Search

A single-layer microstrip patch unit element, which is loaded with eight concentric L-shaped slots, is proposed for reflectarray design. In this case, the lengths of the inner and outer slots are varied concurrently to function as the phase-shifting geometrical parameters. The reflection characteristics of the element are analyzed using the waveguide method, and the simulation results have been verified with experiments. A broad reflection phase range of 631.83° with slow gradient has been successfully achieved with the use of the slotted patch with constant size. Parametric analysis has been performed and it is found that the S-curve can be easily fine-tuned by changing some of the design parameters.

A fiber taper acoustic sensor utilize the ability of taper structure to modulate vibration signal into the fiber transmission power. Currently, there is a lack of detailed study on the bending effect of fiber taper to the fiber transmission power. In this paper, wide-angle propagation method is used to simulate the effect of fiber taper bending. The reconstructed time-domain signal and time-domain signal modulated from vibration has a nonlinear negative relationship and has a correlation coefficient value of 0.9979.

In this paper, a microwave transmission line sensor is investigated and used for bulk liquid permittivity measurement. A microstrip type transmission line is designed and analysed for a frequency range of 150 kHz to 8 GHz. The transmission coefficient magnitude of the microstrip line covered with different liquid samples is calculated numerically and compared with the measurement results. The calculated transmission coefficient magnitudes show good agreement with the normalized measurement results for the sample with a dielectric constant of less than 30 and a frequency range up to 6 GHz. A specific focus of the work is to study the transmission response of the microstrip line sensor when it is implemented on a curved substrate instead of the traditional planar substrate. A semi-flexible microstrip line is designed using a semi-rigid substrate for different curvature and its transmission coefficient is calculated numerically. The curved microstrip line sensor shows good agreement between the calculated and the measured results with minimum effect on the curvature. Furthermore, dielectric constant empirical models are formed and tested for unknown liquid samples. The results show a good match between the microstrip line sensor and the commercial dielectric probe for the determination of dielectric constant at frequency range less than 0.5 GHz and 4 to 8 GHz. The study demonstrated that the empirical models applied for the dielectric constant determination can be developed for low dielectric constant liquid despite of the sensor structure is curved or planar.

In this paper, a low-cost portable microwave reflectometer is designed and developed to measure glucose content in aqueous solution. The proposed microwave measurement system is constructed by using microwave circuit with a non-invasive open-ended coaxial probe sensor. Reflection method is used due to its simplicity and suitability of detecting the glucose concentration. The reflected microwave signal is detected by coaxial probe sensor and converted into voltage signal using power detector. Empirical models between the reflection coefficient and the glucose concentration from 10% to 60% have been developed. The reflectometer measurements are compared with Vector Network Analyser, and validated using different batch of samples. The proposed reflectometer demonstrates reasonable accuracy with an error of less than 4.5%.

A linearly polarized single-layer single-resonator reflectarray, which is designed using a simple circular patch loaded with two unequal rectangular slots, is investigated for the first time. For the proposed design, the linearity and sensitivity of the phase curve (S-curve) can be easily optimized by adjusting the ratio of the two unequal slots changeable according to a simple design equation. Here, the patch radius serves as a phase-shifting geometrical parameter and it is able to achieve a wide phase range of more than 458° with low phase sensitivity and a low reflection loss of less than 0.5 dB. With the use of the optimized phase curve, an offset-fed 13 × 13 full-fledged reflectarray with a square aperture is designed, fabricated and measured. Measurement results show that a −1-dB gain bandwidth of 11.8% and an antenna gain of 23.4 dBi are realizable at the center frequency of 9.3 GHz. Also, the proposed reflectarray has an aperture efficiency of 42% and a radiation efficiency of 98%. The proposed reflectarray has a simple structure and it is able to achieve smooth phase curve, low cross-polarized radiation field and low sidelobes.

This paper presents an ultra-wideband (UWB) and off-optimised Five-Port Reflectometer (FPR) configured by power splitters. The proposed non-multi-state FPR is characterised and realised for complex reflection coefficient determinations. The measurement system can be easily setup using commercial power splitters, three detectors and a microwave source. The transmission lines method is used as calibration standard for FPR measurement system. Both the FPR setup and the transmission lines are characterised with a Vector Network Analyser prior to be used for the off-optimised measurement system. The results show good agreement between actual and calculated reflection coefficient for frequency range of 0.1 to 40 GHz. This novel FPR setup provides a simple, cost effective and accurate alternative in measuring broadband complex reflection coefficient.

