A novel out-of-line series-fed patch array with low cross-polarization is presented in this paper. The element in the array is fed by a stub through one-port. The feeding stub is designed to be a novel curled-horn-shaped geometry, which can effectively suppress the cross-polarization due to its symmetry. The linear array consists of two identical subarrays which are located oppositely. By the antiphase feeding of two subarrays, the cross-polarization is further reduced. Furthermore, the theory analyses of the series-fed array indicate that it is competent for being applied to phased array systems. The simulated results show the cross-polarization levels of the linear array with 20 novel elements in E and H plane are lower than −30 dB and −60 dB, respectively. And, a prototype array is fabricated. Its low cross-polarization levels confirm the effective performance of the proposed design.

A compact double-balanced monolithic star mixer for Ka-band applications using 0.25 μm GaAs pHEMT process is presented. With multi-coupled lines technology, the proposed dual 180° hybrid is produced and applied to a star mixer successfully. The proposed hybrid adopts the power divider and two types of multi-coupled lines to improve the return loss and isolation at the balance outputs of a traditional dual Marchand balun. Output ports are allowed to locate arbitrarily, eliminating a complex layout while the dual 180° hybrid is applied to double balanced star mixers. As the measurement results show, the proposed mixer achieves an operation bandwidth of 27 to 36 GHz with the best conversion loss of 6.3 dB at 28 GHz. In addition, the chip dimension can be manufactured as small as 0.81 mm².

A tunable microwave notch filter is developed on magneto-dielectric material having low saturation magnetization to attain low external dc magnetic field for biasing. A simple microstrip line at 10 GHz is developed on nickel ferrite/low density polyethylene nanocomposite system as substrates and its microwave transmission response is studied in X-band. Composite system is developed by dispersing nano sized nickel ferrite (~6.63 nm) in low density polyethylene to obtain a homogeneous flexible substrate. Saturation magnetization of 4% volume fraction of the composite is found to be 1.8745 emu/g. Tunability of Q value and insertion loss is studied with magnitude of external dc magnetic field and at different angles of its orientation with the axial plane. A very low field up to 250 G is sufficient to tune the selectivity. An insertion loss of ~-30 dB and Q ~ 375 at 10.2 GHz is observed. The interaction of magneto static modes with orientation of the applied dc magnetic bias with respect to rf magnetic field is discussed with couple mode theory. Good cut-off behaviour of more than 28 dB is observed at magnetic field angles from 23.52° to 34.21°. The experimental and theoretical couplings show close proximity.

A novel approach for the design and optimization of spherical lens antennas (SLAs) including practical feed model (PFM) is proposed. The vector spherical wave function expansions (VSWE) combined with differential evolution (DE) algorithm is adopted for the optimal design of SLAs. Moreover, the near-field aperture distributions of a Ku band dielectric loaded horn feed and a Ka band corrugated horn feed were obtained using the full wave simulation and were then taken into account in the DE optimization. The performances of the optimized 2-layer design are compared with previous works, higher directivity is obtained. Additionally, the radiation characteristics of an optimized SLA are presented, and numerical results of a 650 mm diameter 2-layer hemispherical lens antenna (HLA) with ground plane are compared to the experimental results, and good agreements are obtained. An investigation of the influence of the various lens-to-feed distances as well as aperture sizes of SLA on the aperture efficiency for a 2-layer design is also proposed.

There are many applications of beam quality and beam shape in turbulent atmosphere. Because M² factor and kurtosis parameters are often used to descripe beam quality and intensity flatness, the evolution of these two parameters of Hermite-Gaussian beam in turbulent atmosphere have been studied in both theory and numerical calculation. Results show that the spectrum of refractive index fluctuations has a strong effect on these two parameters. For some spectral models, these two parameters are very sensitive to some factors of turbulence. But for other spectral models, the factor is very insensitive to these factors. For example, when the exponent of the spectrum is very small, M² factor is very insensitive to the outer scale of turbulence. But when the exponent of the spectrum is very large, the M² factor is very insensitive to the inner scale. In addition, we also found that there are many differences between the kurtosis parameters under different conditions. For example, the kurtosis parameters may be very large during propagation. Namely, beam shape may be very sharp under some conditions. When the effects of turbulence is very large or very small, beam shape is very flat.

The permittivity of extra thin silk cloth is usually measured through some complex methods in the past. Here we propose a convenient and flexible method to measure the permittivity of extra thin silk cloth using resonant metamaterial structures. The metamaterial structures used here are symmetric split ring resonators (SRRs). The principle is that the resonant frequency of the SRRs is very sensitive to the permittivity of the surrounding medium. Therefore, the relative permittivity of an extra thin medium as silk cloth can be determined. Our experimental measurement shows that the relative permittivity of the silk cloth is 4.5. A piece of printing paper is also measured with a relative permeability of 1.4. The effectiveness of the method in determining the permittivity of a solid medium is very useful in future applications.

