In this paper, the problem of RCS reduction in cylindrical structures with various boundary conditions are investigated comprehensively. It has been done through a general form of boundary conditions called Mixed-Impedance boundary conditions. Genetic algorithm, a powerful optimization method, is used to explore specific conditions that provide major reduction of cylindrical structure's RCS. The optimizations are performed in case of normally and obliquely incident illuminations. Finally, the optimized values are formulated in terms of incident angle to construct a simple and fast way of evaluation of the minimum RCS situation. The results are compared with a cylindrical PEC structure, and it has been verified that the optimized values of MI boundary conditions could result in significant backward RCS reduction for both normal and oblique incident.
A novel microstrip bandpass filter with four transmission zeros is proposed. Four transmission zeros close to the passband are realized to improve the selectivity for the passband. A sixth-order passband is realized with two shorted stubs and a dual-mode ring resonator. The transmission zeros near the passband can be adjusted conveniently by only changing the characteristic impedances of the coupled lines. For demonstration, a planar bandpass filter (3-dB bandwidth 21.9%) was designed and fabricated.
A novel log-periodic dipole antenna for dual-polarized radar systems is presented. The proposed antenna employs meander line technology and matched loads. The simulated and measured results show that the -6 dB reflection coefficient bandwidth of the dual-polarized antenna covers the desired band of 2-8 GHz and the port isolation is higher than 32 dB, along with -20 dB cross-polarization discrimination for both E- and H-planes.
This paper presents the transmission line analysis, thermal and structural analysis of a multi-section coaxial coupler (MSCC) used in traveling-wave tubes (TWTs) to handle high average power over a wide frequency range. Power transmission through coupler from the device demands very good matching between load and source impedances such that low VSWR is achieved. Modeling of the MSCC for wideband TWTs in commercially software packages takes very long iteration time even in high-end computers. An analytical approach has been developed to model MSCC which takes less iteration time even in ordinary computer. Analytical results have been compared to those obtained from CST microwave studio. Finally, thermal and structural analysis has been carried out to study the thermal aspects for handling high average RF power.
A compact microstrip notched ultrawideband patch antenna (UWB) with inverted E- and F-shaped slots is presented. By introducing a new inverted E-shaped notch in the radiating plane, band-notch about 2.68 to 3.55 GHz is achieved. A new type of Defected Ground Structure (DGS) in the ground plane is employed to extend the lower limit of the bandwidth so as to cover ISM 2.4 GHz WLAN-frequency band. The proposed antenna offers 126% bandwidth overall dimension of 13×17×1.6 mm3. The experiment results indicate that the proposed antenna can meet the requirement for UWB communication with size miniaturization.
A novel technique for extrapolation of transient response using early-time and low-frequency data is proposed in this paper. An improved extrapolation scheme using approximate prolate series is presented to obtain a transient electromagnetic response. The approximate prolate series, which has an approximately band-limited and sub-domain nature, is a better choice for extrapolating the time-domain electromagnetic response than orthogonal polynomials, such as Laguerre functions and Hermite functions. A novel regularization method based on truncated generalized SVD is also proposed to solve the ill-posed extrapolation problems, which make the extrapolation technique much less sensitive to noise in the known part of the response. Some numerical results are presented to illustrate the effectiveness and accuracy of the proposed method in extrapolation of transient electromagnetic problems.
An effective technique utilizing neutralization lines to increase the isolation of a compact two-element dual-frequency microstrip antenna array is proposed in this paper. Two neutralization lines connect the two elements at the edge of each radiating patch. The positions and lengths of the two neutralization lines are studied to get the best performance of element isolation. A prototype of the proposed design was fabricated to validate the results. The measured results agree well with the simulated ones. It is shown that an increase of about 25 dB at the lower frequency and that of 17 dB at the upper frequency in isolation between the two antennas have been achieved.
In this article, a novel printed quasi-self-complementary antenna with tri-band characteristic is presented for WLAN and WiMAX applications. A triangular quasi-self-complementary structure, which consists of a radiating patch and its counterpart slot on the ground, is employed to produce two operating bands centered at about 2.5 and 5.2 GHz. Then, by introducing a rectangular slit cut from the patch and its complementary mirror image strip inserted into the slot, an additional resonance at 3.5 GHz is excited and tri-band operation can be realized. A prototype of the proposed antenna has been successfully fabricated and measured. Both the simulated and measured results are obtained to demonstrate the promising performance required for practical applications. Based on the results, it is shown that 10-dB impedance bandwidths of the proposed antenna are 510 MHz (2.25-2.76 GHz), 330 MHz (3.38-3.71 GHz), and 770 MHz (5.1-5.87 GHz), respectively. Also, nearly omnidirectional radiation patterns and acceptable antenna gains can be achieved over the three operating bands.
