A novel two-dimensional elliptical lens monopulse antenna at millimeter-wave frequencies is presented using the technique of dielectric-filled parallel plates where TE10 mode propagates. A cavity-backed aperture-coupled elliptical patch antenna array with sum/difference ports is located at the back of the elliptical lens as a feeding antenna. The lens antenna is designed, fabricated and tested at 35 GHz. Measurements show clean and symmetrical fan-beam patterns are realized for both the sum and the difference beams. The measured 3-dB E- and H-plane beamwidths of the sum pattern are 5.3° and 37°, respectively. A gain of 16.7 dBi is realized for the sum beam (86% radiation efficiency), while a deep null of -32.4 dB is achieved for the difference beam. In addition, a 10-dB impedance bandwidth of 7.1% is measured for both the sum and difference beams.
A modified ultra-wideband (UWB) printed rectangular antenna fed by a microstrip line is proposed. Overall dimension of the antenna is as compact as 14 (0.2 λ) × 14 (0.2 λ) × 1 mm3 where λ is the wavelength of the first resonance of the antenna. The main features of the proposed antenna are its compact size and its filtering characteristic over WLAN band. Through adjusting the dimensions of the elements of the antenna, notch frequency in different ranges of the UWB can be obtained. The resulting VSWR<1.5 impedance bandwidth is between 3.6-9.6GHz. Antenna presents a stable gain and omnidirectional radiation pattern in its operational frequencies.
In this paper, a new computation model of the shielding effectiveness (SE) is proposed in order to calculate the SE of blended electromagnetic shielding fabric (BESF) by some fabric structural parameters. Some computation equations of the SE for the BESF are given according to the theoretical deduction and previous experimental results. And then a shielding coefficient in the computation model is determined by further experiments. The linear region boundary for the model is introduced to segment the computation of the SE. Results show that the SE obtained from the proposed model is consistent with that from experiments and the error is less than 2%. It can be concluded that the proposed model can accurately calculate the SE of plain, twill and satin weaves fabrics.
In this paper, we propose a dual-band frequency selective surface (FSS) in low frequencies with miniaturized element. A dual-concentric square element with two different slot sizes is constructed to realize dual-band passband responses. Each passband is realized by a square slot structure. Besides, we reduce the slot sizes to make the element miniature and compact. Based on this technique, a dual-band FSS with miniaturized element in low frequencies is designed. Both the simulation and experiment results show that such a FSS owes its advantages to miniature element, stable performance with various incident angles and different polarizations, which is suitable for dual-band shipboard communication.
The design criteria of integrated optical biosensors based on the Mach-Zehnder Interferometer and on the Michelson Interferometer are proposed. Sensitive performance has been evaluated for different optical polymeric waveguiding structures such as channel, inverted-rib and strip waveguides. For all the configurations of the examined optical waveguiding interferometric biosensors maximum linearity and sensitivity have been obtained. In particular, the achieved sensitivity, expressed as the ratio between the normalized output power and the protein concentration, is about equal to 1.6 (g/ml)-1 which, for a maximum variation of the output power equal to 100 mW, leads to a non-normalized sensitivity equal to 160 mW/(g/ml).
In this article, one realization version of quad-band filter is firstly proposed, and it is the cascaded structure composed of the shunt open-circuit DCRLH (dual composite right/left-handed) cell and the shunt short-circuit DCRLH cell. The above two cells are initially proposed here in order to improve the inherent limitations of the microstrip DCRLH cell. It is demonstrated that the matching performance and frequency selectivity of these two cells are both better than those of the microstrip DCRLH cell. What is more important, these two cells both exhibit three transmission zeros within the given frequency band and any of them is of great potential to be applied in the design of quad-band filters. In order to get sufficient design freedom, we utilize the cascade connection version based on the shunt open/short-circuit DCRLH cells. Whereas, only the first and second transmission zeros of both the shunt open/short-circuit DCRLH cells are explored. Both the simulated and measured results indicate that the proposed design method is right and effective.
This paper presents a frequency-tunable bandpass filter with constant absolute bandwidth and improved linearity. The proposed resonator is composed of an open-ended transmission line with back-to-back varactor diodes loaded at one end. The back-to-back varactor diodes are used to enhance the linearity of the filter, which is better than that of the single varactor counterparts. A mixed electric and magnetic coupling scheme is utilized to control the overall coupling coefficients so that the absolute bandwidth can be kept constant when the frequency is tuned. For validation, two frequency-tuning filters with 30-MHz and 44-MHz absolute bandwidth are implemented. The experimental and simulated results are presented to verify the proposed design.
