复合材料垂尾隐蔽式短波天线研究

为研究复合材料垂尾对机载短波天线输入阻抗和辐射特性的影响,分析了不同机载隐蔽式短波天线的结构和性能,提出了一种基于复合材料垂尾的新型回线天线结构,并利用基于时域有限差分法的仿真软件XFDTD对这种位于机垂尾前缘的隐蔽式回线天线和传统的机载套筒天线分别进行了建模和仿真。根据仿真结果分析并总结出了复合材料垂尾对这两种机载短波天线输入阻抗和辐射特性的影响情况。通过与传统回线天线的比较,验证了新型回线天线的可行性和优势。仿真结果对实际机载短波天线的研究和设计有一定的参考价值。     

Development of a Cavity-Backed Broadband Circularly Polarized Slot/Strip Loop Antenna With a Simple Feeding Structure

A cavity-backed loop antenna is developed for producing broadband circularly polarized (CP) radiation. The antenna configuration consists of a slot loop and a strip loop. The slot loop radiates a CP wave at a lower frequency while the strip loop produces CP radiation at a higher frequency. A combination of the two frequencies leads to a bandwidth enhancement. The slot/strip loop antenna is fed by a single straight microstrip line. It is demonstrated that the cavity-backed slot/strip loop antenna can achieve an axial ratio (les 3 dB) bandwidth of 19% with good impedance matching. The antenna configuration is described and the operating principles for broadband circular polarization and impedance matching are analyzed. The antenna performance is confirmed by experimental results.     

Circularly polarized twisted loop antenna

A novel wire-loop antenna is introduced for circular polarization. By introducing a small gap at the middle of two nonradiating sides of a one-wavelength square wire loop, a 90/spl deg/ time-phase difference between the currents on the other two radiating sides can be achieved. Then by twisting the square loop to make the radiating sides orthogonal the necessary conditions are satisfied for circularly polarized radiation. The antenna yields nearly ideally circular polarization at broadside as well as excellent input impedance properties near the design frequency. The radiation pattern has a broad beamwidth and good rotational symmetry about the axis. For a demonstrator operating at 1 GHz, a 3-dB axial ratio was maintained over /spl plusmn/30/spl deg/. The mechanism of circular polarization is analyzed based on numerical simulation. Experimental results are presented to verify the theoretical predictions made.     

Switchable Printed Yagi-Uda Antenna with Pattern Reconfiguration

A switchable Yagi-Uda antenna prototype with radiation pattern reconfiguration is presented in this letter. The proposed reconfigurable antenna is based on the concept of switching between the reflector and director of a Yagi-Uda antenna using a radio frequency PIN diode. As a result, the minimum/maximum radiation can be steered towards desired signals or away from interfering signals in opposite directions. The measured 10 dB impedance bandwidth and gain are 210 MHz (7%) and 8.02 dBi at 3 GHz, respectively. Details of the antenna design and its performance are described and empirically analyzed.     

The moment method solution for printed wire antennas of arbitraryconfiguration

A printed wire antenna of arbitrary configuration is analyzed. The electric field tangential to the wire is derived using the current expanded by piecewise sinusoidal functions. These functions are also used to form the impedance matrix elements. Use of the stationary phase method leads to a simple expression for the radiation field. Numerical analyses based on the present formulation yield radiation characteristics of a zigzag dipole antenna, a loop antenna, and a round spiral antenna     

A distributed-feedback antenna oscillator

In this paper, a new design of the active transmitting antenna array, called the distributed-feedback antenna oscillator, is proposed. The active array is formed by serially connecting several unit cells to a closed loop. Each unit cell contains an amplifier and a two-port antenna, with an overall insertion gain larger than 0 dB and a phase delay equal to a multiple of 360°. The signal traveling on the loop is amplified and radiated in each unit cell. The radiation fields from all the antennas are then combined in free space. A four-element feedback antenna oscillator operating at 10 GHz is demonstrated by using two-port aperture-coupled microstrip antennas. Simulation results show that multiple oscillation modes with different frequencies and different radiation beams may be excited in the antenna oscillator. By experiment, it is found that each oscillation mode can be built by tuning the biases of the oscillator. The measured radiation pattern for each mode agrees very well with the predicted one. For a single-mode operation with a broadside pattern, bandstop filters of a simple geometry are designed and embedded in the oscillator to suppress the unwanted oscillation modes. Finally, the influence of the bias condition on the radiation power of the single-mode oscillator is investigated     

Input impedance, radiation pattern, and radar cross section ofspiral antennas using FDTD

A finite-difference time-domain (FDTD) analysis of spiral antennas is performed to calculate input impedance, antenna gain, and scattering. A semicircular spiral mounted on a dielectric substrate was simulated for computing the input impedance versus frequency. The gain and scattering computations were performed on a square Archimedean spiral mounted in a ground plane with a cavity backing. Total-field FDTD calculations are used to compute the impedance and gain patterns, while a specially modified scattered-field approach for aperture antennas in infinite ground planes is used for the scattering results. Comparisons are made with published impedance measurements and gain and scattering calculations done with a finite element method. Good results were obtained for impedance, radiation, and scattering     

