Malcolm Ng Mou Kehn

Bio: Malcolm Ng Mou Kehn is an academic researcher from National Chiao Tung University. The author has contributed to research in topics: Boundary value problem & Antenna efficiency. The author has an hindex of 15, co-authored 82 publications receiving 854 citations. Previous affiliations of Malcolm Ng Mou Kehn include Chalmers University of Technology & University of Winnipeg.

Ultrawideband Metasurface Lenses Based on Off-Shifted Opposite Layers

Abstract: Metasurfaces have demonstrated to be a low-cost solution for the development of directive antennas at high frequency. One of the opportunities of metasurfaces is the possibility to produce planar l ...

Miniaturized rectangular hard waveguides for use in multifrequency phased arrays

Abstract: The elements of a multiband array need to be small to allow elements of other frequencies to be interlaced over the same array aperture. This paper investigates the use of miniaturized open-ended partially dielectric-loaded hard-walled rectangular waveguides for this purpose. Apart from studying its modal properties, we seek to find out how it performs in an infinite planar array environment. Specifically, we study how the various array parameters affect its radiation characteristics. Comparisons are also made with fully filled waveguides. The waveguides are matched at broadside. The results show a narrow-band solution.

Decoupling Efficiency of a Wideband Vivaldi Focal Plane Array Feeding a Reflector Antenna

Abstract: A focal plane array (FPA) feeding a reflector can be used to achieve a large field of view (FOV) with overlapping simultaneous beams. In order to provide a continuous FOV over more than an octave bandwidth, the inter-element spacing in the FPA has to be electrically small over large parts of the band. This will inevitably result in strong mutual coupling effects between the array elements. On transmit, the total lost power due to mutual coupling can be quantified by the decoupling efficiency, a term recently introduced for antenna arrays. This paper presents measured decoupling efficiencies of a Vivaldi element FPA operating between 2.3 and 7 GHz. The radiation patterns of the FPA are calculated for two beam excitations by using measured embedded element patterns, and the corresponding decoupling efficiencies are evaluated by using measured S -parameters between all element ports. The FPA is assumed to illuminate a deep reflector with F/D=0.35 , and the overall reflector aperture efficiencies are computed. The decoupling efficiencies are also determined through the measurements of the total radiation efficiencies in a reverberation chamber, which includes material absorption losses.

Reply to "Comments on 'Decoupling efficiency of a wideband vivaldi focal plane array feeding a reflector antenna'"

Abstract: The authors of the original paper wish to thank Prof. Skobelev for complimenting their work and for his comments. Their response to the two points made in the Comment are provide.

Reconfigurable Loaded Planar Inverted-F Antenna Using Varactor Diodes

Abstract: This letter presents a compact reconfigurable multiband microstrip antenna. The multiplicity of bands is achieved by the use of concentric external metallic semirings around a central internal semicircular microstrip patch. These are all shorted to the ground plane via a vertical metallic wall through the common diametric plane, thereby adopting the concept of the planar inverted-F antenna (PIFA) for size reduction and thus compactness. The operation frequencies are tuned by varactor diodes placed between the inner semicircular patch and the outer half-rings. In addition to tunability, the overall bandwidth may also be widened by combining the tunable range. Theoretical simulations and measurements of manufactured prototypes agree well with each other.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression

Abstract: This study describes the design and experimental verification of the ridge gap waveguide, appearing in the gap between parallel metal plates. One of the plates has a texture in the form of a wave-guiding metal ridge surrounded by metal posts. The latter posts, referred to as a pin surface or bed of nails, are designed to give a stopband for the normal parallel-plate modes between 10 and 23 GHz. The hardware demonstrator includes two 90 bends and two capacitive coupled coaxial transitions enabling measurements with a vector network analyser (VNA). The measured results verify the large bandwidth and low losses of the quasi-transverse electromagnetic (TEM) mode propagating along the guiding ridge, and that 90 bends can be designed in the same way as for microstrip lines. The demonstrator is designed for use around 15 GHz. Still, the ridge gap waveguide is more advantageous for frequencies above 30 GHz, because it can be realised entirely from metal using milling or moulding, and there are no requirements for conducting joints between the two plates that otherwise is a problem when realising conventional hollow waveguides.

Substrate Integrated Waveguide Loaded by Complementary Split-Ring Resonators and Its Applications to Miniaturized Waveguide Filters

Abstract: A substrate integrated waveguide with square complementary split-ring resonators (CSRRs) etched on the waveguide surface is investigated in this paper. The proposed structures allow the implementation of a forward-wave passband propagating below the characteristic cutoff frequency of the waveguide. By changing the orientations of the CSRRs, which are incorporated in the waveguide surface and can be interpreted in terms of electric dipoles, varied passband characteristics are observed. A detailed explanation for the generation and variations of the passbands has been illuminated. The application of this waveguide and CSRR combination technique to the design of miniaturized waveguide bandpass filters characterized by transmission zeros is then illustrated. Filter design methodology is examined. These proposed filters exhibit high selectivity and compact size due to the employment of the subwavelength resonators and an evanescent-wave transmission. By slightly altering the configuration of the CSRRs, we find that the propagation of the TE10 mode can be suppressed and filters with improved selectivity and stopband rejection can be obtained. To verify the presented concept, three different types of filters are fabricated based on the standard printed circuit board process. The measured results are in good agreement with the simulation.

Waveguide miniaturization using uniaxial negative permeability metamaterial

Abstract: A rectangular waveguide filled with anisotropic uniaxial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Three metamaterial-based gap waveguides between parallel metal plates for mm/submm waves

Abstract: This paper presents the basic ideas of how local waveguides and transmission lines can be designed to propagate along desired paths in the air gap between two metal surfaces. The principle of operation is related to the performance of artificial magnetic conductors, EBG surfaces and soft and hard surfaces. Three different major types of gap waveguides are described: ridge gap waveguides, microstrip gap lines and groove gap waveguides. Different realizations of the cut-off structures suppressing normal parallel plate modes are described, as well as expected applications, and possible problem areas preferably seen as research challenges.