Vol. 27

In this paper we present a modification to the QHA whereby a gap is introduced at the current minima points at the centre of the helical sections of the QHA. The linear and rotational movement between the two halves of the QHA against each other is optimised to get current distribution, so that when tilted 90°, it generates omnidirectional radiation pattern required for land communications in addition to hemispherical radiation pattern for space mode which is obtainable in conventional configuration. This makes it possible to use the single antenna for both terrestrial and satellite communications. The simulated results are validated by experimental measurements.

In this paper, a surface micromachined microwave tunable low pass filter, consisting of tunable shunt capacitors and series inductors, has been realized. The filter exhibits insertion loss of less than 1 dB (up to 10 GHz), stop band attenuation of 20 dB at 20 GHz, and cut-off frequency is changed to 8 GHz with the application of DC actuation voltage in the structure. The filter has an overall dimension of 5.5 mm x 2 mm. The characteristics of tunable filter are investigated with and without packaging.

This paper presents a new range Doppler algorithm (RDA) for bistatic synthetic aperture radar (SAR) processing in a general configuration based on a bistatic point target reference spectrum: the improved extended Loffeld's bistatic formula (ILBF). The ILBF spectrum is proved to be comparably accurate with the spectrum derived using the method of series reversion (MSR). Based on the expansion of the ILBF spectrum, a new bistatic RDA is developed to process the azimuth invariant and variant bistatic SAR data. Compared with existing bistatic RDA, the new algorithm has a simpler formulation and is able to cope with moderate or high squint bistatic SAR data. The simulated data in the azimuth invariant and variant bistatic configurations are used to validate the new algorithm.

This paper presents a new three-phase LC-ring voltage controlled oscillator (VCO) using the TSMC 0.18μm 1P6M CMOS process. The VCO consists of three single-ended complementary Colpitts VCOs coupled via a varactor ring. Tuning range of VCO is 0.59 GHz, from 8.22 GHz to 8.81 GHz, while the control voltage was tuned from 0 V to 1.1 V and the VCO core power consumption is 2.82 mW at the supply voltage of 1.1 V. The measured phase noise is -118.14 dBc/Hz at 1 MHz offset frequency from 8.40 GHz. The VCO occupies a chip area of 1.018×0.74 mm² and provides a figure of merit of -192.14 dBc/Hz.

This paper presents the design of a crossed oval-ring microstrip slot antenna to achieve triple-frequency operation for WLAN/WiMAX applications. The proposed antenna is composed of a rectangular microstrip feed line and a ground plane on which three crossed oval-ring slots are etched. The three crossed slot loops finally excite three resonant modes and the resonant frequencies of the proposed antenna are mainly controlled by the dimensions and locations of the slot loops. The antenna prototype is fabricated and the characteristics are experimentally verified. The measured impedance bandwidths for triple operating bands can reach 840/670/940 MHz with return losses larger than 10 dB, which is enough for WLAN/WiMAX communication. In addition, good radiation characteristics with moderate peak gains are obtained and the measured and simulated results show a good agreement.

In this paper, a differential wavelet-based operator defined on an interval is presented and used in evaluating the electromagnetic field described by Maxwell's curl equations, in time domain. The wavelet operator has been generated by using Daubechies wavelets with boundary functions. A spatial differential scheme has been performed and it has been applied in studying electromagnetic phenomena in a lossless medium. The proposed approach has been successfully tested on a bounded axial-symmetric cylindrical domain.

This paper explores the optimal conditions for wave propagation on a microstrip line loaded by a Schottky diode. Investigations are undertaken by studying the transmitted power versus frequency, power and place of injection of a continuous sine high frequency aggression signal. The aggression is injected in a near-field mode. Coupling conditions between the aggression signal in the 500 MHz-3 GHz frequency band and the system is thus determined.

The proposed dipole antenna consists of two printed strips with unequal lengths and is fed by a coplanar strip (CPS) line. As the antenna parameters and port impedance are properly selected, a super wide operating band (|S₁₁|<-10 dB) of 3.5 to 20.0 GHz is realized. Antenna samples were fabricated using standard PCB process. The area of the constructed dipole antenna is 40.0x5.0 mm². The S-parameter measurement was performed via a transition (CPS to double-sided parallel strip line) and transformer (190 to 50 Ohm). The measured fractional bandwidth achieved 139.3% (from 3.4 to 19.0 GHz) as predicted, over which the antenna peak gain is better than 0 dBi.

In three-dimensional space, the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method is weakly conditionally stable, only determined by two space-discretizations, which is very useful for problems with fine structures in one direction. Its numerical dispersion errors with nonuniform cells are discussed and compared in this paper. To enlarge the applicable field of the HIE-FDTD method to open space, the absorbing boundary conditions (ABCs) for this method are also introduced and applied. Two microstrip filters with fine scale structures in one direction are solved by the HIE-FDTD method. Conventional FDTD method and alternating-direction implicit FDTD (ADI-FDTD) method are also used for comparing. Results analyzed by the HIE-FDTD method agree well with those from conventional FDTD, and the required central process unit (CPU) time is much less than that of the ADI-FDTD method.

This paper proposes a new design of coplanar waveguide dual-band bandstop filter (DBBSF) with center frequencies at 1.8 GHz and 2.8 GHz. A lumped element model of four series-connected parallel LC resonators are derived, then implemented using compact CPW resonators patterned in the center conductor. The measured and simulated responses are in good agreement which validates the design.

This work presents a straightforward way to obtain the coupling matrix of a bandstop filtering response from the original bandpass coupling matrix. The generated bandstop coupling matrix implements a response where the bandwidth is defined at the equiripple return loss of the lower and the upper passbands.

