Changiz Ghobadi

Urmia University, Rezâiyye, Āz̄ārbāyjān-e Gharbī, Iran

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Publications (75)49.36 Total impact

  • Davod Ahmadian · Changiz Ghobadi · Javad Nourinia
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    ABSTRACT: A new tunable plasmonic biosensor is proposed by embedding liquid crystals in the slit region of a corrugated plasmonic nanoslit array. The absorption spectrum of the structure and, thus, the sensing wavelength can be controlled by applying voltage to the electrode parts of the device. The interaction between the waveguide mode inside the slit and the surface plasmon polaritons on the corrugation surface can be modified using the electrooptical effect of the liquid crystals. Our numerical simulations with the finite-difference time-domain (FDTD) method reveal a large tuning of the absorption spectrum up to 100 nm. In addition to the tunability feature, the structure has a high sensitivity of 570 nm/RIU. The sensing performance of the device is evaluated by performing homogeneous biochemical sensing simulations. The special feature of the proposed structure gives it an opportunity to be used as an efficient element in integrated photonics circuits for miniaturization and tuning purposes.
    IEEE Photonics Journal 04/2015; 7(2):1-10. DOI:10.1109/JPHOT.2015.2411214 · 2.21 Impact Factor
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    ABSTRACT: A new approach for designing a single-feed circular microstrip antenna with dual-band/multi-band circularly polarized (CP) radiation are demonstrated and studied experimentally. It is presented that by embedding pairs of asymmetrical ring-shaped arc slots to the boundary of both circular patch and the ground plane the impedance bandwidth of the antenna increases. This can be achieved by making use of both mutual coupling between the resonances of the ring-shaped arc slots and the fundamental resonances of the circular antenna. Also, by extending the ring-shaped arc slots out with narrow slots, the circular microstrip patch antenna can perform dual-band/multi-band CP radiation. Further details of the proposed CP microstrip antenna designs are described, and typical experimental results are presented and discussed.
    International Journal of Microwave and Wireless Technologies 01/2015; DOI:10.1017/S1759078714001585 · 0.35 Impact Factor
  • Farzad Alizadeh · Changiz Ghobadi · Javad Nourinia · Rasoul Zayer
    7th International Symposium onTelecommunications (IST); 09/2014
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    ABSTRACT: A compact reconfigurable microstrip slot antenna with switchable single and dual band notch functions for ultrawideband (UWB) applications is presented in this study. In the proposed structure, an additional resonance is excited by etching two symmetrical notches on the feed-line and thereby a UWB characteristic is obtained. Then, by cutting two slots on the radiating patch and embedding two positive-intrinsic-negative (PIN) diodes along these slots, switchable single and dual band notch performances are added to the antenna performance. By changing the bias states of the PIN diodes, the antenna is capable of exhibiting four different performances of UWB spectrum coverage, UWB coverage with single rejection of the wireless local area network (WLAN) band, UWB coverage with single rejection of the WiMAX and C-band spectrum, and UWB coverage with dual band notch function at the WLAN, the WiMAX and the C-band frequencies. Good agreement between the simulated and the measured results is achieved at different performances of the antenna. The designed antenna has a small size of 20 ?? 20 mm2 and the measured results reveal that the fabricated antenna has good radiation behaviour in the UWB frequency spectrum with switchable band notch functions at 3.15-3.85 and 5.43-6.1 GHz which can eliminate the UWB frequency band interference with the WiMAX, the C-band and the WLAN systems.
