Affected by multipath propagation as well as the receiving conditions of an actual array, a distributed source model considering array uncertainties/errors is more consistent with the realistic scenarios. In this paper, a new direction finding method for coherently distributed (CD) sources in the presence of array gain-phase errors is proposed. By exploiting partly calibrated uniform linear arrays (ULA), the gain-phase errors are first estimated according to the relationship of elements of array covariance matrix, and then a two-step iterative procedure is introduced to achieve a joint estimation of nominal DOA and angular spread from sparse recovery perspective. Performance analysis and related Cramér-Rao bound (CRB) are also provided. Numerical examples show that the proposed method can provide improved resolution and estimation accuracy, and performs almost independently of gain-phase errors.
A frequency reconfigurable antenna with conical radiation pattern is presented. The antenna is mainly composed of a suspended circular patch, eight shorting posts, and a ground plane. The circular patch is loaded with two concentric annular slots, and four varactors are placed across the outer annular slot to vary the resonant frequency of the antenna. Simulated results show that the resonant frequency can be tuned from 3.25 to 5.7 GHz as the capacitance of the varactors is varied from 0.2 to 12 pF, and conical radiation patterns are obtained when the antenna is operated at each resonant frequency. In the simulation, the reversed-bias circuit of the varactor is also included, and it is found that a bias tee or an inductor is not necessary for the proposed reconfigurable antenna. Experiments are also realized using two different varactors, and the measured results indicate that the peak gains of the conical radiation patterns occur around θ = ±40˚, and they are about 4.5 ± 1.5 dBi when the constructed prototypes are operated in the frequency range from 3.1 to 5.7 GHz.
This paper develops a circuit theory on bandpass negative group delay (NGD) topology. The NGD active lumped circuit uses a low noise amplifier (LNA). An S-parameter model is formulated. Unfamiliar, NGD function analysis is introduced by analytically defining the NGD value, bandwidth, and central frequency in function of the topology parameters. The synthesis formulas enabling the calculation of cell parameters as a function of the targeted bandpass function specifications. To validate the circuit theory, an NGD proof of concept (PoC) is designed, simulated and tested. As expected, simulations and measurements are in good agreement. Calculated model, simulated and measured results showing NGD level of about -10 ns around the centre frequency 0.5 GHz over the bandwidth 50 MHz validate are obtained.
A composite right/left-handed (CRLH) leaky wave antenna (LWA) using double mushroom-like structures is proposed. With a proper arrangement of the left-handed structures, desirable cross-polarization performance in two orthogonal planes can be obtained based on the differential excitation principle. The CRLH performance of the cascaded LWA is demonstrated, and its improved radiation performance is clarified. Measured results indicate that the proposed antenna operates in 9.7-16.4 GHz with a beam scanning range from -71° to +31°. The cross-polarization levels are less than -30 dB and -20 dB in the beam scanning plane and non-beam-scanning plane, respectively.
Metamaterials have revolutionized the research in conventional electromagnetics. They display unique properties which can be used for the manipulation of electromagnetic waves in unexpected ways. In this research, a diamond nano-antenna is designed and optimized using the CST Microwave Studio, which uses Finite Difference Time Domain (FDTD) method. The designed unit cell shows high polarization conversion rates (PCR) for ultraviolet (UV) frequencies (especially the UV-B band) whilst covering Panchatram-Berry (PB) phase. The unit cell is then used to design metasurfaces that generate light beams carrying Orbital Angular Momentum (OAM) of different orders. Through the design of two dimensional metamaterial surfaces, the behavior of electromagnetic beams can be changed on sub-wavelength scale. This has led to a number of applications related to nanotechnology. A vortex beam carries Orbital Angular Momentum (OAM) which has played a vital role in increasing the bandwidth and data rate of optical communication systems. Therefore, OAM beams having different topological charges have been generated at 294 nm to propose an improvement in Free Space Optical (FSO) communication. Optical links also function as a suitable substitute for applications where Radio Frequency (RF) communications may not be effective. The proposed theoretical model is expected to open new horizons in optical communication by incorporating the use of nanoscale devices with high efficiencies in the ultraviolet regime.
