Millimeter wave (MMW) imaging has found rapid adoption in security applications such as concealed object detection under clothing. However, the imaging quality is often degraded due to resolution limit and low signal level. This study addresses shape feature analysis following concealed object detection. The object region is extracted by multi-level segmentation. Shape features are composed of several descriptors which are object area, perimeter, major and minor axes of the basic rectangle, rectangularity, compactness, and eccentricity. In the experiments, three objects (gun, hand ax, and plastic bottle containing liquid skin aid) concealed under clothing are captured by the passive MMW imaging system. The extracted shape features are compared with the true features from the object model showing good accuracy.
In this paper, a high-gain amplifier module has been presented for millimeter wave applications. In order to suppress oscillation of the high-gain amplification block, a rectangular waveguide (WG) is fully integrated into the metal case, on which a cascaded two-stage amplifier is mounted. Due to the integrated WG, additional WG-to-microstrip line (MSL) transitions are required. Therefore, a low-loss and wide-band WG-to-MSL transition is designed and fabricated on a 5 mil thick RT5880 substrate. Two sets of WG-to-MSL transitions in back-to-back structure are assembled in the metal case for the high-gain amplifier module and are characterized. The measured transition loss and operational returnloss (S11) bandwidth less than -10 dB are less than -0.44 dB/a transition and 15.9 GHz from 34.1 to 50 GHz, respectively. The fabricated high-gain amplifier module shows a high gain over 39.7 dB from 38 to 41 GHz. At 38.7 GHz, its maximum gain of 44.25 dB is achieved.
In this letter, a compact four-element microstrip patch antenna array for BeiDou navigation satellite system (BDS) operation at the B3 (1268 MHz) band is proposed. High permittivity dielectric substrate and slit-loaded microstrip patch are used to reduce the antenna element size down to 40 mm × 40 mm which implies an aperture size of only λ0/6 × λ0/6 at the B3 band. The right-handed circularly polarized (RHCP) radiation is achieved by connecting two coaxial probes to a 0°-90° stripline hybrid. Four identical antenna elements are distributed with the same polarity and an inter-element separation of 80 mm (λ0/3 at the B3 band). The overall size of the antenna array, including the stripline feeding network and supporting ground plane, is only 140 mm × 140 mm × 5.5 mm. A prototype was fabricated and measured to verify the design concept. Simulated and measured results will be presented and discussed, showing that the proposed BDS antenna array is suitable for BDS applications.
The increasing sophisticated power and communication demands have motivated a variety of research on simultaneous wireless information and power transfer system, aiming to provide higher power transfer efficiency and improved communication rate. This letter demonstrates that resonant wireless power transfer system with relays can be a candidate to reach these aims. Based on coupled resonator filter theory, mathematical equations for transmission efficiency and bandwidth are derived for arbitrary number of relays. Improved efficiency and bandwidth are verified by equations, simulation and experiments. Experimental results show that under the distance of two times the diameter of the resonator, system efficiency increases from 5.43% (no relay) to 29.47% (one relay) and 38.02% (two relays), with the fractional bandwidth broadened from 1.33% (no relay) to 3.31% (one relay) and 4.47% (two relays) at operation frequency of 42.55 MHz, providing available channel for simultaneous power and data transfer. The procedure for the design of relays is also listed in detail.
In this paper, the localized pseudo-skeleton approximation (LPSA) method for electromagnetic analysis on electrically large structures is presented. The proposed method seeks the low rank representations of far-field coupling matrices by using pseudo-skeleton approximations (PSA). By using PSA, only part of the original matrix is needed to be calculated and stored which is very similar to the adaptive cross approximation (ACA). Moreover, rank approximation and index finding schemes are given to improve the performance of the method in this paper. Several numerical results are given to demonstrate that the proposed method performs better than the randomized pseudo-skeleton approximation (RPSA) and ACA.
A novel compact differential microstrip antenna is presented. Owing to the introduction of slots in the patch and ground plane, the size of the proposed differential antenna is about 0.45 times that of the traditional microstrip antennas. The measured results show that the proposed antenna can work at 2.45 GHz. The gain is about 5.54 dB and the impedance bandwidth about 150 MHz.
A low-profile broadband omnidirectional MIMO antenna with dual-polarization is proposed for 4G LTE applications. It consists of two orthogonally polarized radiating elements with separate ports. The horizontally polarized element consists of four printed arc dipoles, a broadband balun feeding network, four arc parasitical strips and four double L-shaped parasitical strips. It exhibits a 48.9% fractional bandwidth (return loss > 10 dB) from 1.70 GHz to 2.80 GHz with a cross-sectional size less than 100×100 mm2. The vertically polarized element consists of a discone, a round sleeve, and a top-loading ring shorted to the ground-plane with three equally-spaced pins. It provides a 47.3% fractional bandwidth (return loss > 10 dB) from 1.68 to 2.72 GHz with an overall volume less than 84×84×22 mm3. In addition, an isolation of 25 dB is achieved in the overlapping band of two elements and the cross-polarization levels for both radiating elements are lower than 20 dB.
