An active circuit is described that exhibits the equivalent reactance of a negative inductor. In contrast with previous techniques based on negative impedance converters, the negative inductance is produced by generating an opposing time-varying magnetic flux. The new circuit also enables the inductance to be electronically varied between negative and positive values, can enhance the Q, and defaults to a conventional positive inductor in the event of active component failure. The performance of a prototype with an inductance of -0.344 mH and operating over the frequency range 1-40 kHz is described.
This paper presents a two-probe implementation of microwave interferometry for displacement measurement at an unknown reflection coefficient. Theoretically, the proposed technique gives the exact value of the displacement for reflection coefficients (at the location of the probes) no greater r than 1/√2 and in the general case determines it to a worst-case accuracy of about 4.4% of the operating wavelength. Its experimental verification has demonstrated reasonable measurement accuracy for displacements several times as great as the operating wavelength (in real-time measurements at a free-space wavelength of 3 cm for a peak-to peak vibration amplitude of 15 cm, the maximum error in the determination of the instantaneous relative displacement and the peak-to-peak amplitude was about 3 mm and about 1 mm, respectively).
A novel compact textile antenna with the appearance of a button on clothing for body-centric wireless communications systems (BWCS) is presented. The antenna is placed on a textile substrate and fed by a coaxial line through the ground plane. The operating bandwidth of the antenna has met the requirement of the UWB communication system. The effects of the human body on S11 and S21 are presented and discussed in detail. The proposed antenna has good omni-directional radiation patterns and stable H-plane radiation patterns. The measured results show that the antenna is suitable for BWCS.
In this paper, a new dual-band bandpass (BPF) filter with multi-spurious suppression is proposed, which is composed of step-impedance resonators (SIR) and grounded-step-impedance resonators (GSIR). It is shown that the resonant frequencies of GSIR can be obtained similar to SIR. Then, by determining the dimensions of SIR to have a specified resonant frequencies ratio, the dimensions of GSIR can be calculated. It is also shown that the coupling lengths between SIR and GSIR can create several transmissions zeros and can be used to suppress the unwanted higher order resonant frequencies. A third-order filter is designed and fabricated to operate at two WLAN frequencies of 2.45 GHz and 5.8 GHz. The measured results show a rejection level of 24 dB up to more than 17 GHz (7f1). Simulation and measurement results are in good agreement with each other.
In this work, the propagation loss due to diffraction and insertion losses for indoor scenario at 5.6 GHz band are measured using directive antenna and a Vector Network Analyzer (VNA). It is shown that the insertion loss of a metallic door with porthole window varies from several dB due to the propagation loss via the porthole glass up to 50 dB due to the diffraction by the porthole boards when the line between the transmitting antenna and receiving one is outside the porthole glass. It is shown that the insertion loss of a 12 cm brick wall is 4.8 dB for vertical polarization while it is 6.3 dB for horizontal polarization. Also it is shown the diffraction loss due single or double concrete columns depends on the distance between the transmitting and receiving antennas.
The design of a multi-channel (M = 5) lattice form band pass optical delay line filter is reported. The filter synthesis is based on the division of total transfer function into unit blocks and the circuit parameters are obtained by constrained least square method. This band pass filter has better performance compared with the results obtained in the conventional design techniques. For a filter of order 35, a stop band attenuation greater than 50dB is achieved. Further, the band pass filter is introduced in a optical fiber link and simulated in Optisystem software, to verify its characteristics.
An interesting and original solution to the high channel noise sensibility problem of digital chaotic communications is proposed. The solution idea consist of avoiding disruption of the slave/receiver dynamics by injecting the driving signal. To realize experimentally this pertinent idea, an FPGA-based hardware architecture is developed, firstly to trigger the generation of the slave/receiver chaotic dynamics at each received data detection, and secondly to synchronize the driving signal with the slave generated chaotic signal for the demodulation operation. We have tested and validated the proposed solution through experimental realization of a wireless hyperchaotic communication system based on ZigBee communication protocol. Real-time results of experimental wireless communication tests are presented. The obtained results show the effectiveness and the robustness of the proposed solution against real channel noise in digital chaotic communications.
This paper presents the design of a dual-band microstrip antenna with low wide-angle axial-ratio. The antenna is designed for global positioning satellite operations at 1227 MHz(L2), 1575 MHz(L1) and 1176 MHz(L5, available after 2007). This antenna has another advantage of a much wider band in both VSWR and 3 dB axial-ratio compared with single-fed GPS antennas. Details of the design, simulated and experimental results of this GPS antenna are presented and discussed. The measured results confirm the validity of this design, which meet the requirement of GPS applications.
