Magnetic proximity detection systems (PDSs) used in underground mines occasionally generate false alarms when the miner-wearable component (MWC) is close to nearby conductors such as power cables. This is because the signals from the generators (antennas) of the PDS wirelessly couple to nearby cables, travel along these cables, and then couple back from the cable to a distant MWC to cause a false alarm. In order to manage such a false alarm, it is necessary to understand the basic near-field coupling characteristics from a generator to a long wire. Researchers from the National Institute for Occupational Safety and Health (NIOSH) have developed a method to measure such coupling characteristics for a ferrite-cored antenna to a straight wire. The method is introduced in this paper along with the test results.
This paper presented the effects of Defected Waveguide Structure (DWS) toward wideband monopole antennas. Ultra-wideband (UWB) technology was introduced to support high data rate and maximum bandwidth utilization. Monopole antenna received great attention owing to its appealing features of planar in the structure and is easy to manufacture in miniaturized sizes. Yet, poor gain and directivity are always the drawbacks of the miniaturized antennas. It was found that there was no research work done on the monopole antenna design with DWS. Two wideband monopole antennas with a microstrip feed line and coplanar waveguide (CPW) feed line were proposed. Two waveguides with full copper and square DWS were designed at all the inner walls. Monopole antennas were then integrated in the waveguides. The antenna parameters studied were return loss, efficiency, gain, directivity and radiation pattern to investigate the effects of DWS toward monopole antennas. Both monopole antennas achieved wide bandwidth from 2.5 GHz to 11 GHz and higher efficiency of more than -2 dB. Monopole antennas with waveguide presented a narrower bandwidth from 6 GHz to 11 GHz but a significant directivity improvement of 5 dBi at a lower frequency of 4.5 GHz. Monopole antenna with square DWS demonstrated high directivity and gain in a wide bandwidth of 8.5 GHz. Higher gain was improved around 4 dB at the frequency of 4.5 GHz, and high efficiency of more than -2 dB was achieved. The DWS design served as a guide for future communication system based on the smart technology system.
This paper reports on the development of a compact, low-cost, impulse bi-static UWB radar sensor for its use as non-destructive methods for electrical property measurement in industrial application. This UWB Radar sensor consists of an ultrashort-monocycle-pulse transmitter of 330 ps, an oscilloscope as a UWB sampling receiver with a high wide band of 6 GHz, and two UWB antennas ranging from 0.4 to 6 GHz. A new model of SRD has been introduced in order to decrease the rise time of the impulse. Performance of this UWB radar sensor was veri ed through two kinds of applications: range detection and electrical property measurements. All measurements have been carried out in an anechoic chamber with a distance variation between 80 and 300 cm. The full radar system provides good agreement between the experimental and theoretical results, which demonstrate its application in many fields, especially for electrical Property Measurements.
In the moment method solution of the integral equations for currents of a rectangular microstrip patch reflectarray, the Leontovich boundary condition is employed to determine the conductor loss. If the basis functions contain edge conditions that approach infinity, the moment matrix elements will have diverging integrals in the Galerkin technique. In this paper, we present a criterion to stop the evaluation of these integrals at a distance before the edge, thereby avoiding the divergence problem. The stopping distance derived here is found to work for a range of values of permittivity, loss tangent, and thickness of the substrate, polarization, angles of incidence of the plane wave source, and also for superstrates. Our computed results are in good agreement with measured results and those computed by HFSS.
The derivation of the scattering matrix of hybrid directional couplers with more than four ports is rather difficult to find in the literature. Some particular cases can be found, but a general form is not yet discussed. The aim of this contribution is to develop a simple procedure to write the 2N×2N S-matrix for hybrid directional couplers with N input and N output ports. This procedure is based on the separation of the phase of the scattering coecients in two terms. The first is related to the presence of transmission lines, or phase shifters, connected to the coupler ports and the second to the intrinsic nature of the coupler that imposes particular phase relationships to the scattering coecients to ensure that the S-matrix is unitary. These relationships are due to the presence of one polyphase systems of order N or to m polyphase subsystems of order N/m, if N is multiple of m. Finally, it will be shown that 2N port hybrid directional couplers with phase shift equal to 0 or π are possible only if N is an integer power of 2.