In this letter, a compact stable bandpass frequency selective surface (FSS) operating at 3.14 GHz is proposed by using a novel Y-type element. The measured and numerical results are in good agreement, except a little deviation of resonant frequency and a little change of bandwidth, which show that the proposed FSS has good angle and polarization stability. Numerical results show that the dimension of the element is only 0.042λ0×0.042λ0, where λ0 represents the wavelength at the resonant frequency 3.14 GHz. Thus, the FSS is suitable for practical application in limited space.
In this paper, a new reconfigurable antenna is introduced. This antenna is a printed spiral-shaped monopole antenna with a compact structure. By embedding microwave switches in the structure of the antenna, different resonance frequencies can be achieved in different states of the switches. The introduced antenna is capable to cover two standard frequency bands for biomedical applications, i.e. Medical Implant Communication Service (MICS) and Industrial, Scientific and Medicine (ISM) bands. MICS band covers 402 MHz to 406 MHz and ISM covers 2.4 GHz to 2.5 GHz frequency range. The proposed antenna has a compact size of 32 mm×50.3 mm×1.8 mm, and it is fabricated on an FR4 substrate. The measurement results are in a good agreement with the simulations.
In this paper, a theoretical analysis of numerical dispersion of the three-dimensional (3-D) high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is presented. The phase velocity of numerical wave modes is relevant to the direction of wave propagation, grid discretization and time-scale factor. The formula to determine a suitable time-scale factor is derived. By a theoretical evaluation, the dispersion errors for the 3-D high-order WLP-FDTD scheme with different time-scale factors are obtained. Finally, one numerical example is included to validate the effectiveness of the theoretical solution of the time-scale factor.
A novel method for a dual-band filter and quad-channel diplexer design is presented in this paper. This method, by altering the gap between resonators, realizes a transformation from bandpass to dual-band for the filter and diplexer. At first, a high selectivity bandpass filter (BPF) with four controllable transmission zeros (TZs) is designed. Then altering the gap between resonators, a band gap is generated and utilized to split the passband of the proposed BPF into two bands, which transforms the BPF to a dual-band filter with narrow passband separation. The center frequency and bandwidth of the new dual-band filter are controllable by adjusting the frequency and width of band gap. Based on the dual-band filter, a quad-channel diplexer with stepped impedance T-junction is designed, and it can be transformed to a wideband diplexer. For demonstration, the dual-band filter and quad-channel diplexer are fabricated and measured.
A switchable square loop frequency selective surface (FSS) design is presented. The FSS is switched between reflective and transparent state by using one gap for each unit cell. Measured and simulated results are compared. PIN diodes are integrated to the FSS for electrical switching. The PIN diodes equivalent circuit capacitance element is varied to investigate its effect on the switchable FSS performance. The switchable FSS power percentages of the reflected and transmitted states are presented in tables and discussed.
A new microstrip narrow bandpass filter with good selectivity and wide stopband rejection for Ku-band application is proposed in this letter. The characteristic of the triple-mode stub-loaded resonator has been investigated. The resonance frequencies of the degenerate modes can be adjusted easily to satisfy the bandwidth of the narrow bandpass filter. Two parallel-coupling feed structures with cross-coupling have been used to generate two transmission zeros at the lower and upper stopband, which can improve the filter selectivity. To validate the design theory, a new microstrip Ku-band narrow bandpass filter has been designed, fabricated, and measured. Simulation and experimental results are provided with good agreement.
This paper presents design and development of a Circularly Polarized microstrip antenna array for C-band application. The proposed antenna exhibits convenient trade-off between bandwidth and dimension. The array design is based on the Sequential Phase Arrangement (SPA) of 2×2 non-identical disc based patch elements, operating in modal degeneration. Exploiting the properties of the SPA, capable to force CP even operating on linear polarized elements, each disc is independently detuned to operate on non perfectly overlapped bandwidth. When properly fed by a Sequential Phase Network (SPN), the set of four discs seamlessly covers the wide cumulative bandwidth which is the combination of the four sub-channels. To verify the design, a single-layer via-less array is fabricated in a compact printed square board of side 40 mm, meaning a surface of 0.64λ20 at the center frequency of 6.0 GHz, assembling the elements with a compact space-filling SPN. The measurements show a wide 10 dB return loss bandwidth of 28.5%, a 3 dB Axial Ratio (AR) bandwidth exceeding 1 GHz, and a realized gain ranging from 4.1 dB to 7.25 dB inside the AR bandwidth. The global bandwidth of the proposed array, almost coincident with the AR bandwidth, is 17.0%.
