Impact of amplitude weights on power focusing for near‐field‐focused planar arrays

Near‐field‐focused (NFF) arrays have gained great interest owing to its ability to focus the electromagnetic power at a point near to the antenna. The power focusing can basically be reflected by the sidelobe level and the area of the ?3‐dB focal spot at the focal plane. For an ordinary NFF array with the given phase tapering, it would be an effective way to realize the changing of focused power by controlling the feeding‐current amplitude of the array element. In this article, the effects of the amplitude weights of array element rings on the power focusing with reference to an original NFF array are investigated to address this issue. The focus is on the power focusing changing introduced by amplitude weights changing of element rings, in which different cases of amplitude weights changing are considered. The results from amplitude weights changing are compared with that from an original amplitude weights combination, and compared among those from different cases of amplitude weights changing.     

A WiMAX circularly polarized antenna array using slot‐coupling feeding technique

In this letter, we present a circular polarization antenna array using the novel slot‐coupling feeding technique. This antenna includes eight elements which are installed in line, each array element is fed by means of two microstrip lines with equal amplitude and phase rotation of 90°. The feeding microstrip lines are coupled to a square patch through a square‐ring slot realized in the feeding network ground plane. With the presence of the slots, this antenna array is able to cover the range of frequency of 3 GHz to 4 GHz. The size of the proposed antenna array is 7λ × 1.8λ × 0.4λ. The measured gain is 15.2 dBi and the bandwidth of S11< ?10 dB is 1 GHz (3–4 GHz, 28%). The antenna array is suited for the WiMAX applications. With the use of slot‐coupling feeding technique, the measured bandwidth for axial ratio < 3 dB is about 24% in the WiMAX frequency band (3.3–3.8GHz). The measured HPBW of the y–z planes is larger than 62°. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:567–574, 2016.     

Phase‐only synthesis of planar arrays using autocorrelation matching method

Autocorrelation matching method is proposed for phase‐only synthesis of power pattern of planar antenna arrays. This method is based on equating the autocorrelation coefficients of a planar array having a specified amplitude of excitations to those of a conventionally designed planar array. The effectiveness of the proposed method is verified by synthesis of pencil‐beam and flat‐top patterns.     

Compact broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

Ka‐band phased patch array antenna integrated with a PET‐controlled phase shifter

In this article, a 4 × 4 linear‐phased patch array antenna, consisting of four 1 × 4 patch subarrays and a true time‐delay multiline phase shifter, is proposed on a thin film liquid crystal polymer substrate at Ka‐band. The patch antenna is designed with a gain of 6 dBi at 35 GHz and a bandwidth of 23% centered at 35 GHz. To enhance the gain and symmetrize the beam patterns of the 4 × 4 array, a 1 × 4 patch subarray in the E‐plane was designed and characterized. The subarray produces an enhanced gain of 11 dBi and a wide beamwidth of ±38° in the H‐plane for beam steering. The proposed phase shifter comprises a 1 × 4 microstrip line power splitter and a piezoelectric transducer‐controlled phase perturber. A large phase variation of up to 370° and a low insertion loss of less than 2 dB were demonstrated for the phase shifter at Ka‐band. The integrated phased array attains a gain of 15.6 dBi, and a continuous true‐time delay beam steering of up to 33 ± 1° from 31 to 39 GHz. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:199–208, 2016.     

Wide‐angle scanning circular polarization phased array based on polarization rotation technology

A wide‐beam circular polarization (CP) antenna and a wide‐angle scanning phased array based on novel polarization rotation reflective surface (PRRS) are proposed. The CP wide‐beam pattern is obtained by the combination of the radiation wave from the patch antenna and the orthogonal reflected wave from the PRRS with a 90° phase difference. The proposed CP wide‐beam antenna obtains the patterns with the 3‐dB beamwidth more than 136° and the axial ratio (AR) beamwidth more than 132° in the xoz‐plane. Furthermore, an eight‐element phased array based on the wide‐beam CP antenna element is also developed. The measured results show that the main beam of the array can scan from ?65° to 65° with a gain fluctuation less than 3 dB and the ARs at every scanning angle less than 3 dB.     