Low Profile Miniaturized Planar Antenna With Omnidirectional Vertically Polarized Radiation

A novel miniaturized cavity-backed composite slot loop antenna (CBCSLA) with low profile and omnidirectional radiation similar to a short dipole is presented. The antenna displays vertical polarization while having less than lambda/100 dimension in height. The geometry of the antenna is inspired from a small magnetic loop which is realized using a slot configuration on metallic ground. Since a small slot loop antenna cannot be impedance matched, a composite geometry is devised that acts like as a small slot loop and can easily be impedance matched using this configuration. The diameter of the CBCSLA can be made as small as lambda/10 or smaller. The feeding mechanism is designed in a manner to create a circumferentially-constant current distribution around the composite loop while effectively matching to a 50 Omega coaxial feed from the antenna center. Additional methods are discussed to further enhance the bandwidth and achieve a dual-band response. The antennas are designed, fabricated, and measured. It is shown that despite their small lateral dimension and extremely small height, the miniaturized cavity-backed slot loop features extremely well input impedance match, uniform radiation pattern, low cross-polarization levels and expected gain.     

基于阻尼振荡法的甚低频天线阻抗测量

为了准确测量甚低频发射天线在实际工作环境和工作频点上的输入阻抗,本文提出了一种基于RLC阻尼振荡法的阻抗测量方法,并推导了天线阻抗、电容、电感和电阻的测量公式;该测量方法可通过提高测量电压来提高测量信噪比和测量精度;测量系统谐振于被测天线的工作频点或其附近,使甚低频发射天线输入阻抗的测量值更接近天线在实际工况下的真实值.试验表明,本文提出的测量方法简单可行,具有较高的精度和稳定性,可实现甚低频发射天线输入阻抗的现场测量.     

A 60-GHz Wideband Slot Antenna Based on Substrate Integrated Waveguide Cavity

This paper proposes a new wideband W-band substrate integrated waveguide (SIW) cavity-backed slot (CBS) antenna. The SIW cavity suppresses the backward radiation and ensures this antenna have a very low profile (only about 4% of the operating wavelength). Several techniques, such as slot resonator with semicircular end, quarter-wavelength microstrip resonator, are introduced to improve impedance matching. The studied results demonstrate that this antenna has wide operating bandwidth in 54.3–67 GHz (about 20.9% of the fractional bandwidth), unidirectional radiation pattern and good linear polarization characteristic. These properties are very suitable for RF front-end system-on-package (SoP) design in millimeter wave wireless communication systems.     

Conditions of Oscillation for Waveguide Mounted Tunnel Diodes

Double frequency oscillation was observed in a waveguide mounted tunnel diode circuit, due to the frequency dependency of the waveguide's distributed parameters. A general analysis of the frequency dependent diode load is made and conditions of oscillation are formulated. The analysis is extended to a 1N3219A diode mounted in a tapered RG-52/U waveguide used as an oscillator. The load impedance to the tunnel diode is derived with the diode mounted at the center of the waveguide. A numerical example involving the RG-52/U waveguide mount is presented verifying the existence of double frequency oscillation and exemplifying the oscillation conditions stated. Off center diode mounting is examined. It is concluded that the waveguide mount's distributed parameters are highly frequency dependent at the center of the guide and thus double frequency oscillation can exist when a tunnel diode is mounted at that point. With the diode mounted at any other point, only one oscillation frequency can be observed. The frequencies of oscillation of a waveguide mounted tunnel diode oscillator are determined only by the real roots of the resistive component of the total tunnel diode load impedance.     

Printed square monopole antenna with semicircular base for ultra-wide bandwidth

A modified printed square monopole antenna with semicircular base has been proposed, which gives ultra-wide bandwidth ratio of 11.31:1. A frequency-dependent design curve, for the microstrip feedline, is presented for this modified configuration. Experiments have been performed to measure impedance bandwidth and radiation patterns of the monopole, which are in agreement with the simulated results     

A fast MoM calculation technique using sinusoidal basis and testing functions for a wire on a dielectric substrate and its application to meander loop and grid array antennas

The input impedance matrix element of the method of moments (MoM) for an arbitrarily shaped wire antenna printed on a dielectric material Z/sub m,n/ is formulated to be composed of three terms Z/sup /spl psi/s//sub m,n/, Z/sup /spl psi///sub m,n/, and /spl Delta/Z/sub m,n/ involving single-, double-, and triple-integral calculations, respectively. The MoM based on the Z/sub m,n/ formulated in this paper (new MoM) is applied to two antennas-a meander loop antenna and a grid array antenna-as well as a simple loop used as a reference antenna. The computation time to obtain the current distribution of each antenna by the new MoM technique is compared with the time required for the conventional MoM, which has an impedance matrix element composed of four terms, all involving triple-integral calculations. It is revealed that the new MoM drastically reduces the computation time: for example, by a factor of 937 for the grid array antenna. In addition, the radiation characteristics of these two antennas are discussed. It is found that a reduced-size meander loop (62% smaller than the simple loop reference) has a radiation pattern similar to the simple loop reference. It is also found that the grid array has an axial beam radiation pattern without side lobes in the principal planes.     

