Wideband digital beamforming (WDBF) technology is a key for the rapidly developing wideband digital array radar (WDAR). In this paper,by comprehensively considering the characteristics of WDAR and the current hardware and software capabilities for radar in engineering, several practical WDBF technologies based on accurate digital true time delay (TTD) are studied. WDBF technology at radio frequency (RF) is applied and tested on a WDAR test-bed. Besides, WDBF technologies at baseband by implementing fractional delay filers at element level and subarray level are presented and simulated.
A novel dual-band circularly-polarized slot array antenna aimed at LEO satellites communications where up-link and down-link operate at different frequencies is introduced. By using higher order modes, the slots can be placed at points where current distributions are null for the fundamental mode. According to this idea, at the receiver frequency band the slots are placed to be excited by mode TE10 currents distribution, and at the transmitting band slots are forced to radiate according to mode TE20 currents distribution. A matching load termination is used to generate the required travelling wave to obtain the circular polarization, introducing low dissipation losses. Additionally, in this investigation an antenna feeder is also designed. Both the feeder and the slot antenna array are designed using Substrate Integrated Waveguide (SIW). The use of SIW makes easier the design of the transitions from the array to the microstrip input lines and the grounded-coplanar termination as well, relaxing fabrication constraints and tolerance.
In this paper, a differentially-fed, multi-band patch antenna with bandpass filtering response is proposed. The antenna consists of two pairs of crossed dipoles, four Γ-shaped feedlines, and four steeped-impedance microstrip lines. With the introduction of Γ-shaped feedlines and U-shaped slots on the radiating patch, extra radiation nulls are induced, four operation bands with band-pass filtering response are obtained. More importantly, the filtering response of the antenna is generated without any filtering circuit, which is easy to design for antenna engineers. Measured results of the prototype show that the proposed antenna has stable radiation patterns with low cross-polarization of better than -26 dB. Besides, bandpass filtering response of the realized gain with deep roll-off can also be observed between different operation bands. Excellent radiating performance make it a promising candidate for 5G wireless communication systems.
Advancements in functionalities and operating frequencies of integrated circuits lead to the necessity to study Electromagnetic Compatibility/Electromagnetic Emissions (EMC/EMEs) from these devices. In this work, a methodology is developed, which combines near field electromagnetic measurements and 3D layout simulation of an Integrated Circuit (IC), to identify the sources of EME from a commercial IC. This methodology can help to narrow down the area of key importance with respect to EME sources, instead of the entire IC, before it is fabricated. Consequently, IC designers can optimize their design to minimize the EME before fabrication, saving cost and time significantly.
In this paper, a simple and effective side-lobe suppression technique is proposed by using integrated high refractive index matematerial (HRIM). It is known that current reversal, which occurs at the third harmonic of the dipole natural frequency, disturbs the omnidirectional radiation pattern of a dipole antenna, and the main beam splits into two side lobes. For suppressing the two side lobes and maintaining consistent radiation pattern purposes, two regions of HRIMs are integrated along the side-lobe radiation direction of a reflector-backed dipole antenna to tilt the two side lobes toward the broadside radiation direction. The HRIM is constructed with 2X3 H-shaped unit-cells periodically printed on the single side of dielectric substrates. The beam-tilting approach described here uses the phenomenon that the EM wave undergoes a phase shift when entering a medium of different refractive indices. Simulation and measurement results show that by implementing the HRIMs, the two side lobes are tilted toward the broadside radiation direction, and as a result, the side lobe is suppressed, and radiation consistency for the first and third harmonic resonances is realized. Moreover, the antenna gain for the third harmonic is achieved as high as 7.8 dBi, which is an increase of approximately 3 dBi compared with the fundamental resonance.
This paper proposes a coplanar waveguide-fed slot antenna with vertical rounded bow-tie slots for wideband harmonic suppression. Higher-order harmonics up to nine times the fundamental resonant frequency (9fo) of the slot antenna was successfully suppressed by adding the slots in the middle of the two slot arms. A prototype of the antenna that resonates at 1 GHz was fabricated. The measured input reflection coefficient of the antenna remains over -3 dB at up to 9.15 GHz, which demonstrates the wideband harmonic suppression capabilities.
