Muhammad Amin | Universiti Teknikal Malaysia Melaka (original) (raw)
Papers by Muhammad Amin
Iet Microwaves Antennas & Propagation, 2007
IEEE Microwave and Wireless Components Letters, 2005
I. INTRODUCTION QUADRIFILAR helix antennas (QHAs) are often used to provide the broad beam circul... more I. INTRODUCTION QUADRIFILAR helix antennas (QHAs) are often used to provide the broad beam circularly polarized patterns which are required for satellite communications [1]. The QHA consists of four helical conductors which are excited in phase quadrature at the feed point ...
IEEE Microwave and Wireless Components Letters, 2006
Electronics Letters, 2005
ABSTRACT Introduction: The quadrifilar helix antenna (QHA) is used widely for terrestrial [1] and... more ABSTRACT Introduction: The quadrifilar helix antenna (QHA) is used widely for terrestrial [1] and space communication systems [2], where it is necessary to generate a circularly polarised cardioid-shaped radiation pattern with a high front-to-back ratio and low cross-polarisation. The radiating structure comprises four helical conductors which are excited in phase quadrature at the feed point, which is usually located at the centre of the top radials. The physical size of the quadrifilar antenna can be reduced by dielectric loading [3] or by meandering the printed linear elements [4]. However, in the former arrangement dielectric absorption reduces the radiation efficiency of the antenna, and the latter technique is not suitable for constructing free standing wire structures, which are normally used for spacecraft payloads in the VHF and UHF bands [2]. This Letter shows that a significant reduction in the axial length of a 1/2 turn half-wavelength QHA can be achieved by modifying the geometry of the helices in the region around the midpoint where a current null exists. Simulated and experimental results at L band are used to show that a size reduction of up to 15% is possible without significantly degrading the pattern shape and the bandwidth.
IEEE Transactions on Antennas and Propagation, 2008
... Quadrifilar Helix Antenna With Dual Mode Operation Muhammad Amin, Robert Cahill, and Vincent ... more ... Quadrifilar Helix Antenna With Dual Mode Operation Muhammad Amin, Robert Cahill, and Vincent F. Fusco, Fellow, IEEE AbstractWe show that by introducing a gap at the center of the helical sections (where the current is minimum) of a 2 quadri-...
In this paper we present the results of a study to quantify the mutual coupling between the two b... more In this paper we present the results of a study to quantify the mutual coupling between the two bifilars of a 1/2 turn 1/2 wavelength quadrifilar helix antenna (QHA). A new circuit model approach is used which is suitable for computing the impedance when the structure is fed by a single voltage source as in the case of a self phasing QHA. The validity of the circuit model is first confirmed by comparisons with simulated results obtained from the literature for various configurations of parallel fed dipoles.
Ocean Dynamics, 1986
The variances, or squared standard errors, of estimates of tidal harmonic constants from analyses... more The variances, or squared standard errors, of estimates of tidal harmonic constants from analyses of a month or a year of tide-gauge data are analysed in terms of spectral properties of their noise continuum, modelled as exponential cuspsE 1 superimposed on a smoothly monotonic non-tidal spectrumE 0. Taking 5 representative stations, each with 19 years of data,E 0 is evaluated from the inter-species noise levels, andE 1 from the ratio of the variances from monthly and yearly analyses. It is shown that the cusps surrounding the diurnal tides are dominated byE 0, whereas the more important semi-diurnal and higher species cusps are fitted by an exponential form forE 1 with bandwidth of a few cycles per year. The variance ratios (monthly: yearly analyses) for diurnal harmonics are somewhat greater than the value expected for white noise, partly because of residual tidal lines in the monthly analyses which cannot be related to the major constituents. The corresponding ratios for semi-diurnal and higher species harmonics are less than the white noise value, on account of the cusps. The standard errors of yearly estimates of the larger tidal constituents may be predicted as proportional to their mean amplitude, as a very rough guide, in the approximate ratio of 11 mm/m. Die Varianzen — oder Quadrate der Standardabweichungen — der Abschätzungen von harmonischen Gezeitenkonstanten aus Analysen monatlicher bzw. jährlicher Pegelbeobachtungsreihen werden nach den spektralen Eigenschaften ihres Rauschens analysiert. Dieses wird durch exponentielle SpitzenE 1, die einem glatten monotonen NichtgezeitenspektrumE 0 überlagert sind, dargestellt. Anhand 19 jähriger Beobachtungsreihen von 5 repräsentativen Stationen wirdE 0 