This letter presents the design of a novel wideband omnidirectional antenna with the usable bandwidth enhanced. The antenna is designed for wireless applications and proposed to operate within WLAN (2.4 GHz-2.484 GHz) and WiMAX (2.3 GHz, 2.5 GHz and 3.5 GHz) frequency bands. The bandwidth is enhanced through the use of balun, while the radiation patterns remain stable. This antenna has a much wider VSWR band (47.5% for VSWR < 2) with high radiation pattern stability compared with printed dipole antennas. Details of design, simulated and experimental results of this omnidirectional antenna are presented and discussed. The measured results confirm the validity of this design which meet the requirement of wireless applications.
This paper deals with the measurement of the magnetic flux generated by the armature of electromagnetic rail launchers linked with external pick-up loops. In particular we discuss possible methods to experimentally evaluate measurement uncertainty when the magnetic flux is obtained by numerical voltage integration. These methods aim at an approximate identification of the correlation among voltage samples introduced by the analog-to-digital converter, only based on the available measurements without requiring additional tests and instruments. An estimate of this correlation allows to better evaluate the overall measurement uncertainty, thus providing the applicability limits of the proposed inductive technique and contributing to a better understanding of the current and force distribution in the armature.
A simple and novel method for increasing the gain at low elevation angle and widening the beamwidth of quadrifilar helix antenna (QHA) is presented. By adding cross dipoles as a reflector, the right hand circular polarization (RHCP) gain at 5° elevation angle (theta=85°) increases by about 1.4 dB. Parametric studies are performed to explore the performance improvements. An antenna for CNSS (Compass Navigation Satellite System, 2.492 GHz) application is realized based on the studies. The RHCP gain at 5° elevation angle is about 0.6 dB, and 3dB beamwidth is greater than 220°. 10 dB impedance bandwidth is more than 24%, and 3dB axial ratio bandwidth is more than 32%. Measured results are presented to validate the proposed method.
A novel dual-polarized dipole antenna with compact size is presented for wireless communication applications. The proposed antenna is composed of a dual-polarized cross dipole, a small-sized tapered reflector, a square patch director, and an octagon ring as a parasitic element. Low VSWRs (<1.5) are achieved in aimed operating band of 2500-2690 MHz at both ports, which can cover the LTE2600 frequency band. High port isolation (>38 dB) and symmetric broadside radiation patterns are also achieved. Two dual-polarized reference antennas are also developed. Contrast results show that the proposed antenna can obtain improved radiation patterns compared with the reference antennas. Moreover, the proposed antenna is very compact in size (0.52λ0×0.52λ0×0.32λ0, λ0 refers to the center frequency of operating band), which achieves about 20% size reduction than Ref 2. Experimental results are also carried out to verify the simulation analysis.
A novel slot-line filter with stop-band up to 30 GHz is proposed in this paper, and the theoretical analysis is illustrated in detail. This filter is designed on a Rogers RT/duroid 5870 substrate. The rectangular micro-strips can generate transmission zero to give a great suppression for the spurious response around 5f0 while the L slot lines can create transmission zeros to suppress the spurious response around 7f0, 9f0 and 11f0. f0 is 2.43 GHz in this paper and represents the center frequency of the main passband. The compact size of this novel filter is 23.7 mm * 14.725 mm (0.152λ * 0.103λ (λ is the working wavelength of this filter)). Besides, the external quality factor of this filter can be as high as about 29.6. To demonstrate the transmission function, the compact filter has been fabricated and the measured results show the feasibility of this structure.
In this manuscript, a novel design of ultra-wideband (UWB) monopole antenna with dual frequency band-stop performance is proposed. The proposed antenna consists of an ordinary square radiating patch with a pair of rotated T-shaped slits, and a modified ground plane with an inverted Ω-shaped and a pair of rectangular-ring slots. In the presented structure, by cutting a pair of rectangular-ring slots in the ground plane, additional resonances are excited and hence much wider impedance bandwidth can be produced, especially at the higher band that the antenna provides a wide usable fractional bandwidth of more than 140% (2.8-17.5 GHz). In order to generate single band-notched characteristic, we cut a pair of rotated T-shaped slits in the square radiating patch. Finally, by inserting an inverted Ω-shaped slot in the ground plane, a dual band-notched function is achieved. The measured results reveal that the presented dual band-notch monopole antenna offers a very wide bandwidth with two notched bands, covering all the 5.2/5.8 GHz WLAN, 3.5/5.5 GHz WiMAX and 4 GHz C bands. The designed antenna has a small size of 12×18 mm2. Good return loss, antenna gain and radiation pattern characteristics are obtained in the frequency band of interest. Simulated and measured results are presented to validate the usefulness of the proposed antenna structure for UWB applications.