Inspired by research technology of RFID in flexible substrate, a new era of microwave sensor in more flexible form is indeed an interesting and important research area. One of the most common and suitable microwave sensor that suitable to be transformed into flexible structure is microstrip. In this project, a semi-flexible microstrip sensor was designed and simulated with soft substrate for difference curvature angles. The sensor was investigated and critically analyzed to study the effects of curvature. The designed sensor was fabricated and experimental result are measured by Vector Network Analyzer for frequency range 150 kHz to 8 GHz. The transmission coefficient of curvature sensor that covered with sample of various dielectric values were measured. All the parameters are compared to flat microstrip sensor. The potential and performance of the curvature microstrip sensor are intensively examined.

A linearly polarized (LP) Yagi-Uda-like transmitarray element, which consists of multiple strips in parallel, has been proposed for achieving broad phase range. A 6-layer unit element has been demonstrated using the Floquet method to achieve a transmission phase range of 364o. The element is then used to design a 5×5 full-fledged transmitarray to generate an antenna gain of ∼ 17dBi, a broad 1-dB bandwidth of 11.86%, and an aperture efficiency of 44.3%. To ease the design procedure, a curve-fitted equation is also provided.

A new method of tuning a multi-wavelength Brillouin-erbium fiber laser (BEFL) within a Fabry–Perot cavity by incorporating a low-cost biconic tapered fiber is reported. The biconic tapered fiber was fabricated using a flame elongation technique and it was incorporated into the BEFL system to position the self-lasing cavity modes over a tuning range of 5.5 nm within the erbium-doped fiber gain profile. By injecting the Brillouin pump near to the tunable self-lasing cavity modes, it suppresses the modes and generates stable cascaded Brillouin–Stokes lines with more than 20 dB signal-to-noise ratio.

A circular step-index fibre with a helical winding on the core-cladding boundary is proposed and investigated analytically with a new type of boundary condition. Using cylindrical coordinate system (r, ϕ, z), new boundary conditions are imposed and longitudinal field components are obtained. The equation involves Bessel and modified Bessel functions. Numerical computations are made. Dispersion curves are obtained for different pitch angles. The main effect of the helical winding on the characteristics is to introduce band gaps.

This paper presents a comparative study of dispersion characteristics of the circular waveguide with helical windings. Our waveguide is doubly unconventional in the choice of reverse boundary condition, in the choice of normal boundary condition and further with the presence of sheath helix between the core and cladding parameters. Two methods of winding the helix between the core and cladding are considered namely from right to left and left to right. Through mathematical analysis using field components and boundary conditions the modal characteristics are derived for both conditions. Normal boundary condition and reverse boundary conditions are used respectively to represent the helical windings. Here the characteristic equation is obtained in the form of Bessel and modified Bessel for both waveguides. Using the modal characteristic equation the dispersion curves are plotted for numerous angles and wavelengths. We find that the method of wrapping the helical material has significant effect on the dispersion properties with regards to the way the modes propagate.

A new reflectarray is designed using two co-joined L-shaped probes. In this case, the horizontal lengths of the two L-shaped probes are functioning as the phase-shifters. The unit element is simulated using the Floquet cell, and simulation shows that the unit element is able to provide a linear phase range of 454.2°. A full-fledge reflectarray consisting of 121 elements is designed, fabricated, and measured. The proposed reflectarray is able to achieve an antenna gain of 20.43dBi and a −1dB gain bandwidth of 15.38%.

A simple and efficient variable optical attenuator (VOA) is achieved by using microbend gratings on single-mode fiber (SMF). The flatness of the attenuator is maintained for 100 nm along the C+L band spectrum. Controlling the pressure will vary the attenuation depth of the device. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 463–465, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20668

The biconic tapered fiber has been fabricated using flame elongation technique by heating and stretching a piece of single mode fiber (SMF). Intermodal interference occurs in the abrupt biconic tapered fiber. The modulated spectral response was characterized to determine the strain effect. It was found that the shifting of peak modulated spectral response was well matched to the phase change introduced by Michelson-type transmission equation.

We demonstrate a multiwavelength Brillouin Erbium fiber laser with double channel spacing operating at room temperature using a hybrid linear-ring cavity. 7 simultaneous lines with 0.175nm line spacing using both a 100mW pump at 980nm and a 4dBm Brillouin pump are achieved by circulating the odd-order Stokes signals in a 7km long single mode fiber based sub-ring cavity, allowing for the formation of even-order Stokes signals at the output