectively, but also maintains a high isolation better than 32 dB over the entire common frequency band. Meanwhile, within the main lobes, the cross polarization levels, both in E-plane and in H-plane, stay lower than -25 dB for Port 1 and -20 dB for Port 2. In addition, the proposed antenna with a profile of 0.13 achieves the maximum gains of 8.4 dBi for horizontal polarization and 8.2 dBi for vertical polarization.

For coherent jammers to wideband linear frequency modulation (LFM) radar, the ratio between jamming energy and signal energy is always constant. To enhance the jamming to signal ratio (JSR), a two-dimensional (2D) discretized coherent noise jamming (2D-DCNJ) method is first proposed in this paper, where the covering area of the noise jamming results in 2D imaging is limited to a certain shape and further discretized to centralize the jamming energy. Moreover, the idea of weighting is applied to 2D-DCNJ to control the distribution of jamming energy, which can present some particular deceptive characteristics. The relationship between jamming results and modulated noise is analyzed, based on which the procedure of generating the jamming signal is detailed, and the JSR performance is compared with the previous ones. Finally, the validity of the proposed method is demonstrated via numerical simulation.

In this article, a compact dual-band bandpass filter (BPF) using coupled open-loop resonators and an embedded center-grounded stepped-impedance resonator (CGSIR) is proposed. This filter operates at 2.1/5.2 GHz for WCDMA/WLAN applications. The first passband is generated by the proposed CGSIR, and the second one is created by the coupled open-loop resonators. Each passband can be controlled independently by adjusting the dimension parameters of corresponding resonators. Five transmission zeros (TZs) are generated due to the 0° feed structure and signal cancellation effects between electric couplings and magnetic couplings, which improve the filter band-to-band isolation level and skirt selectivity significantly. Moreover, the overall circuit size is very compact due to the embedded configuration. The measured filter performances are in good agreement with the simulated ones.

Based on the conventional finite-difference time-domain (FDTD) method, a novel dual-meshed technique is presented to deal with the underwater detection problems applying in low frequency electromagnetic wave. A transformation surface connecting the coarse cell with the fine cell is implemented by applying a total-field scattered-field source (TSS) technique, which is carried out by two-step FDTD simulation. The ratio of a coarse cell size to a fine cell size can be set as an arbitrary integer, such as N=10. Moreover, it is illustrates that non-physical reflection fields from the TSS surface are avoided by introducing the TSS surface. We have derived, in detail, the update equations of fields on grids of the TSS surface. Three cases of dealing with different underwater electromagnetic problems are discussed. Numerical results show that by analyzing the magnitude and phase of scattered fields from obstacles underwater we can distinguish the category of the obstacles which belongs to either a high resistivity body or a low resistivity body. Therefore, the proposed method provides us an effective tool for analyzing the electromagnetic response of materials underwater.

A novel Quasi-Yagi antenna with low radar cross section (RCS) is proposed in this paper. By using arrow-shaped Koch dipoles as the driver and director and cutting the ground of the antenna, the RCS can be reduced in the operating band of 5 GHz-8 GHz when the incident wave is perpendicular to the antenna plane. Wideband radar absorbing material (WRAM) with frequency selective surface (FSS) is devised to replace the metallic reflect plate of the antenna to reduce the RCS in the maximum radiation direction. The average RCS reduction of the antenna in the frequency band of 3 GHz-12 GHz is 8.0 dB. The simulated and measured results show that there is a considerable RCS reduction of the Quasi-Yagi antenna with WRAM, and the radiation performance is preserved at the same time.

This paper presents a dual-mode stub loaded ring resonator (SLRR) to design a tunable dual-band bandpass filter (BPF) with two independently controllable passbands. The proposed resonator principally comprises a stepped-impedance ring resonator (SIRR) loaded with three stubs and two varactor diodes. Two independently tunable passbands are implemented by employing two varactors to control the dominant even-mode resonant frequency and odd-mode resonant frequency, respectively. Moreover, a new stub loaded double-ring resonator (SLDRR) is proposed to design the second tunable dual-band filter by shorting two stubs of the SLRR. With the same tuning method, the second filter can achieve two independently controllable passbands. In order to suppress the harmonics, defected ground structures (DGSs) are introduced at input and output feeding lines without degrading the passbands characteristics. The simulated and measured results are found in good agreement with each other.

A wideband planar printed quasi-Yagi antenna with band-notched characteristic is presented. The proposed antenna consists of a microstrip-to-slotline transition structure, a gradient driver dipole, and two parasitic strips as directors. Meanwhile, the arms of the driver and two directors are rotated in a certain angle to improve gain. Employing a microstrip-to-slotline transition, a driver dipole and two parasitic strips, the proposed antenna achieves a wide bandwidth for ultra-wideband applications. The driver dipole is connected to the slotline with a coplanar stripline. To avoid the frequency interference from WLAN operating in the frequency band from 5.15 GHz to 5.825 GHz, an L-shape slot etched on the driver dipole element is adopted to achieve notched band ranging from 4.8 GHz to 6.1 GHz. The ground plane is symmetrically added two stubs to implement the lateral size reduction. The measured bandwidth, determined by the reflection coefficient less than -10 dB, covers from 3 GHz to 10.8 GHz. Better than 8.1 dB F/B ratio and the measured antenna gain varying between 4.7 and 8.3 dBi are also achieved in the operating bandwidth excepting in the notched band.

