This paper proposes a novel signal processing approach to thermal non-destructive testing by incorporating Gaussian window function onto the linear frequency modulated incident heat flux to achieve better pulse compression properties. The present work highlights a finite element analysis based modeling and simulation technique in order to test the capabilities of the proposed windowing scheme over the conventional frequency modulated thermal wave imaging method. It is shown that by using Gaussian weighted chirp thermal stimulus, high depth resolution can be achieved.
A broadband circularly polarized (CP) slot antenna array fed by a coplanar waveguide (CPW) is proposed. A fan-shaped feed line and three L-shaped grounded strips are embedded in the square slot antenna element to enlarge the bandwidth. Simulated results show that the antenna element can obtain a wide impedance bandwidth with -10 dB reflection coefficient covering 1.7-6.3 GHz (about 115% relative bandwidth) and 3 dB axial ratio (AR) bandwidth covering 2.6-5.2 GHz (about 66%). Using four elements with sequential phase feed, the measured impedance bandwidth and axial ratio bandwidth of the antenna array can be enhanced to 105% (1.65-5.35 GHz) and 71.3% (2.3-4.85 GHz), respectively. Good radiation characteristics with the peak gain of 10.8 dBic over the operating band can be obtained.
A wideband unidirectional bowtie antenna with stable radiation patterns is proposed and investigated. It is fed by a wideband microstrip balun, using a coupling triangular structure to induce more balanced currents. Particularly, the corners of the conventional triangular bowtie dipole are rounded to achieve an impedance BW of 106.9% for |S11| ≤ -10 dB ranging from 1.97 GHz to 6.49 GHz. Additionally, a special small circular reflector between the ground plane and the bowtie dipole is used to stabilize the radiation patterns. The antenna achieves a stable gain of around 9.5 dBi with a little variation of 1.4 dBi and unidirectional radiation patterns over the whole operating band.
The tuning of electromagnetically-induced-transparency-like (EIT-like) phenomenon in metamaterials based on microstrip system is investigated. The tunability of EIT-like effect mainly arises from the controllable elements of varactor diodes loading on the ``dark'' resonators of EIT-like metamaterials. The results show that the frequency range of transparency window of our EIT-like metamaterials can be continuously and reversibly adjusted along with the varying external voltages applied on the varactor diodes. Moreover, the transmittance maximum hardly changes with the shift of transparency window. Such tunable EIT-like metamaterials may be applied in tunable slow-wave filters and switch devices.
A novel (2x2) high-gain circularly-polarized cylindrical dielectric resonator antenna array integrated with helical exciter is proposed. The array offers a maximum gain of 13.8 dBi at the operating frequency. The circular polarization is obtained by incorporating helical exciter in the array structure. A prototype of the proposed configuration integrated with helical exciter has been fabricated, tested and the idea has been verified. A good agreement has been obtained between the measured and the simulated results.
Inductive-coupling scheme for microstrip bandpass filters with quarter-wavelength stepped-impedance resonators is proposed. This is realized by a short-end stub which behaves as a K-inverter. It is investigated that the coupling coefficient of the resonators can be easily controlled by the length of the short-end stub. The filter has a compact size and good stopband rejection by employing the quarter-wavelength stepped-impedance resonators. The design procedure of this kind of filter is provided. Two filters working at 2.4 GHz are designed and fabricated to demonstrate the proposed method.
With the development of nano-optic technology, the optical nano-antenna has been widely used in the fields of novel light sources, high-sensitive biological sensors, nanometer lithography, and nano-optical imaging. The relationship between the structural parameters of the antenna and the Purcell factor is very important for engineering applications. The electric near field profile of the antenna was calculated and analyzed by using the finite-difference time-domain (FDTD) method, and the influence of the structural parameters on the Purcell factor and the electric field was thoroughly investigated. A careful comparison of bowtie antenna radiation characteristics with different structural parameters was carried out. The results show that the thickness, the length and the curvature radius have great effects on the Purcell factor and the optical antenna's electric near field. These findings are promising for improving the performance of the optical bowtie nano-antenna.
