Cosite interference between wire antennas on helicopter structuresand rotor modulation effects: FDTD versus measurements

As telecommunication systems become more complex and more antennas are placed on the same structure (e.g., helicopter airframe) the problem of interference becomes significant for the performance of the systems. The finite-difference time-domain (FDTD) method is used to calculate coupling between wire elements; e.g., monopoles and loops mounted on ground planes and helicopter airframes. Also, rotor modulation effects on coupling are investigated. All the numerical results obtained by FDTD are validated by comparison with measurements     

Computation of aperture antenna mutual coupling using FDTD andKirchhoff field transformation

A new method for computing the mutual coupling between aperture antennas using the finite-difference time-domain (FDTD) method together with the Kirchhoff near-field to near-field transformation is described. The method offers a reduction in computer storage, particularly for widely spaced antenna elements in an array     

A simple FDTD model for transient excitation of antennas bytransmission lines

A simple FDTD model is developed for use with antennas that are fed from transmission lines. The model is especially designed for use with transient excitations, where the incident and reflected waveforms within the transmission line are of interest, and the latter is determined directly in the FDTD calculation. The model is verified for both transmission and reception of transient waveforms by comparison with measured results for a cylindrical monopole antenna with a plane reflector     

Analysis of arbitrary shape printed line microstrip antennas

A rigorous solution for arbitrary-shape printed line antennas is developed using the microstrip Green's functions. The current distribution of the line is determined by a moment method and the use of sinusoidal basis functions. Analytical expressions for the far zone fields are obtained using an asymptotic method for evaluating the Sommerfeld integrals. Examples illustrating the accuracy of the method and characteristics of selected printed antennas are presented. It is found that, for undulated printed line elements, the resonance length increases when the undulation height increases. Various examples of undulated printed line elements which are useful for array design are investigated. The effect of the undulation height on the radiation characteristics of the printed line is studied     

An Equivalent Feed Model for the FDTD Analysis of Antennas Driven Through a Ground Plane by Coaxial Lines

For the finite-difference time-domain (FDTD) analysis of antennas excited by coaxial lines, an equivalent model of the antenna feed is presented here. Under the quasi-static approximation, the coaxial aperture is simply represented as the equivalent magnetic-frill current and the equivalent load circuit including the effects of the coaxial line. It leads us to a simple modification of the standard FDTD update equation at the aperture without any additional cell modeling of the line. The validity of the proposed model is confirmed by comparing of the FDTD results and the measured data.      

基于FDTD方法的车载天线耦合特性分析

本文采用FDTD法对处于地面附近的车载通信天线的电磁兼容性进行了分析计算.克服传统方法存储量大,计算困难等缺点,并提高了计算速度和精度.文章最后以某军通信车为实体建模,计算仿真了车上3副天线的耦合度.所用方法及所得结果可作为通信率电磁兼容分析与设计的手段和依据.     

FDTD analysis and measurement of aperture antennas based on thetriplate transmission-line structure

First, two aperture antennas designated as P-type and C-type antennas are analyzed using the finite-difference time-domain (FDTD) method. Each antenna is made of a triplate transmission line (TTL). A square aperture is cut out of the top plate of the TTL for both antennas to allow radiation. The bottom of the TTL is a planar plate for the P-type antenna and a plate with a hollow cavity for the C-type antenna. The power flow is expressed using Poynting vectors. It is revealed that parallel-plate mode power in the TTL is lower in the C-type antenna, compared with that in the P-type antenna. Second, an array antenna composed of two C-type elements is analyzed. The Poynting vector distribution in the aperture is found to remain almost unchanged when the element spacing is varied. The input impedance of the array antenna converges at an element spacing of approximately 0.9 wavelength. The theoretical radiation patterns are in good agreement with measured data     

FDTD结合变分法计算线天线间耦合度

线天线的自阻抗、互阻抗及耦合度是工程应用中迫切需要但又很难计算准确的。该文将时域有限差分法和变分原理相结合,求解了线天线之间的互阻抗,从而得到了耦合系数。其结果与FEKO,NEC仿真均吻合良好,表明该文方法可以获得比传统FDTD计算方法更加准确的计算结果。     

