In this paper, two dimensional multi-port method is used to analyze substrate integrated waveguide by using Green's function approach to obtain the impedance matrix of equivalent planar structure. Modes propagation constant of substrate integrated waveguide, as a periodic structure, is calculated by applying Floquet's theorem on the impedance matrix of a unit cell. Field distribution of the propagating mode is obtained by this method. Results obtained by this method are verified, in a broad range of dimensions, by comparing with published results and also those calculated by commercial electromagnetic simulator, HFSS. Electromagnetic band gaps and mode conversion phenomenon as properties of periodic structures are also observed and investigated. Mode conversion in SIW is reported for the first time by our proposed method.
In this paper, we present a novel class of microstrip bandpass filters with improved upper rejection band. The proposed filters are composed of two half-wavelength resonators and two shortended microstrip feed lines for input and output. Using voltagewave analysis, we examine the resonance and coupling properties at harmonic frequencies. It is found that different combinations of the feed line and the resonator with proper selection of the coupling regions can suppress spurious responses. Benefiting from this approach, two single-band and one dual-band bandpass filters are designed, fabricated and measured. Simulated and measured results indicate that the upper rejection bands of the proposed filters are increased up to near thirdand fifth-order harmonics, respectively. And the rejection level during the stop-bands is kept below 20 dB.
In this paper, novel composite right/left-handed (CRLH) leaky-wave antennas based on folded substrate-integrated-waveguide (FSIW) structures are proposed. The proposed leaky-wave antennas were realized by periodically loading the radiating slots on the top metallization of the FSIW-based CRLH transmission lines. The structural advantages of the FSIW combined with the unique dispersion characteristics of the CRLH transmission line enable the proposed leaky-wave antennas to present continuous beam-scanning capability from backfire to endfire directions, occupy smaller footprint size, and provide more design flexibility than the conventional CRLH leaky-wave antennas. Two of such CRLH leaky-wave antennas were developed. In addition to the continuous beam scanning, it is found that the radiation efficiency and polarization of the FSIW-based leaky-wave antennas can be easily tuned by means of the slot size and slot orientation, respectively, indicating their potential for versatile applications. Calculated and experimental results are presented and compared. A good agreement is obtained. To the best of our knowledge, it is the first time that the leaky-wave antenna exploits both of the dispersion behavior of the CRLH transmission lines and the structural benefits of the FSIW configuration.
In this paper, a new decoupled Unitary ESPRIT algorithm for two-dimensional (2-D) direction-of-arrival (DOA) estimation is presented. By exploiting the centro-symmetric array configurations of two parallel uniform linear arrays (TP-ULAs) and utilizing the via rotational invariance techniques, the proposed algorithm has advantages as listed below. First, the algorithm enables decoupling the estimation problem into a two-step estimation problem and obtains the automatically matched 2-D DOAs. Second, employing the elements of the array fully, the algorithm can estimate 2-D DOAs up to 2(M−1), where 2M is the sensor number of the array. Besides, the computational complexity of the proposed algorithm is lower than other representative 2-D DOA estimation methods. Simulation results are presented to show the effectiveness of the proposed method.
A new accurate Volterra-based model is introduced for behavioral modeling and digital predistortion (DPD) of power amplifiers (PAs). This model extends the GMP model with specific cross terms, and these augmented terms significantly increase the model's performance. The proposed model's performance is assessed using a LDMOS Doherty PA driven by two modulated signals (a 4-carrier WCDMA signal and a single carrier 16QAM signal). The experimental results in both behavioral modeling and DPD applications demonstrate that the proposed model outperforms the hybrid memory polynomial-envelope memory polynomial (HME) model and generalized memory polynomial (GMP) model. Compared with the HME model, the proposed model shows an average normalized mean square error (NMSE) improvement of 2.2 dB in the behavioral modeling, average adjacent channel power ratio (ACPR) improvement of 2.8/2.5 dB in the DPD application, and 20% reduction in the number of coe±cients. In comparison with the GMP model, the proposed model achieves higher model accuracy and better DPD performance, but reduces approximately 40% of coefficients.
