This paper proposes two methods for increasing the Gain of Vlasov Antenna. The first method, using a Parabolic Cylinder Reflector, results in a 7dB increase in the Gain. The second method, constructing a Horn on the aperture, increases the Gain by about 5dB. The results were checked using a prototype antenna and there was a close agreement.
The purpose of this paper is to introduce the concept of fractals and its use in antenna arrays for obtaining multiband property. One type of fractals namely, Cantor set is investigated. Cantor set is used in linear array antenna design. Therefore, this array know fractal Cantor linear array antenna. A comparison with conventional non-fractal linear array antenna is made regarding the beamwidth, directivity, and side lobe level. MATLAB programming language version 7.2 (R2006a) is used to simulate the fractal and conventional non-fractal linear array antenna and their radiation pattern.
This paper describes a fast pattern synthesis method for a broadband array antenna using the particle swarm optimization (PSO) and cubic spline interpolation (CSI). Being an indispensable part of a high speed space-division communication system, the array antenna operates in a wide frequency band (200-400 MHz) and has stable patterns with 60-degree half power beam width (HPBW) in the whole frequency band. Firstly, by establishing a versatile objective function, the complex excitations of the circular array at the selected seven frequency points are determined via the PSO algorithm. Then, the complex excitations of the circular array at arbitrary frequency points in the whole working frequency band are calculated effectively using the CSI method. A uniform circular array with six broadband dipole elements is examined. The broadband patterns with 60-degree HPBW and the accuracy of the interpolation method are demonstrated.
A novel radiation pattern and frequency reconfigurable microstrip antenna is introduced in this paper. This antenna is designed on a thin substrate for the application of conformal phased antenna future. The proposed antenna make the operating frequency range 6 times larger than that of a simple rectangular microstrip antenna, and make the beam covering from -70。∼70。 compared with the traditional rectangular microstrip antenna beam which only covers -50。∼50。. It is potential on the application of wide-band and wideangle.
In this paper, a new method is proposed to avoid crowding phenomenon in extracting the permittivity of ferroelectric thin films. Polynomial curve fitting technique is used to determine the filling factor while the thickness of the thin film is very small. Conformal mapping (CM) combining with partial capacitance approach (PTA) is used to obtain the relationshipb etween the effective permittivity of multiplayer coplanar waveguide (CPW) and the permittivity of each layer. A CPW with a thin film layer is simulated and the permittivity of thin film is extracted, the results show that, by using the proposed method, the crowding phenomenon can be avoided successfully and the permittivity of thin films can be extracted accurately.
A novel design with low parasitic effect for eliminating the simultaneous switching noise (SSN) in high-speed circuits is proposed by using the aperiodic high-impedance surface (A-HIS) structure. The A-HIS configuration is proposed in this work, revealing suppression of the SSN from 1.1∼1.85 GHz. It is shown that the HIS structure with aperiodic design, the SSN will be effectively suppressed. The undesired resonances of the proposed A-HIS structure are less than that of the conventional structure below 1 GHz. Less undesired peaks will ensure the electromagnetic interference (EMI) and signal integrity (SI). The measured results show very well compared with the conventional periodical HIS structures. The suppression results of the proposed A-HIS structure is checked by both measurement and simulation results. By using this proposed method, the simplicity of the structure is easier to fabricate as well as to route signal lines with a perfect power/ground planes. In addition, the proposed designs provide excellent SSN suppression and good signal integrity (SI) as the conventional structure.
This paper presents the calculations of transmission line loss factor by extracting from the Q-factor measurement of the quarterwavelength open stub resonators over the designed frequency and other resonant frequencies. A comparison of the loss factor of the design frequency with other resonant frequencies of each of the stub's quarter-wave resonances is provided in this paper. The radiation and discontinuity losses are undesirably included in the unloaded Q-factor measurement andit shows that the unloadedQ-factor is not repeatable at different designed frequency. The implementation of the loss factor measurement by quarter-wavelength open stub resonators is becoming more andmore important to be consideredwith the increase of using the electronic circuits operating at high frequencies.
A planar half mode substrate integrated waveguide (HMSIW) broadband bandpass filter is proposed. It is realized by cascading a lowpass filter and a highpass filter. A transmission line with half mode substrate integrated waveguide (HMSIW) on the circuit board has the characteristic of highpass, while a periodic uniform photo band structure (PBG) array has the characteristic of bandstop. Combining these two structures, a novel compact broadband bandpass filter (BPF) is fabricated and measured. Measured results show that the proposed BPF has wide bandwidth from 11.8 GHz to 23.8 GHz, all the measured insert loss are less than 2.1 dB, return loss are less than 9 dB in the passband. The BPF achieves a wide stopband with 34 dB attenuation low to 5GHz and 27 dB attenuation up to 35GHz.
Copper-cobalt ferrites with general chemical formula CuxCo1-xFe2O4 (with x = 0.0, 0.4, 0.6 & 1.0) were prepared by ceramic method. The solid state reaction was confirmed by XRD patterns. DC conductivity was measured by two probe method. Electrical resistivity is found to increase on lowering of sintering temperature and time. At x = 1.0, the conduction is mainly due to hopping of electrons leading to n-type conductivity while at x = 0.0, conduction is due to holes leading to P-type conductivity. The lowest conduction at x = 0.4 is attributed to the electron hole compensation. SEM micrographs were obtained from JEOL scanning electron microscope. The micrographs reveal that an average grain size increases with sintering temperature and time as a result of decrease in porosity. This leads to the decrease in resistivity with sintering temperature and time. One of the factors for higher conductivity in ferrites is an increase in average grain size and decrease in pore concentration during the heat treatment.