A complete electromagnetic simulation of the separated-aperturesensor for detecting buried land mines

The detection of buried land mines is a problem of military and humanitarian importance. Electromagnetic (EM) sensors (ground-penetrating radars) use signals at radio and microwave frequencies for this purpose. In the past, EM sensors for land-mine detection have been empirically developed and optimized. This has involved experimental tests that are complicated, time consuming, and expensive. An alternative is to carry out initial development and optimization using accurate numerical simulations. One objective of this paper is to show, for the first time, that such simulations can be done using the finite-difference time-domain (FDTD) method. The separated-aperture sensor has been under investigation by the United States Army for land-mine detection for many years. It consists of two parallel dipole antennas housed in corner reflectors that are separated by a metallic septum. It is a continuous-wave sensor tuned to a particular frequency (typically 790 MHz). When the sensor is over empty ground, the coupling between the antennas is very small. As the sensor is moved over a buried mine, the coupling between the antennas increases indicating the presence of the mine. In this paper, the complete EM system composed of the separated-aperture sensor, air and soil, and buried land mine is modeled using the FDTD method. The finite computational volume is truncated with an absorbing boundary condition: the generalized perfectly matched layer. Detailed studies made with the simulation increase the understanding of this sensor. Results computed from the simulation are in good agreement with experimental measurements     

An Efficient FDTD Model for Resistively Loaded Cylindrical Antennas With Coaxial Lines

A full coarse-grid based finite-difference time-domain (FDTD) model is proposed for an efficient analysis of resistively loaded cylindrical antennas driven by coaxial feed lines. In the case of the electrically thin resistive antenna, the thin-wire approximation is applied to the near fields around the antenna. The resistive antenna is equivalently represented by a series connection of piecewisely lumped resistors along the antenna axis. And the coaxial line is replaced by an equivalent source over the feed aperture of the line. Then the corresponding FDTD update equations make it possible to implement the full coarse-grid model without additional grid refinements for the antenna and the feed line. The transient reflected feed voltage and the input impedance of resistive antennas are calculated numerically and compared with those of a full fine-grid.      

Short helical antenna array fed from a waveguide

An array consisting of short helical antennas is fed from a single rectangular waveguide. Stubs are introduced near the array elements in order to make a matching condition between the array elements and the waveguide. On the basis of a transmission line theory, a coupling phase and a coupling factor are determined. The mechanical rotation is applied to each array element so that in-phase condition at the aperture may be formed. Excellent agreement between the calculated and experimental results is demonstrated in the arrays of five, seven, and nine helical antennas.     

Design of aperture coupled microstrip antenna array fed bydielectric image line

A novel design for a linear array of microstrip antennas, aperture coupled to a dielectric image line has been developed. The design is based on a simplified theory to determine the impedances of the antennas at their apertures, and in turn, the coupling to each antenna from the image line. The theory developed is verified using an eight-element linear array and the experiment results are very good     

Performance analysis of antennas for hand-held transceivers usingFDTD

The design of antennas for hand-held communications devices depends on the implementation of simulation tools that can accurately model general topologies. The paper presents the analysis of small antennas mounted on hand-held transceivers using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, with particular emphasis placed upon modeling of the source region. The technique is used to predict the gain patterns and broadband input impedance behavior of monopole, planar inverted F, and loop antenna elements mounted on the handset. Effects of the conducting handset chassis, the plastic casing around the device, and lumped elements integrated into the antenna design are illustrated. Experimental results are provided to verify the accuracy of the computational methodology. The concept of antenna diversity is discussed, and key assumptions and expressions are provided that characterize the multipath fading fields. Several computational examples demonstrate the diversity performance of two receiving antennas on a single handset     

双极化口径耦合微带天线FDTD分析

本文应用时域有限差分法（FDTD）分析了双极化口径耦合多层微带贴片天线。文中结果表明,FDTD在分析多层复杂结构的微带天线时是非常有效的。采用Gauss脉冲激励,通过FFT,一次计算就可得到天线谐振频率、耦合、频带宽度、增益等参数的宽频带特性。计算结果对天线的优化设计具有一定的指导作用。     

