In this paper, a compact two ports Multiple Input Multiple Output (MIMO) antenna for Ultra Wide Band (UWB) application has been proposed. The presented antenna consists of two symmetrical radiators, developed on an FR4 substrate with overall size of 34 × 18 × 1.6 mm3. The proposed antenna is fed with a 50 Ω microstrip line. The antenna has good impedance matching in the range of UWB band. The isolation is lower than -15 dB from 3.1 to 5 GHz and < -18 dB from 5 GHz to 11 GHz. Envelope Correlation Coefficient (ECC) < 0.01 and Diversity Gain (DG) > 9.96 dB. The performance of the proposed antenna is analyzed and examined in term of return loss, gain, radiation efficiency, ECC, DG, and isolation between two ports.
The ideality of operating environment of radar systems is extremely scarce while the demand for these systems is growing at a rapid pace. Technology of adaptation is therefore of primary concern in the design of their future strategies. The difficulty in finding a solution based on a single adaptive algorithm to deal with diverse noise environments has led to the development of composite adaptive procedure. Therefore, fusion of particular decisions of the single adaptive variants through appropriate rules provides a better final detection. This paper is intended to analyze the fusion strategy of cell-averaging (CA), order statistics (OS) and trimmed-mean (TM) schemes in heterogeneous environments. The tested target and the spurious ones are assumed to follow χ2-distribution with two- and four-degrees of freedom in their fluctuations. A closed form processor performance is derived. The results show that for the heterogeneous operation, this approach is more realistic. Particularly in multi-target situations, it exhibits higher robustness than CA, OS, or TM architecture. Additionally, our results reveal that it exhibits a homogeneous performance outperforming that of the Neyman-Pearson (N-P) detector which is the yardstick in the world of adaptive detection.
The efficiency of the standard tapered windows as applied to sidelobe suppression in compressed pulses with linear frequency modulation (LFM) or chirp pulses corresponds to the literature data only in the case of rather great values of the pulse duration-bandwidth product B≥100. With comparatively small values of B (several dozens or so) the side-lobe levels prove to be essentially greater than those announced in the literature. In the paper, the output signal of the chirp-pulse compression filter is analyzed in order to look into causes of discrepancy between the sidelobe level obtainable using standard tapered windows and the literature data. Expressions are derived for estimating the maximum number of zeros and maxima in the response of the optimum filter of chirp-pulse compression and separation between adjacent and ``like'' (with the same numbers) zeros and maxima in dependence on the signal duration-bandwidth product. The amount of loss in the signal-to-noise ratio due to application of smoothing functions is determined. The case of applying window functions in the form of cosine harmonics of the Fourier series, which describes a rather great number of the standard windows, is analyzed in detail. Analytical expressions are presented for the output signal of the chirp-pulse compression filter on the basis of such windows and the amount of loss in the signal-to-noise ratio. A comparative analysis of the Hamming and Blackman windows is made in dependence on the pulse duration-bandwidth product B. It is shown that application of the Hamming window is more efficient up to B≈80. For greater values of B, the Blackman window shows a higher efficiency. As B increases, the efficiency of both windows steadily increases asymptotically approaching the figure declared in the literature. Coefficients of window functions containing 2 cosine harmonics of the Fourier series have empirically been selected which made it possible to reduce the sidelobe level by approximately 0.34 dB for B=21 and by more than 1 dB for B=7 as compared with the Hamming window. The obtained results allow concluding that the optimization problem for the window function parameters in the case of small values of the pulse duration-bandwidth product should be solved individually for each specific value of B. Most likely it would be impossible to obtain the extremely low sidelobe level; however, a certain improvement of the characteristics of the chirp-pulse compression filter seems quite possible.
Electrically small antennas are of intense and increasing academic and industrial interest due to the advent of ubiquitous RFID devices and more generally within the Internet of Things (IoT) applications. For most of these applications antennas will have to be as small as possible, when being integrated within a transceiver, while maintaining significant efficiency values. Of particular interest are antennas that can radiate omnidirectionally along a planar surface, thus establishing optimal connectivity capabilities for devices surrounding the corresponding transmitter. Such antennas are important not only for energy harvesting but also for near-field wireless charging applications. In this paper, we report an electrically small antenna of size ka ≈ 0.25, where a is its effective radius and k the wave vector at operating frequency. The antenna geometry is a 3-dimensional folded meandering loop and contains its own ground, so that it becomes insensitive to the integration environment. The radiation efficiency of the antenna is 70%, and it radiates as a vertically polarized dipole. The operating frequency chosen in this paper targets RFID/IoT applications at 915 MHz, and the impedance matching bandwidth, as realized, is narrow but appropriate for such applications and may be further increased if appropriate matching networks are used.
