Volume 68, Issue 1-2

In this paper, a compact 4-element antenna array with the dimension of 150 mm × 150 mm is proposed for BeiDou navigation satellite system (BDS) anti-jamming applications. The proposed antenna array comprises of four identical microstrip right-handed circularly polarized (RHCP) antenna elements. The four microstrip antenna elements are placed in the same polarity with a distance of 80 mm between adjacent elements. The antenna element which employs dual probe-fed structure has a relatively small volume of 45 mm × 45 mm × 5 mm. The antenna array has been fabricated and measured. The experimental results show that the proposed antenna array is quite suitable for BDS anti-jamming application.

A performance analysis of coaxial fed stacked dual patch electromagnetic–coupled microstrip antenna useful for satellite communication working in X/Ku band is presented. A simplified structure of stacked dual patch antenna is proposed with adjustable foam-gap between patches. Few important geometrical parameters were chosen on which the performance of stacked dual patch antenna mainly depends. Dimension of lower square patch, upper square patch and height of foam-gap between two patches are the parameters, which were varied one by one keeping other parameters constant. The performance was observed through the reflection coefficient (dB) and smith chart impedance plot, obtained from the numerical simulator (IE3D) for the dual resonance frequency and bandwidth. Proposed geometry of stacked dual patch antenna was also analyzed with cavity model and artificial neural network modeling technique. Dual resonance frequencies and associated bandwidth were calculated through them and results were cross checked in the laboratory with a few experimental findings.

In this paper, a dual-band circularly polarized stacked annular-ring microstrip antenna which covers the bands of Galileo (E5a, E5b, E1, E2, L1), GPS (L1, L2, L5) and GLONASS (L1, L2, L3) is presented. The antenna is composed of two concentric annular-ring patches that are etched on a substrate to generate a dual-band response. Four H-shaped apertures are added to improve the coupling between the microstrip lines and rings. And a wide-band feeding network is used to broaden the axial-ratio bandwidth. Good agreement is achieved between the simulation and measurement, which shows that the return loss of the proposed antenna is less than −15 dB in the whole band and the 3-dB axial-ratio (AR) bandwidths for the lower and upper band are 12.5% and 20.8% respectively. The measured results confirm the validity of the designed antenna which is suitable for Global Navigation Satellite System.

This paper presents a wideband gap coupled assembly of rectangular microstrip patches applicable in lower and upper band of Wi-Max applications utilizing six directly and parasitically coupled patches. Considered assembly of patches on glass epoxy FR4 substrate has overall dimension of 40.0 mm by 52.88 mm. The proposed antenna is designed to function in the lower band (2.4–2.69 GHz) and upper band (5.25–5.85 GHz) of Wi-Max systems. The antenna is simulated using IE3D simulation software in view of the Wi-Max standards adopted by IEEE 802.16 working group. The simulated and measured results are well in agreement and show that antenna resonates in two bands proposed for wireless communication applications and successfully achieves the bandwidth of 11.2% (at VSWR: 1.5) with respect to the center frequency of 2.84 GHz in lower band and 9.7% with respect to the center frequency of 5.39 GHz in upper band. Gain and efficiency of antenna in these two bands are however low due to lossy substrate but radiation patterns in each of these two bands are identical in shape in entire bandwidth region. In lower band maximum radiations may be achieved normal to patch geometry but in upper band, direction of maximum radiations is inclined at θ = 60° perhaps due to the generation of higher mode.

In this paper, a broadband and low-loss sequential feeding network is proposed and developed on the basis of substrate integrated waveguide (SIW). Phase shift is not only generated by adding delay line but also using unequal-width SIW, which can make the feeding network operate over a broadband. The amplitude imbalance is within 0.7 dB while the phase error is less than 10° over the frequency band from 16.9 to 23.6 GHz or 33.4% relative bandwidth. Measured and simulated results of the proposed structure are in a good agreement. This sequential feeding network has wide band and low insertion loss, so it is attractive to be used in the design of broadband SIW circularly polarized antenna arrays.

A novel hybrid SIW-GCPW cruciform coupler is proposed and demonstrated. This coupler consists of a cross-over of substrate integrated waveguide (SIW) and ground coplanar waveguide (GCPW) in a square junction. Efficient coupling is achieved by adding two inductive metallic posts on the diagonal line of the junction. Taking advantages of low profile, low insertion loss of SIW and flexibility of GCPW, this coupler structure can be integrated in microwave and millimetre-wave planar circuits, especially in beam-forming networks. A 3 dB coupler is designed and fabricated operating around 33 GHz. Characteristics of 15 dB isolation between the input port and isolated port are achieved over 18% bandwidth. Design considerations and simulated as well as measured results are presented and discussed.