A novel 3D Frequency Selective Surface (FSS) architecture based on a circular ring unit element is presented. The circular ring was made 3D by creating a cylindrical element of a certain length, adding an extra degree of freedom into the structure. The length of the cylinder is shown through electromagnetic simulation to have a significant effect on the frequency characteristics of the FSS. Increasing the length of the cylinder can change the FSS from a band-stop to a band-pass filter response. The center frequency of both band pass and band stop responses can also be tuned with adjustment to the length. Dielectric materials are introduced in the center of the cylindrical unit cell elements to simultaneously obtain a stop and pass band with a sharp transition. For high dielectric filling materials, the 3D periodic structure exhibits negative refractive index metamaterial properties. A parametric analysis was conducted on these new cylindrical unit elements, and a prototype 3D FSS structure has been constructed and experimentally validated.
If sampling frequency is not high enough, the effect of adaptive memory polynomial predistortion linearizer is not very good for TWTA linearization. In order to keep the adaptive memory polynomial predistortion linearizer valid, usually the output power level of the TWTA must be reduced, which corresponds to a reduced efficiency of the TWTA. In this paper, we present a digital predistortion linearizer by combining LUT (Look-Up-Table) and memory-effect compensation technique, which may provide good linear performance with less reduction of the output power and relatively low sampling frequency. The results of simulations and experiments show that good linearity improvement can be reached for an X-band TWTA with this predistortion linearizer.
A compact linear tapered slot antenna with wideband performance is proposed. The antenna consists of a microstrip to slotline transition and a linear tapered slot structure which is connected to the slotline. Due to the linear tapered slot, the antenna can realize unidirectional radiation in wideband band. The microstrip to slotline transition is implemented by using a tapered cross, which can easily obtain impedance transformation. Furthermore, this transition can be realized with a small size. The antenna is fabricated and optimized numerically. Both simulated and measured results validate the performance of the antenna in frequency and time domains. The results show that the antenna achieves a bandwidth up to 118% from 2.6 -10.1 GHz. The simulated time domain response of the antenna also shows its good performance in time-domain. The antenna can be well applied to ultra-wideband system.
This paper presents propagation measurements results using Integrated Services Digital Broadcast - Terrestrial (ISDB-T) to investigate the characteristics of 6 MHZ wideband Digital Terrestrial Television channel at 677 MHz for fixed and portable reception. Empirical measurements were done at predetermined measurement points consisting of 21 radials for a total of 92 locations extending to 20 kilometers around the National Broadcasting Network (NBN) digital transmitter. Characterizations were conducted using antenna heights of 9 m (fixed reception), 3 m (fixed reception), and 1.5 m (portable reception). Modulation Error Rate (MER), power received, field strength and delay profiles were captured to help characterize the channel in an urban area in and around Metro Manila at day time for temperatures ranging from 26°C to 32°C. Measured field strength was compared to NTC F (50, 90) curves. Polynomial fit using least square errors was used to plot the field strength coverage of NBN. For large-scale fading, it is observed that signal power conforms to Log Normal distribution. The study helped identify problem sites within the coverage. These are locations within the coverage area or at the outskirts of the coverage area where DTV signal is not received at all. A more accurate description of the DTT channel will lead to a better design of the parts of the Digital Television system from the network to transmitting system and receiving equipment. Path loss exponents computed for the three antenna heights can be helpful in developing empirical prediction models.
A compact dual band-notched Ultra-Wideband antenna with sharp band-notched characteristics and controllable notched bandwidths is presented. The antenna consists of a spade-shaped microstrip-fed Ultra-Wideband planar monopole antenna and two sets of band-notched structures. The band-notched structures are employed to generate the desired lower and upper rejection bands with good frequency selectivity and sufficient rejection bandwidths. Moreover, the bandwidth of the lower and upper rejection bands can be independently adjusted by changing the size of the band-notched structures. Finally, a UWB antenna is successfully designed with the dual notched bands for the lower WLAN band (5.15-5.35 GHz) and upper WLAN band (5.725-5.825 GHz). A good impedance match is obtained in 3.1-10.6 GHz frequency range (|S11|<-10 dB), except the lower and upper WLAN band (|S11| >-5 dB). The ratios of the notched bandwidths between -5 dB and -10 dB in the two stop bands are greater than 0.73.