An FDTD/MoM hybrid technique for modeling complex antennas in thepresence of heterogeneous grounds

Calculating the current distribution and radiation patterns for ground-penetrating radar antennas is a challenging problem because of the complex interaction between the antenna, the ground, and any buried scatterer. Typically, numerical techniques that are well suited for modeling the antennas themselves are not well suited for modeling the heterogeneous grounds, and visa versa. For example the finite-difference time-domain (FDTD) technique is well suited for modeling fields in heterogeneous media, whereas the method of moments (MoM) is well suited for modeling complex antennas in free space. This paper describes a hybrid technique, based upon the equivalence principle, for calculating an antenna's current distribution radiation pattern when the antenna is located near an air-ground interface. The original problem is decomposed into two coupled equivalent problems: one for the antenna geometry and the other for the ground geometry, with field information passing between them via a rapidly converging iterative procedure. The fields in each region may be modeled using numerical techniques best suited to them. Results for several test cases are presented, using FDTD to model the ground problem and MoM for the antenna problem, that demonstrate the accuracy of this hybrid technique     

Simple transmission line feed model for microstrip antennas in two-sided structure with coaxial probe coupling

A simple transmission line feed model is presented for microstrip antennas in a two-sided structure coupling through a coaxial probe. The parameters of the model are extracted directly from the feed structure. The validity of the feed model combined with the recently developed transmission line model of microstrip antennas is verified by measurement.<>     

Modelling of coaxial-fed microstrip patch antenna by finite difference time domain method

A direct three-dimensional finite-difference time-domain (FDTD) method is applied to coaxial-fed microstrip antennas. The model is shown to be an efficient and accurate tool for modelling coaxial-fed structures. The reflection coefficient can be determined from the simulated time-domain wave that is reflected down the coaxial line. Excellent agreement over a wide frequency range is shown in two cases between the measured and FDTD derived results.<>     

High-Efficiency Angled-Dipole Antennas for Millimeter-Wave Phased Array Applications

A high-efficiency microstrip-fed endfire angled-dipole antenna has been developed for millimeter-wave phased array applications. The antenna is built on both sides of a Teflon substrate (epsiv_r = 2.2) and this allows a wideband feed from the single-ended microstrip line to the differential dipole. The design results in wide radiation patterns for scanning purposes with a gain of around 2.5 dB at 20-26 GHz and a cross-polarization level of < -15 dB at 24 GHz. A mutual coupling of < -23 dB is measured between adjacent elements with 6.8 mm center-to center spacing (0.50-0.54 lambda₀ at 22-24 GHz). A variant of the angled-dipole antenna with a magnetic ground plane edge was also developed, and shows a measured gain of > 6 dB at 23.2-24.6 GHz and very low mutual coupling between elements (<-23 dB for a 6.8 mm spacing). Both antennas result in a radiation efficiency of > 93% when referenced to the microstrip line feed (including mismatch loss). The usefulness of these antennas as phased array radiators is demonstrated by several eight-element linear arrays at 22-24 GHz with scan angle up to 50 degrees. The application areas are in automotive radars and high data-rate communication systems.     

Optimization of bow-tie antennas for pulse radiation

Resistively loaded bow-tie antennas are considered as radiators for temporally short, broad-bandwidth pulses. Analysis is by the finite-difference time-domain (FDTD) method. The geometrical details of the antenna and the resistive loading along the antenna are chosen to optimize this antenna for pulse radiation. Theoretical results for the reflected voltage in the coaxial feed line and the time-varying radiated electric field are compared throughout with experimental measurements. The optimized, resistive bow-tie antenna is shown to radiate a pulse that more closely resembles that of the excitation than is radiated by a metallic bow tie of comparable size. Issues involving the use of the FDTD method for modeling fully three-dimensional antennas are also discussed. These issues include the use of a simple feed model and the staircasing of the edges of the antenna