The 2-D finite-difference frequency-domain method (FDFD) combined with the surface impedance boundary condition (SIBC) was employed to analyze the propagation characteristics of hollow rectangular waveguides at Terahertz (THz) frequencies. The electromagnetic field components, in the interior of the waveguide, were discretized using central finite-difference schemes. Considering the hollow rectangular waveguide surrounded by a medium of finite conductivity, the electric and magnetic tangential field components on the metal surface were related by the SIBC. The surface impedance was calculated by the Drude dispersion model at THz frequencies, which was used to characterize the conductivity of the metal. By solving the Eigen equations, the propagation constants, including the attenuation constant and the phase constant, were obtained for a given frequency. The proposed method shows good applicability for full-wave analysis of THz waveguides with complex boundaries.

A novel polarization splitter based on photonic crystal fibers (PCFs) is proposed in this paper. It is a new kind of highly birefringent dual-core PCFs which the orthogonal polarization modes with dissimilar coupling lengths is separated from each other easily. Compared to the traditional methods achieving high birefringence, the designed highly birefringent PCFs uses hollow ring defects in its one direction and then breaks the structural symmetry of PCFs. And also the design or fabrication limitations for the PCF-based polarization splitter can be partly overcome by this new type of PCFs. The transmission properties, the coupling lengths for the two orthogonal polarizations and the performance of the proposed polarization splitter are investigated respectively and analyzed numerically. The results show that it is possible to obtain a 0.50-mm long polarization splitter. Its bandwidth is about 30.6 nm or 16.0 nm as the splitting ratio is better than −10 dB or −20 dB.

In the paper, we design a broadband ultra-flattened dispersion photonic crystal fiber (PCF). Its structural parameters are calculated and optimized by using the genetic algorithm (GA). The calculated results show that a dispersion value of 24 ps/nm/km was achieved from the wavelength of 1.45 to 1.9 μm with a variation of +/−0.1 ps/nm/km (or 0.42%). It implies that the GA method is an effective way for the ultra-flattened dispersion PCF design.

In this paper, the birefringence effects on fiber Bragg grating (FBG) written into standard single mode fiber under transverse load are analyzed. The evolutions of states of polarization (SOPs) of transmitted light in linear birefringence gratings are studied. We demonstrate that the first normalized Stokes parameter ( s 1 ) of the transmitted light in FBG has monotonous relationship with linear birefringence induced by transverse load and can be advantageously used for real-time transverse strain sensor, which is different from the basic sensing theory of the FBG sensors based on direct spectral analysis. The evolution of s 1 of FBG in transmission with respect to the transverse load is studied experimentally, and a sensitivity of about 0.089/N is obtained. We also design a special gratings structure to reduce the effect of cross-sensitivity which is typically a limitation of most FBG sensors. The simulations show a great dependence of measurement performances with respect to the shape of transmission spectrum.

A reflection-transmission based rectangular waveguide approach for measuring the effective constitutive properties of metal powders at 2.45 GHz is presented. The measured effective dielectric properties of these metal powders are quite important for sintering of metal powders using microwaves, which is a new area of research. The proposed method is based on placing the metal powders of varying density into a standard glass tube, which is then positioned inside a specially designed waveguide holder for measuring the scattering coefficients at 2.45 GHz using a vector network analyser. The effective constitutive properties of the metal powders are obtained in terms of the measured scattering coefficients using the proposed two step approach. In order to validate the accuracy of the measured material properties, an electromagnetic core-shell model of the metal powders is developed. Finally, the effective dielectric properties of Cu and stainless steel powders are measured and compared with the values obtained using the electromagnetic model.

In a travelling wave tube, much of the waste power is dumped into the collector. If the waste heat is not properly managed, it might pose a serious problem causing even failure of tube. In this paper, the optimal choice of thermal management of a highly efficient multistage depressed collector designed for a space TWT has been made based on several criteria. The structural deformations and stresses developed due to thermal impact have been evaluated. The influence of thermal deformations on the collector electrical performance and high voltage withstanding capability has been studied during hot condition.