Sajad Mohammad-Ali-Nezhad (M'15) received the B.Sc. degree in electronic engineering from Shahid Chamran University, Ahwaz, Iran, in , and the M.Sc. and Ph.D. degrees in communication engineering from Shahed University, Tehran, Iran, in 2010 and 2015, respectively. Currently, he is the Head with the Department of Electrical and Electronics Engineering, University of Qom, Qom, Iran. His research interests include leaky wave antennas, printed circuit antennas, array antennas, phased array antennas, MIMO antennas, RFID tag antennas, frequency selective surface, electromagnetic compatibility, microwave filters, and electromagnetic theory.
A novel ridged SIW leaky-wave antenna (LWA) with controllable side lobe level and low cross-polarization is proposed and fabricated. Longitudinally continuous asymmetric ridges beside SIW sidewalls provide an asymmetric field distribution around the long slot centered on the upper plane of the structure, in way that the slot can radiate. An accurate transverse equivalent network analysis is presented for calculating the properties of the proposed LWA. The wavenumbers of the leaky-mode are calculated theoretically and numerically. The designed ridged SIW LWA shows a good SLL and cross polarization. Measurement results are also consistent with the simulation results. Index Terms-Leaky wave antenna, ridged substrate integrated waveguide (RSIW), transverse equivalent (TE). 0018-926XAlireza Mallahzadeh (M'12) received the B.S. degree in electrical engineering from Isfahan University of Technology, Isfahan, Iran, in 1999 and the M.S. and the Ph.D. degrees in electrical engineering from Iran University of Science and Technology, in 2001 and 2006, respectively.He is a member of academic staff, Faculty of Engineering, Shahed University, Tehran, Iran. He has participated in many projects relative to antenna design, which resulted in fabricating different types of antennas for various companies. Also, he is interested in numerical modeling, and microwaves. Sajad Mohammad-Ali-Nezhad received the B.Sc. degree in electronic engineering from Shahid Chamran University, Ahwaz, Iran, in 2008, and the M.Sc. degree in communication engineering from Shahed University, Tehran, Iran, in 2010, where he is currently working towards the Ph.D. degree in communication engineering.His main areas of interest are leaky wave antenna, printed circuit antennas, array antennas, phased array antennas, MIMO antennas, RFID tag antenna, frequency selective surface, electromagnetic compatibility, microwave filters and hybrids, and electromagnetic theory.
Alireza Mallahzadeh (M'12, SM'15) received the B.S. degree in electrical engineering from Isfahan University of Technology, Isfahan, Iran, in 1999 and M.S. and the Ph.D. degree in electrical engineering from Iran University of Science and Technology in 2001 and 2006 respectively. He is a member of academic staff, Faculty of Engineering, Shahed University, Tehran, Iran. He has participated in many projects relative to antenna design, which resulted in fabricating different types of antennas for various companies. Also, he is interested in numerical modeling, and microwaves. Sajad Mohammad-Ali-Nezhad (M'15) received the B.Sc. degree in electronic engineering from Shahid Chamran University, Ahwaz, Iran, in 2008 and The M.Sc. and PHD degree in communication engineering from Shahed University, Tehran, Iran, in 2010 and 2015 respectively.Currently, he is a head of the Electrical and Electronic Engineering department at University of Qom, Qom, Iran. His main areas of interest are leaky wave antennas, printed circuit antennas, array antennas, phased array antennas, MIMO antennas, RFID tag antennas, frequency selective surface, electromagnetic compatibility, microwave filters and electromagnetic theory.
A periodic long slot leaky-wave antenna (LWA) based on a ridged substrate integrated waveguide (RSIW) is proposed. To reduce the cross polarization, the long slot is placed on the SIW centerline, and a sinusoidal ridge is used to produce a controllable asymmetric electric field around the long slot. Also, only a small stopband occurs when the beam is scanned through the broadside. Varying the amplitude and width of the sinusoidal ridge provides a fixed phase constant and controllable leakage rate to achieve the desired sidelobe level of less than 30 dB. Measurement results are consistent with the simulation results.Index Terms-Leaky-wave antenna (LWA), substrate integrated waveguide (SIW) and long slot antenna.