The propagation equation, written in a curvilinear coordinate system, is solved by using a perturbation method inspired from quantum physics and extended to imaginary eigenvalues and evanescent waves. The parameter of perturbation is the groove depth which is small compared to the period. The method is expanded up to second order for the non-degenerate problem. In this way the solutions have analytical form compared to a numerical method. They present the advantage to put in evidence the evolution of the energy distribution for different diffraction orders as a function of the magnitude of the perturbation. The efficiencies which are deduced from these analytical solutions are compared of those obtained by the curvilinear coordinate method. The good agreement between the two methods occurs for a groove depth with respect to the wavelength less than or equal to 0.16. Thus, this new approach opens a new range of applications for inverse problems.

Conventional interferometric ISAR (InISAR) imaging requires a radar system with at least three antennas, and the hardware complexity may be a main obstacle to practical realization. In this paper, we propose an InISAR three-dimensional imaging algorithm using only one antenna. Interferometric processing is carried out among ISAR images obtained during three near measurement intervals. The scatterer position in the range direction is obtained from range cell number in ISAR images, and the azimuth/height information is estimated from interferometric phases and geometrical relationship. Moreover, the target track requirements of the proposed method are also investigated. Simulations have shown the effectiveness of the proposed method.

The design of concentric ring arrays for isoflux radiation is presented in this paper. This design considers the reduction of the side lobe level and isoflux radiation requirements for Medium Earth Orbit (MEO) satellites. The optimization problem considers the spacing among rings and levels of amplitude excitations. The well-known method of Particle Swarm Optimization (PSO) is utilized for this design case. The obtained results could cause the satellite hardware to be reduced significantly even more than that presented previously in the literature.

In the future, mobile handsets might incorporate more than 20 separate radios, creating a difficult antenna design problem due to the sever space restrictions. This paper proposes a reconfigurable wideband antenna, for use within clamshell mobile handsets. The impedance bandwidth of the new antenna was selected in order to meet current and future demands within the industry. It has been suggested that a portable Cognitive Radio must be capable of simultaneous communication (via a narrowband antenna) and spectrum sensing (via a wideband antenna). For this reason a narrowband slot antenna has also been integrated within the wideband radiator.

Conjugately characteristic-impedance transmission lines (CCITLs) are a class of transmission lines possessing conjugately characteristic impedances (Z₀^±) for waves propagating in the opposite direction. A typical Z₀ uniform transmission line is a special case of CCITLs whose argument of Z₀^± is equal to 0^o. This paper aims to generalize the CCITL system by demonstrating a theoretical study of CCITLs and their applications in the microwave transistor amplifier design. It is found that the bilinear transformation plays an important role in transforming circles in the reflection coefficient Г₀-plane in the Z₀ system to the Г-plane in the CCITL system. In addition, Meta-Smith charts, a graphical tool developed for solving problems in the CCITL system, are employed to design matching networks to achieve desired amplifier properties. Results show that stability regions on Meta-Smith charts can be determined, and source and load reflection coefficients can be selected properly to obtain desired operating power gain. In addition, an example shows that Meta-Smith charts offer a simple approach for matching network design using open-circuited single-stub shunt tuners.

This paper presents a development of a wideband delta-sigma modulator for fully digital GHz transmitters. The fully digital RF transmitter is developed as a promising solution for software defined radio (SDR) terminals and applications. The fully digital transmitter consists of a delta-sigma modulator, a high-speed multiplexer and a switching-mode power amplifier. The speed limitation of delta-sigma modulator is the main limitation to increase the signal bandwidth in fully digital transmitters. In this paper, the bandwidth of the fully digital transmitter is increased 8 times using parallel processing time-interleaved architecture, while maintaining the same signal quality. This architecture was implemented on FPGA and tested for different standards (WiMAX and LTE) with a signal bandwidth up to 8 MHz. The concept was assessed in terms of SNDR by using a differential logic analyzer at the output of FPGA, and the SNDR was found to be around 60 dB.

In this paper, a new kind of printed TEM horn antenna with high-gain fed by balanced microstrip line is proposed. The radiation part of the antenna (printed on the FR4 epoxy substrate) is composed of two symmetrical triangular metal foil branches fed by balanced microstrip line. The antenna has been simulated by CST MICROWAVE STUDIO^® software, and the simulated results show that the proposed antenna is a kind of traveling wave antenna. Besides, an equivalent adopted V-shaped antenna model is proposed to describe the radiation characteristic of the antenna. The simulated and measured results indicate that in the frequency range from 1.64 GHz to 9 GHz, the reflection coefficient of the antenna is less than -6 dB, and in the work frequency band, the average gain value is over 8.2 dB. The antenna gain will be improved greatly by extending the length of the dielectric slab appropriately (in the main radiation direction) without influencing the bandwidth. The measured and simulated results have a good consistency. This antenna will have wide application in the UWB field.