In most existing transmitted-reference ultra-wideband (TR-UWB) communication systems, receivers use the standard Gaussian approximation (SGA) for multiuser interference (MUI). It is an assumption used in most conventional multiuser systems, where the MUI tends to a Gaussian process by the central limit theorem, and convergence is relatively fast with respect to the number of users. However, for TR-UWB systems which are developed for short-range applications, we have a small number of active users. In this case, significant performance degradation is found in TR-UWB receivers due to the impreciseness of SGA. In this paper, we show that the Middleton class-A model is a more appropriate statistical model for MUI modeling in TR-UWB systems than the often used SGA. A closed-form expression for the probability density function (PDF) of the TR-UWB system under MUI, Gaussian noise and impulsive alpha-stable interference is developed. All these analytical results are confirmed by numerical simulations.
Recently, a new radiation model for the partial element equivalent circuit (PEEC) technique has been proposed. This model makes use of the concept of generalized complex inductance to account for the radiation effect and preserve the (quasi-)static condition for the capacitance. Therefore, PEEC models with the radiation effect included consists of real-valued capacitors but complex-valued inductors. In this paper, a method for deriving a concise and physically intuitive equivalent circuit from such a radiating PEEC model is presented. The method is based on the Y-to-Δ transformation to eliminate all "unimportant" internal circuit nodes and results in an equivalent circuit with only a few nodes left. The equivalent circuit for a short electric dipole is first derived analytically to offer a simple explanation to the basic principles. The proposed method is then applied to several practical and electrically small antennas for more detailed demonstrations. Numerical results obtained from these examples suggest that a physically intuitive circuit model can potentially be derived for arbitrary radiating multi-conductor structures, showing the method is useful for analysis and design of modern integrated and electrically small antennas.
A novel bandstop filter with wide-stopband performance is proposed and discussed in this paper. This circuit configuration includes two-section coupled lines and three open-circuit transmission-line stubs. Due to the symmetry of this proposed structure, closed-form equations for scattering parameters are investigated. Transmission zeros and poles location for different circuit parameters are discussed, and the corresponding design curves are given. In order to verify this new filter circuit structure and its corresponding design theory, several typical numerical examples are designed, calculated and illustrated. Furthermore, a practical wideband bandstop filter with -20 dB fractional bandwidth of 94% centered at 3 GHz with sharp rejection characteristics is fabricated to validate the theoretical prediction. The measured frequency response of the filter agrees excellently with the predicted result.
A novel compact microstrip slot antenna applied to WLAN/WiMAX applications is presented.The proposed antenna consists of a trapezoid and ellipse slot, a pair of symmetrical inverted L-strips, an elliptical-arc-shaped stub and a monopole radiator.By adjusting the dimensions and positions of these structures, the antenna can effectively generate three different resonances to cover the WLAN/WiMAX bands while maintaining small size and simple structure.Based on this concept,a prototype of the proposed antenna has been successfully fabricated and measured.The experimental and numerical results show that the antenna has impedance bandwidth with 10 dB return lossof 360 MHz (2.33-2.69 GHz) and 2630 MHz (3.24-5.87 GHz), which can cover both the WLAN 2.4/5.2/5.8 GHz bands and the WiMAX 2.5/3.5/5.5 GHz bands. In addition, good monopole-like radiation characteristics with sufficient antenna gains are obtained over the operating bands.
This paper proposes a compact zeroth-order resonant (ZOR) antenna with improved gain and efficiency. The proposed CRLH unit cell is based on the coplanar waveguide (CPW) structure. The proposed ZOR antenna is designed for a 2.45 GHz frequency band, and it has the characteristic of monopolar radiation. Shunt inductance is implemented by microstrip short-circuit stubs, and a metal-isolator-metal (MIM) capacitator provides series capacitance, where a large capacitance can be achieved in a small footprint. The proposed antenna comprises two interleaving composite right-/left-handed CRLH unit cells, where the size of one unit cell is measured at only 0.12λ0 x 0.098λ0. Because the field is loosely confined within the CPW-based unit cell, a good antenna peak gain of 2.03 dBi, and a radiation efficiency of over 68% is achieved when fabricated on a thin substrate. The proposed antenna did not require an additional matching network, reducing the total antenna footprint. This paper presents antenna parameters such as the return loss, radiation pattern, antenna gain, and radiation efficiency to validate the proposed design, which achieved good simulation results.
A broadband circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) is presented. The DRA is excited by an L-shaped microstrip feed line through the coupling of an annular slot in the ground plane. The broadband CP radiation is achieved by using two CP radiators, DRA and annular slot. Broadband impedance match is obtained by introducing an impedance transformer. The optimal configuration offers a 3-dB axial ratio bandwidth of 15.9%, from 6.22 to 7.28 GHz, and a 10-dB impedance bandwidth of 21.3%, from 5.78 to 7.16 GHz. The measured results for the constructed prototype are also exhibited and discussed.
Guided-mode resonance filters (GMRFs) are highly compact structures that can produce a strong frequency response from a single thin layer of dielectric. When a GMRF is formed onto a curved surface, the local angle of incidence varies over the aperture of the device and the overall performance significantly degrades. In the present work, we spatially varied the grating period of a curved GMRF to perfectly compensate for the local angle of incidence. The performance of the curved device actually surpassed that of a flat device because it also compensated for the spherical wave front from the source. This paper summarizes our design process and experimental results obtained around 25 GHz.