In this paper, a novel X-band push-push oscillator employing dual-feedback sub-oscillators and a half-wavelength microstrip line resonator is presented. The dual-feedback sub-oscillator consists of a series feedback commonly used in conventional oscillators due to its good phase noise performance and a parallel feedback circuit which improves both the output power and stability. The resonator and power combiner form a single circuit allowing compact size. Measured results show that an excellent output power of +13.3 dBm was obtained at the second harmonic frequency of 9.81 GHz. Moreover, superior phase noise of -105.0 dBc/Hz and -123.5 dBc/Hz were achieved at 100-kHz and 1-MHz offset frequencies, respectively. The suppression of undesired harmonic signals, namely fundamental and third harmonic signals, are 27.9 dB and 55.7 dB, respectively. With a simple design structure and compact size the proposed push-push oscillator achieved very good performance.
In this paper, the polarizations of single-feed crossed-dipole antennas loaded with different near-field resonant parasitic (NFRP) elements are investigated. The antennas are placed above a metallic reflector for a broadside radiation pattern. Meander line with an arrowhead-shaped ending is applied in all arms of the crossed-dipole and NFRP elements for the compactness. By adjusting the ending sizes of the NFRP element, the polarization of antenna can be right-hand circularly polarized (RHCP) - linearly polarized (LP) - left-hand circularly polarized (LHCP). For validation, two antennas with RHCP and LHCP performances are implemented and measured. The RHCP antenna yields a |S11| < -10 dB bandwidth of 1.454-1.668 GHz (214 MHz) and a 3-dB axial ratio (AR) bandwidth of 1.525-1.585 GHz (60 MHz). The LHCP antenna yields a |S11| < -10 dB bandwidth of 1.475-1.702 GHz (227 MHz) and a 3-dB AR bandwidth of 1.535-1.580 GHz (45 MHz). Moreover, both antennas yield a good broadside radiation with a gain of > 6.0 dBic and a radiation efficiency of > 65% across their operational bandwidth.
A compact composite right/left-handed (CRLH) bandpass filter with wide out-of-band rejection, which utilizes a substrate integrated waveguide (SIW) and modified complementary split-ring resonators (CSRRs) is presented. By incorporating two sets of CSRRs resonators (the top and bottom CSRRs) into SIW cavity, the proposed filter obtains a high selectivity. Besides, the filter has the CRLH property, and no additional areas are required because of the structure of the top CSRRs and the gap between them. At the same time, two slots of etched units used in feeding lines are replaced to obtain a wide out-of-band rejection. Finally, the measured results show that the filter has a wide stopband with rejection over 20 dB up to 4.3 times of the center frequency, implying that the experimental results are in good agreement with simulated ones.
This paper describes a wideband transmitting adaptive digital beamforming (ADBF) scheme with nulls in the direction of interference. The scheme partitions the wideband transmit signal into independent sub-bands using an analysis filter bank behind each array element. In each channel, sub-band ADBF weight vector is computed based on the minimum variance criterion with multiple linear constraints to form the sub-band transmit beam. Finally, a wideband transmit adaptive beam is reconstructed through the synthesis filters. Theoretical analysis and simulation experiments show that this algorithm can form a wideband transmit beam with deep nulls, and the pointing direction of the null keeps unchanged regardless of frequency. The algorithm proposed in this paper has little computation load and is efficient to implement in engineering applications.
A three layered low profile dodecagon shaped band stop frequency selective surface (FSS) is presented in this paper for X band rejection applications. The three layers are placed in a manner which is complement to each other. The low profile three layered FSS with unit cell dimensions on the order of 0.2λ0x0.2λ0 (at lower center frequency of 8.2 GHz) with overall thickness of three layers including air gap of 5.2 mm is presented. For experimental verification, a three layered FSS has been fabricated and measured. Simulation results show that the designed three layered FSS can provide a stopband from 8 GHz to 12.5 GHz with two transmission zeros of 8.2 GHz and 10.2 GHz with a fractional bandwidth of 45%. The complete design and equivalent circuit model (ECM) of the three layered FSS are presented in this paper.