    IET Microwaves Antennas & Propagation 06/2014; 8(8):541-548. DOI:10.1049/iet-map.2013.0311 · 0.91 Impact Factor
  • Source
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    ABSTRACT: A novel printed planar monopole antenna for LTE multi-input and multi-output (MIMO) application is proposed. By adding six ellipticals on top of the antenna, we enhance the lower frequency bandwidth. The idea for this is gotten from [1, 2]. These papers designed by using log periodic technique with the number of rectangle and flare elements . Also, by cutting E-shaped slots in the ground plane, additional resonance is excited, and hence much wider impedance bandwidth can be produced. The proposed antenna provides all of the LTE bands between 0.65 GHz to 4 GHz. In order to provide low mutual coupling and envelope correlation, two of the antennas are combined with orthogonal polarizations. The mutual coupling and envelope correlation coefficient (ECC) of the antenna are lower than -21 dB and 0.002 across the operation bands, and total active reflection coefficient (TARC) is less than 0.35. The designed antenna has small size area of 55 × 94 mm 2 , which has a small size with respect to recently reported antennas. Index Terms -Long term evolution (LTE), multi-input and multi-output (MIMO), monopole antenna, and mutual coupling.
    Applied Computational Electromagnetics Society Journal 01/2014; 29(1):54-61. · 0.81 Impact Factor
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    ABSTRACT: In this paper, a compact ultra-wideband (UWB) band-pass filter with sharp roll-off and improved out-of –band performance is designed and manufactured. In the proposed structure, modified one quarter-wavelength cross-shaped coupled lines (CCLs), and also radial stub loaded resonator (RSLR), are implemented in order to reduce the total size of the UWB BPF. The RSLR is able to control two tuneable transmission zeros (TZs) separately and the CCLs can be properly designed so that the unwanted pass band is rejected. A prototype of the proposed UWB BPF is fabricated and tested. The measured results are in good agreement with the simulated data and the proposed structure shows a sharp selectivity and good filtering performance in the frequency band of interest. Keywords: Band-pass filter (BPF), Cross-Shaped Coupled Lines (CCLs), multiple-mode resonator (MMR), radial stub loaded resonator (RSLR), stub-loaded resonator (SLR), ultra-wideband (UWB).
    Electrical Engineering (ICEE), 2013 21st Iranian Conference on, Mashhad; 05/2013
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    ABSTRACT: This letter presents the investigation results on a novel circularly polarized square-slot antenna (CPSSA) array designed to operate at a frequency of 5.5 GHz. In order to realize the proposed antenna array, four miniature circular polarized square-slot antennas are used with L-shape grounded strips located at the slots' opposite corners to reduce cross polarization. The antenna is fed by symmetric coplanar waveguide. The CPSSA element achieves a bandwidth of 16.6% for an axial ratio ≤ 3 dB. The CPSSA's performance is further enhanced with the construction of a novel 2 × 2 antenna array that is designed using sequentially rotated feed technique. The 3-dB axial ratio of the array extends to approximately 2 GHz with an impedance bandwidth of 31%. The CPSSA array was designed to operate over the frequency range between 4 and 6.825 GHz corresponding to an impedance bandwidth of 52% for VSWR
    IEEE Antennas and Wireless Propagation Letters 01/2013; 12:128-131. DOI:10.1109/LAWP.2013.2237744 · 1.58 Impact Factor
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    ABSTRACT: A compact broadband circularly polarized elliptical slot antenna (CPESA) composed of two linked elliptical slots is presented. In order to realize the proposed CP antenna, two rectangular stubs are embedded in the feedline structure to excite two orthogonal E vectors. By embedding two rectangular stubs in the feedline structure and removing of four rectangular slits from the ground plane, the return loss and the axial-ratio (AR) bandwidths are noticeably increased. The designed CPESA with the compact size of 20 × 20 × 1 mm3 operates over the frequency band between 4.3-8 GHz (60%) for and exhibits a 40% (4.3-6.5 GHz) CP bandwidth. Throughout this letter, the design process of the proposed antenna is presented and discussed in detail .