This paper presents a modified design of directional monopole antenna with parabolic-shaped ground plane. To increase the directivity, axis of parabola in the ground plane is rotated 45 degrees (in comparison with the previous antenna) to extend throughout the direction of the substrate's diagonal. Consequently, vertex of the parabola is placed at the optimum point in the corner of the substrate. The aim of this attempt is to design an extended and symmetrical ground plane around the patch, with more clarity, to maximize its capability as a reflector. Directivity is further improved by inserting parabolic-shaped slots at the corners of the ground plane. Simulation and measurements show that the proposed antenna has stable directional radiation pattern and higher gain compared to the previous directional monopole antennas. Impedance bandwidth of the antenna covers the frequency range of 4-9 GHz. Measured HPBW is among the degrees 54-22 between 4 and 9 GHz. Gain and HPBW of the antenna are improved 1.3-3.1 dB and 5-15 degrees, respectively among the bandwidth in comparison with previous antenna. Results confirm the good characteristics of the antenna for use in microwave imaging, where high resolution is required.
A design of coplanar waveguide (CPW)-fed circularly polarized slot antenna is presented. The proposed antenna consists of two orthogonal slots. By making use of the symmetric current and electric-field distributions of the two gaps of CPW-fed, a simple power divider is easily achieved. By adjusting the length of the two orthogonal slots and CPW-fed bent slot, a circularly polarized wave of two orthogonal modes with equal amplitude and phase difference of 90 degree is excited. The numerical results show that the 10 dB return loss bandwidth and 3 dB axial ratio (AR) bandwidth are 50.8 % and 11.2 % respectively. A prototype antenna is fabricated and measured, the measured results show that the proposed antenna achieves a good performance of circularly polarization.
A new antenna with dual-band circular polarization for the reception of WiMAX and WLAN is presented in this article. The circular polarization is achieved by a symmetrical U-slot together with an L-slot. The width of the signal strip is narrowed at the end of the feed point to widen the 3-dB axial ratio (AR) bandwidth and create a good impedance matching for the proposed antenna. A parametric study is conducted using a commercial simulation software based on the method of moments, and the antenna prototype is constructed and measured for providing the simulation validation. Experimental results show that the measured AR bandwidths are about 16.6% and 16.2% with respect to the center frequency at 3.5GHz and 5.3GHz. The radiation characteristics of the proposed antenna are also presented.
In this paper, a novel approach, namely nonlinear subprofile space (NSS), is proposed for radar target recognition using high-resolution range profile (HRRP). First, the HRRP samples are mapped into a high-dimensional feature space using nonlinear mapping. Second, the nonlinear features, namely nonlinear subprofiles, are extracted by nonlinear discriminant analysis. Then, for each class, the nonlinear subprofile space is formed using all the training nonlinear subprofiles of class. Finally, the minimum hyperplane distance classifier (MHDC) is used for classification. The aim of NSS method is to represent the feature area of target using nonlinear subprofile space, and effectively measure the distance between the test HRRP and feature area via minimum hyperplane distance (MHD) metric. The experimental results of measured data show that the proposed method has better performance of recognition than KPCA and KFDA.
The design and synthesis of quasi-elliptic triple-mode filter with three transmission poles and three transmission zeros are presented in this paper. The transfer and reflection filtering functions are obtained to get the even- and odd-mode admittance. The synthesized admittances give the even- and odd-mode networks, routing structure and coupling matrix of the filter. The microstrip prototype of the quasi-elliptic triple-mode filter is designed and realized to prove the feasibility of the approach. The filter is realized by having a capacitive coupling between the input and the output of a proposed triple mode resonator. The results show an excellent agreement with the theories.
An alternative approach for robust electromagnetic pulse (EMP) protection circuit was proposed by using a parallel coupled band-pass filter (BPF) with high thermal conductivity AlN substrate in between with a traditional gas discharge tube (GDT) and fast response metal oxide varistor (MOV). This proposed configuration can suppress slow as well as fast voltage surges. The fabricated BPF with a center frequency of 2.5 GHz on the high thermal conductive (180~200 W/m·K) AlN substrate could efficiently suppress high power over voltage surge. Through the purposed cascade protection configuration, it is observed that 6KV ESD fast introduced pulse (5 ns/50 ns) and 4 KV lightning surge pulse(1 us/50 us) were attenuated to 511V and 396 V, respectively, and that is capable to be applied to an EMP protection circuit in the front end of a linear amplifier applications.