A compact broadband folded dipole antenna element with a ball grid array packaging is proposed in this letter. The compact antenna element is fabricated on a low-cost FR4 substrate consisting of only one dielectric layer. The solder balls are mounted on the square ground metal plane of the antenna element to form the ball grid array (BGA) packaging, which allows the antenna element to be surface mounted with other surface-mount devices (SMDs). Furthermore, ball grid array packaging has great potential for minimizing the size of antenna elements. The dimension of the proposed antenna element is only 6 mm × 6 mm × 1.6 mm. Parameter analysis shows that the solder balls have little effect on antenna performance. The proposed folded dipole antenna element is fed by a 50 Ω grounded coplanar waveguide (GCPW) transmission line on the evaluation board. The antenna prototype has been designed, analyzed, and manufactured. Measured results of the prototype show that the -10 dB impedance bandwidth is 45.4 % (22.3-35.4 GHz), and the peak gain achieves 6.62 dBi at 35 GHz. The measurement results show that the proposed antenna element has great potential for the 5G millimeter wave application.
An ultra-wideband (UWB) flexible antenna with a dual band-notched property is designed in this letter. This antenna is fed by a coplanar waveguide (CPW) tapered transmission line to achieve an impedance bandwidth of 1.95-35 GHz for VSWR<3. A double C-shaped slot within the monopole radiation patch and two L-shaped slots etched on the ground are introduced to reject the bands of 3.5 GHz (3.1-3.9 GHz) and 5.5 GHz (4.7-5.74 GHz) respectively, which are assigned to WiMax and WLAN applications. A Rogers4350 substrate is used to realize a low profile (0.29λL×0.22λL×0.00065λL, where λL is the free-space wavelength of the lowest operating frequency). The measured results show that the antenna has a UWB omnidirectional radiation characteristic that is suitable for UWB wireless communications.
This paper proposes a novel wideband filter based on a quintuple-mode substrate integrated waveguide (SIW) resonator. Two metallic vias loading a rectangular SIW cavity diagonal line are used to excite five resonant modes. A pair of the complementary split ring resonators (CSRRs) etched on the top plane to further control the degenerating modes. A quintuple-mode filter is implemented based on this resonator. One transmission zero (TZ) at the lower frequency side and three TZs at the upper frequency side were obtained to improve the filter selectivity. A seven-order filter with wide stopband rejection is investigated under the use of a pair of microstrip low-pass filters (LPFs). The proposed SIW cavity filter has been designed, manufactured, and measured as an experimental example to verify the proposed concept. Simulation and measurement results agree with 49.8% of fractional bandwidth at 5.3 GHz central frequency.
This letter shows 50 percent memory saving for a regular Hierarchal Matrix (H-matrix) by converting it to symmetric H-matrix for large electrodynamic problems. Only the upper diagonal near-field and compressed far-field matrix blocks of the H-matrix are stored. Far-field memory saving is achieved by computing and keeping the upper diagonal far-field blocks leading to compressed column block U and row block V at a level. Due to symmetry, the lower diagonal far-field H-matrix compressed column is the transpose of V, and the compressed row block is the transpose of U. Storage and computation of lower diagonal blocks are not required. Similarly, in the case of near-field, only the upper diagonal near-field blocks are computed and stored. Numerical results show that the proposed memory reduction procedure retains the accuracy and cost of regular H-matrix.
A design of a compact wideband harmonic suppressed rat-race coupler (RRC) is presented in this paper. The present coupler is obtained by replacing each quarter wave length transmission line of a conventional double section rat-race coupler with a triple stub M-shape unit. The M-shape unit with 3 stubs is used to enhance the bandwidth, suppress the harmonics, and reduce the size of the coupler. Design guidelines are established using the lossless transmission line model. Theoretical predictions are verified by fabricating a prototype coupler. The proposed double section RRC provides harmonic suppression up to seventh of operating frequency and 62.4% size reduction with wide bandwidth, which is useful for wireless communication systems.