In this paper, a compact MIMO antenna with an electromagnetic bandgap structure is proposed for isolation enhancement. The proposed antenna design is coupled with an electromagnetic bandgap (EBG) structure to minimize mutual coupling between the antenna elements and to enhance the performance of the MIMO antenna configuration. The antenna is fabricated on an FR4 substrate having a dimension of (27.9×38×1.6 mm3). The EBG structure is analyzed, and the effect on antenna performance is studied using parametric analysis. The antenna is fabricated, and the measured results are compared with simulated ones. The antenna achieves a reduction in transmission coefficient |S21| ≥ 16 dB for simulated and |S21| ≥ 25 dB for measured results, and attains the minimum ECC of 0.09 which is very close to the ideal value of zero and hence makes it a better choice for MIMO applications.
In this study, a star-wheel design of single crystal sapphire optical fiber is proposed to achieve single mode operation in the infrared regime. In the azimuthal direction the structure retains a reduced core of higher refractive index. It is connected to the outer boundary viastar-wheel configuration of segments. The region of alternating symmetrical truncated cavities of lower refractive index is air. The enclosed alternating layers of sapphire and air cavities around the reduced core function as cladding. Fiber structure in the azimuthal directionis uniformly distributed in the radial direction. Finite element method is employed to analyze the modal characteristics of fundamental and higher order modes. Under strongly guided approximation, the structure can effectively eliminate the large modal interference. The proposed waveguides, at operating wavelength of ~1.55 µm, with the diameter of ~50 µm, 75 µm, 100 µm, and 125 µm diameter, exhibit confinement loss of ~0.0314 dB/m, 0.0072 dB/m, 0.0023 dB/m, and 0.0009 dB/m, respectively. It is anticipated that such fiber can be a potential candidate in addressing a wide range of optical sensors and communication systems, which unable to sustain in extremely harsh environments. COMSOL multi-physics ® is used to perform numerical investigations.
In the present scenario, multiple-input-multiple-output (MIMO) elements provide the capacity to generate more than one radiation pattern with different polarizations, which show a prodigious role in the modern telecommunication sector. A new two-element MIMO antenna with minimization in mutual coupling is presented in this paper. The proposed design reduces mutual coupling between antenna elements. The strip-line mechanism is used as a feed and is simulated using HFSS v 15. MIMO element design is done with four T-shaped slots in all directions of the patch, further enhancing the cross-correlation. MIMO antenna consists of two radiators on a 50 x 25 mm2 FR-4 substrate. A T-shape ground stub, along with a slot, reduces mutual coupling (MC) and Impedance Bandwidth (IBW) of the proposed design. The design provides multi-band characteristics in the entire UWB range with practical applications like WiMAX (3.5 GHz), WLAN (5.9 GHz), X-band SATCOM applications (7.9 GHz) and Radar, Mobile phones, and commercial WLAN (9.3 GHz). The spacing between elements is in the order of 0.215λ0. MC reduction of 20 dB is achieved at every resonant frequency.
This paper presents a compact generalized T-shaped printed pseudo-monopole antenna (GeT-PPMA) driven dual-band Yagi-type pattern diversity antenna. In contrary to the common practice, here impedance matching at the lower band is attained by increasing the quality factor (Q) through folding a monopole strip. Afterwards, a GeT-PPMA having relatively lower Q than that of the T-PPMA is proposed. Compared to the simple T-PPMA, the GeT-PPMA has 1.5 times more bandwidth (BW) at the lower band. The dual-band GeT-PPMA is 15.11% more compact than the corresponding straight PPMA(S-PPMA). A highly compact dual-band Yagi-type pattern diversity antenna of size 45.5×63 mm2 i.e. 0.35λ0 x 0.48λ0, where λ0 is the free space wavelength at the lowest frequency of operation, is designed by using a novel arrangement of two directors and two common folded reflectors. The compactness owes to the folding of the reflectors. The length of the reflector is optimized for providing good front-to-back-ratio (FBR) in the lower band. The length of the two directors is optimized to improve the FBR at the upper band. Usage of the folded reflector is found to degrade the isolation level in the lower band. Near-field analysis is carried out to investigate the mechanism of mutual coupling. Being guided by the near-field study, a λg/2 isolator, where λg is the guided wavelength at the lower band, is placed in the gap of the folded reflectors, and the mutual coupling is reduced by about 5 dB.
A wideband coplanar waveguide (CPW) fed monopole antenna designed for Wi-Fi5 and Wi-Fi6 applications is proposed. The proposed antenna (main radiator) has a designed footprint of only 20 × 8.7 × 0.4 mm3, which is composed of an oval-shaped ring radiator with three concentric rings and a double-T structure loaded with a J-shaped slot. The main novelty of this work is that the measured wideband operation of 34.5% (5.15-7.29 GHz) is contributed by only a single resonance at 6.2 GHz, conforming to the bandwidth requirement of Wi-Fi5 (5.15-5.85 GHz) and Wi-Fi6 (5.925-7.125 GHz). Furthermore, the proposed antenna also exhibits good radiation characteristics, including a gain around 2.25 dBi, a radiation efficiency above 80%, a total efficiency above 70%, and omnidirectional radiation patterns with a low magnitude of cross polarization throughout the bands of interest.