A novel design for a transparent circularly polarized circular slot antenna fed by a coplanar waveguide (CPW) is presented in this paper. The circular polarization is achieved by introducing a tapered split gap in the ring patch of the circular slot antenna in combination with unequal CPW ground arms. The antenna is designed using AgHT-4 laminated on a 2 mm thick glass with a relative permittivity of 7. The proposed antenna is designed to operate at 5.8 GHz for WLAN applications. The tapered split gap and inequality in the lengths of the CPW ground arms contribute to a 3 dB axial ratio bandwidth from 5.4 to 6.2 GHz. The proposed antenna has been studied theoretically and fabricated. The measured results show that the proposed antenna has a gain of 0.92 dB at 5.8 GHz. Reflection coefficient (S11), axial ratio (AR), and radiation patterns are presented and briefly discussed.
In this article, the design and analysis of a compact asymmetrical coplanar strip (ACS) feed multiband monopole antenna operating over the frequency range of Bluetooth/IMT-E (2.4-2.484/2.5-2.6 GHz), worldwide interoperability for microwave access (WiMAX: 3.3-3.6 GHz) and wireless local area network (WLAN: 5.15-5.825 GHz) for Personal Wireless Communication Systems (PWCS) applications has been investigated. The proposed antenna consists of a semi-circular arc and L-shaped stub which forms a vertically flipped G structure that facilitates the multi-band operation at 2.4 GHz and 3.5/5.5 GHz respectively. The antenna is fabricated on a low cost FR-4 substrate having thickness of 1 mm and has compact dimensions of 24 × 10 mm2. The proposed antenna yields a highly isolated measured impedance bandwidth of 2.3-2.7 GHz, 3.25-3.65 GHz and 5.1-6 GHz for Bluetooth/IMT-E, WiMAX and WLAN bands respectively and exhibits symmetrical radiation pattern, stable gain across all operating frequency bands which makes the antenna a suitable candidate for PWCS applications.
The eikonal equation for inhomogeneous anisotropic metamaterials with equal relative permittivity and permeability tensors (ε(r) = μ(r)) is derived from a free boundary variational principle. An original approach is proposed considering the wavefront as a moving discontinuity surface in an extended continuous media described by the Lagrangian density of electromagnetic fields. The eikonal equation arises as natural (non prescribed) boundary conditions for variational problems.
As we all know, traditional transmission electromagnetic pulse simulator has restricted test space problem. This paper proposes a new directed radiation fast rising time electromagnetic pulse (FREMP) simulator scheme which is based on transverse electric magnetic (TEM) wave antenna of a wire edge curl structure. Through numerical simulation, we study the influence of the parameters of wire edge curl TEM horn antenna and the effect of absorption resistance on radiation field. The simulation results show that the wire edge curl TEM horn antenna can effectively improve the ability of low frequency radiation. It can provide a theoretical support for developing FREMP simulator. We also demonstrate the feasibility of developing FREMP simulator using wire edge curl TEM horn antenna through experiments. Finally, the experimental results show that the radiation field of FREMP simulator developed by wire edge curl TEM horn antenna can meet high-altitude nuclear electromagnetic pulse (HEMP) requirements.
An improved mutual coupling calibration approach based on the element pattern reconstruction (EPR) method is proposed in this paper. Compared to previous calibration methods in which the calibration is carried out in the entire space, the space angle ranges to be calibrated in this method is partitioned according to the interested directions. Through the partition of the space angle region, the angle ranges to calibrate are narrowed, and thus more accurate calibration matrix can be obtained in corresponding angle regions. With the employment of the calibration matrix on 2-D DOA estimation, more effective mutual coupling calibration and more accurate DOA estimations are achieved by alternate iteration in each angle region. The validity of this method is verified by an L-shaped microstrip antenna array, and the performance of mutual coupling calibration is presented by the better accuracy in 2-D DOA estimations.
εThis paper presents an analytical solution to study the reflection and transmission of an electromagnetic wave impinged upon a multilayered structure. The structure is composed of a fractal slab sandwiched by ordinary material on either side. Modified Maxwell equations for fractional dimension space are used to represent the fields in a fractal slab. The electromagnetic characteristics of the structure are studied for different dimensions (D) and numerical results are presented for both the classical (D is integer) and fractal (D is non-integer) slabs. This study provides foundations for investigating the waveguides filled with fractal media and electromagnetic waves propagation in multilayered structures at fractional boundaries.
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