The analysis of waves propagation in homogeneous anisotropic media constitutes a classical topic in every field of science and has been preferentially discussed using locally plane waves. Specific physical quantities and their behaviour laws are really what make the difference. Although the use of Fourier transform enables an approach formally analogous to that of plane waves in linear evolution equations, its application to constitutive equations of inhomogeneous media involves cumbersome convolution products that mask the solution. This paper proposes a polar representation (amplitude and phase) of electromagnetic fields, that appears to be more suitable and provides two sets of equations that can be easily decoupled, reducing the problem to the superposition of two simpler ones. The procedure is based upon the following steps: a) The identification of dispersion equation with Hamilton-Jacobi equation yields the evolution laws of rays and/or wave-fronts. b) From the knowledge of tensor ε(r) at any point r of the wave front (or the ray), the use of the intrinsic character (conjugation relations) of fields, introduced by the authors in a previous work, together with ray velocity or phase gradient (found in the first step) the remaining fields are immediately obtained.

A new compact printed tri-band antenna for WLAN/WiMAX applications is presented. The proposed antenna consists of three inverted L-shaped strips whose geometry looks like a ``bent fork''. These strips are attached to the feed line through a horizontal strip. By optimizing the geometries of the inverted L-shaped strips, distinct resonant points can be effectively created for different frequency bands. The overall size of the proposed antenna is 18 x 33 mm². Simulated and measured results show that the presented antenna can cover 2.5/3.5/5.5 WLAN and WIMAX bands with fairly stable radiation patterns. The antenna structure is simple, small, easily configurable and tuneable, and therefore suitable for practical applications.

In the 150 years that scientists and engineers have used Maxwell's equations to describe electromagnetic phenomena, canonical scattering and radiating problems have played a very important role, providing explanations of and insights into their underlying physics. With the same intent, a variety of active coated nano-particles are examined here theoretically with regard to their ability to effectively enhance or jam(cloak) the responses of quantum emitters, e.g., fluorescing molecules, and nano-antennas to an observer located in their far-field regions. The investigated spherical particles consist of a gain-impregnated silica nano-core covered with a nano-shell of a specific plasmonic material. Attention is devoted to the influence of the over-all size of these particles and their material composition on the obtained levels of active enhancement or jamming. Silver, gold and copper are employed as their nano-shells. The over-all diameters of the investigated coated nano-particles are taken to be 20 nm, 40 nm, and 60 nm, while maintaining the same ratio of the core radius and shell thickness. It is shown that the jamming levels, particularly when several emitters are present, are significantly larger for particles of larger sizes. These configurations are also shown to lead to the largest enhancement levels of the surrounding quantum emitters. Furthermore, for a fixed particle size and for a gain constant that produces the largest enhancement peak at optical wavelengths, it is demonstrated that these larger levels are most notable when the nano-shell is gold.

An asymmetrical coupled-line circuit is proposed to design planar microstrip balun, which has the advantages of compact structure and complex source to complex load impedance transformation. This balun consists of three pairs of coupled lines and two tapped transmission-line stubs. Based on the traditional even-odd mode technique and ABCD parameters, closed-form mathematical equations for circuit electrical parameters are obtained. To demonstrate our design theory, a practical microstrip balun is designed, simulated and measured. The results show that the return loss is larger than 25 dB, the insertion loss S₂₁ (S₃₁) 3.15 dB (3.129 dB), and the output phase difference -180.22˚ at the operating frequency. Good agreements between the simulated and measured results verify our design theory.

Scattering from array antennas is a complicated problem, containing the structural and mode items in nature. The complexities in analyzing the latter one also come from the feeding network that follows antenna unit ports, where active or anisotropy devices may exist. Therefore, it is significant that an efficient method can be constructed to analyze array antenna scattering with arbitrary port reflections. In this work, we address this problem by adopting the S-matrix model for the antenna array, aiming to efficiently and accurately compose the mode scattering in case of arbitrary reflections at feeding ports. In the numerical process, the antenna reciprocity is utilized in obtainning the basis for the scattering composition analysis. In case of various loading conditions, numerical results are presented, showing that the composed scattering results by the S-matrix model agree well with that obtained by direct full scale simulations. Then the methods for obtaining radiation and scattering of a large antenna array based on results of a small array, are reviewed and extended in composing the large antenna array scattering in case of variable loading conditions. And, promising results are obtained.