An extremely close integration of a dual band sub-6 GHz 4G antenna with a 28 GHz 5G antenna is proposed in this article. Firstly, a dual band 4G LTE (Long term Evolution) antenna is designed on an inexpensive substrate. The proposed antenna operates in the 2.5 GHz and 3.5 GHz LTE bands. The antenna has dimensions of 63 x 5.6 x 0.5 mm3, indicating an electrically small design. As the width of the antenna is less than 7 mm, it could be easily mounted on commercial mobile devices. The patterns for both the bands are almost omnidirectional as desired by the low frequency antennas. The proposed antennas do not carry any additional miniaturization or tuning circuitry hence simplifying fabrication process. Secondly, an angled dipole with Yagi topology is proposed, which works in the 28 GHz mmWave 5G band. The angled dipole has dimensions 28.3 x 5.6 x 0.5 mm3, which is also electrically compact and has a high front to back ratio. The microwave and millimetre wave antennas are placed orthogonally for minimal mutual coupling. The characteristics of both the antennas are not affected by the presence of the other element. Detailed results are shown in this article.
This article presents a compact, single feed dual-band dual-polarized (DBDP) microstrip antenna. The proposed design involves an inverted Y-shaped radiating patch and a rectangular open-loop positioned near its right corner that creates mutual coupling to attain wideband circular polarization (CP). To achieve enhanced axial ratio bandwidth (ARBW), a semi-rectangular ground plane with two asymmetric truncated L-shaped slots has been used. An L-shaped slotted quarter wave microstrip line feed is used here for broader ARBW and proper impedance matching. The measured dual impedance bandwidths (IBW) in the range 5.85-6.52 GHz (centre resonance frequency frc1 = 6.19 GHz, 10.66%) in lower frequency region and 7.25-13.64 GHz (frc2 = 10.445 GHz, 61.18% bandwidth) in higher frequency region. The two ARBW bands span over 7.22-10.99 GHz (fc1 = 9.105 GHz, 41.41%) and 11.67 GHz-12.25 GHz (fc2 = 11.96 GHz, 4.85%). The measured peak gains between 3.20 and 4.96 dBi over the entire IBW range makes the LP and CP bands suitable for ITS (5.9 GHz), U-NII-5 of 6 GHz band, some C-band, ITU-8 GHz, some X-band, and Ku-band applications.
A conductor backed CPW-based S-band filter using Multiple Ring Resonators (MRR) is presented. The resonator is coupled with the feed line through inter-digital coupling. Square resonator structure joined with inter-digital coupling on both sides on conductor plane and multiple ring resonators implemented with equal spacing at the ground plane forms a conductor backed CPW filter model. Adjusting the size and gap factor of MRR, the wide tuning ranges of desired frequencies are achieved. The filter has an outstanding bandwidth range from (2-4) GHz which fits for Satellite S-Band applications. The S-Band has low insertion loss (-0.95 dB), lower return loss (-35 dB), wide bandwidth (fractional bandwidth 66.6%) at the center frequency 3 GHz are obtained. The size of the filter performance characteristics are investigated and compared with measured results. The complete measurement of filter is (39×7.2×1.6) mm. The measured values of S11 and S21 are about -25 dB and -1.92 dB respectively.
This work presents an efficient method that allows to accurately calculate the time-harmonic vertical magnetic field generated at the center of a large current-carrying coil of wire positioned above a layered ground. The method consists of evaluating the integral representation for the vertical magnetic field by using a hybrid procedure. At first, the direct and ideal reflected fields are extracted from the total magnetic field and expressed in explicit form. Then, the non-analytic part of the integrand of the remaining contribution is replaced with a sum of partial fractions, obtained by using a rational function fitting algorithm. Finally, the resulting sum of integrals is analytically evaluated and turned into a sum of modified Bessel functions of the second kind. The obtained expression for the magnetic field is then used to evaluate the voltage induced in a small receiving loop co-axial with the transmitting loop.
A novel and efficient higher order convolutional perfectly matched layer (CPML) method is put forward and also applied to cut off the finite-difference time-domain (FDTD) computational domain full of the unmagnetized plasma. A Drude model can be used to represent the unmagnetized plasma, and the plasma can be solved by using the trapezoidal recursive convolution (TRC) method. In order to verify the validity of the presented method, a numerical example in three-dimensional computational domain is provided. The numerical example results show that the proposed formulations have better absorbing performance than the first-order CPML in terms of attenuating low-frequency and evanescent waves. Besides, by using the proposed method, computational time and memory can be reduced compared to the second order PML implemented by using the auxiliary differential equation (ADE) method.