A method of loaded patch antennas with shorting pins and erected walls in between patch antenna arrays is introduced to reduce surface wave and free space wave coupling in both E and H-plane. This simple technique works equally well in both orientations by reducing coupling up to -19 dB and -15 dB (measured value) in E-plane and H-plane, respectively, as compared to a conventional patch antenna array. The scattering parameters are studied, and conclusions are made on amounts of mutually coupled power and the bandwidth of the rejection band (S12). A parametric study of the variation in the level of mutual coupling with respect to height of the wall has been carried out in both E and H-planes. The simulation results are well verified through measurements.
This work presents a noninvasive measurement technique to detect the blood glucose level for diabetic individuals using a fractal microwave resonator printed on an FR-4 substrate. The proposed fractal is based on the 1st order of Minkowski open loops (MOL) coupled with an open-stub transmission line (OSTL) to increase the resonator selectivity at 2.45 GHz. Moreover, an air gap in the middle path of the OSTL is filed with multi wall carbon nanotubes patch (CNT) to increase the field fringing at a specific region. The proposed resonator is designed numerically with CST Microwave Studio. The size limitations for biomedical devices are considered to account for wearable applications. Later, an analytical study is presented on the proposed resonator sensitivity. The detection technique is based on the resonant frequency tuning, bandwidth variation, impedance matching change, and phase displacement for the S-parameters in the S11 and S12 spectra. The sample under test is mounted on an CNT patch of the OSTL which employs the characterization of the specimen. The proposed design idea could be generalized for a wide variety of biomedical detection liquids.
In wide-angle synthetic aperture radar (SAR), the scattering behavior of many illuminated objects might vary with the observation angle, which results in the degradation of the resolution and interpretability of the reconstructed imagery. To solve this problem, a sparse-based methodology is proposed in this paper to implement the separation of the anisotropic scattering target data and imaging processing simultaneously. The distinct reflection characteristics of the illuminated targets are employed to formulate a composite projection operator. Then, the sparse constraint is utilized to suppress cross-projection energy. Finally, the imagery of the anisotropic scattering targets could be derived with improved focal quality and interpretability. Numerical simulations could verify the validity of the proposed methodology.
Designs of a polygon shape microstrip antenna for increasing number of side lengths are studied. A detailed analysis is presented for the variations observed in the first and second order mode resonance frequencies in a polygon shape patch, from triangle to square to pentagon, ending up in a circle. Among all the polygon shapes, close spacing between the first two frequencies is obtained in the pentagon shape patch. A design of a pentagon shape microstrip antenna with a pair of slots is proposed. It gives impedance bandwidth of more than 700 MHz (>55%), which is maximum amongst all the polygon shapes employing a pair of rectangular slots. The proposed design offers peak broadside gain of 9 dBi over the bandwidth. A resonant length formulation and subsequent design methodology for the pentagon shape patch and its slot loaded variation are presented. This helps in the redesigning of a similar configuration in a given frequency range, using proximity and coaxial feeds.
A compact wearable antenna operating at 2.45 GHz with a novel Electromagnetic Band Gap (EBG) structure as a reflector is proposed. The broadband monopole is used as the main radiator of the antenna, and the gradient feeder structure and etched slot on the ground are used to adjust the matching effect of the antenna port. The current path is extended, and the structure is made more compact by slotting the surface of the EBG cell. Then, a 3 x 3 EBG reflector is constructed and loaded to the bottom of the antenna to improve the antenna gain performance and reduces the specific absorptivity (SAR). A three-layer human model (skin-fat-muscle) has been built in High Frequency Structure Simulator (HFSS) to analyse the influence of human tissue on the wearable antenna system. Combined with the practical application background, the radiation performance of the system under bending is also explored. The simulation results show that the application of EBG reflector can increase the antenna gain by about 4.77 dBi and the front-to-back ratio by 17dB, reduce SAR by more than 95%, and the overall size of the system is only 60.3 x 60.3 x 3.5 mm3 (0.49λ). The antenna system has the characteristics of simple structure, small size, high gain, and low SAR value, which is of certain reference value for the research on the wearable antenna.