In this paper, a compact planar monopole antenna with eight-band LTE/WWAN (LTE700/2300/2500/GSM850/900/1800/1900/UMTS) operation for laptop computer application is presented. This design structure comprises a bent driven strip and two coupled strips, which can contribute multiple resonance modes to combine two wide operating frequency bands covering 665-1023 MHz and 1612-2924 MHz. The proposed antenna fed by a 50-Ω coaxial cable occupies a small size of only 65(L)x11(W)x0.4(H) mm3, so it can be flexibly embedded inside the casing of the laptop computer as an internal antenna. A fabricated prototype of the antenna is tested and analyzed. Experimental results exhibit that nearly omnidirectional coverage and stable gain variation across the desirable LTE/WWAN bands can be obtained with the antenna.
In this paper, an improved L1-SVD algorithm based on noise subspace is presented for direction of arrival (DOA) estimation using the reweighted L1 minimization. In the proposed method, the weighted vector is obtained by utilizing the orthogonality between the noise subspace and the subspace spanned by the array manifold matrix. The presented algorithm banishes the nonzero entries whose indices are inside of the row support of the jointly sparse signals by smaller weights and the other entries whose indices are more likely to be outside of the row support of the jointly sparse signals by larger weights. Therefore, the sparsity at the real signal locations can be enhanced by using the presented method. The proposed approach offers a good deal of merits over other DOA techniques. It not only increases the robustness to noise, but also enhances resolution in DOA estimation. Furthermore, it does not require an exact initialization. Simulation results show that the presented algorithm has better performance than the existing algorithms, such as MUSIC, L1-SVD algorithm.
Conical log spiral antennas are famous for being appropriate for tracking, telemetry and command (TT&C) applications in low earth orbit (LEO) satellites. In this work, a conical linear (not log) spiral antenna is introduced and investigated for the same purpose. The electric field integral equation (EFIE) technique is applied to a triangular-patch surface model of the conical equiangular linear spiral antenna. This antenna is optimized to produce the radiation characteristics required for TT&C applications for LEO satellites. The input impedance, polarization and radiation patterns of this antenna are investigated over a wide band of frequencies. Some of the obtained results especially those concerning the input impedance, radiation pattern, polarization and bandwidth are verified experimentally. It is shown that the proposed antenna is quite appropriate for TT&C in LEO satellite applications.
In this paper, cellular communications from Stratospheric platforms (SPs) is studied, and the coverage footprint analysis and design is demonstrated. In the analysis, two coverage schemes are introduced; flat-earth and real-earth models and cell footprint are determined in each case. The flat-earth provides simple footprint equations describing the cell dimensions especially for the cells of higher elevation angles while more accurate coverage equations, which well determine the geometry of the cells of lower elevation angles, can be obtained from the real-earth scheme. The design of a cellular system using the proposed coverage models is then introduced through a procedure that determines the cells locations and dimensions on the ground according to the teletraffic information. The procedure takes into considerations the cell broadening when going outwardly from the central cell to the outer lower elevation cells and constructs a cellular layout that has the most proper cells overlap and uniform coverage edges, which helps the linking between different SPs coverage areas.
A reconfigurable stacked patch antenna is introduced for wireless power reception and data telemetry application in sensors. The proposed antenna operates at 5.8 GHz with 9.4 dBi gain and 7.6% bandwidth. At a lower frequency 2.45 GHz the antenna operates as a planar inverted-F antenna (PIFA) with 3.3 dBi gain and 2% bandwidth. Switching between the two regimes of operation is achieved using PIN diodes. It is proposed that the antenna can be used for wireless power reception in sensors at 5.8 GHz and for data telemetry in between a sensor and a control station at 2.45 GHz. The wireless power reception ability of this antenna was tested and verified by developing a high efficiency schottky diode rectifying circuit. The RF-to-DC conversion efficiency was 85% for an input power density level of 1 mW/cm2.