Two absorbing boundary conditions (ABC's) are derived for the cylindrical MRTD grids. The first one is the convolutional perfectly matched layer (CPML) based on stretched coordinates with complex frequency shifted constitutive parameters, and the other is the straightforward extension of CPML named quasi-CPML (QCPML) as it is no longer perfectly matched for cylindrical interfaces. Unlike the Berenger's PML, the implementations of the two ABC's are completely independent of the host material. Numerical results show that both ABC's can provide a quite satisfactory absorbing boundary condition, and can save more CPU time and memory than the Berenger's PML, while the QCPML has an advantage of CPML at the proposed absorbing performance, CPU time and memory saving. Moreover, it is shown that the QCPML is more effective than the PML and CPML at absorbing evanescent waves.

The present paper describes an integrated approach for design, fabrication and encapsulation of RF MEMS switches in view of the optimal performance subsequent to packaging. `Top and bottom contact' fabrication approaches are explored using different RF MEMS switch topologies. In the `bottom contact package (BCP)' the packaging cap alignment is less critical as compared to the top contact packaging (TCP) approach where contact via is an integral part of the cap. In this case, the connection layout through silicon via holes is independent of the cavity geometry. For the devices under consideration, bulk etched silicon cavity height has been optimized to 50 μm for optimal RF performance e.g. isolation and insertion loss. Parasitic effects of top silicon cap are reduced by altering CPW impedance. Mechanical parameter damping is simulated for different cavity heights and found to be independent from cavity height after 20 μm onwards.

In this paper, we present a detailed analysis on the invalidation of the polar format algorithm (PFA) for the dechirped echo signals in inverse synthetic aperture radar (ISAR) imaging. After the translational motion compensation, the polar section of the dechirped signals is often undermined, and then the PFA is invalid. A revised method by range shifting is proposed to compensate the echo signals, and the standard polar section is obtained. An improved performance was achieved on the simulated and real data experiments. The theoretical analysis and the proposed method are confirmed.

Vector and scalar potential formulation is valid from quantum theory to classical electromagnetics. The rapid development in quantum optics calls for electromagnetic solutions that straddle quantum physics as well as classical physics. The vector potential formulation is a good candidate to bridge these two regimes. Hence, there is a need to generalize this formulation to inhomogeneous media. A generalized gauge is suggested for solving electromagnetic problems in inhomogenous media which can be extended to the anistropic case. The advantages of the resulting equations are their absence of low-frequency catastrophe. Hence, usual differentialequation solvers can be used to solve them over multi-scale and broad bandwidth. It is shown that the interface boundary conditions from the resulting equations reduce to those of classical Maxwell's equations. Also, classical Green's theorem can be extended to such a formulation, resulting in similar extinction theorem, and surface integral equation formulation for surface scatterers. The integral equations also do not exhibit low-frequency catastrophe as well as frequency imbalance as observed in the classical formulation using E-H fields. The matrix representation of the integral equation for a PEC scatterer is given.

In this letter, we present a diplexer implemented on a substrate integrated waveguide (SIW) with stepped impedance complementary S-shaped resonators (CSSRs). The variable frequency response of the stepped impedance concept adjoining SIW technology leads to improved device performance in terms of matching and isolation. Simulated and measured results show input matching, |S₁₁|, better than -15 dB and output isolation, |S₃₂|, below -30 dB for the frequency range 1-4 GHz. Furthermore, CSSRs offer a degree of freedom to design fundamental and higher order frequencies by selectively tuning the geometrical parameters. This simple yet effective approach eliminates the complexity to design diplexers based on complementary split ring resonator (CSRRs).

This study proposes an accurate estimation of whole-body averaged specific absorption rate (WBA-SAR) for far-field exposure of an isolated human body in the frequency range of 10-200 MHz based on a lossy homogenous cylindrical antenna model of the human body. Equations are derived for the total induced axial current and the whole-body averaged SAR based on a rigorous treatment of cylindrical antenna theory. An explicit formula for the resonance frequency in terms of the anatomical parameters and the dielectric properties of the body is proposed for the first time. Moreover, important phenomena in far-field radio frequency (RF) dosimetry, such as, the cause of resonance and the SAR frequency characteristics are discussed from an antenna theory perspective.

In this work, sensor abilities of a chiral metamaterial based on split ring resonators with double splits (SRDS) are demonstrated both theoretically and experimentally in X band range. This study is based on transmission measurements and simulations monitoring the resonance frequency changes with respect to the thickness of the sensing layer and permittivity values. Experimental and simulated results show that the resonance frequency of the chiral metamaterial based SRDS sensor is linearly related to permittivity and the thickness of the sensor layer which creates a suitable approach for sensing environment and organic parameters. When the sensor layer filled with the related material, changes in the tissue temperature, sand humidity and calcium chloride density lead to resonance frequency changes. The physical mechanisms are explained by using both equivalent circuit model and the fundamental sensitivity theorem of chiral sensors. This is the first study as a sensing mechanism based on the chiral metamaterials in X band range.