A compact dual-band multiple-input-multiple-output (MIMO)/diversity antenna is proposed. This antenna is designed for 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX applications in portable mobile devices. It consists of two back-to-back monopole antennas connected with a T-shaped stub, where two rectangular slots are cut from the ground, which significantly reduces the mutual coupling between the two ports at the lower frequency band. The volume of this antenna is 40 mm * 30 mm * 1 mm including the ground plane. Measured results show the isolation is better than -20 dB at the lower frequency band from 2.39 to 3.75 GHz and -25 dB at the higher frequency band from 5.03 to 7 GHz, respectively. Moreover, acceptable radiation patterns, antenna gain, and envelope correlation coefficient are obtained. These characteristics indicate that the proposed antenna is suitable for some portable MIMO/diversity equipments.
A compact tri-band slot antenna based on a mesh-grid structure, which is suitable for WLAN/WiMAX applications, is presented. The proposed antenna is optimized by a Boolean differential evolution algorithm (BDE). Then an experimental prototype is fabricated and measured. Results of simulation and measurements indicate that the proposed antenna has |S11|<-10dB in the three chosen frequency bands from 2.35 to 2.85 GHz, from 3.1 to 4.4 GHz and from 4.8 GHz to 5.85 GHz, which covers WLAN bands (2.4/5.2/5.8 GHz) and the WiMAX bands (2.5/3.5/5.5 GHz), respectively. In addition, good radiation performances such as omnidirectional and doughnut-shaped directivity and reasonable gain over the operating bands have been obtained. This example also demonstrates the applicability of the BDE/MOM optimization algorithm to efficient and in potential automated method for the antenna design.
Coherent Change Detection (CCD) using multi-temporal Synthetic Aperture Radar (SAR) is one of the most important applications of remote sensing technology. With the advent of high-resolution SAR images, CCD has received a lot of attention. In CCD, the interferometric coherence between two SAR images is evaluated and analyzed to detect surface changes. Unfortunately, the sample coherence estimator is biased, especially for low-coherence values. The consequence of this bias is the apparition of highly coherent pixels inside the changed area. Within this context, the detection performance will considerably degrade, particularly when using high resolution SAR data. In this paper, we propose a new CCD method based on cleaning of coherence inside changed areas, which is characterized by high Local Fringe Frequencies (LFF) values, followed by a space-averaged coherence method. According to the proposed method, the results obtained with Cosmo-SkyMed (CSK) SAR data show an enhancement of change detection performance of about 6% while preserving subtle changes.
The paper presents the design of a novel ultra-wideband microwave crossover for the use in microstrip circuits. The proposed structure includes a double microstrip-coplanar waveguide (CPW) vertical interconnect in single-layer substrate technology which allows an inclusion of a finite-width coplanar waveguide (CPW) on the top side of the substrate to achieve the required cross-link. The presented design is verified using the full-wave electromagnetic simulator Ansoft HFSS v.13 and experimental tests. The obtained experimental results show that in the frequency band of 3.2-11 GHz, the crossover has an isolation of 20 dB accompanied by insertion losses of no more than 1.5 dB.
This paper presents differential-fed patch antennas with excellent cross-polarization. This paper provides a detailed graphic illustration of factors that lead to deteriorated H-plane cross-polarization by the conventional single-ended feeding probes. A novel differential rat-race feeding structure was constructed to allow easy impedance matching. An experimental antenna was realized on low-temperature co-fired ceramic (LTCC) at 8 GHz. An excellent cross-polarization of less than -22.5 dB was achieved. When the operation frequency is high, the parasitic inductance caused by feeding probes may degrade the performance of antennas. This paper further proposes the use of differential aperture-coupled structures at high frequencies. An aperture-coupled antenna, realized at 40 GHz with low cross-polarization <-15 dB has been achieved.
Circular synthetic aperture radar (CSAR) imaging based on compressive sensing with random step frequency (RSF) as transmitted signal is introduced. CSAR is capable of obtaining both two-dimensional high resolution image and three-dimensional image due to a circular collection trajectory. RSF signal shares good characteristics of noise signals including ``thumbtack-shape" ambiguity function, low probability of interception, and strong anti-jamming capability. As a result, CSAR adopting RSF signal can make use of advantages of both CSAR and RSF signal. Compressive sensing is a new data acquisition and reconstruction theorem for sparse or compressible signals, which needs fewer samples to reconstruct signals than traditional Nyquist theorem. Simulation results show that both two-dimensional and three-dimensional targets can be well reconstructed from few samples by applying compressive sensing to RSF CSAR imaging.