A hepta-band covering GSM850/900/1800/1900/ UMTS/LTE2300/LTE2500 handset antenna array is presented. The antenna array consists of two symmetric antenna elements, A T-shaped protruded ground(TP) and three slots. The antenna element consists of a feed strip and two radiation strips (RS1, RS2), which only occupies a planar size of 15×25 mm2 and generates dual-mode resonances at λ/8 and λ/4. The three slots and T-shaped protruded ground are utilized to reduce mutual coupling. Different slots can adjust different frequency bands independently. The working mechanism of the three slots is analyzed based on S-parameters and surface current distributions. The measured S11 and S12 are lower than −6 dB and -15 dB in the working bands, respectively. The radiation patterns and diversity performance are presented.
This paper deals with reciprocity relations derivation for a nonlinear, stationary, homogeneous and isotropic plasma-like medium in an external homogeneous magnetic eld. A special case of such a medium is the charge carriers collective in semiconductors. It is shown that the classical reciprocity relations will be valid even in the presence of nonlinearity, and they can be used for Hall magnetometer bias compensation.
A topology of high-frequency field intensity in the work area of a saddle-shaped coil for a nuclear qaudrupole resonance spectrometer was studied. With a view to determine magnetic field topology, a computational domain was created which is a model of a saddle-shaped coil physical structure. Finite element method was used to perform numerical simulation in COMSOL Multiphysics software. According to the results of calculations performed and the field maps obtained, the relative volume of coil work area was determined which makes 28.12% of its full volume. For such a volume the recommended size of samples under study is 12×18×10 mm3.
In this paper, a very compact ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna, with a high isolation and triple notched bands, is proposed. Its size is dramatically decreased to 30×26×0.8 mm3 on a cost-effective FR4 substrate. It consists of two rectangular printed monopole (PM) elements and a simple stepped ground stub to enhance wideband isolation. For two different rejected bands of the wireless local area network (WLANs) covering 5.15-5.35 and 5.72-5.825 GHz, four parasitic C-shaped split-ring resonators (PCSRR) are placed on either side of the feed line. By etching two inverted U-shaped slots on the center of the patch, the notched frequency at 4 GHz C-band (3.7-4.2 GHz) of satellite communication systems is obtained. The results of simulation and measurement prove a bandwidth of S11<-10 dB and S12<-21 dB over the whole band (3.1-11.2 GHz) excluding the three independently adjustable rejection bands. Hence, the proposed UWB MIMO antenna has a very small size, simple structure, higher isolation and three narrower notched bands which effectively save more useful frequencies. Moreover, it is a good candidate for wireless portable UWB MIMO applications.
A novel compact tri-band band-pass filter (BPF) with transversal signal interaction concepts, based on composite right/left-handed transmission lines (CRLH-TLs) resonator and parallel stepped impedance resonator (SIR), is presented. The main path is based on a dual-mode CRLH-TL resonator, which exhibits the first two passbands. The secondary path is a SIR, which contributes to the third passband and generates another transmission zero between the first and second passbands simultaneously. The proposed filter has been simulated, fabricated and measured. Both the simulated and measured results show that the filter has a high selectivity with a compact size as small as 0.18λg×0.12λg.
A broadband via-hole less transition from a conductor-backed coplanar waveguide (CBCPW) to a parallel coupled microstrip line (CMS) via microstrip section (MS) is reported in this paper that is realized on a MCL FX-2 substrate (100 μm thick). This transition should find a wide variety of applications due to its demonstrated broadband (from 4.5 GHz up to 39.5 GHz) behavior, ease of fabrication, and low manufacturing cost. In addition, utilization of the MS section between the CBCPW and CMS sections allows putting ground electrode in a different plane than the signal electrodes. This exibility made possible by electromagnetic field coupling between the bottom and top ground planes simplifies the transition manufacturing and facilitates the characterization of optical components driven with CMS line using coplanar probes.