This paper presents single and dual notch ultra-wideband bandpass filters (UWB BPFs) to mitigate interference with coexisting wireless communication systems in ultra-wideband (UWB). The single and dual notch UWB BPF is developed by using signal interaction concept loaded with stub loaded resonator. The stub loaded resonator creates notches in the passband to avoid the interference with coexisting wireless communication systems. The notch frequency can be placed at the points of interest within passband by selecting a proper length of stub loaded resonator. Transmission zeros are introduced to enhance the selectivity of stopband. It presents UWB BPF with single notch at the frequency of 6.5 GHz and dual notch at the frequencies of 6.3 GHz and 8.0 GHz. The circuit size of proposed filters is 6 mm x 6 mm and 6 mm x 6 mm. The proposed filters exhibit good performance in terms of compact size, good fractional bandwidth and sharp selectivity. All the filters are simulated and fabricated on a Rogers R03010 substrate with relative permittivity of 10.2 and thickness of 1.28 mm. There is good agreement between simulated and measured results.
The boundary element method is considered for solving scattering problems and is accelerated using the hierarchical matrix format. Thus, some matrix blocks chosen by geometrical criteria are approximated by low-rank matrices using a robust compression method. In this paper, we validate the use of the hybrid cross approximation which is quite new in this area, and we apply it to several examples. The validation is done on a conducting sphere, as well as less canonical objects such as the scattering by a rough (Weierstrass) surface or a plane.
A novel compact ultra-wideband (UWB) multiple input multiple output (MIMO) slot antenna with band notch characteristics is presented for portable wireless UWB applications. The antenna comprises co-planar waveguide feed (CPW) and two radiating monopoles oriented in orthogonal orientation for providing orthogonal radiation patterns. A Minkowski fractal parasitic stub along with a Minkowski fractal grounded stub has been placed at 45° between the monopoles to reduce the coupling between them which in turn establish high isolation between the radiators. An excellent band notch characteristic is obtained at 5.5 GHz by etching a modified E-shaped compact slot on the radiators. At the centre of notched band, the efficiency and gain of the antenna drop significantly which indicates a good interference suppression. Results show that the designed antenna meets -10 dB impedance bandwidth and -17 dB isolation throughout the entire operating band (3.1-12 GHz). Novelty of this design lies in improving isolation using compact fractal structures which occupy less space than conventional isolation mechanisms in MIMO structures. The simulated and measured results show that the proposed antenna is convenient for MIMO diversity systems.
High-order fractal characteristics of low-resolution radar echoes provide a supplementary description of the dynamic characteristics of the echo structure of a target, which provides a new way for the classification and recognition of targets with low-resolution radars. On basis of introducing the definition of high-order fractal statistic-lacunarity as well as its calculation method and the lacunarity characteristics of a target echo under additive fractal clutter background, this paper analyzes the characteristics of the lancunarity parameter variation of target echoes from a surveillance radar at a VHF band, and puts forward a classification method for aircraft based on the feature of the echo lacunarity scale change rate from the viewpoint of pattern recognition. The target classification experiments using real recorded echo data show that, as a high-order fractal characteristic parameter, the lacunarity scale change rate can be used as an effective feature for aircraft target classification and recognition, and the proposed method has good classification performance.
Compact antenna test range (CATR) is one of the most commonly used antenna measurement techniques, particularly in the microwave/millimetre wave range. A conventional industry standard for the quiet zone of a CATR is ±0.5 dB amplitude variation and ±5º phase variation to conduct measurement with acceptable accuracy. Such a high standard, however, has not been rigorously verified in theory. And it is in contrast to 22.5º phase variation condition for the far-field method. Being inspired by many measurements, where the quiet zone is not up to the industry standard while satisfactory results are still obtained, this paper systematically investigates the effect of quiet zone performance on the radiation pattern measurement. It aims at searching for a guideline specifications for the construction of a CATR. Theoretical models have been built to predict the quiet zone performance on the antenna pattern measurement, particularly on the main beam. Many factors have been considered, such as amplitude and phase ripple, amplitude/phase taper, and electrical size. In coupling with experimental study, it is shown that a much more relaxed condition can be followed depending on the required measurement accuracy.
