The geometryof a broadband (0.7-2 GHz) monopole antenna intended to be inserted in a narrow borehole for ground penetrating crosshole application is proposed. The monopole antenna is supposed to be designed on a printed circuit board (PCB) using the low-cost microstrip technology. Based on the FDTD approach, the modeling of the antenna surrounded byits environment has been made, and the influence of several parameters on the radiated waveforms has been studied in details. The modeling of a transmission link has also been considered. Such a studyaims at the realization of a narrow broadband antenna.
With the recent advent on communication and satellite industry, there is a great need for efficient Reflector antennas systems, therefore more powerful techniques are requested for analysis and design of new reflector antennas in a quick and accurate manner. This work aim first to introduce wavelet-based moment method in 3D, as a recent and powerful numerical technique, which can be applied on a large reflector antennas, also the physical optics (PO) analysis technique is well known among the designers as an asymptotic method quick and powerful, ideally to predict far field and near field pattern, may be combined with the wavelet-based moment method therefore computing time and memory space can be saved, in this issue knowing the limit of use of this asymptotic technique is worth well.
Free standing planar frequency selective surfaces (FSSs) are studied when utilized as spatial filters for linearly polarized antennas. The antenna spatial filter investigated in the present work is constructed up as a finite planar array of conducting strip dipoles. The electric field integral equation (EFIE) technique with the Rao-Wilton-Glison (RWG) basis functions are used to get the current distribution on the conducting strips. The current distribution and backscattered electric field due to an incident plane wave are calculated and compared to some published work. The effect of polarization on the scattered field, and the frequency response of the spatial filter are studied. To test the operation of the proposed planar FSS, a bowtie antenna is used with the FSS employed as a spatial filter. The field transmitted by the antenna and passed over a wide frequency band through the FSS is calculated. It is shown that such a free standing planar FSS can operate as a band stop filter for linearly polarized antennas. It is also shown that even when the size of the array is reduced, the FSS maintains its frequency response with a very slight change in the center frequency of the stop band. The effect of element size, spacing between the elements, and interleaving the columns of the FSS on the frequency response of the FSS are studied. The effect of the spatial filter on the antenna input impedance is studied over a wide frequency band. The radiation pattern of the bowtie is calculated in the presence of the spatial filter. It is shown that the existence of the later causes considerable reduction in the radiation pattern within the stop band of the filter.
A new CPW-fed antenna with triple-band is presented for simultaneously satisfying wireless local area network (WLAN) and world interoperability for microwave access (WiMAX) applications. The investigated antenna consists of a T-shaped monopole with a trapeziform ground plane and two parasitic elements to generate triple-band. The design methodology is outlined and the overall size is 32×15×1 mm3. This antenna was numerically designed using Ansoft HFSS simulation software package. The measured 10 dB bandwidth for return loss is from 2.35 to 2.71 GHz and 3.35 to 3.72 GHz and 4.9 to 6.1 GHz, covering all the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands.
In this paper, He's energy balance method is applied to nonlinear oscillators. We illustrate that the energy balance is very effective and convenient and does not require linearization or small perturbation. Contrary to the conventional methods, in energy balance, only one iteration leads to high accuracy of the solutions. It is predicted that the energy balance method can be found wide application in engineering problems.
A novel planar bow-tie aperture antenna is proposed for ultra-wide band (UWB) application in this paper. Beveling technique is employed to increase the impedance bandwidth, and slot loading is introduced to improve the impedance matching. The measured impedance bandwidth is from 2.7 to 12 GHz for S11 < -10 dB, proving the effectiveness of these two techniques. The measured radiation patterns are relatively stable almost over the entire ultra-wide band of 3.1 to 10.6 GHz with low cross-polarization levels of at least -10 dB. Moreover, the proposed antenna maintains the advantages of ease of fabrication and relatively small electrical size.
We have studied the optical properties, band structures and group velocities, of one dimensional photonic crystal (1-D PC) containing negative index materials using translational matrix method (TMM). The 1-D PC containing negative index materials is a periodic arrangement of positive index material (PIM) and negative index material (NIM). The observed group velocity of such structure is larger than the speed of light in certain range of normalized frequency which shown abnormal behaviors. The group velocity of the PC containing negative index materials have found larger than the speed of light. The values of the group velocity become zero, negative and positive for normalized frequencies. The structure containing negative index materials can be used to trap the photons inside the PC i.e., light localization occurs without introducing the defects.
The discrete complex image method stands as one of the most efficient techniques that is able to represent the Green's functions of multilayered structures accurately in the near- and intermediate-field regions. In order to extend the validity of the method to the far region, the surface waves are extracted. Although the extraction process yields accurate results in the intermediate and far-field regions, erroneous results are observed in the near-field region. In this paper, this problem is treated by extracting the contribution of an additional number of artificial poles. Using this scheme, the discrete complex image method can provide accurate representation of Green's functions in both the near- and far-field regions.
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