In this paper, we propose a new kind of broadband microwave gain equalizer in microstrip circuit. The equalizer uses open stepped impedance resonators (SIRs) to increase the adjust parameters so that the equation curve can be more flexible. Simplified topology of the gain equalizer is used to make the match net easier. The power distribute on each resistance is analyzed and the error analysis of the resistance values is done. Finally we design and manufacture a gain equalizer, and the measured results show that the equalization curve meets requirements well and proves that this structure is practical and effective.
In this paper, a novel G-shaped defected microstrip structure (DMS) is presented. Compared with the conventional DMS, the proposed G-shaped DMS exhibits lower resonant frequency and wider stopband. A lowpass filter with 3 dB cutoff frequency at 3.17 GHz using four pairs of parallel cascaded G-shaped DMS units is designed and fabricated. The measured results show that the transition band is only 0.09 GHz and the stopband over 25 dB attenuation covers 3.4 GHz to 10 GHz.The measured and simulated results are in good agreement.
In this letter, a novel compact dual-mode tri-band microstrip bandpass filter (BPF) is proposed using three sets of dual-mode resonators, i.e., the quarter-wavelength resonator (QWR) which is designed for the first passband, and two sets of stub loaded resonators (SLR) for the second and third passband, respectively. The center frequencies and bandwidths of three passbands can be flexibly tuned and designed. Multiple transmission zeros can be generated to improve the selectivity. Meanwhile, the BPF can obtain more compact size by adopting the folded resonators and extended feed lines. Finally, a tri-band microstrip BPF prototype with fractional bandwidths 18.3% at 1.8 GHz, 5.5% at 3.6 GHz and 12.2% at 5.25 GHz is designed. The measured results are in good agreement with the full-wave simulation results.
A fully integrated CMOS wideband distributed variable delay line for time array beam-formers is presented. The delay line works over a full differential mode, and the delay cell function is based on differential amplifiers with active inductive peaking loads. A delay resolution of 15 ps is obtained with a maximum delay capability of 150 ps . The designed active delay line provides 3 scanning angles with 8.6o degrees of spatial resolution. This delay line is applicable for a 4 channel beam-former with an operational bandwidth of 500 MHz centered at 5 GHz. Our active delay line consumes up to 352 mW of power from 2.5 V supply. The circuit is simulated in standard 0.25 μm BiCMOS process and occupies 252 μm × 123 μm of silicon area.
Transmission characteristics of 1-D photonic crystal (PC) structure with a defect have been studied. We consider a Si/ZnS multilayer system. We also consider the refractive index of both layers to be dependent on temperature and wavelength simultaneously. The refractive indices of Si and ZnS layers are functions of temperature as well in the wavelength of incident light. This property can be used while tuning defect modes at desired wavelength. As defect modes are function of temperature, one can tune the defect modes to desired wavelength. It is found that the average change in central wavelength of each defect mode is 0.07 nm/K. This property can be exploited in the design of a tunable wavelength demultiplexer for DWDM application in optical communication.
Basic equations of quasi-isotropic approximation (QIA) of geometrical optics method are presented, which describe electromagnetic waves propagation in weakly inhomogeneous and weakly anisotropic media. It is shown that in submillimiter range of electromagnetic spectrum plasma in all modern thermonuclear reactors, both acting and under construction, manifest properties of weakly inhomogeneous and weakly anisotropic medium, even for extreme electron density Ne ~ 1014 cm-3 and magnetic field B0 ~ 5 T accepted for project ITER. In these conditions QIA serves as natural theoretical basis for plasma polarimetry in tokamaks and stallarators. It is pointed out that Stokes vector formalism (SVF), widely used in polarimetry, can be derived from QIA in a generalized form, admitting the rays to be curvilinear and torsiened. Other important result of QIA is development of angular variables technique (AVT), which deals directly with angular parameters of polarization ellipse and operates with the system of two differential equations against three equations in form of SVF.
In this paper, we present a new type of a double-negative metamaterial (MTM) absorber based with resonant-magnetic structures, with a periodic array composed of a split-ring resonator (SRR) and two open complementary split-ring resonators (OCSRRs). In contrast to common absorber configurations, the absorber proposed in this paper does not use a metallic back plate or a resistive sheet. In order to eliminate the need for this metallic back plate, a planar array of SRRs is placed parallel to the incident wave propagation direction. An appropriately designed combination structure of two OCSRRs and a SRR exhibits negative permittivity and negative permeability in the same frequency band. Each unit cell is printed on both sides of an FR-4 substrate. A prototype absorber was fabricated with a planar array of 75 × 42 unit cells. Both simulations and experiments verify the effectiveness of the proposed backplane-less MTM absorber. The proposed backplane-less absorber can be used for microwave applications.