A Substrate Integrated Waveguide (SIW) planar array is presented using a right handed circularly polarized (RHCP) element with four crossed tilted radiating slots. In addition, a pair of metallic tuning vias is included to really improve the reflection of longest slots. A corporate feeding network over SIW has been designed for distributing the input signal to 128 radiating elements, divided into 8 progressive wave linear arrays of 16 elements each. The designed planar array has been manufactured and measured to verify the antenna performance. 25.5 dB gain, 2.33 dB axial ratio, as well as 85% radiation efficiency values have been experimentally achieved at 17 GHz. A 3% usable bandwidth (16.75-17.25 GHz) is obtained due to the typical frequency main beam tilt dispersion in the elevation plane of the progressive wave arrays.
In recent years, active Radio Frequency Identification (RFID) tags have crossed into ultra low power domain. With obvious advantages over passive tags, a setback for active tag growth is the need for battery replacement and limited operational life. Battery life could be extended by scavenging surrounding Wi-Fi signals using rectenna architecture which consists of a receiving antenna attached to a rectifying circuit. A seven stage Cockroft-Walton voltage multiplier optimized for low input power (below 0 dBm) is proposed. Prototype was fabricated on RT/Duroid 5880 (RO5880) printed circuit board (PCB) substrate with dielectric constant and loss tangent of 2.2 and 0.0009 respectively. Experimental results show that 2 V output voltage can be harvested from an operating frequency of 2.48 GHz with -9 dBm (0.13 mW) sensitivity with 1.57 mm board thickness.
A rectangular slot antenna for UWB applications is proposed in this paper. The slot is designed in stepped configuration and is excited by an L-shaped microstrip line flared at the end. The measured impedance bandwidth (-10 dB) from 3 GHz to 27 GHz is achieved. The radiation patterns are bidirectional in the E plane and omnidirectional in the H plane with the measured peak gain around 5 dBi throughout the band. The experimental results are in good agreement with the simulated results. A detail parametric study is done for the flare angle and the flare width to axis ratio and their effect on the impedance bandwidth and the reflection coefficient is described.
This paper addresses the problem of direction-of-arrival (DOA) estimation of correlated and coherent signals, and two sparsity-inducing methods are proposed. In the first method named L1-EVD, the signal-subspace eigenvectors are represented jointly with well-chosen hard thresholds attached to the representation residue of each eigenvector. Then only the eigenvector corresponding to the largest eigenvalue is reserved for DOA estimation via sparse representation, which aims at highly correlated signals, and a method named L1-TEVD (TEVD: Truncated EVD) is proposed. Simulation results show that, L1-EVD and L1-TEVD both surpass L1-SVD in DOA estimation performance and computation efficiency for highly correlated and coherent signals.
A compact interdigital capacitor coupled dual-behavior resonator (DBR) filter with high spurious responses suppression is proposed in this paper. The technique is based on two equivalent topologies of J-inverter and dual-line equivalent circuit of open-circuited stubs. The first compact equivalent topology capacitive inverter is a high pass structure, and consequently, the spurious responses can be suppressed effectively at low frequencies. The second equivalent topology π-network is employed in realizing a compact size and adding new transmission zeros dedicated to the spurious responses suppression at high frequencies. Further compactness is achieved with a dual-line equivalent circuit of open-circuited stubs. The relevant equations are given in the paper. Finally, a 3rd-order compact DBR filter is designed and measured. This structure has a high degree of miniaturization(83%) in comparison to the classical one. Measurement results show good agreement with the simulated ones.
A low-profile microstrip planar monopole antenna with triple-band operation for WiMAX and WLAN applications is proposed in this paper. The antenna has a simple structure which consists of a rectangular ring patch, two inverted L-shaped strips extending from the rectangular ring patch, and a microstrip feed line. By adding two L-shaped strips on the rectangular ring patch, three resonant modes can be excited independently. The antenna has a simple structure and a compact size of 21 × 33 × 1.6 mm3. The measured -10 dB impedance bandwidth of the proposed antenna covers 2.39-2.51 GHz, 3.26-4.15 GHz, and 5.0-6.43 GHz, which can fully cover the 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. A prototype is fabricated, and then measured. The experimental and simulation results show good impedance bandwidth, radiation pattern and stable gain across the operating bands.
A compact multiband Inverted-F Antenna (IFA) for the use in a mobile phone is presented. By adopting a novel folded 3-D structure, a quarter-wave resonator and a parasitic strip, the proposed antenna covers eight bands and exhibits reduced electrical size and low profile. S11 less than -6 dB is obtained in the GSM900, GSM1800, DCS, Bluetooth, Wi-Fi, WLAN5.2, WLAN5.8 and the WiMAX bands. The dimensions of the proposed antenna with the 3-D structure are only 39.6×4.3×3.4 mm3, which are very small in respect with other antennas in mobile terminal devices. A prototype of the proposed antenna is fabricated and measured. Measured and simulated results exhibit good bandwidth, radiation patterns and efficiency across all eight bands.