In this paper, a novel compact dual band-rejected ultra-wideband (UWB) multiple-input multiple-output (MIMO) Vivaldi antenna is introduced and fabricated. The MIMO antenna with a small size of 26 × 28 mm2 contains a modified ground plane and two microstrip-slot balun structures. A T-slot is etched on the ground to achieve miniaturization and high isolation, and the simulated |S11| of -10 dB impedance bandwidth is from 2.7 to 10.9 GHz. An isolation of better than 15 dB is acquired over the UWB range (3.1-10.6 GHz). Meanwhile, by introducing two split ring resonator (SRR) slits on the ground and adding two split ring resonators (SRRs) close to the microstrip-slot balun structures, dual band rejection at both WLAN (5.15-5.85 GHz) and IEEE INSAT/Super-Extended C-band (6.7-7.1 GHz) can be achieved. The MIMO antenna has high gain and very low envelop correlation coefficient (ECC < 0.02). The measured results agree with the simulated ones, demonstrating that the UWB MIMO Vivaldi antenna is suitable for the UWB diversity applications.
A dual mode shared aperture antenna consisting of two planer arrays of ring antennas is designed for L and S bands. The array of larger dimension surrounds the array of smaller dimension. The antennas are isolated from one another and fed separately. The antenna dimensions are optimized and prototyped. The antennas radiate separately in L and S bands with least coupling or no coupling. Measured results are in agreement with the simulations, depicting good performance in terms of impedance bandwidth, isolation, and gain.
A simple and efficient explicit solution is derived for the mutual inductance of two non-coaxial coplanar circular loops, which is valid in the quasi-static as well as non-quasi-static frequency ranges. The solution is obtained by rigorously evaluating the Sommerfeld Integral describing the inductance, starting from expanding the integrand into a power series of the loop radius. As a result, a sum of simpler integrals is obtained, and term-by-term analytical integration is straightforwardly performed. The inductance is finally expressed as a series of spherical Hankel functions, with algebraic coefficients depending on the electrical size of the loops. Conducted numerical tests lead to conclude that, accuracy being equal, the proposed expression offers advantages in terms of time cost over conventional numerical integration techniques.
In this work, a novel planar four-port microstrip triplexer is designed and analyzed to operate at 1.9 GHz, 2.5 GHz, and 3.35 GHz for wireless communication applications. The proposed structure consists of a compact patch and spiral cells. The main advantage of this triplexer is its very compact size, with a cross size of only 15 mm×15 mm (0.017λg2). Sharp frequency response at the edges of all passbands, low insertion losses (0.25 dB, 0.4 dB and 0.11 dB), and high return losses (45 dB, 54 dB and 40 dB) in all channels are the other advantages of the designed triplexer. Additionally, the triplexer has reasonable isolations (S23, S24, S34), better than 20 dB. To verify the design method, both EM simulation and measurement results are obtained. The comparison shows that the measured and simulated results are in good agreement, which proves the feasibility of this work.
A substrate-integrated-waveguide (SIW) cavity multiple-input-multiple-output (MIMO) antenna using hybrid boundaries and anti-symmetric U-shaped slots is proposed. Unlike conventional SIW cavities completely shorted by metallic vias, the proposed two cavities possess opened edges. Since shorted and opened cavity edges can be regarded as electrically and magnetically conducting boundaries, respectively, hybrid resonating boundaries are achieved. Excited by coaxial ports, antenna elements can radiate cavity energy through the opened edges. Moreover, antenna isolation can be significantly enhanced by introducing a pair of anti-symmetric U-shaped slots on the top and bottom planes. This design has been validated by experiments. With the overall size of 0.44λ0 × 0.44λ0 × 0.04λ0, the fabricated MIMO antenna exhibits operating frequency of 3.51 GHz, high isolation of 20.18 dB, peak gain of 3.15 dBi, and low envelope correlation coefficient of 0.12, which has potential applications for wireless systems.
In this paper a frequency reconfigurable pixel antenna is implemented using PIN diodes. The overall dimension of the patch antenna is 26.9x24.5 mm, and it is fabricated on an FR4 substrate. The design is investigated by the simulation and measurement of S11 parameters and radiation patterns. With different combinations of PIN diode biasing conditions, the antenna can be set to 2.5 GHz, 3.9 GHz, and 10 GHz. The antenna shows a consistent radiation pattern at all the reconfigured frequency bands. In the accessible frequency range, an average gain of 6 dB and low level of cross polarization are also recorded. A good agreement between the measured and simulated results validates the presented concept of frequency reconfiguration.
In order to reduce far-end crosstalk between two differential line pairs of microstrip, this paper proposes a method of reducing far end crosstalk by polarity inversion. In this way, the signal line is placed in the middle of PAD of one capacitor to achieve polarity reversal at the AC coupling capacitor of the differential line. The simulation results show that, in this way, the far end crosstalk can be reduced by 63.6%, and this method of far end crosstalk suppression has an effect on both pairs of differential lines.