It is proposed that the application of defected ground structures (DGS) and electromagnetic bandgap (EBG) reduce the phase velocity, increase effective permittivity of microstrips and reduce the effective the wavelength which eventually lead to the reduction of overall length of Wilkinson power dividers. Furthermore, the adjacent strip lines may approach each other, which cause coupling problems. The undesired coupling maybe cancelled by connecting a capacitance in parallel with the isolation resistor of Wilkinson power divider. Application of DGS and EBG will not only reduce the dimensions of the divider, but also improves its scattering parameters.
A 2×2 quasi-Yagi antenna array fed by a novel orthogonal T junction is presented. The orthogonal T junction is constructed with a traditional microstrip T junction, two planar microstrip to CPW transitions and two orthogonal microstrip to CPW transitions. The orthogonal T junction can be integrated with the quasi-Yagi array element directly. A 2×2 prototype operated from 7.6 GHz to 12 GHz is fabricated and measured.
Turbo equalization is applied to microwave channel in this paper, and we bring forward an improved Turbo equalization algorithm named Max-Log-Map. A simulation based on a given microwave fading channel has been made. The results show that performances are close to each other between improved TE-Max-Log-Map and Log-Map, and the coding gain is 1 dB at 10-4 of BER compared with Max-Log- Map. The improved Max-Log-Map method improves the reliability of microwave communication.
A method of moment based analysis of the co-channel interference at waveguide joints has been presented using Multi Cavity Modeling Technique (MCMT). The proposed analysis has good agreement with the theoretical; CST microwave studio and HFSS simulated data.
A new antenna structure comprising a semicircular microstrip patch alongside a small rectangular shape ground proximity fed by a microstrip line is proposed. On a thin substrate this antenna achieves in the range of 5.8-12.9 GHz an impedance bandwidth of almost 75%. Details of the antenna design, simulation and measured results on the return loss and the E and H-plane radiation pattern of the proposed antenna are presented.
In this paper, equations are derived for solving the important geometrical parameters of the ring-focus antenna with a variable focal distance for forming an elliptic beam, a simple and efficient method for this antenna is presented, and measured and calculated patterns are given. This antenna can form a high-efficiency elliptic beam.
Circular polarization (CP)designs of circular and rectangular microstrip patch antennas are demonstrated. Proximity coupled feed and aperture coupled feed methods are used. The proposed CP designs are achieved by implementing a suitable crossslot either on the patch (in the case of proximity coupled feed method) or on the ground plane (in the case of aperture coupled feed method), which results in excitation of two near degenerate orthogonal modes of near equal amplitudes and 90。 phase difference. Attempts are made to change the geometry of slots' ends to introduce a novel structure in order to achieve a better matching performance.
A novel printed version of the classic volcano smoke antenna is presented and investigated in this article. The effects of some important parameters on the VSWRof the proposed antenna have been investigated in the design. The measured bandwidth of VSWR<2 is from 1.80 to 14.35 GHz, which covers all UWB (3.1- 10.6 GHz) and 2.4 GHz WLAN (2.4-2.4835 GHz) bands. Moreover, the antenna features near omnidirectional characteristics in the operation range and good radiation efficiency. A gain variation from 2.04 to 7.02 dBi (2-13 GHz) is obtained.
Scattering of dipole field by a perfect electromagnetic conductor (PEMC) cylinder is studied theoretically. Electric dipole and magnetic dipole are considered separately as source of excitation. Plots are given for different values of admittance parameter of the PEMC cylinder.
In this paper, a carrier frequency offset estimation scheme in orthogonal frequency division multiplexing is proposed. We focus on increasing the correlation of each PN sequence code repeated in one preamble. We aim at getting an efficiency like using many preambles. The proposed method can improve the performance of the system by estimating fine frequency offset. Also, the proposed method enhances reliability by maximizing the number of correlations compared with the established method in time domain.
Acompact planar microstrip ultra-wideband (UWB) bandpass filter is presented in this paper. The proposed UWB filter is realized by cascading a high pass filter (HPF) and a lowpass filter (LPF). HPF with short-circuited stubs is used to realize the lower stopband and a lowpass filter based on a defected ground array in the ground plane employed to attenuate the upper stopband. One such a bandpass filter is designed and simulated.
A broadband stacked U-slot microstrip patch antenna is presented using circuit theory concept. The antenna shows two resonance frequencies that are very closely spaced to give broadband characteristics. The frequency band of 186MHz (36.4% impedance bandwidth) is achieved for the proposed antenna. The theoretical results are in good agreement with the simulated results.
Fractal structures have been widely used in many fields of science, such as biology, physics and chemistry. In this article, we analyze the basic properties of a fractal-like square lattice of air holes, with most of the holes having a lattice constant of Λ while others are repeated with a lattice constant of 2Λ. We change the radii of these holes and analyze their effects on the bandgap regions and transmission properties. The analysis conducted here is based upon band diagrams and 2D Finite difference time-domain (FDTD) solution of the full-wave Maxwell's equations. We show that this structure provides flexibility in tuning the bandgap of the photonic crystal structure and we show the appearance of mini-bandgap regions along certain directions.
In this paper, the Contiguous Partition Method (CPM) is applied to the optimization of the directivity of difference patterns in monopulse planar array antennas. Since the excitations providing maximum directivity of planar arrays can be analytically computed and because of the excitation matching nature of the CPM, the problem at hand is recast as the synthesis of the difference compromise solution close as much as possible to the reference pattern with maximum directivity. Selected results are shown to point out the potentialities of the CPM-based approach.