A RF to DC Voltage Conversion Model for Multi-Stage Rectifiers in UHF RFID Transponders

This paper presents a RF to DC conversion model for multi-stage rectifiers in UHF RFID transponders. An equation relating the RF power available from the antenna to the DC output voltage produced by a multi-stage rectifier is presented. The proposed model includes effects of the nonlinear forward voltage drop in diodes and impedance matching conditions of the antenna to rectifier interface. Fundamental frequency impedance approximation is used to analyze the resistance of rectifying diodes; parasitic resistive loss components are also included in the analysis of rectifier input resistance. The closed form equation shows insights into design parameter tradeoffs, such as power available from the antenna, antenna radiation resistance, the number of diodes, DC load current, parasitic resistive loss components, diode and capacitor sizes, and frequency of operation. Therefore, it enables the optimization of rectifier parameters for impedance matching with a low-cost printed antenna and shunt tuning inductor, in order to improve the RF to DC conversion efficiency and the operational distance of UHF RFID transponders. Three diode doublers and three multistage rectifiers were fabricated in a 130 nm CMOS process with custom no-mask added Schottky diodes. Measurements of the test IC are in good agreement with the proposed model.      

Broadband loop antenna for DCS-1800/IMT-2000 mobile phone handsets

A rectangular loop antenna is proposed for DCS-1800 and IMT-2000 mobile phone handsets. By introducing a small gap in the wire loop, an impedance bandwidth of 24% can be achieved. The antenna mounted on a metal box is simulated using the FDTD method. It is found that the introduction of a small gap also results in a radiation pattern with desirable polarization independence and a reduced gain in the direction of the user's head. The simulated and measured results are presented.     

Analysis of a printed wire loop antenna

The current distribution and radiation pattern of a printed thin-wire circular loop antenna are computed rigorously using an entire-domain moment method analysis. A computationally efficient algorithm using the FFT is implemented. The input impedance of the loop and the far-zone radiation pattern are computed as a function of the substrate dielectric constant and thickness and as a function of the loop circumference. The space-wave launching efficiency and z-directed power gain of the antenna are also computed as a function of the substrate thickness     

部分浸没于海水中天线阻抗及辐射效率分析

针对海洋环境中浮标天线的辐射性能问题,基于海水中短波、超短波频段高衰减的特性,提出了以海面为分界面,将天线分为水上、水下两部分考虑的假设,建立了部分浸没于海水中天线的理论计算模型,开展了天线输入阻抗测试实验,验证了假设和模型的正确性.应用该模型,确定了天线的水上、水下部分阻抗共轭匹配条件下的工作频率范围,分析了不同入水...     

Frequency tunable monopole coupled loop antenna with broadside radiation pattern

A frequency tunable antenna made with an open-circuit monopole coupled loop antenna associated to a varactor diode is presented. The proposed antenna shows a 35.8% relative bandwidth, covering the 470?675 MHz frequency range. Theoretical and experimental results of S₁₁, radiation patterns and gain have been performed and show good agreement.     

有源集成天线的谐波平衡法分析

本文首先利用矩量法计算平面馈电型微带贴片天线的输入阻抗,并对其进行实验测量;其次,使用谐波平衡法分析了以Ｃｕｎｎ管为振荡源的有源微带天线电路。在求解谐波平衡方程时采用Ｐｏｗｅｌｌ优化法,得出整体电路的振荡频率和振荡电压;再次,仍使用谐波平衡法对肖特基二极管与微带贴片天线集成的接收型有源天线进行大信号的小信号分析,同样经过优化,得出其在本振电压作用下,非线性部分的谐波电压以及在小信号电压作用下的变频     

m=0角向模表面波等离子体柱天线辐射特性

根据表面波在非磁化等离子体柱中的色散关系,理论计算得到存在电子-中性原子碰撞、径向与轴向等离子体密度非均匀分布条件下m=0角向模表面波波矢实部与虚部随信号频率、等离子体密度的变化关系.然后利用波矢的实部与虚部、等离子体柱天线表面指数分布电流模型、等离子体阻抗,推导得到等离子体柱天线的辐射方向图随信号频率、等离子体密度的变化关系;最大增益、天线辐射阻抗随信号频率的变化关系;天线径向能量辐射随等离子体密度的变化关系.理论计算结果表明等离子体柱天线辐射方向图随信号频率、等离子体密度的改变而变化非常明显,信号频率对最大增益、天线辐射阻抗的影响显著;同时,这些理论计算结果与他人实验实测结果吻合,这对于设计高精度要求的等离子体天线提供了重要的理论参考价值.