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Papers by mohammad mohammadirad

IEEE Antennas and Wireless Propagation Letters, 2015

A novel broadband unit-cell is proposed in this paper. This new cell element consists of three co... more A novel broadband unit-cell is proposed in this paper. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 o of phase swing. The cross polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal or circular polarization. Finally a moderate size reflectarray, 27×27 cm 2 , is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1 dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB which is equivalent to 59.2% efficiency. Also, the measured sidelobe level and cross polarization of this antenna are about-20 dB and-25 dB, respectively.

Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2016

2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011

The effect of changing the feed position on performance of a broadband reflectarray is investigat... more The effect of changing the feed position on performance of a broadband reflectarray is investigated in this paper. An offset-fed broadband reflectarray is designed based on a unit-cell with wideband properties in X-Ku band. The proposed cell element consists of three concentric rectangular loops on a two-layer structure. The dimensions of the cell element have been optimized to achieve linear

IEEE Antennas and Wireless Propagation Letters, 2015

A novel broadband unit-cell is proposed in this paper. This new cell element consists of three co... more A novel broadband unit-cell is proposed in this paper. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 o of phase swing. The cross polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal or circular polarization. Finally a moderate size reflectarray, 27×27 cm 2 , is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1 dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB which is equivalent to 59.2% efficiency. Also, the measured sidelobe level and cross polarization of this antenna are about-20 dB and-25 dB, respectively.

International Journal of RF and Microwave Computer-Aided Engineering, 2012

A new cell element is introduced for broadband reflectarray applications. The presented unit cell... more A new cell element is introduced for broadband reflectarray applications. The presented unit cell exhibits linear phase response which makes it a suitable candidate for broadband X-Ku band applications. This cell element consists of three concentric rectangular loops etched on a two-layer grounded substrate. The dimensions of the cell element have been optimized to achieve linear phase response in the operation band. A square offset-fed reflectarray of 40 cm  40 cm was designed and fabricated based on this unit cell with wideband performance at X-Ku band. Considering three different feed positions, the whole reflectarray was simulated in CST and good agreement between simulated and measured results was observed. A maximum gain of 32 dBi was obtained which is equivalent to 58% aperture efficiency. Also, a remarkable value of 36%, 1.5-dB gain bandwidth was measured which is higher compared to previously reported designs in the literature. Another investigation that is carried out in this development through theory and simulation is determination of the effect of feed movement along the focal axis on the operating band of the reflectarray. It is shown for the first time that changing the feed location leads to a considerable shift in the operation bandwidth and maximum gain of the designed broadband reflectarray.

IEEE Antennas and Wireless Propagation Letters, 2012

ABSTRACT In this letter, the effect of moving the feed on the operation bandwidth of a broadband ... more ABSTRACT In this letter, the effect of moving the feed on the operation bandwidth of a broadband reflectarray is investigated through simulation and measurement. A new broadband cell element with optimized dimensions to achieve linear phase shift is proposed in this investigation. A square reflectarray of 40×40 cm2 comprising this particular unit cell was designed and fabricated to demonstrate wideband operation at X-Ku band. The effect of feed movement on the operating band was studied by exciting the reflectarray with a plane wave and monitoring the near field on the line passing through the assumed feed locations over a wide frequency band. Considering three different feed positions, the reflectarray was simulated, and good agreement between simulated and measured results was observed. It is shown that changing the feed location leads to a considerable shift in operating frequency window of the reflectarray and also its maximum gain, which gives rise to the possibility of changing the operating band without redesigning the reflectarray by only moving the feed. Moreover, a remarkable value of 36% of 1.5 dB gain-bandwidth was measured, which is higher compared to previously reported designs in the literature.