    IEEE Antennas and Wireless Propagation Letters 01/2013; 12:1094-1097. DOI:10.1109/LAWP.2013.2280457 · 1.58 Impact Factor
  • Wireless Engineering and Technology 01/2013; 04(04):177-180. DOI:10.4236/wet.2013.44026
  • Maryam Majidzadeh · Changiz Ghobadi · Javad Nourinia
  • Maryam Majidzadeh · Javad Nourinia · Changiz Ghobadi
    The 2 nd Asian Symposium on Electromagnetics and Photonics Engineering (ASEPE); 01/2013
  • Nasrin Tasouji · Javad Nourinia · Changiz Ghobadi · Farzad Tofigh
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    ABSTRACT: A novel printed ultrawideband (UWB) slot antenna with reconfigurable band-notch characteristics is presented in this letter. The proposed antenna consists of a modified rectangular radiation patch with a circular and three rectangular-shaped slots etched on it. Additionally, by cutting two triangular-shaped slits on a modified ground plane, practical fractional bandwidth of more than 120% (3.12-12.51 GHz), defined by -10 dB return loss, is achieved. In order to generate single and dual band-notch characteristics, two p-i-n diodes are mounted across the circular slot. The designed antenna has small size of 20 × 20 mm2 with switchable single notched bands of 3.12-3.84 GHz WiMAX and 5-6.07 GHz WLAN, when diode 1 and diode 2 are respectively on. Also, dual bands of 3.12-3.82 and 4.9-6.06 GHz are eliminated from whole frequency band when both diodes are concurrently on.
    IEEE Antennas and Wireless Propagation Letters 01/2013; 12:922-925. DOI:10.1109/LAWP.2013.2273452 · 1.58 Impact Factor
  • Maryam Majidzadeh · Javad Nourinia · Changiz Ghobadi
    Applied Computational Electromagnetics Society Journal 01/2013; 28(10):938-943. · 0.81 Impact Factor
  • Farnaz Mirzamohammadi · Javad Nourinia · Changiz Ghobadi
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    ABSTRACT: A new modified microstrip monopole antenna with dual-band operation is presented for mobile communication applications. For this purpose, radiation patch and ground plane of the antenna are considerably modified. By using these modifications, including of a pair of modified U-shaped slots in the ground plane and a complex form of the slot, etched on the patch, two frequency wide bands of 1.38-3.98 GHz (97%) and 5.15-6.2 GHz (18%) are achieved. In the second design of the antenna, a very small slot as a switch is employed in the special positions on the ground plane to change and control the frequency response. Different cases such as multiple and single bands as well as narrow and wide bands between 1.5 and 6 GHz can be covered. The total size of the antennas is only 20 × 34 mm2. Full parametric simulation of the proposed modifications and measurement results of two manufactured prototypes are presented and discussed.
    IEEE Antennas and Wireless Propagation Letters 12/2012; 11:289-292. DOI:10.1109/LAWP.2012.2190130 · 1.58 Impact Factor
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    ABSTRACT: A novel single-layer dual band-notched printed circle-like slot antenna for ultrawideband (UWB) applications is presented. The proposed antenna comprises a circle-like slot, a trident-shaped feed line, and two nested C-shaped stubs. By using a trident-shaped feed line, much wider impedance bandwidth is obtained. Due to inserting a pair of nested C-shaped stubs on the back surface of the substrate, two frequency band-notches of 5.1–6.2 (WLAN) and 3–3.8 GHz (WiMAX) are achieved. The nested stubs are connected to the tuning stub using two cylindrical via pins. The designed antenna has a total size of 26$\,\times\,$ 30 mm$^{2}$ and operates over the frequency band between 2.5 and 25 GHz. Throughout this letter, experimental results of the impedance bandwidth, gain, and radiation patterns are compared and discussed .
    IEEE Antennas and Wireless Propagation Letters 12/2012; 11:543-546. DOI:10.1109/LAWP.2012.2199274 · 1.58 Impact Factor
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    ABSTRACT: A new incorporated planar ultrawideband (UWB)/reconfigurable-slot antenna is proposed for cognitive radio applications. A slot resonator is precisely embedded in the disc monopole radiator to achieve an individual narrowband antenna. A varactor diode is also deliberately inserted across the slot, providing a reconfigurable frequency function in the range of 5–6 GHz. The slot is fed by an off-centered microstrip line that creates the desired matching across the tunable frequency band. The measured antenna parameters are presented and discussed, confirming the simulation results.