In this paper, we introduce a new technique for an electronic beam scanning/directivity reconfigurable which can be carried out by using a joint array of Metallic Electromagnetic Band Gap (M-EBG) sectoral antennas. This study opens new avenues of research on M-EBG sectoral antennas by combining multiple radiating elements in an array. Usually M-EBG structures are designed in passive configurations to radiate fixed/shaped beams thanks to a specific radiating aperture at the surface of the M-EBG antenna. However by opting this new technique, we are able to control the radiating aperture, and therefore provide a tunable directivity/beam pattern. The objective of the paper is to propose a solution for M-EBG antennas in order to achieve Beam Scanning and Directivity reconfigurability. The main advantage of the proposed technique is that the array have negligible mutual coupling between the radiating elements, simplifying therefore the conception of the beam-forming network and the problems of constrained beam scanning. Another objective of the paper is to be able to achieve wide angle beam scanning -/+58 degrees. This method makes it possible to obtain in a simple way an agile M-EBG antenna without the need of the expensive active electronic components. Several results show the effectiveness and the capabilities of the proposed technique.
An array of conformal antenna structures mounted on a bending surface exhibits a substantial shift in main beam direction. This paper demonstrates a method to compensate for the induced beam shift by using the change in length of the surface produced by the bend. This change in length modifies the capacitance in a composite right/left-handed transmission (CRLHTL) line, causing a phase shift in the line. A potential implementation is proposed that can correct an 18º beam shift with only an induced change in length of 0.144%. The paper establishes that this passive compensation concept is feasible and provides significant benefits over active compensation systems in terms of weight reduction, cost, simplification and the ability to operate in radio silence.
A family of miniaturized substrate integrated waveguide (SIW) dual-mode filters with a series of cross-slot structures etched on the waveguide surface are investigated and presented. By introducing the series of cross-slot structures: pure cross-slot, T-shaped loaded cross-slot and H shaped loaded cross-slot in original dual-mode SIW filters, size reductions of 22.15%, 30.56% and 56.25% are achieved, respectively. Moreover, the proposed family of SIW dual-mode filters can produce two controllable transmission zeros. Compared with SIW dual-mode filters in references and original filter, proposed filters exhibit compact size while retain good performance of bandwidth and minimum insertion loss. To verify the presented design, three SIW dual-mode filters are fabricated on the standard printed circuit board process. The measured results are in good agreement with the simulation.
This paper presents a novel 377 Ω rectangular stepped patch antenna with partial ground plane at downlink radio frequency range of GSM-900 band. Two steps are incorporated into the patch antenna, and bandwidth expansion was investigated by the currents flowing through the patch antenna. The antenna simulation was carried out in the ADS 2009 environment. The fabricated antenna on FR4 substrate indicates an impedance bandwidth of 32.7% (310 MHz) at 947 MHz centre frequency with return loss of -28.12 dB. The simulated, test and field results of the antenna design are discussed.
In this paper, a new circuit configuration composed of two main and reference paths is proposed for the modified multi-section Schiffman phase shifter, which improves its bandwidth. The method of least squares (MLS) is developed for its design, based on a circuit model including dispersion relations and dissipation effects. The differential phase shift and reflection coefficients from the input ports are obtained by conversions among the impedance, admittance, ABCD and scattering matrices of the circuit model. Then, an error function is constructed, whose minimization is performed by the combination of genetic algorithm and conjugate gradient method, which gives the optimum values of the physical dimensions of the metallic strips. The impedance matching function of the proposed phase shifter circuit makes it a dual action device, leading to some circuit miniaturization. Three phase shifter circuits with single, double and quadruple sections are designed and one prototype model is fabricated and measured. The MLS, full-wave simulation softwares and measurement results agree very well, which validate the proposed circuit configuration and MLS design procedure. The multi-section phase shifters have actually increased the frequency bandwidth.
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