A compact multiple-input-multiple-output (MIMO) antenna with very high isolation is proposed for ultrawideband (UWB) applications. The antenna with a compact size of 30.1 × 20.5 mm 2 (0.31λ 0 × 0.21λ 0) consists of two planar-monopole antenna elements. It is found that isolation of more than 25 dB can be achieved between two parallel monopole antenna elements. For the lowfrequency isolation, an efficient technique of bending the feed-line and applying a new protruded ground is introduced. To increase isolation, a design based on suppressing surface wave, near-field, and far-field coupling is applied. The simulation and measurement results of the proposed antenna with the good agreement are presented and show a bandwidth with S 11 ≤ −10 dB, S 12 ≤ −25 dB ranged from 3.1 to 10.6 GHz making the proposed antenna a good candidate for UWB MIMO systems. 1. INTRODUCTION MIMO technology has aroused interest because of its application in 4G, RFID, Digital Home, and WLAN. Demand for high data rate and, as a result, huge bandwidth is increasing. In 2002 US-FCC approved unlicensed use of 3.1-10.6 GHz frequency band at low energy level [1]. Therefore in order to improve the capacity of the system, UWB MIMO antenna has been developed for commercial systems. UWB MIMO antenna with high isolation has application in short-range high-data-rate, transmission automotive communications, and radar imaging systems [2, 3]. When several antennas are in close proximity, they suffer from severe mutual coupling, which results in lower antenna efficiency and loss of bandwidth, and further degrades the performance of either diversity gain or spatial multiplexing schemes [3]. So the question then arises as to how to put together antenna elements with low coupling and occupying the least possible space. Because these two properties contradict each other, the problem is very challenging. The mutual coupling is also attributed to three phenomena: near-field coupling, far-field coupling, and surface wave coupling [4]. Many techniques and MIMO structures have been proposed for compact MIMO systems. In [5-7], the size of the proposed antenna was not small enough for the present portable devices. In [8, 9], the proposed antenna was not able to cover the entire UWB bandwidth allocated by the FCC [1]. In [3, 5] and [10-13] unlike our purposed antenna, the antenna elements were perpendicular to each other. None of the above could attain a very high isolation with S 12 < −30 dB in such a small size while covering the whole UWB bandwidth. Certain techniques are also reported to improve isolation. Methods include using simple and fractalbased DGS [14], EBG [15], soft surface structures [16], and Metamaterial-Inspired Isolatorin between the antenna elements [17], etc. Among the aforementioned designs, none of them could achieve very high isolation in such a small size at low-frequency levels because in small size structures reducing mutual coupling at these frequencies due to long wavelength is very challenging.
A simple technique to reduce the mutual coupling between patch antenna arrays is proposed. Mutual coupling phenomena in patch antenna array are investigated and according to the coupling characteristics, a simple rectangular slot(s) placed in between the patch elements is proposed. An equivalent circuit of the proposed structure is obtained through the reciprocity method. In the proposed technique, the series equivalent circuit of the slot is used to reduce the mutual coupling level without changes to the back lobe as well as cross‐polarisation levels compared to conventional arrays. The mutual coupling reduction is >20 dB when compared with the conventional array. Applied to a phased array antenna, the reduction in the mutual coupling results in a wider scan range, up to 75°. A parametric study is carried out for different parameters of the slot that affect the mutual coupling and the scan range. A prototype of the antenna array is fabricated and the measured results are compared to the simulation.
A miniaturized multiband bandstop frequency selective surface (FSS) based on square loop structures with wideband spurious rejection is proposed. This structure can eliminate the spurious frequency up to 30 GHz when the loop structure act as a spatial band stop filter at 7.2 GHz. Significant capacitor achieved by parasitic patch loading of the structure create a new resonance at a lower frequency when the lumped inductor added and made a new compact multiband FSS structure. The proposed FSSs has similar attribute for TE and TM incident polarizations, also. Moreover, the measurement results show good agreement with the simulation ones. The simplicity, compact size, flexibility in multiband tuning, wideband spurious rejection and insensitive polarization operation verify the ability and capability of the proposed structure for many applications. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:888–893, 2017
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