    IEEE Antennas and Wireless Propagation Letters 12/2012; 11:77-80. DOI:10.1109/LAWP.2011.2182631 · 1.58 Impact Factor
  • Sedigheh Alidoost · Changiz Ghobadi · Javad Nourinia · Golzar Eydi
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    ABSTRACT: This paper develops a novel ultra-wideband bandpass filter with high selectivity, deep stop band and compact size. By linking a broadband bandstop filter at two sides with two feed lines via interdigital coupled lines with enhanced coupling degree, an initial ultra-wideband bandpass filter is created. In this filter, all undesired pass bands are rejected by broadband bandstop filter embedded in middle of ultra-wideband filter. Then, stepped impedance open stubs are used for realizing transmission zeros in pass band edges to increase selectivity. Finally, a neuro-genetic method is applied for optimizing of proposed ultra-wideband bandpass filter. For this task, first a nonlinear relation is established between the input (layout parameters) and output (electrical responses) data by using neural network. Then, genetic algorithm is used in conjunction with neural network model for optimizing the ultra-wideband bandpass filter parameters. The designed filter was fabricated and measured that showed good characteristics including deep stop band and very high pass band selectivity.
    Wireless Personal Communications 08/2012; 71(3). DOI:10.1007/s11277-012-0928-4 · 0.65 Impact Factor
  • Seyed Ramin Emadian · Changiz Ghobadi · Javad Nourinia
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    ABSTRACT: A compact dual band-notch ultra-wideband circle-like slot antenna fed by coplanar waveguide line is proposed.The U- and L-shaped slots are used to create dual-band notch characteristics. The antenna is as small as 26 × 26 × 1.6 mm3. The designed antenna offers a wide bandwidth from 2.75 to 14.2 GHz (135%), defined by VSWR < 2, with two notched bands, covering all the 5-/6-GHz WLAN, 3.5-/5.5-GHz WIMAX and 4-GHz C bands. An equivalent circuit model of the antenna is presented to discuss the mechanism of the dual band-notched UWB antenna. Impedance, radiation, and gain characteristics of the proposed antenna are also discussed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1365–1368, 2012; View this article online at DOI 10.1002/mop.26862
    Microwave and Optical Technology Letters 06/2012; 54(6). DOI:10.1002/mop.26862 · 0.57 Impact Factor
  • changiz ghobadi · nasrin ehteshami
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    ABSTRACT: In this article, an efficient compact two dimensional finite-difference frequency-domain (2-D FDFD) method has been used to model photonic Crystal fiber (PCF). Different values of dispersion coefficient can be obtained by changing fiber parameters using FDFD method. Since for each one of these parameters there exists a different value for dispersion coefficient, selection of optimal point will be a time consuming process. Here, first of all, we calculate parameter K, which is the key factor to design dispersion compensated fibers, so the design process will be faster and easier. The optimal value for K parameter is around 301.8 nm for transmission line fibers. So, it is enough to sketch both dispersion curve and K parameter versus PCF parameters, in a single coordinate system. Proper parameters will be obtained by analyzing the curves.
    Journal of Optical Communications 05/2012; 33(2):75-78. DOI:10.1515/joc-2012-0017
  • R. Emadian · M. Mirmozafari · C. Ghobadi · J. Nourinia
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    ABSTRACT: A novel modified circle-like slot antenna with dual band-notched characteristics for various UWB applications is presented. Two shorting pins running through the substrate connect the tuning stub to the L-shaped stubs printed on the bottom of the substrate to highly increase the antenna bandwidth. By etching two L-shaped slots in the ground plane connected to the circle-like slot and embedding two parasitic strips inside the circle-like slot, the antenna provides dual band-notched characteristics. The designed antenna offers a very wide bandwidth from 2.1 to 20 GHz (162%) with two notched bands covering all the 5/6 GHz WLAN and 3.5/5.5 GHz WiMAX bands.
    Electronics Letters 03/2012; 48(7):356-357. DOI:10.1049/el.2011.4024 · 0.93 Impact Factor