In this paper, a dual-band high-gain antenna based on the split ring resonators (SRRs) and corrugated plate is presented. By combining the SRRs and corrugated plate, the presented antenna resonating at different frequencies with high performance is easily achieved based on the superposition of the electric fields radiated by the SRRs and the grooves. Both the simulated and measured results show that the gain is improved by 6 dB at 12.7 GHz and 6.5 dB at 14.2 GHz respectively compared with the conventional flat antenna without grooves. Moreover, half-power beam width (HPBW) of E-plane is reduced by more than 100 degrees at 12.7 GHz and 14.2 GHz.
In this article, a compact tri-band microstrip bandpass filter (BPF) using asymmetric stepped-impedance resonators (SIRs) is proposed. Only one set of asymmetric SIRs are used in designing this filter to achieve triple passband response with high selectivity and band-to-band isolation level. By properly selecting the impedance and electrical length ratios of the asymmetric SIRs, the tri-band BPF is designed. By using a cross-coupled configuration and 0˚ feed structure, high selectivity frequency responses with six transmission zeros are achieved. The three bands of the proposed tri-band filter are located at 1.57/3.9/7 GHz, respectively, and the circuit size is much smaller in comparison with previous works using the same substrate. Measured results are in good agreement with electromagnetic (EM) simulation.
Quantum properties of a modified Caldirola-Kanai oscillator model for propagating electromagnetic fields in plasma medium are investigated using invariant operator method. As a modification, ordinary exponential function in the Hamiltonian is replaced with a modified exponential function, so-called the q-exponential function. The system described in terms of q-exponential function exhibits nonextensivity. Characteristics of the quantized fields, such as quantum electromagnetic energy, quadrature fluctuations, and uncertainty relations are analyzed in detail in the Fock state, regarding the q-exponential function. We confirmed, from their illustrations, that these quantities oscillate with time in some cases. It is shown from the expectation value of energy operator that quantum energy of radiation fields dissipates with time, like a classical energy, on account of the existence of non-negligible conductivity in media.
In the ongoing search for new materials for microwave absorption applications, Carbon Nanotubes deserve a special consideration due to their outstanding properties. In this paper, microwave absorbing properties of epoxy resin based composites containing commercial MultiWalled Carbon Nanotubes used as fillers have been analyzed. The complex permittivity of the composites was measured in a wide frequency band (3-18 GHz). The absorbing properties of a single-layer absorber backed by a metallic plate considering several concentration of CNTs was simulated taking into account the measured permittivity.
This paper proposes a method for the quick estimation of the average voltages at terminal loads when the transmission line translate randomly and analyzes the sensitivities of the loads' voltages to the translation. Because nonuniform transmission lines can be approximated as n-cascaded uniform lines, the study of uniform lines is the basis. Based on the transmission-line equations, the equations are derived to estimate the average voltages, the voltage variations, and the sensitivity of the voltage to the random translation when transmission lines have random translation in their cross sections. With these equations, the average voltages at the loads, the probability distributions of the voltage variations, and the sensitivity of the voltage to the random translation can be obtained quickly. A two-wire line over the ground is studied by using the proposed method. The average voltages and the voltage variations' probability distributions agree well with those via the Monte Carlo (MC) method and the proposed method is more efficient. The results show that the sensitivities of the voltages at the loads to the random height increase with the terminal sources but decrease with the height.
When the metal film is thicker than the skin depth in the working frequency band, the transmission characteristics of outer coated type are superior to the transmission properties of inner coated type under the same size. Further more, the transmission properties of the single, double, three and four groove both for inner coating and outer coating terahertz (THz) polystyrene (PS) tubes are studied in this paper. In result, the transmission properties of single and double slot are good, but the three and four slots' transmission characteristics deteriorate. In addition, slots width affects the transmission characteristics of PS tubes evidently, and the attenuation coefficient of outer coated PS tube with single slot is proportional to the slot width, so as to optimize the transmission properties of PS tube. It is a compromise for the slot width (it is better to choose appropriate slot width).
The design of a compact coplanar power divider with novel structure is presented by making a full use of the theories of microstrip-to-slotline transition. To obtain two in-phase signals over a wide frequency range, the two output branches are placed in the same layer. Moreover, a half-wavelength slotline is employed to expand the working frequency range. The presented compact power divider shows a low insertion and good return loss performance at input port. The simulated and measured results have shown a good agreement over the frequency range 2.2 GHz-11 GHz.
