Symposium on Antenna Technology and Applied Electromagnetics [ANTEM 2000], 2000
Using surface equivalence principle and multiple network theory (SEMN) several finite microstrip ... more Using surface equivalence principle and multiple network theory (SEMN) several finite microstrip antennas were analyzed and their numerical results were compared with those of ENSEMBEL (an electromagnetic simulation software for microstrip antennas) [1]. It was derived that an infinite substrate assumption is considered in ENSEMBEL which results in zero electromagnetic radiation patterns at grazing angles and inaccurate numerical results for small substrate dimensions. In SEMN method, it was derived that a large number of surface segments are required for finite microstrip antennas that their substrates are not electrically too small.
This paper investigates the miniaturization capability of split ring array antennas embedded in a... more This paper investigates the miniaturization capability of split ring array antennas embedded in a low-permittivity dielectric substrate, in comparison with the same-sized high-permittivity dielectric resonator antennas (DRAs). In order to understand the miniaturization performance, a size-fixed dielectric substrate with different split ring arrays is studied. The simulation results show that the miniaturization capability increases with decreased unit cell resonant frequency and/or increased unit cell induced permeability. Miniaturizations as high as 25.54 times that of a high-permittivity DRA are obtained with split rings, etched on a dielectric substrate having a low permittivity of 2.2. Furthermore, this excessive miniaturization does not come at the expense of excessive deterioration of the antenna impedance bandwidth, gain, and radiation efficiency. Consequently, the miniaturized split ring arrays still provide high gains over wider bandwidths. This inference is further verifie...
IEEE Antennas and Propagation Society International Symposium. Transmitting Waves of Progress to the Next Millennium. 2000 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.00CH37118)
IEEE Antennas and Propagation Society International Symposium. Digest. Held in conjunction with: USNC/CNC/URSI North American Radio Sci. Meeting (Cat. No.03CH37450)
... C. Shafai*. L. Shafai, S . Sharma and Dwayne D. Chlusch Depamnent of Electrical & Compute... more ... C. Shafai*. L. Shafai, S . Sharma and Dwayne D. Chlusch Depamnent of Electrical & Computer Engineering University of Manitoba, Winnipeg, Manitoba, Canada R3T 5V6 ... Sweden, pp. 384. June 1995. [3] HCctor 1. De Los Santos, "Application of MEMS Technology to ...
2012 15 International Symposium on Antenna Technology and Applied Electromagnetics, 2012
ABSTRACT We present a preliminary study on the design of a dual-band microstrip antenna array whi... more ABSTRACT We present a preliminary study on the design of a dual-band microstrip antenna array which operates at the centre frequencies of 1.25 GHz for L-band and 9.65 GHz for X-band. Since the ratio of the L-band and X-band frequencies is approximately a factor of eight, the inter-element spacing of X-band patches must be smaller by the same factor. In order to share the same aperture, the L-band and X-band patches must be integrated. A perforated L-band patch design is used, permitting the X-band patches to be placed within the same planar geometry. Design variations, such as feeding mechanisms and stacked patch configurations, are examined and discussed.
IEEE Transactions on Antennas and Propagation, 1972
Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimens... more Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimensional problem using an integral equation method. Because of practical interest, the computed patterns are shown for only small to moderate sizes of the strips and small to moderate separation distances of the antenna.
Antennas and Propagation Society Symposium 1991 Digest
A comparative study between different approaches to modeling thin wire scatterers using the finit... more A comparative study between different approaches to modeling thin wire scatterers using the finite-difference-time-domain (FDTD) numerical technique is presented. These approaches include nulling of the electric fields on the wire, modeling the wire to be one FDTD cell in thickness, and contour integral wire modeling. The method of moments adopted by the numerical electromagnetic code is used as a basis for comparison. The equal cell area-wire cross-section procedure gave accurate results but was expensive in memory requirements, while the contour integral method provided an efficient and accurate wire modeling technique
A dual-parabolic-cylinder antenna structure for producing elliptical beams of arbitrary elliptici... more A dual-parabolic-cylinder antenna structure for producing elliptical beams of arbitrary ellipticity (Sanad and Shafai, 1985 and 1986) is investigated analytically, with a focus on the cross polarization behavior. The effects of offset angles and edge diffraction are studied, and the results are presented in diagrams and graphs. The peak cross-polarization level is found to depend mainly on the feed offset angle in the symmetric plane, regardless of the offset configuration employed.
IEEE Transactions on Antennas and Propagation, 2003
AbstractA novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) C... more AbstractA novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) Cassegrain system is described. In this system a Feed-Reflector is used to illuminate a reconformable hyperboloid subreflector with 5 10 m diameter, located 500 m above the ...