Fractional slots concentrated windings (FSCWs) are characterized with high magnetic motive force (MMF) harmonics which results in undesirable effects on permanent-magnet (PM) machines. A new design technique is reported in this paper in order to simultaneously reduce the sub- and high MMF harmonics. By using multiple layer windings and different turns per coil, a new 18-teeth/10-poles FSCWs PM machine is designed. Then, this machine is evaluated as compared with a conventional 12-teeth/10-poles FSCWs PM machine. Both machines are designed under the same electrical and geometrical constrains. The obtained results verify the high performances of the newly designed machine. Due to the adopted new winding type, the proposed design can effectively reduce eddy current loss in PMs as compared with the conventional design.
A compact omnidirectional vertical-polarized broadband slot antenna for indoor distributed antenna systems is presented. The proposed antenna consists of a deformed printed monopole on one side of the substrate and a polygon slot in the circular ground plane on the other side. Due to the utilization of the wideband slot structure, the antenna achieves small electrical dimension of 0.327λ×0.327λ×0.0046λ at the lowest operating frequency, and an impedance bandwidth of about 129% (0.66-3.07 GHz) for VSWR≤1.5 is achieved, covering all frequency bands for 2G, 3G, 4G and some Wi-Fi communications. The proposed antenna has stable radiation patterns over the operating bands. The measured gains of the antenna range from 1.5 dBi (lower band) to 5.5 dBi (higher band). Compact planar structure makes the proposed antenna a perfect candidate for ceiling or surface mounted indoor distributed antenna applications.
In this study, a dumbbell-shaped metamaterial (MTM) antenna has been proposed for dual-band applications using finite difference time domain (FDTD) technique. Such a composite MTM antenna consists of dumbbell-shaped patch, microstrip and partial ground plane. The proposed antenna shows dual-band behavior having impedance bandwidths (|S11| < -10 dB) of 28.5% and 8.7% at 1.72 GHz and 3 GHz respectively. It has been designed to operate at various cellular standards such as GPS, GSM1800 and WCDMA. Design and analysis have been carried out using FDTD code based on uniform meshing and convolutional perfectly matched layer (CPML) absorbing boundary conditions. Further, simulation results have been verified using HFSS, and a prototype has been fabricated to validate the results experimentally. The overall electrical size of the proposed antenna is 0.287λo × 0.346λo × 0.009λo. The proposed dual-band antenna offers excellent radiation characteristics with a gain of 1.2 dBi and 1.5 dBi at 1.72 GHz and 3 GHz respectively with omnidirectional radiation patterns in xz-plane.
A compact multiband bow-tie dipole slot antenna fed by coplanar waveguide (CPW) is proposed in this paper. Multiple resonant mode technique and notch-band technique have been combined in this design to form triple-band operation just by adding single elements. Based on this, a pair of hairpin-shaped branches is implemented on each arm of the bow-tie slot antenna. A notch-band property is achieved compared with the original wideband bow-tie antenna (without branches). Meanwhile, a new lower resonant frequency is obtained by using this kind of structure, which means the size is compact in nature and the triple-band operation is achieved. The notch-band and lower resonant frequency can be tuned by changing the length of the branch. The parameters of the antenna, including reflection coefficients, current distributions, radiation patterns and gain, are achieved by numerical simulations and measurements. The results indicate that the slot size of the proposed antenna is 52.4 mm×22.3 mm, and the proposed antenna can offer triple-band operation at 2.39-2.50 GHz (4.5%), 3.38-3.79 GHz (11.4%) and 4.87-6.23 GHz (24.5%), which is suitable for WLAN in the 2.4/5.2/5.8-GHz bands and WiMAX in the 3.5/5.5-GHz bands.
Novel compact dual-band branch-line couplers are presented. By using ahalf elliptical-ring impedance stub as a basic unit, dual-band branch-line couplers are obtained. Sincea couple of half elliptical-ring impedance stubs can be folded inward to its enclosed areawithout overlap, the branch-line couplercan be miniaturized. In order to verify the effectiveness of the half elliptical-ring impedance stub, two different branch-line couplers operating at 2.4/5.8 GHz are designed, fabricated and tested. Measured results agree well with simulated ones. Compared with the stepped-impedance-stub branch-line couplers, sizes of the proposed couplers are reduced by 43% and 30%, respectively.
Two novel microstrip bandpass filters with improved selectivity based on dual-mode ring resonators are proposed. Tow and four transmission zeros close to the passband are realized to improve the selectivity for the passband. Sixth-order passband is realized with two open/shorted stubs and a dual-mode ring resonator. The transmission zeros near the passband can be adjusted conveniently by changing the characteristic impedances of the coupled lines. For demonstration, two planar bandpass filters (3-dB bandwidths 20.9%, 20.2%) are designed and fabricated.