In this letter, a novel dual-band metamaterial absorber is presented and analyzed. The absorber is composed of four patches on the top of a thin grounded dielectric substrate which can absorb incident wave at two different frequency bands effectively. Then the absorber is loaded on the dual-band microstrip antenna, whose working frequency bands are overlapped with that of the absorber, to reduce the in-band RCS (Radar Cross Section) of antenna. The prototype is simulated, manufactured and measured. Simulated results show that the absorption of the absorber is as high as 98.6% at 4.29 GHz and 99.8% at 6.49 GHz. As to the dual-band antenna loaded with the proposed absorber, its radiation performance is unchanged while the RCS has declined by 8.59 dB at 4.29 GHz and 9.9 dB at 6.49 GHz respectively. There is a good agreement between simulated and measured results, which verifies that this absorber can be used for in-band RCS reduction of dual-band antenna so as to improve its in-band stealth performance.
A lowpass filter with sharp transition and wide stopband using a novel coupling stepped-impedance triangular resonator is presented. The L-C equivalent circuit is developed for designing this type filter and analyzing the mechanism for improving roll-off and rejection property. The stopband width, passband edge, roll-off rate and overall suppression level are affected by coupling capacitance. The effect of coupling capacitance is analyzed using calculated frequency response. Coupling triangular stubs provide adequate coupling capacitance resulting in balance among transition property, stopband width and suppression level easily. A single LPF unit is designed and fabricated with cutoff frequency of 860 MHz. The single LPF unit exhibits 40-dB suppression level from 1.11 GHz to 2.28 GHz. A cascaded LPF with three asymmetric units provides 40-dB suppression level from 1.1 GHz to 6.76 GHz, and roll-off rate of 154 dB/GHz with compact size as small as 0.23λg × 0.05λg, where λg is guided wavelength at cutoff frequency.
A topology for a 3-dB broadband and small-size ring coupler is proposed. It consists of fullydistributed Composite Right-/Left-Handed phase shifters and a Lange coupler. For the fabricated coupler, the frequency bandwidth is one octave, centered on 1.5 GHz, while the footprint area is 25% compared to the conventional ring coupler topology. The experimental results are in good agreement with the expected ones, obtained by electromagnetic simulation.
With a view to extending techniques for THz antenna near-field/far-field prediction, this communication derives general analytic expressions for calibrated phase shifting holography (PSH) and introduces a new 120º three-step PSH method that avoids switching off the reference field and has symmetrical performance over the entire complex plane, providing spurious free far-field prediction. Numerical tests with simulated near-field patterns at 372GHz confirm the convenience of the method and give an indication of the precision required for the phase shifts.
A new small, low-profile and light-weight helical antenna element was designed for L-band satellite communications. The novelty of the antenna is that its input impedance matching has been improved by adjusting the copper strip matching stub, while its circular polarization performance has been enhanced by changing the parasitic radiation patch loaded in the front of the antenna. The optimal antenna structure for INMARSAT application has been fabricated and measured. The proposed antenna can produce a gain of higher than 9 dB, a 3-dB axial ratio bandwidth of nearly 15%, and a |S11|<-15 dB impedance bandwidth of nearly 19%. A good agreement between measurements and simulations is obtained. The proposed antenna is compact in size and easy to tune. It provides a promising antenna element for antenna array applications.
An innovative technological process is investigated to easily manufacture inhomogeneous Luneburg lenses. A unique foam material is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The performance of such 60 GHz antenna is described and the antenna prototype is measured in terms of gain and radiation patterns. The results show a good efficiency (60% with a directivity of 18-19 dBi) and demonstrate the feasibility of this kind of Luneburg lens, through the use of a simple technological process. The lens with a diameter of 56 mm and a thickness of 3 mm operates in the 57-66 GHz bandwidth. The magnitude of S11 parameter is under -10 dB in the whole bandwidth and an half-power beamwidth of 5° and 50° in H-plane and E-plane respectively is reached.