Electromagnetics, 2014

ABSTRACT This article describes the analysis and design of a new beam-scanning dual-reflectarray ... more ABSTRACT This article describes the analysis and design of a new beam-scanning dual-reflectarray antenna in an offset Gregorian configuration. The phase distribution on sub-reflectarray is introduced based on a new formulation. In this method, the distances between the real and virtual focal points of the reflectarray and its nth element are taken into account. Introducing a progressive phase-shift term into the basic equation, the produced pencil beam is scanned accordingly. Actually, the large main reflectarray emulates a parabolic reflector, and by introducing phase control into the elements of the small sub-reflectarray, beam scanning is achieved. These elements are based on an ideal reconfigurable element, while a wideband multi-loop element is considered on the main reflectarray. The beam-scanning performance of this dual-reflectarray antenna is investigated in the XZ-plane and also for eight beams around the broadside direction at 12.5 GHz.

AEU - International Journal of Electronics and Communications, 2011

ABSTRACT In this paper the electric-type dyadic Green’s function for a conducting and a homogeneo... more ABSTRACT In this paper the electric-type dyadic Green’s function for a conducting and a homogeneous dielectric sphere in a uniaxial anisotropic media is presented. For this purpose we use the modified spherical vector wave functions in the uniaxial unbounded media. In the uniaxial media ϵ¯¯ and μ¯¯ are tensors. The coefficients for scattered dyadic Green’s function (DGF), are derived based on scattering superposition method. Deriving these DGFs, and knowing the current source distribution, the electromagnetic fields will be known throughout the medium.

2010 14th International Symposium on Antenna Technology and Applied Electromagnetics & the American Electromagnetics Conference, 2010

This paper presents a new microstrip-fed wideband low-profile planar quasi-monopole antenna with ... more This paper presents a new microstrip-fed wideband low-profile planar quasi-monopole antenna with total size of 30×40×0.79mm3. Practically, this antenna is a modified and improved version of Planar Inverted Cone Antenna (PICA). The proposed antenna consists of a quasi-triangular radiating element with two slits and a deformed ground plane, which provides wide bandwidth about 7.2GHz (3.8-11 GHz). This frequency range includes the Wireless Local Area Network (WLAN) band; hence we use a U-shape slot in radiating element to reject 5GHz-WLAN band. Simulated and measured results exhibit large impedance bandwidth and appropriate radiation pattern that is desired for UWB applications.

IEEE Antennas and Wireless Propagation Letters, 2015

A novel broadband unit-cell is proposed in this paper. This new cell element consists of three co... more A novel broadband unit-cell is proposed in this paper. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 o of phase swing. The cross polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal or circular polarization. Finally a moderate size reflectarray, 27×27 cm 2 , is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1 dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB which is equivalent to 59.2% efficiency. Also, the measured sidelobe level and cross polarization of this antenna are about-20 dB and-25 dB, respectively.

Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2016

2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011

The effect of changing the feed position on performance of a broadband reflectarray is investigat... more The effect of changing the feed position on performance of a broadband reflectarray is investigated in this paper. An offset-fed broadband reflectarray is designed based on a unit-cell with wideband properties in X-Ku band. The proposed cell element consists of three concentric rectangular loops on a two-layer structure. The dimensions of the cell element have been optimized to achieve linear

IEEE Antennas and Wireless Propagation Letters, 2015

A novel broadband unit-cell is proposed in this paper. This new cell element consists of three co... more A novel broadband unit-cell is proposed in this paper. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 o of phase swing. The cross polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal or circular polarization. Finally a moderate size reflectarray, 27×27 cm 2 , is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1 dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB which is equivalent to 59.2% efficiency. Also, the measured sidelobe level and cross polarization of this antenna are about-20 dB and-25 dB, respectively.

International Journal of RF and Microwave Computer-Aided Engineering, 2012

A new cell element is introduced for broadband reflectarray applications. The presented unit cell... more A new cell element is introduced for broadband reflectarray applications. The presented unit cell exhibits linear phase response which makes it a suitable candidate for broadband X-Ku band applications. This cell element consists of three concentric rectangular loops etched on a two-layer grounded substrate. The dimensions of the cell element have been optimized to achieve linear phase response in the operation band. A square offset-fed reflectarray of 40 cm  40 cm was designed and fabricated based on this unit cell with wideband performance at X-Ku band. Considering three different feed positions, the whole reflectarray was simulated in CST and good agreement between simulated and measured results was observed. A maximum gain of 32 dBi was obtained which is equivalent to 58% aperture efficiency. Also, a remarkable value of 36%, 1.5-dB gain bandwidth was measured which is higher compared to previously reported designs in the literature. Another investigation that is carried out in this development through theory and simulation is determination of the effect of feed movement along the focal axis on the operating band of the reflectarray. It is shown for the first time that changing the feed location leads to a considerable shift in the operation bandwidth and maximum gain of the designed broadband reflectarray.