Recently, manipulation and measurement of quantum states, especially in quantum cavities, have attracted the attention of many researchers in different fields, such as: quantum optics, quantum information, quantum computation, and so on. In this paper a non-demolition method for the measurement of squeezing parameter via atomic Mach-Zehnder interferometer, is presented. An experimental setup was also proposed which included two quantum cavities, in different arms of an atomic Mach-Zehnder interferometer. Each quantum cavity was settled between two classical cavities. Quantum cavities were contained entangled states with arbitrary squeezed photons. It is shown that the outgoing atomic states of Mach-Zehnder interferometer carry on the properties and situation of quantum states of the cavities. The squeezing parameter of photonic state forone of cavities, is obtained by the detection of excited and non-excited probabilities of Mach-Zehnder interferometer's outgoing ports, for a train of incoming two-level Rydberg atoms.
An asymmetrical cross-shaped microstrip resonator is proposed. It is analyzed on its characteristic impedance and resonant conditions. A first order triband bandstop filter (BSF) and a second order triband BSF are designed using this resonator. Both filters are simulated on Sonnet Suite software. Simulation results show that both filters generate three stopbands at 2.0, 3.0, and 4.5 GHz. The second order BSF is also fabricated and measured using a microwave network analyzer. Simulation and measurement results on the second order BSF agree well.
In this paper, we demonstrate the design of a polarization-independent wideband absorber of light that consists of a perforated graphene sheet on top of a lossless dielectric spacer placed on a metallic reflector. The single layer absorber is duly designed based on impedance matching concept. The simulated results indicate that the structure produces 0.98 THz broad absorption from 1.80 THz to 2.72 THz with absorptivity larger than 90% at the normal incidence. The electromagnetic (EM) field distributions and the plots of surface power loss density have been illustrated to explain the absorption mechanism of the structure. The variation of chemical potential from 0.8 to 1.2 eV keeps 90% absorption bandwidth as much as 1 THz band. The polarization-insensitive feature and the properties under oblique incidence are also investigated. Finally, the interference theory is used to analyze and interpret the broadband absorption mechanism.
Rapid development of the electronic industry has increased the frequency of communication devices which lead to higher intensity of electromagnetic (EM) wave production. Too much exposure of EM wave can cause harm to health besides imposing disturbances in performances of other electronic devices. Hence, this research studies the structural and electromagnetic properties of materials that can act as electromagnetic shielding material at x-band frequency. Different compositions of magnetite powder/Fe3O4 (0, 10, 20 and 100 wt.%) were prepared to be dispersed in gypsum powders to form gypsum-magnetite composites. The structural properties of composites were characterized using Scanning Electron Microscopy (SEM) to observe homogeneity of the composites. The X-Ray Diffraction (XRD) was used to determine phase composition of the gypsum-magnetite composites. Scattering parameters of reflection coefficient, S11, and transmission coefficient, S21, were measured using Vector Network Analyzer (VNA). These parameters will be used to calculate the shielding effectiveness (SE) of gypsum-magnetite composite at x-band frequency. The results show that the total SE of the gypsum-magnetite composites were increased by adding magnetite powders.
Two dual-band microstrip antennas with filtering responses are proposed in this letter. By introducing symmetrical slots (One is a U-shaped slot, and the other is an inverted H-shaped slot) at the edge of rectangle patches, additional resonant modes are induced, and both of the antennas have dual operation bands. More importantly, extra radiation nulls are observed between the two bands. In addition, the proposed antennas are fed by microstrip lines with two pairs of symmetrical open stubs, which offer two more radiation nulls at low frequencies. Thus, dual-band filtering responses for the proposed antennas are obtained. Simulated and measured results show good agreements with unidirectional radiation patterns, as well as high selectivity of realized gains.
A dispersive delay line (DDL) with compact size, good group delay, and all pass response in 200-800 MHz band is presented. The proposed DDL is composed of a main microstrip transmission line with two shunted open stubs and two complementary slot lines, and a coupling slot line in ground plane. The length of the complementary slot line is reduced approximately from λg/2 to λg/4 through the upper end being opened, hence achieves miniaturization for the proposed DDL (λg is the guided wavelength at the center frequency). The overall area is 0.196×0.093λg2 with a peak group delay time of 3.2 ns. The proposed DDL has the advantages of compactness, good capability, and easy fabrication without any external matching network.
A general auxiliary differential equation (ADE) finite difference time-domain (FDTD) method with Crank-Nicolson (CN) scheme is proposed to model electromagnetic wave propagation in dispersive materials in this paper. The proposed method introduces an ADE technique that establishes the relationship between the electric displacement vector and electric field intensity with a differential equation in dispersive media. The CN scheme applies only to Faraday's law, resulting in reduced memory usage and computing time. To validate the advantages of the proposed approach, two examples with plane wave propagation in dispersive media are calculated. Compared with the conventional ADE-CN-FDTD method, the results from our proposed method show its accuracy and efficiency for dispersive media simulation.