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A figure of merit in a time-modulated array
, Article IEEE Antennas and Wireless Propagation Letters ; Volume 18, Issue 10 , 2019 , Pages 2086-2089 ; 15361225 (ISSN) ; Fakharzadeh, M ; Akbari, M ; Safavi Naeini, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
In this letter, we use G/T as a figure of merit to evaluate the performance of time-modulated arrays (TMA). The noise performance of a receiver, which is periodically switched on and off, is quite different from that of a conventional receiver. We analytically investigate the noise performance of a TMA. Based on this analysis, the figure of merit, G/T, of the TMA structure is investigated, including the details of the receiver hardware. Moreover, the G/T of the TMA is compared with that of a phased array. The comparison indicates that the TMA structure provides the same or even better performance compared to a phased array system, which demonstrates the capability of TMA in providing...
A time modulated array with polarization diversity capability
, Article IEEE Access ; Volume 9 , 2021 , Pages 53735-53744 ; 21693536 (ISSN) ; Fakharzadeh, M ; Akbari, M ; Safavi Naeini, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebandsare exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed,...
Reciprocity condition in synchronously time-periodic bianisotropic materials
, Article Physical Review B ; Volume 106, Issue 21 , 2022 ; 24699950 (ISSN) ; Memarian, M ; Mehrany, K ; Rejaei, B ; Sharif University of Technology
American Physical Society
2022
Abstract
In this paper, a sufficient reciprocity condition for general time-periodic modulated bianisotropic media is extracted from first principles. Reciprocity of various cases of significant importance, including stationary bianisotropic media, time-varying (TV) isotropic media, TV anisotropic media, and TV bianisotropic media, are investigated using this condition. We prove that synchronous time modulation of stationary bianisotropic yet reciprocal media (chiral, pseudochiral, and achiral) does not lead to nonreciprocity, unless the modulation function breaks time reversal symmetry. This is in contrast to recently published research. The theoretical results are validated using in-house finite...
Efficiency enhancement of time-modulated arrays with optimized switching sequences
, Article IEEE Transactions on Antennas and Propagation ; Volume 66, Issue 7 , July , 2018 , Pages 3411-3420 ; 0018926X (ISSN) ; Fakharzadeh, M ; Akbari, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
The conventional time-modulated arrays (TMAs) have a low radiation efficiency, since each antenna turns off at specific time slots. In this paper, first, the efficiency of TMA is investigated analytically. Next, the optimized switching sequences are proposed to enhance the radiation efficiency of a specific sideband, while preserving the level of the other sidebands. The practical hardware limitations are considered in the switching sequence design. Moreover, a low-cost flexible eight-element printed dipole array operating at 1.2-1.4 GHz is implemented to verify the proposed algorithms. The measured radiation patterns indicate that by applying the proposed sequences, the TMA efficiency...
A cost-effective set-up for time modulated array measurement using software defined radio
, Article 12th European Conference on Antennas and Propagation, EuCAP 2018, 9 April 2018 through 13 April 2018 ; Volume 2018, Issue CP741 , 2018 ; Amjadian, M. R ; Khalili, H ; Akbari, M ; Fakharzadeh, M ; Sharif University of Technology
Institution of Engineering and Technology
2018
Abstract
In this paper a new measurement technique suitable for Time Modulated Array antennas is proposed, which utilizes a low-cost, small form factor, versatile Software Defined Radio (SDR). Performance of the SDR is compared to a spectrum analyzer and the difference is extracted for further calibration. Radiation pattern of a TMA with a defined switching sequence is measured by the SDR, and compared to the simulated array factor. The measured and simulation results are in good agreement, which confirms the accuracy and reliability of the proposed measurement technique. © Institution of Engineering and Technology.All Rights Reserved
A mixture of modular structures to describe human motor planning level: A new perspective based on motor decomposition
, Article 2011 18th Iranian Conference of Biomedical Engineering, ICBME 2011 ; 2011 , Pages 199-204 ; 9781467310055 (ISBN) ; Andani, M. E ; Fattah, A ; Parnianpour, M ; Sharif University of Technology
Abstract
A modular hierarchical structure is developed to describe human movement planning level. The modular feature of the proposed model enables it to generalize planning a task. The movements are planned based on decomposing a task into its corresponding subtasks (motion phases). There is a module responsible for one condition. The final plan is constructed using soft computing of the plans proposed by different modules. Each module estimates the kinematics of the joints at the end of each subtask; we call them kinematic estimator modules (KEMs). A timing module estimates the duration of motion and a gating module determines the responsibility of each KEM under different conditions. To evaluate...