In this paper, a novel miniaturized circularly polarized (CP) antenna for BeiDou Satellite Navigation System (BDS) applications is presented. The proposed antenna is composed of three substrates with the same size, which are combined by four shorting pins. Parasitic strips are used to reduce the size, and the radiation patch is fed by two coupling feeding patches with the same amplitude and 90° phase difference. The overall dimension of the proposed antenna is only 18 mm x 18 mm x 23.5 mm (about 0.08λ0 x 0.08λ0 x 0.1λ0), and its weight is about 25 grams. The performance study with different geometric parameters has been conducted. A prototype based on optimized dimensions has been fabricated and measured, and the tested results exhibit a good impedance matching bandwidth ranging from 1.2 to 1.35 GHz centered at 1.268 GHz. This antenna also has stable hemispherical radiation patterns and good CP characteristics. Good agreement between analytical and experimental results is obtained.
Rectangular grid antennas are widely used in practice due to their advantages and versatility. This paper simplifies the design procedures of such antennas by optimizing their radiation characteristics using minimum number of the optimized elements while maintaining the same performance. The method consists of partitioning a fully square grid array into two unequally sub-planar arrays. The first one contains the inner and the most central elements of the initial planar array in which they are chosen to be non-adaptive elements, while the remaining outer and boundary elements which constitute L number of the square-rings are chosen to be adaptive elements. Then, the optimization process is carried out on those outer rings instead of fully planar array elements. Compared to a standard N×M planar array with fully adaptive elements, the number of optimized elements could be reduced from N×M to 2{2L(N-L)}, so as to significantly reduce the system cost without affecting the overall array performance. Results of applying the proposed method to optimize a small 9×9, medium 20×20, and large 40×40 size planar arrays with various values of L are shown.
Compared with the conventional coaxial magnetic gear, magnetic harmonic gear (MHG) is a device with large transmission ratio. In order to improve the transmission torque, an MHG with double fan-shaped Halbach arrays is proposed in this paper. According to the theory of magnetic field modulation and the unique unilateral effect of Halbach array, both inner and outer permanent magnets (PMs) are arranged in a Halbach array. In addition, all PMs are fan-shaped. The air gap magnetic field and torque of MHG are analyzed by two-dimensional finite element method. Compared with the conventional MHG, the proposed MHG enhances the air-gap magnetic flux density, reduces the air-gap harmonic content, and increases the torque density.
A low-profile, electrically compact, and cost-effective antenna for wireless communication is presented. The antenna comprises self-complementary dipole elements on each side of the resonator surface. The dipole is excited using co-axial feed for an efficient impedance matching. An electrically compact antenna has dimensions of 0.13λ × 0.26λ at the lower frequency. The dipole covers 1.57 GHz and 3.65 GHz frequencies offering the measured impedance bandwidth in the order of 1.83% and 2.30% respectively. The self-complementary structure of the dipole having multiple coupling elements permits adequate tuning of the antenna on target frequencies. The resonant modes of the antenna can be tuned by merely modifying the position of the complementary structure on each side of the dipole. The engineered slots in the dipole permit further fine-tuning. The antenna presents gain in the order of 0.71 dBi and 1.27 dBi and stable radiation patterns for the two frequencies.
In this letter, a novel design of independently reconfigurable upper and lower bands of a Yagi-Uda antenna is presented. The reconfiguration approach used in this antenna is based on keeping either the upper or lower band edge fixed with gradually increasing the bandwidth to the lower or upper ones. In this system, PIN diodes are used to control the length of the resonator and the slot-line of Yagi-Uda antenna to achieve upper and lower bandwidths limit reconfigurability. An antenna prototype was fabricated and tested in order to validate the design approach of the bandwidth reconfiguration. The proposed antenna has several different modes of operation with capability of tuning the fractional bandwidth (FBW) from 7% to 33% and 18% to 72% when using resonator and slot-line, respectively. This antenna can be a good candidate for cognitive radio applications that need adjusting the frequency bandwidth.
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