aus dem Hintergrundrauschen ermittelt undE 1 aus dem Verhältnis der Varianzen aus monatlichen und jährlichen Analysen. Es wird gezeigt, daß die Spitzen im Bereich der eintägigen Tiden vonE 0 beherrscht werden, die wichtigeren Spitzen der halbtägigen Tiden und der Tiden höherer Ordnung werden dagegen durch einen exponentiellen Ausdruck fürE 1 mit einer Bandbreite von einigen Perioden pro Jahr angenähert. Die Verhältnisse der Varianzen (aus monatlichen zu jährlichen Analysen) für eintägige Harmonische sind etwas größer als der Wert, den man für weißes Rauschen erwarten würde, zum Teil deshalb, weil bei monatlichen Analysen nicht alle Tiden den Hauptkomponenten zugeordnet werden können. Die entsprechenden Verhältnisse für halbtägige und höhere Harmonische sind wegen der Spitzen kleiner als der Wert für weißes Rauschen. Die Standardabweichungen der jährlichen Abschätzungen größerer Gezeitenkomponenten können grob als proportional zu ihrer mittleren Amplitude geschätzt werden mit einem Verhältnis von etwa 11 mm/m. Les variances, ou carrés des écarts types, des estimations de constantes harmoniques de marée provenant d'analyses portant sur un mois ou une année de données marégraphiques sont analysées en terme de propriétés spectrales de leur continuum de bruit, modélisé comme des pics exponentielsE 1 superposés à un spectre ne provenant pas de la marée sensiblement monotoneE 0. Si l'on prend 5 stations représentatives, chacune comportant 19 années d'observations,E 0 est évalué par les niveaux de bruit inter-espèces, etE 1 par le rapport des variances provenant des analyses mensuelles et annuelles. On montre que les pics entourant les marées de type diurne sont dominés parE 0, alors que les pics plus importants de type semidiurne et d'espèces supérieures sont bien approximés par une forme exponentielle pourE 1 avec une largeur de bande de quelques cycles par an. Les rapports de variance (analyses mensuelles/annuelles) des harmoniques diurnes sont un peu plus grands que la valeur attendue pour le bruit blanc, partiellement à cause des composantes de marée résiduelles dans les analyses mensuelles qui ne peuvent pas être rattachées aux composantes majeures. En raison des pics, les rapports correspondants pour les harmoniques des espèces supérieures et semi-diurnes sont inférieures à la valeur du bruit blanc. Les écarts types des valeurs estimées annuelles des composantes principales de marée peuvent être définis grossièrement comme proportionnels à leur amplitude moyenne, en admettant un rapport de proportionnalité approximatif de 11 mm/m.
Iet Microwaves Antennas & Propagation, 2007
IEEE Microwave and Wireless Components Letters, 2005
I. INTRODUCTION QUADRIFILAR helix antennas (QHAs) are often used to provide the broad beam circul... more I. INTRODUCTION QUADRIFILAR helix antennas (QHAs) are often used to provide the broad beam circularly polarized patterns which are required for satellite communications [1]. The QHA consists of four helical conductors which are excited in phase quadrature at the feed point ...
IEEE Microwave and Wireless Components Letters, 2006
Electronics Letters, 2005
ABSTRACT Introduction: The quadrifilar helix antenna (QHA) is used widely for terrestrial [1] and... more ABSTRACT Introduction: The quadrifilar helix antenna (QHA) is used widely for terrestrial [1] and space communication systems [2], where it is necessary to generate a circularly polarised cardioid-shaped radiation pattern with a high front-to-back ratio and low cross-polarisation. The radiating structure comprises four helical conductors which are excited in phase quadrature at the feed point, which is usually located at the centre of the top radials. The physical size of the quadrifilar antenna can be reduced by dielectric loading [3] or by meandering the printed linear elements [4]. However, in the former arrangement dielectric absorption reduces the radiation efficiency of the antenna, and the latter technique is not suitable for constructing free standing wire structures, which are normally used for spacecraft payloads in the VHF and UHF bands [2]. This Letter shows that a significant reduction in the axial length of a 1/2 turn half-wavelength QHA can be achieved by modifying the geometry of the helices in the region around the midpoint where a current null exists. Simulated and experimental results at L band are used to show that a size reduction of up to 15% is possible without significantly degrading the pattern shape and the bandwidth.
IEEE Transactions on Antennas and Propagation, 2008
... Quadrifilar Helix Antenna With Dual Mode Operation Muhammad Amin, Robert Cahill, and Vincent ... more ... Quadrifilar Helix Antenna With Dual Mode Operation Muhammad Amin, Robert Cahill, and Vincent F. Fusco, Fellow, IEEE AbstractWe show that by introducing a gap at the center of the helical sections (where the current is minimum) of a 2 quadri-...