The design of radio frequency energy harvesting and radio frequency‐based wireless power transfer system for battery‐less self‐sustaining applications

In this paper, the RF energy harvesting system and RF‐based wireless power transfer system are proposed and designed for battery‐less self‐sustaining application. For energy harvesting, the designed antenna array improves the received RF power effectively and also can harvest RF energy in multi‐frequency bands. For wireless power transfer, the proposed helical antenna realizes the system design in miniaturization. Subsequently, the T shape LC matching network are designed between the antenna and the rectifying circuit to obtain more power transmission. The measured results show that the proposed Wi‐Fi rectifier and 433 MHz rectifier offer a maximum conversion efficiency of 66.8% and 76% in case of the input power is ?3 dBm and 0 dBm, respectively. Finally, the performance of the RF‐based wireless power transfer system and RF energy harvesting system are attested by experimentally measurement, the measured results indicate that these systems can be used to power electronic.     

Computationally feasible narrow‐band antenna modeling using response features

Accurate and low‐cost models of input characteristics are of primary importance from the point of view of efficient design of antenna structures. Yet, the modeling problem is difficult because reflection responses are highly nonlinear functions of frequency and change considerably when adjusting antenna dimensions. Conventional approximation‐based models require massive datasets and often fail to provide required accuracy. This work demonstrates a possibility of dramatic reduction of the number of training samples, which is achieved by reformulating the modeling problem in a space of appropriately defined response features. The key factor is that dependence of feature point coordinates (both frequency and level) on antenna dimensions is less nonlinear than for the standard responses (S‐parameters vs. frequency). Our methodology permits construction of reliable surrogates using much smaller datasets than those required by conventional approaches. Experimental validation indicates that our models provide accuracy that is sufficient for practical antenna design.     

Beam scanning annular slot‐ring antenna array with via‐fence for wireless power transfer

Wireless power transfer has been the field of research for many decades, and with technological advancement and increase in wireless mobile devices, the future of wireless power transfer technology is very promising. The major requirement of wireless power transfer is an efficient and compact antenna array with high gain and flawless scanning performance. In this article, a 4 × 8 element array is proposed with a gain of 18 dB and scanning capability of ±45^° in azimuth and elevation plane at 5.8 GHz. The overall size of the array is 100 mm × 200 mm. The element separation in the array is only 0.48 λ. There was strong mutual coupling due to smaller separation, which has been minimized with the application of via‐fence around the antenna element. A dual feed circularly polarized annular slot‐ring antenna is proposed and analyzed with via‐fence to develop an array of 4 × 8 elements. The antenna array reflection coefficient obtained is less than 20 dB for different scan angles and the gain of the array obtained is also within 2 dB for ±45^° scan angles.     

Broadband T‐bar fed slot antenna array with stable horizontally polarized omnidirectional radiation

A broadband horizontally polarized omnidirectional antenna array is proposed, which consists of a circular array of four identical broadband T‐bar fed cavity‐backed slot antenna elements and a 1‐to‐4 power divider. The proposed omnidirectional antenna array has a compact diameter of only 0.44λ₀, a broad bandwidth of 75.9% (450‐1000 MHz) and a favorable omnidirectional radiation pattern in the azimuth plane with a gain variation below 3 dB in the operating band. Moreover, the cavity‐backed structure makes the proposed antenna array hardly affected by metal environment and the all metal construction allows for high‐power applications, and the reserved cable channel behind the cavities of the antenna elements ensures the extensionality and stability of the proposed array when longitudinal array expansion is needed. Design procedures of the proposed antenna array have been described in detail, simulations and measurements of the proposed antenna array have also been carried out to validate its performance in this article.     

A high‐isolation dual‐polarized quad‐patch antenna fed by stacked substrate integrated waveguides for millimeter‐wave application

A high‐isolation dual‐polarized quad‐patch antenna fed by stacked substrate integrated waveguide (SIW) that is suitable for millimeter‐wave band is proposed in this paper. The antenna consists of a quad‐patch radiator, a two‐layer SIW feeding structure and two feeding ports for horizontal and vertical polarization. The two‐layer stacked SIW feeding structure achieves the high isolation between the two feeding ports (|S₂₁| ≤ ?45 dB). Based on the proposed element, a 1 × 4 antenna array with a simple series‐fed network is also designed and investigated. A prototype working at the frequency band from 38 to 40 GHz is fabricated and tested. The results indicate that the proposed antenna has good radiation performance at 38 GHz that covers future 5G applications.     