IEEE Transactions on Antennas and Propagation, 2004
This paper presents the simulation and experimental investigations of a printed microstrip slot a... more This paper presents the simulation and experimental investigations of a printed microstrip slot antenna. It is a quarter wavelength monopole slot cut in the finite ground plane edge, and fed electromagnetically by a microstrip transmission line. It provides a wide impedance bandwidth adjustable by variation of its parameters, such as the relative permittivity and thickness of the substrate, width, and location of the slot in the ground plane, and feed and ground plane dimensions. The ground plane is small, 50 mm 80 mm, and is about the size of a typical PC wireless card. At the center frequency of 3.00 GHz, its width of 50 mm is about 2 and influences the slot impedance and bandwidth significantly. An impedance bandwidth (11 = 10 dB) of up to about 60% is achieved by individually optimizing its parameters. The simulation results are confirmed experimentally. A dual complementary slot antenna configuration is also investigated for the polarization diversity.
IEEE Transactions on Antennas and Propagation, 2012
An analytic model for the primary feed of offset reflector antennas is presented that facilitates... more An analytic model for the primary feed of offset reflector antennas is presented that facilitates a more general investigation of the cross polarization reduction in both asymmetric and inter-cardinal planes. It includes both first and second order azimuthal modes, primarily the ${\rm TE}_{11}$ and ${\rm TE}_{21}$ type modes, and allows selection of symmetric and asymmetrical patterns, with different field tapers in the principal planes. Using this model first the influence of the second order ${\rm TE}_{21}$ mode on the cross polarization of an offset reflector with a circular rim is investigated. Then, the problem for an offset reflector with an elliptic rim is also studied. It is shown that minimizing the cross polarization in the asymmetric plane does not necessarily reduce it globally, as in the inter-cardinal plane it remains high. The procedure for reduction of the cross polarization globally and its effects on the sidelobe levels of the reflector antenna are also investigated. With the proposed feed model, the aperture efficiency of the reflector antenna is improved compared with a standard Gaussian feed with the same edge taper. Based on this study, a dual-mode circular waveguide horn is also proposed and designed. Its performance on an offset reflector antenna is studied and shown that the cross polarization levels are reduced quite satisfactorily within a respectable frequency band.
Symposium on Antenna Technology and Applied Electromagnetics [ANTEM 2000], 2000
Using surface equivalence principle and multiple network theory (SEMN) several finite microstrip ... more Using surface equivalence principle and multiple network theory (SEMN) several finite microstrip antennas were analyzed and their numerical results were compared with those of ENSEMBEL (an electromagnetic simulation software for microstrip antennas) [1]. It was derived that an infinite substrate assumption is considered in ENSEMBEL which results in zero electromagnetic radiation patterns at grazing angles and inaccurate numerical results for small substrate dimensions. In SEMN method, it was derived that a large number of surface segments are required for finite microstrip antennas that their substrates are not electrically too small.
This paper investigates the miniaturization capability of split ring array antennas embedded in a... more This paper investigates the miniaturization capability of split ring array antennas embedded in a low-permittivity dielectric substrate, in comparison with the same-sized high-permittivity dielectric resonator antennas (DRAs). In order to understand the miniaturization performance, a size-fixed dielectric substrate with different split ring arrays is studied. The simulation results show that the miniaturization capability increases with decreased unit cell resonant frequency and/or increased unit cell induced permeability. Miniaturizations as high as 25.54 times that of a high-permittivity DRA are obtained with split rings, etched on a dielectric substrate having a low permittivity of 2.2. Furthermore, this excessive miniaturization does not come at the expense of excessive deterioration of the antenna impedance bandwidth, gain, and radiation efficiency. Consequently, the miniaturized split ring arrays still provide high gains over wider bandwidths. This inference is further verifie...
IEEE Antennas and Propagation Society International Symposium. Transmitting Waves of Progress to the Next Millennium. 2000 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.00CH37118)
IEEE Antennas and Propagation Society International Symposium. Digest. Held in conjunction with: USNC/CNC/URSI North American Radio Sci. Meeting (Cat. No.03CH37450)
... C. Shafai*. L. Shafai, S . Sharma and Dwayne D. Chlusch Depamnent of Electrical & Compute... more ... C. Shafai*. L. Shafai, S . Sharma and Dwayne D. Chlusch Depamnent of Electrical & Computer Engineering University of Manitoba, Winnipeg, Manitoba, Canada R3T 5V6 ... Sweden, pp. 384. June 1995. [3] HCctor 1. De Los Santos, "Application of MEMS Technology to ...