In this paper we present the results of a study to quantify the mutual coupling between the two b... more In this paper we present the results of a study to quantify the mutual coupling between the two bifilars of a 1/2 turn 1/2 wavelength quadrifilar helix antenna (QHA). A new circuit model approach is used which is suitable for computing the impedance when the structure is fed by a single voltage source as in the case of a self phasing QHA. The validity of the circuit model is first confirmed by comparisons with simulated results obtained from the literature for various configurations of parallel fed dipoles.
Ocean Dynamics, 1986
The variances, or squared standard errors, of estimates of tidal harmonic constants from analyses... more The variances, or squared standard errors, of estimates of tidal harmonic constants from analyses of a month or a year of tide-gauge data are analysed in terms of spectral properties of their noise continuum, modelled as exponential cuspsE 1 superimposed on a smoothly monotonic non-tidal spectrumE 0. Taking 5 representative stations, each with 19 years of data,E 0 is evaluated from the inter-species noise levels, andE 1 from the ratio of the variances from monthly and yearly analyses. It is shown that the cusps surrounding the diurnal tides are dominated byE 0, whereas the more important semi-diurnal and higher species cusps are fitted by an exponential form forE 1 with bandwidth of a few cycles per year. The variance ratios (monthly: yearly analyses) for diurnal harmonics are somewhat greater than the value expected for white noise, partly because of residual tidal lines in the monthly analyses which cannot be related to the major constituents. The corresponding ratios for semi-diurnal and higher species harmonics are less than the white noise value, on account of the cusps. The standard errors of yearly estimates of the larger tidal constituents may be predicted as proportional to their mean amplitude, as a very rough guide, in the approximate ratio of 11 mm/m. Die Varianzen — oder Quadrate der Standardabweichungen — der Abschätzungen von harmonischen Gezeitenkonstanten aus Analysen monatlicher bzw. jährlicher Pegelbeobachtungsreihen werden nach den spektralen Eigenschaften ihres Rauschens analysiert. Dieses wird durch exponentielle SpitzenE 1, die einem glatten monotonen NichtgezeitenspektrumE 0 überlagert sind, dargestellt. Anhand 19 jähriger Beobachtungsreihen von 5 repräsentativen Stationen wirdE 0 aus dem Hintergrundrauschen ermittelt undE 1 aus dem Verhältnis der Varianzen aus monatlichen und jährlichen Analysen. Es wird gezeigt, daß die Spitzen im Bereich der eintägigen Tiden vonE 0 beherrscht werden, die wichtigeren Spitzen der halbtägigen Tiden und der Tiden höherer Ordnung werden dagegen durch einen exponentiellen Ausdruck fürE 1 mit einer Bandbreite von einigen Perioden pro Jahr angenähert. Die Verhältnisse der Varianzen (aus monatlichen zu jährlichen Analysen) für eintägige Harmonische sind etwas größer als der Wert, den man für weißes Rauschen erwarten würde, zum Teil deshalb, weil bei monatlichen Analysen nicht alle Tiden den Hauptkomponenten zugeordnet werden können. Die entsprechenden Verhältnisse für halbtägige und höhere Harmonische sind wegen der Spitzen kleiner als der Wert für weißes Rauschen. Die Standardabweichungen der jährlichen Abschätzungen größerer Gezeitenkomponenten können grob als proportional zu ihrer mittleren Amplitude geschätzt werden mit einem Verhältnis von etwa 11 mm/m. Les variances, ou carrés des écarts types, des estimations de constantes harmoniques de marée provenant d'analyses portant sur un mois ou une année de données marégraphiques sont analysées en terme de propriétés spectrales de leur continuum de bruit, modélisé comme des pics exponentielsE 1 superposés à un spectre ne provenant pas de la marée sensiblement monotoneE 0. Si l'on prend 5 stations représentatives, chacune comportant 19 années d'observations,E 0 est évalué par les niveaux de bruit inter-espèces, etE 1 par le rapport des variances provenant des analyses mensuelles et annuelles. On montre que les pics entourant les marées de type diurne sont dominés parE 0, alors que les pics plus importants de type semidiurne et d'espèces supérieures sont bien approximés par une forme exponentielle pourE 1 avec une largeur de bande de quelques cycles par an. Les rapports de variance (analyses mensuelles/annuelles) des harmoniques diurnes sont un peu plus grands que la valeur attendue pour le bruit blanc, partiellement à cause des composantes de marée résiduelles dans les analyses mensuelles qui ne peuvent pas être rattachées aux composantes majeures. En raison des pics, les rapports correspondants pour les harmoniques des espèces supérieures et semi-diurnes sont inférieures à la valeur du bruit blanc. Les écarts types des valeurs estimées annuelles des composantes principales de marée peuvent être définis grossièrement comme proportionnels à leur amplitude moyenne, en admettant un rapport de proportionnalité approximatif de 11 mm/m.