Extended theoretical analysis method on the performance of high‐efficiency power amplifiers by solving nonlinear waveform determination process

Classical analysis of high‐efficiency power amplifiers (PA) is usually based on ideal voltage and current waveforms limited to optimal states. A transistor's nonlinear I‐V curves are not usually taken into consideration because of their complexity. With a computer‐aided calculation tool developed herein, a direct waveform determination method involving nonlinear I‐V curves is realized. Using this approach and simplified I‐V curves, a PA's extended theoretical performance from the back‐off region to saturation can be investigated. If using practical dc I‐V curves, this method can also give good performance analysis results even at microwave frequency. Numerical examples of different PA settings are given to verify this method. Nonlinear calculations, harmonic balance simulations, and measurements of a class‐E PA operating at 3 GHz are shown with consistent results to prove this waveform determination method.     

Ten switched‐beams with 2 × 2 series‐fed 2.4 GHz array antenna and a simple beam‐switching network

This article presents a 2 × 2 series fed 2.4 GHz patch antenna array having multiple beam switching capabilities by using two simple 3 dB/90° couplers to achieve required amplitude and phase excitations for array elements with reduced complexity, cost and size. The beam switching performance with consistent gain and low side lobe levels (SLL) is achieved by exciting the array elements from orthogonally placed thin quarter‐wave (λ_g/4) feeds. The implemented array is capable to generate ten (10) switched‐beams in 2‐D space when series fed elements are excited from respective ports through 3 dB quadrature couplers. The dual polarized characteristics of presented array provide intrinsic interport isolation between perpendicularly placed ports through polarization diversity to achieve independent beam switching capabilities for intended directions. The implemented antenna array on 1.575 mm thick low loss (tan δ = 0.003) NH9450 substrate with ε_r = 4.5 ± 0.10 provides 10 dB return loss impedance bandwidth of more than 50 MHz. The measured beam switching loss is around 0.8 dB for beams switched at θ = ±20°, Ф = 0°, 90°, and 45° with average peak gain of 9.5 dBi and SLL ≤ ?10 dB in all cases. The novelty of this work is the capability of generating ten dual polarized switched‐beams by using only two 3 dB/90° couplers as beam controllers.     

A novel substrate integrated waveguide cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic

This article presented a substrate integrated waveguide (SIW) cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic. The proposed array consists of 16 SIW cavity‐backed slot antennas. The SIW cavity‐backed slot antenna can be fed by two separate ports to resonate at two different frequencies and achieve high isolation better than 20 dB between two input ports. The proposed element is a typical self‐diplexing antenna. These cavity‐backed slot antennas are shunt‐fed by a compact 1 to 16 SIW power divider and series‐fed by a set of microstrip lines, respectively. As a result, this array achieves an unidirectional radiation pattern at 10.2 GHz with high gain of 15.10 dBi, and a frequency beam scanning characteristic from 7.0 to 9.0 GHz ranging from ?50° to 46°.     

Design of multi‐beam antenna based on Rotman lens

A planar Rotman lens antenna that generates multiple beams is presented over a wide angular range. The proposed multi‐beam antenna consists of a Rotman lens and a ten‐element printed Yagi antenna array. By properly comparing optical aberrations, expressing as the normalized path length errors Δl, the suitable ratio of on‐axis to off‐axis focal length (g = G/F) is acquired so as to minimize phase errors for the array elements. Ten dummy ports are employed to reduce the performance deterioration caused by energy reflection. A prototype with seven input ports was fabricated and measured, covering a wide scanning angle of 60° (–30°, 30°). The measured beam patterns show that the seven beam gains are distributed from 11.9 to 13.6 dBi under operating of 8.15 GHz. Both the simulated and measured results are used to verify the design approach.     