Traditional long vector-based MUSIC methods require 4D spectral search, which suffers from heavy computational complexity. This paper develops a joint DOA and polarization estimation method named as dimensionality reduction MUSIC (DR-MUSIC) method for a passive radar direction finding (PRDRF) system using spatially separated single-component circular electromagnetic vector sensor array (SSSC-EVSA), where 4D spectral search is transformed into 2D spectral search by exploiting rank deficiency of the signal component of cost function. Polarization parameters are estimated via the generalized eigenvector of matrix pencil, which can be utilized for the recognition of radar and decoy. In addition, the estimation performance of the proposed DR-MUSIC method is also studied considering the phase inconsistency among multi-channels. Simulation results demonstrate the effectiveness of the DR-MUSIC method.
Angular log-periodic meander line (ALPML) traveling wave tube (TWT) is one kind of low voltage miniature TWT. In order to decrease high frequency loss, avoid charge accumulation and enhance coupling impedance, the conformal microstrip ALPML TWT based on silicon substrate is proposed in this paper, which means that the projections of silicon supporting structure and metallic microstrip meander line are same in the top view. The microfabrication technology DRIE can be used to fabricate this structure. Compared with the conventional microstrip ALPML TWT, the coupling impedance of conformal microstrip ALPML TWT increases 50%. The particle-in-cell (PIC) simulation results reveal that the output power of conformal microstrip ALPML TWT can reach 220 W at 35 GHz, while the efficiency is 20%. The 3-dB bandwidth reaches 14 GHz in the frequency range between 28 GHz and 41 GHz when the operating voltage and radial sheet beam current are 3600 V and 0.3 A, respectively.
Compressive sensing for through-wall radar imaging (TWRI) is a promising method to obtain a high-resolution image with limited number of measurements. The capability of the existing method in the framework of CS is limited due to the model error stemmed from the approximated signal model which does not consider multipath returns or only consider first-order interior wall multipath returns. In order to exploit various multipath returns, finite-difference time domain (FDTD) technique is used to obtain the scattered signal for each assumed target position and then to construct the exact forward scattering model. Then, sparse reconstruction is used to solve this linear inverse problem. Numerical results demonstrate that the proposed approach performs better at ghost suppression in the same condition of the signal-to-noise ratio (SNR).
This paper proposes a new two-stage channel estimation (TSCE) method to estimate the cascaded channels in amplify-and-forward (AF) one-way relay network (OWRN) with multiple transmit and receive antennas. Different from the existing estimation methods, the proposed TSCE estimates the cascaded channel matrix by utilizing the special structure of the received signal in the destination and by exploiting the correlations among the cascaded channel matrix entries. The TSCE not only obtains the channel state information (CSI) when receiving training sequences, but also improves the accuracy of CSI when receiving the data sequences. Simulation results demonstrate that the proposed TSCE can improve estimation accuracy compared with traditional channel estimation schemes.
A low-profile dual tuning stub loaded microstrip line-fed multi-slot antenna is presented in this paper, which covers most of the significant 4G LTE bands from 850 MHz to 2800 MHz and beyond. The slot antenna consists of three wide slot sections: two orthogonal slots and a circular slot at the junction of those two slots. This multi-slot antenna is excited by a microstrip feed line loaded with dual stubs, which is on the other side of the dielectric substrate. The stubs are terminated across the width of orthogonal slots. Two of these slots along with feed lines are placed on two corners of the ground plane for pattern diversity. Numerical simulation and measurement results on a fabricated prototype demonstrate excellent agreement in scattering parameters. Good port isolation and gains are also obtained. This design is suitable for use in LTE mobile terminals.
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