IEEE Antennas and Wireless Propagation Letters, 2012

ABSTRACT In this letter, the effect of moving the feed on the operation bandwidth of a broadband ... more ABSTRACT In this letter, the effect of moving the feed on the operation bandwidth of a broadband reflectarray is investigated through simulation and measurement. A new broadband cell element with optimized dimensions to achieve linear phase shift is proposed in this investigation. A square reflectarray of 40×40 cm2 comprising this particular unit cell was designed and fabricated to demonstrate wideband operation at X-Ku band. The effect of feed movement on the operating band was studied by exciting the reflectarray with a plane wave and monitoring the near field on the line passing through the assumed feed locations over a wide frequency band. Considering three different feed positions, the reflectarray was simulated, and good agreement between simulated and measured results was observed. It is shown that changing the feed location leads to a considerable shift in operating frequency window of the reflectarray and also its maximum gain, which gives rise to the possibility of changing the operating band without redesigning the reflectarray by only moving the feed. Moreover, a remarkable value of 36% of 1.5 dB gain-bandwidth was measured, which is higher compared to previously reported designs in the literature.

Electromagnetics, 2014

ABSTRACT This article describes the analysis and design of a new beam-scanning dual-reflectarray ... more ABSTRACT This article describes the analysis and design of a new beam-scanning dual-reflectarray antenna in an offset Gregorian configuration. The phase distribution on sub-reflectarray is introduced based on a new formulation. In this method, the distances between the real and virtual focal points of the reflectarray and its nth element are taken into account. Introducing a progressive phase-shift term into the basic equation, the produced pencil beam is scanned accordingly. Actually, the large main reflectarray emulates a parabolic reflector, and by introducing phase control into the elements of the small sub-reflectarray, beam scanning is achieved. These elements are based on an ideal reconfigurable element, while a wideband multi-loop element is considered on the main reflectarray. The beam-scanning performance of this dual-reflectarray antenna is investigated in the XZ-plane and also for eight beams around the broadside direction at 12.5 GHz.

AEU - International Journal of Electronics and Communications, 2011

ABSTRACT In this paper the electric-type dyadic Green’s function for a conducting and a homogeneo... more ABSTRACT In this paper the electric-type dyadic Green’s function for a conducting and a homogeneous dielectric sphere in a uniaxial anisotropic media is presented. For this purpose we use the modified spherical vector wave functions in the uniaxial unbounded media. In the uniaxial media ϵ¯¯ and μ¯¯ are tensors. The coefficients for scattered dyadic Green’s function (DGF), are derived based on scattering superposition method. Deriving these DGFs, and knowing the current source distribution, the electromagnetic fields will be known throughout the medium.

2010 14th International Symposium on Antenna Technology and Applied Electromagnetics & the American Electromagnetics Conference, 2010

This paper presents a new microstrip-fed wideband low-profile planar quasi-monopole antenna with ... more This paper presents a new microstrip-fed wideband low-profile planar quasi-monopole antenna with total size of 30×40×0.79mm3. Practically, this antenna is a modified and improved version of Planar Inverted Cone Antenna (PICA). The proposed antenna consists of a quasi-triangular radiating element with two slits and a deformed ground plane, which provides wide bandwidth about 7.2GHz (3.8-11 GHz). This frequency range includes the Wireless Local Area Network (WLAN) band; hence we use a U-shape slot in radiating element to reject 5GHz-WLAN band. Simulated and measured results exhibit large impedance bandwidth and appropriate radiation pattern that is desired for UWB applications.