Design of a printed log‐periodic dipole array antenna with high gain for millimeter‐wave applications

In this article, a V‐band printed log‐periodic dipole array (PLPDA) antenna with high gain is proposed. The antenna prototype is designed, simulated, fabricated, and tested. Simulation results show that this antenna can operate from 42 to 82 GHz with a fractional impedance bandwidth of 64.5% covering the whole V‐band (50–75 GHz). The antenna has a measured impedance matching bandwidth that starts from 42 to beyond 65 GHz with good agreement between the experimental and simulated results. At 50 and 65 GHz, the antenna has a measured gain of 10.45 and 10.28 dBi, respectively, with a gain variation of 2.6 dBi across the measured frequency range. The antenna prototype exhibits also stable radiation patterns over the operating band. It achieves side‐lobe suppression better than 17.26 dB in the H‐plane and better than 8.95 dB in the E‐plane, respectively. In addition, the cross‐polarization component is 18.5 dB lower than the copolarization with front‐to‐back ratio lower than 24.1 dB in both E‐ and H‐planes across the desired frequency range. Based on a comparison of performance among the reported work in the literature, we can say that the proposed PLPDA antenna is a proper candidate to be used in many applications at V‐band frequency. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:185–193, 2015.     

Millimeter‐wave wideband circularly polarized monopulse antenna using the sequential rotation feeding technique

This article presents the design and implementation of a single‐layer wideband millimeter‐wave circularly polarized (CP) monopulse cavity‐backed antenna based on substrate integrated waveguide (SIW) technology. The antenna consists of a 2× 8 array of CP cavity‐backed antenna elements, a 90° 3‐dB coupler, power dividers, and phase shifters. In order to enhance the operating bandwidths, the sequential rotation feeding technology is adopted in the design of the monopulse antenna. To validate the proposed concept, a prototype operating at 42 GHz was fabricated and measured. The measured 3‐dB axial ratio (AR) bandwidth for the sum beam can cover a frequency range from 37 to 46 GHz. The measured gain for the sum beam at the center frequency of 42 GHz is 17.5 dBiC, while the null‐depth of the difference beam is measured to be ?36.8 dB. The proposed monopulse antenna has advantages of low‐cost, easy‐fabrication, and easy integration with planar circuits.     

A parameter‐reduced volterra model for dynamic RF power amplifier modeling based on orthonormal basis functions

A nonlinear dynamic behavioral model for radio frequency power amplifiers is presented. It uses orthonormal basis functions, Kautz functions, with complex poles that are different for each nonlinear order. It has the same general properties as Volterra models, but the number of parameters is significantly smaller. Using frequency weighting the out‐of‐band model error can be reduced. Using experimental data it was found that the optimal poles were the same for different input powers and for the different nonlinear orders. The optimal poles were also the same for direct and inverse models, which could be explained theoretically to be a general property of nonlinear systems with negligible linear memory effects. The model can be used as either a direct or inverse model with the same model error for power amplifiers with negligible linear memory effects. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Broadband planar dipole array Antenna with double C‐shaped slit elements for digital TV broadcasting transmission

This research has proposed a planar rectangular dipole antenna enclosed in double C‐shaped parasitically slit elements (i.e., radiator element) on a double‐cornered reflector for bandwidth enhancement. In the study, simulations were first carried out to determine the optimal parameters of the radiator element and then a radiator element prototype was fabricated and mounted onto a double‐cornered aluminum reflector. The simulated and measured |S₁₁|<–10 dB of the antenna element covered the frequency ranges of 451–901 MHz (66.6%) and 455–886 MHz (64.3%), respectively. The gain was enhanced by the subsequent deployment of multiple radiator elements to fabricate a four‐element vertically array antenna on an elongated double‐cornered reflector. The simulated and measured |S₁₁|20 and 相似文献   

Reduced‐cost surrogate modeling of input characteristics and design optimization of dual‐band antennas using response features

In this article, a procedure for low‐cost surrogate modeling of input characteristics of dual‐band antennas has been discussed. The number of training data required for construction of an accurate model has been reduced by representing the antenna reflection response to the level of suitably defined feature points. The points are allocated to capture the critical features of the reflection characteristic, such as the frequencies and the levels of the resonances, and supplemented by the additions (infill) points, which is necessary to provide sufficient data that allows restoring the entire response through interpolation. Because the coordinates of the feature points exhibit less nonlinear behavior (as a function of antenna geometry parameters) compared to S‐parameters as a function of frequency, surrogate model construction can be realized with a smaller number of data points. The presented modeling approach is demonstrated using an example of a planar dipole antenna. Also, the feature‐based method is favorably compared to direct modeling of reflection characteristics using kriging. The relevance of the technique is further verified by its application for design optimization.