In this article, a new hybrid algorithm based on Honey Bees Mating Optimization (HBMO) combined with the Tabu Search (TS) for null steering beamformer in adaptive antenna array is presented. The proposed method HBMO/TS is applied to a set of random cases to estimate the excitation weights of an antenna array that steer the main lobe towards a desired signal, place nulls towards several interference signals and achieve the lowest possible value of side lobe level. Moreover, the proposed algorithm is tested and compared with two other wellknown approaches that are the Least Mean Squares (LMS) and Genetic Algorithm (GA). The abovementioned methods have been performed considering uniform linear antenna array and achieved by controlling only the phase of each array element. Results obtained prove the effectiveness of our proposed approach HBMO/TS.
A compact coplanar waveguide (CPW)-fed printed monopole antenna comprising of two symmetrical C-shaped radiating elements, a parasitic E-shaped strip, and a truncated CPW ground for WLAN/WiMAX applications is proposed. By embedding a parasitic E-shaped strip inside the two symmetrical C-shaped radiating elements, four resonant frequencies and three operating bands are obtained. By etching two quarter-circles in the CPW ground, impedance matching condition of the third operating band is significantly improved. A prototype of the proposed antenna has been constructed and experimentally studied. The measured results show that three distinct operating bandwidths with 10 dB return loss are about 500 MHz (2.33-2.83 GHz), 700 MHz (3.27-3.97 GHz) and 2.37 GHz (4.3-6.67 GHz), covering all the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands. Furthermore, the antenna has a simple planar structure and a small volume of only 31 × 21 × 1.6 mm3. Good radiation characteristics and acceptance peak realized gains are obtained over the operating bands.
A novel branch-line coupler which can operate at two frequencies is presented in this paper. The proposed planar topology, which is different from the conventional one, is analyzed and designed. The new coupler maintains not only compact but also dual-band characteristics. The length of the proposed stepped-impedance lines can be adjusted flexible according to the required operation frequency. In order to verify the method, a dual-band micro-strip coupler operating at 0.9 and 2.1 GHz is fabricated and measured. The simulated and measured results show good agreements.
In this paper, a frequency reconfigurable antenna for cell-phone applications is presented. The proposed structure is based on a conventional PIFA. In addition, two stubs, each with a varactor diode, are incorporated. In order to to achieve wideband characteristics, the first two resonant frequencies (f1 and f2) of the proposed antenna are controlled independently by the supplied voltages with variation of the capacitances. The equivalent circuit of the varactor diode has been extracted in order to accurately predict the performance of the proposed antenna. In addition, parametric studies regarding the capacitance and antenna length have been conducted. The measurement results show that the proposed antenna has a tunable bandwidth defined by a VSWR < 2.5 of 45.7% (606 MHz ~ 965 MHz) and 47.5% (1343 MHz ~ 2181 MHz) at f1 and f2, respectively. Therefore, f1covers the LTE (698 MHz ~ 798 MHz), CDMA (824 MHz ~ 894 MHz), GSM (880 MHz ~ 960 MHz) bands, and f2 covers the DCS (1710 MHz ~ 1880 MHz), PCS (1850 MHz ~ 1990 MHz), WCDMA (1920 MHZ ~ 2170 MHz) bands. The measured average gains varied from -4.3 dBi to -1.5 dBi at f1 and -6.4 dBi to -2.7 dBi at f2.
In this paper, a new approach to build a dual-band impedance transformer is presented. The transformer can handle impedances that are complex and vary with frequency. This transformer contains a Pi-section structure, which can be equivalent to having two different electrical lengths at the two operating frequencies. One of the electrical lengths serves as complementary angle of the other. In this way, the conjugate impedances obtained through previous process are transformed to real impedance concurrently. All parameters are derived from closed-form equations. In addition, several simulations as well as a fabricated power amplifier (PA) are presented to verify the proposed transformer. The measured result performs a good agreement with the simulated one in return loss and gain. This transformer may find use in different stages of a transceiver such as power amplifiers which operate at two independent frequencies.
In this paper, we propose a wideband internal Planar Inverted-F Antenna (PIFA) by novel feeding structure at practical mobile handset. The proposed antenna by novel feeding structure shows 33.49% wideband impedance bandwidth, compared to 16.92% impedance bandwidth of normal feeding structure of PIFA. We explain novel feeding structure antenna by using equivalent circuit. The normal feeding structure of conventional PIFA has the inductive reactance structurally. To reduce its inductive reactance, a shunt inductive reactance using a novel feeding structure is added to normal feeding structure of conventional PIFA, structurally. So, reactance of PIFA is decreased and impedance bandwidth of PIFA is increased. The size of proposed antenna is 29.2 × 8.2 × 8.3 mm3. As well as, the implemented antenna has a good radiation pattern and high antenna gains despite very small volume.