In this paper, a microstrip circuit structure for a K-Band Wilkinson power divider is presented. The designed power divider is composed of two-step taper stubs based on empirical equations. The symmetry of this circuit allows a half circuit analysis through looking at the odd- and even-model excitations. To demonstrate its performance, the proposed Wilkinson power divider has been fabricated and tested. Results show that the measured insertion loss is less than 0.3 dB and that the output reflection, input reflection and isolation are better than 16 dB, 22 dB, 16 dB, respectively, in the frequency range from 18 GHz to 27 GHz.

A simple and novel printed monopole antenna with dual broad operating bands is presented. The antenna fed by a 50-Ω microstrip line is composed by dual twin-pair inverted-L shaped strips as well as a small back truncated ground. By properly selecting widths of these inverted-L shaped stripes, dual broad bandwidths formed from triple resonances to meet the band requirement of the 2.4/5.2/5.8 WLAN or the 2.5(3.5)/5.5 GHz WiMAX standard can be achieved. Experimental results for case of the obtained antenna prototype suitable for use in a 2.4/5.2/5.8 GHz WLAN system have been done and shown good agreement with simulation. Good radiation performances including dual wide bandwidths of 270 MHz and 3.16 GHz, high average antenna gains of ≥ 2.6 and 4.6 dBi, and monopole-like radiation patterns over the two operating bands, respectively, make this antenna a good candidate for use in the modern dual-broadband wireless communication system.

A novel trapezoidal slot patch antenna with an embedded trapezoidal strip is proposed for satisfying wireless local area network (WLAN) and worldwide interpretability for microwave access (WiMAX) applications simultaneously. The proposed antenna consists of a rectangular radiation patch with an etched trapezoidal slot and an embedded trapezoidal strip on the top and a beveled ground on the bottom side. By carefully selecting the width of the radiation patch and length of the beveled ground, the proposed antenna can generate two separate bands. The measured results show that the 10 dB return loss bandwidths of the proposed antenna are 430 MHz (2.30-2.73 GHz) and 3460 MHz (3.21-6.67 GHz), which can cover both the WLAN bands (2.4-2.484 GHz, 5.15-5.35 GHz, and 5.725-5.825 GHz) and the WiMAX bands (2.4-2.6 GHz, 3.4-3.6 GHz, and 5.25-5.85 GHz). Furthermore, good omnidirectional radiation patterns with appreciable gain are obtained over the operating bands.

In the present study, we show that it is possible to achieve multi-channel filters in one-dimensional photonic crystals using photonic quantum well structures. The photonic quantum well structure consists of different 1-D photonic structures. We use (AB)₈/C_n/(BA)₈ structure, where A, B and C are different materials. The number of defect layers (C) can be utilized to tune the multi-channel filtering. The filter range can be tuned for desired wavelength with the change in angle of incidence for multi-channel filtering.

Some interesting results are presented in this paper by investigating the characteristics of square high-order mode cavities. Based on the standard printed circuit board (PCB) process and the substrate integrated waveguide (SIW) technology, two different square cavities which exhibit dual-mode filtering response are studied and implemented. Their bandwidths can be controlled by adjusting the eigen-frequencies of the resonating modes and the coupling apertures. The proposed configurations also allow implementing transmission zeros to improve the selectivity in an easy way. A Q-band quasi-elliptic filter using such two cavities in a folded configuration is designed, fabricated and measured. High selectivity and small insertion loss are achieved which are in good agreement with the simulated results.

This paper proposes a miniaturization method for conventional Wilkinson Power Divider(WPD) by replacing the quarter wave sections with the help of fractals. The performance degradation is compensated by using Defected Ground Structure (DGS). The resultant device occupies 56% of the area in comparison to the conventional WPD. The simulation results show a reflection coefficient of -66.98 dB and isolation of 24.1021 dB at the centre frequency of 1.8 GHz. Finally a prototype model is developed on a low cost FR4 Glass Epoxy substrate and tested. The experimental results show a good agreement with the simulation results.

Because of the asymmetry of six-port junctions and the nonlinearity of diode detectors, the calibration of direction finding receivers have to be carefully considered. It is generally believed that an efficient tool for numerical approximations, the artificial neural network (ANN), may be used for such calibrations. In this paper, a new calibration technique based on the ANN is proposed for direction finding receivers at a bandwidth of 1 GHz. The direction finding system adopts a zero-intermediate frequency receiver architecture, which offers the advantage of fast response times. The key modules of this receiver consist of two six-port networks used to measure phase differences and operating frequencies. The results indicate that the calibration technique achieves a high accuracy of 0.192°.

On the basis of backward coupling and left-handed microstrip line, new designs of duplexers and multiplexers will be presented and tested in different configurations. By using microstrip lines with Complementary Split Ring Resonators (CSRRs) etched on the ground plane along with series capacitive gaps in the upper conductor, forward coupling will be inverted into backward coupling. Compact size and fully planar fabrication techniques are important characteristics in the devices proposed.

A compact dual-band ortho-mode transducer is presented in this paper. Two orthogonally polarized signals received by a square waveguide are separated into two orthogonal channels at 10.7-12.75 GHz and 10.3-11.9 GHz, respectively, while a single-polarized signal is transmitted at 14-14.5 GHz. To obtain good isolation between the transmit (Tx) and receive (Rx) channels of the same polarization with a compact size, an irregularly shaped diaphragm is proposed as a compact dual-function resonator, which has one transmission zero at the Tx band and one pole at the Rx band. The designed OMT is fabricated and measured in a back-to-back configuration. Measured results agree very well with simulated ones and the isolation improvement by the diaphragm is about 15 dB, which verifies our design.