The adaptive sliding-mode observer has been widely used to estimate the rotor flux and rotor speed in inverter-fed sensorless induction motor drives. However, the technique requires setting a priori the sliding-mode observer constants and also knowledge of the induction motor parameters. This particular aspect can cause significant errors in the estimation of the rotor speed used in sensorless control schemes. Changes in the induction machine parameters due to temperature or different saturation levels will affect the dynamic operation of the observer despite its adaptive nature. In this context, a sensitivity study of the adaptive sliding-mode observer is presented and discussed in this paper. Various experiments are performed on a sensorless indirect vector-controlled induction motor drive under a variety of conditions to verify the observer robustness.

In this paper, we propose the design of high sensitivity and selectivity metamaterial-based biosensors operating in the THz regime. The proposed sensors consist of planar array of resonant metallic structures, whose frequency response is modified through the variation of the surrounding dielectric environment. We consider different resonator geometries, such as the squared, circular, asymmetrical, and omega ones, and the analysis of the biosensors is conducted through proper equivalent quasi-static analytical circuit models. The metallic particles are assumed deposited on a glass substrate through proper titanium adhesion layers. Exploiting the proposed analytical model, which is verified through the comparison to full-wave numerical simulations, we study the biosensor resonance frequencies as a function of the geometric parameters of the individual inclusions. Finally, we optimize the structure in order to obtain high sensitivity and selectivity performances. The numerical results show that the proposed structures can be successfully applied as biosensors working in the THz region.

A miniaturized printed log-periodic fractal dipole antenna is proposed. Tree fractal structure is introduced in an antenna design and evolves the traditional Euclidean log-periodic dipole array into the log-periodic second-iteration tree-dipole array (LPT²DA) for the first time. Main parameters and characteristics of the proposed antenna are discussed. A fabricated proof-of-concept prototype of the proposed antenna is etched on a FR4 substrate with a relative permittivity of 4.4 and volume of 490 mm × 245 mm × 1.5 mm. The impedance bandwidth (measured VSWR < 2) of the fabricated antenna with approximate 40% reduction of traditional log-periodic dipole antenna is from 0.37 to 3.55 GHz with a ratio of about 9.59 : 1. Both numerical and experimental results show that the proposed antenna has stable directional radiation patterns and apparently miniaturized effect, which are suitable for various ultra-wideband applications.

In this paper, we consider a dense array of metallic circular patches printed on a electrically thin metal-backed dielectric substrate. Since the sub-wavelength dimensions, the array and the metal-backed substrate can be described in terms of a lumped capacitance and a lumped inductance, respectively. Around the resonant frequency, the structure, known as high-impedance surface, reflects totally an incident electromagnetic wave with zero shift in phase. Due to this property, it is widely employed in antenna systems as compact back reflector with improved performances with respect to typical metal reflector. Starting from the concept of the grid capacitive reactance of a planar array of squared patches and its related formulas, we investigate on the field distribution on the array plane and properly modify the formulas for the case of the circular patches. We present two new analytical formulas which can be effectively used for the fast design of 2D-isotropic circular HISs. In order to validate the models, we compare the resonant frequency of the array obtained through our approaches to the one resulting from full-wave numerical simulations and from other analytical methods available in the open technical literature.

Based on quasi-static electromagnetic field theory, recently grounding system under alternative currents (AC) substation has been studied with equal potential and unequal potential models. In these numerical models, the closed form of Green's function for a point source within a horizontal multilayered earth model and its quasi-static complex image method have been fully discussed. However, less information about how to achieve the closed form of Green's function through Matrix Pencil method is presented in these references. In this paper, we discuss how the kernel of the Green's function can be expanded into a finite exponential series.

A novel microstrip dual-mode tri-band bandpass filter is presented. The filter consists of an open stub loaded dual-mode resonator and two short stub loaded dual-mode resonators. By utilizing the odd- and even-mode resonance properties of the proposed dual-mode resonators and the introduced source-load coupling (S-L coupling), the filter is designed with two transmission zeros at both sides of each passband, which will improve the selectivity of the filter. To validate the design theory, one 100 MHz 3 dB absolute equal bandwidths dual-mode tri-band filter with three passbands located at the centre frequencies of 1.8, 2.4 and 5.0 GHz, respectively, is designed and fabricated. Both experimental results agree well with the simulations.

Rain attenuation is an important aspect of signal propagation above 10 GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modified by incorporating an effective slant path model. The effective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007-2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.