2012 15 International Symposium on Antenna Technology and Applied Electromagnetics, 2012
ABSTRACT We present a preliminary study on the design of a dual-band microstrip antenna array whi... more ABSTRACT We present a preliminary study on the design of a dual-band microstrip antenna array which operates at the centre frequencies of 1.25 GHz for L-band and 9.65 GHz for X-band. Since the ratio of the L-band and X-band frequencies is approximately a factor of eight, the inter-element spacing of X-band patches must be smaller by the same factor. In order to share the same aperture, the L-band and X-band patches must be integrated. A perforated L-band patch design is used, permitting the X-band patches to be placed within the same planar geometry. Design variations, such as feeding mechanisms and stacked patch configurations, are examined and discussed.
IEEE Transactions on Antennas and Propagation, 1972
Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimens... more Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimensional problem using an integral equation method. Because of practical interest, the computed patterns are shown for only small to moderate sizes of the strips and small to moderate separation distances of the antenna.
Antennas and Propagation Society Symposium 1991 Digest
A comparative study between different approaches to modeling thin wire scatterers using the finit... more A comparative study between different approaches to modeling thin wire scatterers using the finite-difference-time-domain (FDTD) numerical technique is presented. These approaches include nulling of the electric fields on the wire, modeling the wire to be one FDTD cell in thickness, and contour integral wire modeling. The method of moments adopted by the numerical electromagnetic code is used as a basis for comparison. The equal cell area-wire cross-section procedure gave accurate results but was expensive in memory requirements, while the contour integral method provided an efficient and accurate wire modeling technique
A dual-parabolic-cylinder antenna structure for producing elliptical beams of arbitrary elliptici... more A dual-parabolic-cylinder antenna structure for producing elliptical beams of arbitrary ellipticity (Sanad and Shafai, 1985 and 1986) is investigated analytically, with a focus on the cross polarization behavior. The effects of offset angles and edge diffraction are studied, and the results are presented in diagrams and graphs. The peak cross-polarization level is found to depend mainly on the feed offset angle in the symmetric plane, regardless of the offset configuration employed.
IEEE Transactions on Antennas and Propagation, 2003
AbstractA novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) C... more AbstractA novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) Cassegrain system is described. In this system a Feed-Reflector is used to illuminate a reconformable hyperboloid subreflector with 5 10 m diameter, located 500 m above the ...
IEEE Transactions on Antennas and Propagation, 2004
This paper presents the simulation and experimental investigations of a printed microstrip slot a... more This paper presents the simulation and experimental investigations of a printed microstrip slot antenna. It is a quarter wavelength monopole slot cut in the finite ground plane edge, and fed electromagnetically by a microstrip transmission line. It provides a wide impedance bandwidth adjustable by variation of its parameters, such as the relative permittivity and thickness of the substrate, width, and location of the slot in the ground plane, and feed and ground plane dimensions. The ground plane is small, 50 mm 80 mm, and is about the size of a typical PC wireless card. At the center frequency of 3.00 GHz, its width of 50 mm is about 2 and influences the slot impedance and bandwidth significantly. An impedance bandwidth (11 = 10 dB) of up to about 60% is achieved by individually optimizing its parameters. The simulation results are confirmed experimentally. A dual complementary slot antenna configuration is also investigated for the polarization diversity.
IEEE Transactions on Antennas and Propagation, 2012
An analytic model for the primary feed of offset reflector antennas is presented that facilitates... more An analytic model for the primary feed of offset reflector antennas is presented that facilitates a more general investigation of the cross polarization reduction in both asymmetric and inter-cardinal planes. It includes both first and second order azimuthal modes, primarily the ${\rm TE}_{11}$ and ${\rm TE}_{21}$ type modes, and allows selection of symmetric and asymmetrical patterns, with different field tapers in the principal planes. Using this model first the influence of the second order ${\rm TE}_{21}$ mode on the cross polarization of an offset reflector with a circular rim is investigated. Then, the problem for an offset reflector with an elliptic rim is also studied. It is shown that minimizing the cross polarization in the asymmetric plane does not necessarily reduce it globally, as in the inter-cardinal plane it remains high. The procedure for reduction of the cross polarization globally and its effects on the sidelobe levels of the reflector antenna are also investigated. With the proposed feed model, the aperture efficiency of the reflector antenna is improved compared with a standard Gaussian feed with the same edge taper. Based on this study, a dual-mode circular waveguide horn is also proposed and designed. Its performance on an offset reflector antenna is studied and shown that the cross polarization levels are reduced quite satisfactorily within a respectable frequency band.
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Papers by L. Shafai