A compact U-shaped ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with novel complementary modified Minkowski fractal (CMMF) for isolation enhancement is proposed. This antenna consists of two identical U-shaped monopole elements, a novel CMMF and a slot in the bottom of the ground plane for the isolation enhancement. The novel CMMF is designed by a technique iterated function system (IFS). The overall dimension of this compact antenna is 22 x 28 mm2. The impedance bandwidth of this antenna is 10.35 GHz, ranging from 3.06 GHz to 13.41 GHz. The minimum isolation is 17.07 dB for the operating frequency range and 18.4 dB for the UWB frequency range 3.1 to 10.6 GHz. The diversity parameters are also determined for the proposed MIMO antenna, and all are found satisfactory. The proposed MIMO antenna is fabricated, and its prototype measured results are found in good agreement with the simulated ones.
This paper presents a modified version of minimum description length (MDL) method, referred as multifrequency MDL (FMDL), for scatterers enumeration before using the multiple signal classification (MUSIC) algorithm in microwave imaging applications. The inclusion of data from multiple frequencies should make an attempt to reduce the error in number estimation due to noise and multiple scattering. Data fusion in multiple frequencies is performed based on two schemes called averaging and maximization rules. The solution for MDL criterion which is a minimum for one frequency is not likely to be the solution for other frequencies, so by averaging the MDL criterion over the total frequencies or by maximization of the solution for each frequency, we can achieve the correct source number. Furthermore, a whitening step before applying FMDL method is employed to compensate the aspect limitations of the measured data due to the limited number of antennas. The superiority of the proposed FMDL approach with respect to the other competing methods is confirmed by both the numerical examples and the Institut Fresnel experimental dataset. The results indicate that the FMDL yields more accurate estimate of the targets number specially for the cases of low SNR values and very colsely spaced scatterers.
This paper describes a theoretical characterization of a Transverse Electric (TE)-polarized vortex beam antenna in the microwave range. The main body of the antenna consists of a cylindrical waveguide that is excited by a traveling-wave current ring feeder. A new design of the feeder is proposed. Closed-form formulas are obtained for the fields and the antenna input impedance following a conventional derivation based on the electric vector potential. A detailed dispersion analysis is used for accurate evaluation of the relevant spectrum and propagation properties. The effectiveness of the theoretical derivations is validated via full-wave numerical simulations.
In this paper, the effectiveness for inferring the responses to electromagnetic threats of the finite difference time domain method combined with a multi-conductor, multi-shield and multi-branched cable harness transmission line solver is validated by comparing simulation results with measurements performed on an equipped cockpit partially made by carbon fiber composite. A complete lightning indirect effects and high-intensity radiated field testing campaign was carried out in this cockpit within the scope of the European research and technology project Clean Sky 2 whose main goal is to reduce the aviation environmental impact by, for instance, building low-weight aircrafts with the increasing use of carbon fiber. Simulations are performed with EMA3D and MHARNESS obtaining very good agreement with measurements for a variety of observables and in a wide frequency range, thus proving the predictive capacity of these numerical methods for estimating the electromagnetic behavior of complex structures.
In this article, a novel dual-band multi-port compact rectenna design for RF energy harvesting is proposed. An E-shaped coaxial fed microstrip antenna combined with an inverted L-shaped structure is used to achieve a dual-band operation at 0.9 GHz (GSM900) and 2.4 GHz (WiFi) frequency bands with gains of 0.8 dBi and 4.4 dBi, respectively. A shorting post is incorporated in the design, which restricts the antenna size to 50 mm x 47 mm, making the overall rectenna compatible with any sensor nodes. Further, a compact rectifier circuit covering both the frequency bands is designed to obtain a conversion efficiency up to 50% for an input power as low as -20 dBm. The matching circuit ensures that the nonlinear impedance of the rectifier matches with that of the antenna under varying operating conditions. Finally, the rectennas designed are combined and arranged together to form a cubical structure to produce an output voltage as large as 0.5 V for an input power of -20 dBm. With 360˚ coverage and orthogonal polarization reception, the cubical antenna arrangement ensures improved harvesting efficiency making the proposed design suitable for powering low power IoT devices.
A novel two-step synthesis method of sparse nonuniform-amplitude concentric ring arrays (SNACRAs) to maximize the beam collection efficiency (BCE) for microwave power transmission (MPT) is proposed in this paper. In the first step, beetle antennae search (BAS) algorithm is used to optimize the radius of each ring of the SNACRA, to obtain the maximum BCE and the equivalent continuous excitation of each ring. In the second step, we find the least array element on each ring to discretize the continuous excitation on each ring by using the binary search (BS) algorithm directly under the restriction conditions and then find the excitation of each element. Through the above two steps of optimization, the optimal synthesized parameters of the SNACRA, including the maximum BCE, layout, excitation and power pattern, can be obtained highly efficiently. Many representative numerical results under different ring numbers, apertures, and receiving areas are presented. Comparing these numerical results with those of other three arrays for MPT, it is proved that the SNACRA synthesized by the two-step method can get higher BCE with less elements and have a relatively simple feed network.