Design and Implementation of Ka-band SPDT Switch for Array Antenna Beam Steering
, M.Sc. Thesis Sharif University of Technology ; Fakharzadeh, Mohammad (Supervisor)
Abstract
In this thesis, study the design of a compact low-cost integrated time modulated array(TMA). In TMAs, a switch is used instead of a phase shifter, which reduces the area, complexity, power consumption and the final price of the array. The TMAs uses the switch as a control element for array weighting that causes beamforming and beam steering. For the lower cost, designed IC compacted as small as possible and use inexpensive CMOS 180nm technology of TSMC fabrication. Initially, maximum layout size forced 0.7 by 1.5 mm2. The proposed switch type is SPDT that one of its output paths terminated by a matched load and another end to a pad and then by a bond wire connected to an external board that...
A 12 Bit Delta-Sigma Modulator For Wireless Applications
, M.Sc. Thesis Sharif University of Technology ; Hajsadeghi, Khosrow (Supervisor)
Abstract
Analog to digital converters are one of the most important component of Bluetooth and GSM receivers. The pipeline and Successive Approximation Register (SAR) ADCs are mainly used in these receivers. However, the pipeline ADCs consume lots of power and SAR ADCs suffer the resolution in advanced technologies. On the other hand, the Delta-Sigma ADCs are capable of achieving high resolution with a low power. So in this thesis, the various kinds and different implementations of Delta-Sigma Modulators are introduced. The system level design and the conversion between Discrete-Time Modulators and Continuous-Time Modulators are explained. The non-ideality effects such as limited gain and bandwidth...
Full quaternion based finite-time cascade attitude control approach via pulse modulation synthesis for a spacecraft
, Article ISA Transactions ; Volume 58 , 2015 , Pages 567-585 ; 00190578 (ISSN) ; Pasand, M ; Soltani, B ; Sharif University of Technology
ISA - Instrumentation, Systems, and Automation Society
2015
Abstract
In the aspect of further development of investigations in the area of spacecraft modeling and analysis of the control scheme, a new hybrid finite-time robust three-axis cascade attitude control approach is proposed via pulse modulation synthesis. The full quaternion based control approach proposed here is organized in association with both the inner and the outer closed loops. It is shown that the inner closed loop, which consists of the sliding mode finite-time control approach, the pulse width pulse frequency modulator, the control allocation and finally the dynamics of the spacecraft is realized to track the three-axis referenced commands of the angular velocities. The pulse width pulse...
Design guidelines for a tunable SOI based optical isolator in a partially time-modulated ring resonator
, Article IEEE Photonics Journal ; Volume 14, Issue 5 , 2022 ; 19430655 (ISSN) ; Mehrany, K ; Memarian, M ; Jamshidi, K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
In this paper, we present the design guidelines for a tunable optical isolator in an SOI-based ring resonator with two small time-modulated regions. By considering a physical model, the proper geometrical and modulation parameters are designed, based on a standard CMOS foundry process. The effect of the variation of the key parameters on the performance of the isolator is explained by two counter-acting mechanisms, namely the separation between the resonance frequencies of counter-rotating modes and energy transfer to the side harmonic. We show that there is a trade-off between these parameters to obtain maximum isolation. Consequently, by applying the quadrature phase difference one can...