Changiz Ghobadi

Urmia University, Rezâiyye, Āz̄ārbāyjān-e Gharbī, Iran

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Publications (65)47.52 Total impact

  • [Show abstract] [Hide abstract]
    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. · 0.84 Impact Factor
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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. · 1.01 Impact Factor
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    Bahman Mohmmadi, J. Nourinia, C. Ghobadi, A. Valizade
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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; · 1.67 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. · 1.67 Impact Factor
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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. · 1.67 Impact Factor
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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 wileyonlinelibrary.com. DOI 10.1002/mop.26862
    Microwave and Optical Technology Letters 06/2012; 54(6). · 0.59 Impact Factor
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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 01/2012; · 1.67 Impact Factor
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    ABSTRACT: A simple compact printed slot antenna fed by coplanar waveguide (CPW) with a pair of parasitic patches that are added in back side of antenna is presented. By embedding an H-shaped strip to the feed line and symmetrical inverted L-shaped strips that are connected to the H-shaped strip, the impedance matching has improved and the bandwidth (BW) is extremely enhanced. The total size of the antenna is 25×25×1mm3 and operates over the frequency range of 3-15.5GHz. For the fabricated antenna, omni-directional pattern is observed over the whole UWB frequency range.
    Electrical Engineering (ICEE), 2012 20th Iranian Conference on; 01/2012
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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 01/2012; 11:543-546. · 1.67 Impact Factor
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    ABSTRACT: Self-complementary structures are used to design a novel compact band-stop filter for X-band applications. By cutting a rectangular slot with five pairs of L-shaped protruded strips inside the slot on the ground plane and by inserting five pairs of L-shaped stubs in the microstrip transmission line, the self-complementary structure is created, hence a constant and flat impedance bandwidth at the X-band can be produced. The operating frequencies of the filter can be easily controlled by changing the dimensions of the protruded L-shaped strips and stubs, without changing the area taken up by the structure. Experimental results show good agreement with simulation results and demonstrate that excellent stop-band performance could be obtained through the proposed band-stop filter.
    Electronics Letters 01/2012; 48(23):1483-1484. · 1.04 Impact Factor
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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 01/2012; 48(7):356-357. · 1.04 Impact Factor
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    ABSTRACT: A novel microstrip-fed monopole antenna with modified structure is presented for ultra wideband (UWB) applications. The main body of the antenna consists of a quasi square radiating patch with tapered steps and a modified slotted ground plane. Due to the repeatedly cutting of three notches on the radiating patch and also inserting a rectangular slot and three tapered steps on the ground plane, new resonances and a wide bandwidth are obtained. By applying two sleeves with proper sizes to the antenna structure, even wider impedance bandwidth is achieved. The antenna has a compact size of 18×12×1.6mm3 and covers the frequency range of 2.34 - 21.43 GHz (9.15:1; 160%). The impedance bandwidth improvement process of the proposed antenna is presented and discussed in detail.
    Electrical Engineering (ICEE), 2012 20th Iranian Conference on; 01/2012
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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 01/2012; 11:77-80. · 1.67 Impact Factor
  • A. Habashi, J. Nourinia, C. Ghobadi
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    ABSTRACT: A sufficient and simple method to minimize the mutual coupling between closely-spaced microstrip antennas in a H-plane array format, operating at the same frequency is presented. More isolation can be provided through multiple rectangular defected ground structures (DGSs) between the antennas. Inter element mutual coupling before and after using the proposed DGSs is investigated. The length, width and number of the rectangular DGSs have been optimized for more mitigating the mutual coupling (S12). Position of the DGSs is also the other important factor to have a best performance. By using this technique, more than 31 dB isolation between two patch antennas with a side by side distance of only 1/4 free-space wavelength at resonance frequency of 9.2 GHz can be obtained.
    Electrical Engineering (ICEE), 2012 20th Iranian Conference on; 01/2012
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    ABSTRACT: This letter presents a new printed monopole antenna with super-wideband performance useful for various ultra wideband communication applications. The antenna has a compact structure, and the total size is 24 × 24 × 1.6 mm3. The antenna structure consists of a hexagonal patch radiator with a modified 50 Ω coplanar waveguide line for excitation. By using a trident shaped feed line structure the super wide bandwidth is obtained. Measurement results show that the impedance bandwidth for S11 ≤ −10 dB is enhanced largely to more than 174%. Radiation patterns are given at 4, 6, and 9.5 GHz. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26090
    Microwave and Optical Technology Letters 07/2011; 53(7). · 0.59 Impact Factor
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    ABSTRACT: A new form CPW-fed broadband circularly polarized square slot antenna (CPSSA) with three inverted-L-shape grounded strips around the corners of the slot is proposed and fabricated. In comparison to the previous CPSSA structures, the axial-ratio (AR) bandwidth of the antenna is increased, which is two times wider than the previous proposed design. By embedding the L-shape strip to the ground plane and using the vertical stub to the feed line, very good axial-ratio bandwidth is obtained. The measured impedance bandwidth and AR of the realized CPSS antenna with optimized parameters is from 2 to 7 GHz (3.5:1, 110%) for VSWR ≤ 2 and 2-5 GHz (2.5:1; 85%) for AR ≤ 3 dB respectively. Throughout this letter, the improvement process of the AR and S<sub>11</sub> properties is completely presented and discussed.
    IEEE Antennas and Wireless Propagation Letters 02/2011; · 1.67 Impact Factor
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    ABSTRACT: This letter presents a new design for a circularly polarized square slot antenna (CPSSA). The proposed single-layer antenna composed of a square ground plane embedded with two unequal-size inverted-L strips around two opposite corners is capable of generating a resonant mode for exciting two orthogonal E vectors. In this model, compared to the previous CPSSA structures, the impedance bandwidth and the axial ratio bandwidth of antenna are increased, which is four times wider than the impedance bandwidth of previous similar designs. The designed CPSS antenna with size 60 × 60 × 0.8 mm<sup>3</sup> operates over the frequency band between 2.67 and 13 GHz (4.74:1, 132%) for VSWR <; 2, exhibiting a 32.2% (4.9-6.9 GHz, 1.5:1) circular polarization (CP) bandwidth. Throughout this letter, the improvement process of the axial ratio (AR) and S\ properties are presented and discussed in detail.
    IEEE Antennas and Wireless Propagation Letters 02/2011; · 1.67 Impact Factor
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    ABSTRACT: A novel modified microstrip-fed ultrawide-band (UWB) printed Pythagorean tree fractal monopole antenna is presented. In this letter, by inserting a modified Pythagorean tree fractal in the conventional T-patch, much wider impedance bandwidth and new resonances will be produced. By only increasing the tree fractal iterations, new resonances are obtained. The designed antenna has a compact size of 25 × 25 × 1 mm<sup>3</sup> and operates over the frequency band between 2.6 and 11.12 GHz for VSWR <; 2. Using multifractal concept in modified Pythagorean tree fractal antenna design makes monopole antennas flexible in terms of controlling resonances and bandwidth. In this letter, the improvement process of the impedance bandwidth has been presented and discussed.
    IEEE Antennas and Wireless Propagation Letters 02/2011; · 1.67 Impact Factor
  • Hadi Jalali Lak, Changiz Ghobadi, Javad Nourinia
    Wireless Engineering and Technology. 01/2011; 2:235-239.