Antenna Distortion Research Articles

Ultra-Wideband Bow-tie Antenna for Ground Penetrating Radar Applications

The Ground-penetrating radar (GPR) system is used for the detection of buried objects inside the earth and the classification of the subsurface structures. Ultra-wide band antenna is one of the major component of the GPR system; which is used to transmit and receive short pulse of electromagnetic nature. The performance of the GPR system in detecting buried object is mainly affected by the reflections of the GPR antenna. The reflections from the antennas itself is a basis of late-time ringing and distortion of antenna. These factors create problem in the identification of the objects. Several UWB antennas are used in the GPR system. This paper presents theoretical study for the design of ultra-wideband Bow-tie antenna as a GPR antenna. Bow-tie antenna is designed for a frequency range of 4-18 GHz. Transient and spectral behavior of the antenna is simulated. The time behavior of the antenna shows a reflected signal from the bow-tie antenna of the duration of 2.0 ns. The antenna provides a VSWR less than 2.0 and a return loss of less than -15 dB in the operating frequency range. Bow-tie antenna is then modeled and simulated in the GPR environments which includes the buried object (i.e. scatterer) and beam floor. The design, modeling and simulations are performed by using CST Microwave Studio.

Iteration Path-Length Error Correction Approach to Subreflector Shaping for Distortion Compensation of Large Reflector Antenna

At the stage of structural optimization, the subreflector structure should be designed such that it compensates for the residual error or relaxes the accuracy requirement of the main reflector to a certain extent. However, there is no fast and effective means to shape the subreflector during the structural optimization process. This communication is based on the application of geometrical optics (GO)/physical optics (PO) analysis to shape a subreflector for antenna distortion compensation. Thus, a method performing an iterative approximation to the GO/PO analysis is proposed. Unlike GO shaping or optimization, the proposed method is not formulated by simultaneous nonlinear ordinary differential equations. Therefore, the main contribution of this communication is that the method does not entail computationally intensive calculation and optimization, and thus, it does not require a large amount of time to complete the calculation. The proposed method is very suitable for a large reflector antenna with a small-amplitude deformation and smoothly varying errors such that the shaped subreflector does not have a significant effect on the amplitude of the main reflector’s electric field. An example with regard to the symmetric system is presented. The obtained results demonstrate that the proposed method is effective.

An efficient error estimation method for antenna distortions in space based radar

The phased array antenna plays an important role in determining the performance achievable in a space based radar system. However, the array position errors caused by the antenna distortions in the complex cosmic vacuum environment will distort the antenna pattern, which significantly degrades the performance of the radar systems. Most of the conventional estimation methods are proposed based on the random position errors without the consideration of the distortion character for spaceborne arrays, resulting in a large estimation error. In this paper, to address this issue, an efficient array error estimation method is proposed to compensate the antenna distortion errors. In the proposed method, the initial sensor positions can be obtained based on the measured results from the units distributed over the array surface. Then the distortion model parameters can be estimated by solving an optimization problem. Based on this, the sensor positions can be corrected with high accuracy at the lth iteration. In this way, the proposed method can improve the accuracy and the robustness of the estimation simultaneously. Several simulated results are presented to validate the proposed method for the position error estimation in a space based radar system.

TCR Antenna For Small Satellite Application

The results of this study are interesting about antenna technology generation used in small satellite. A new design optimized of the TCR (tracking, command and ranging) antenna has been presented. It has a good impedance matching to the 50 Ohm coaxial line which has been radically enhanced with different geometric features. For the Ku band frequency band, the VSWR of 1.15 is not exceeded. In its optimized version, it is compact and aesthetic and this property reduces antenna distortions. Design considerations for this antenna performance in terms of coverage gain, side lobe isolation, and cross-polar isolation are discussed. The paper also discusses the possibilities of extending the frequency coverage of the antenna system into the Ku-band system can increase the capabilities and operational flexibility of existing earth stations as well as adapts with new current and future technology trends are presented.

B-spline surface fitting and simplified GO/PO analysis of subreflector correction for large Cassegrain antenna distortion compensation

The main surface of a large Cassegrain antenna consists of a large number of panels. There are inevitably random and systematic errors which will degrade the antenna pattern and limit its applicability when working at high frequencies. Correcting the subreflector surface is difficult to describe by a global expansion effectively with a small amount of data. This paper presents a simple and clear way for correcting the subreflector surface of a large Cassegrain antenna for achieving such compensation. The advantage of the method is that the geometrical optics (GO) analysis is extremely simplified by the concept of equivalent prime-focus paraboloid, and corrected deformations of the subreflector surface are determined by simple formulas which represent the relationship between distortions of the subreflector surface and phase of the main surface current. The final shape of the subreflector surface is represented by a B-spline surface. To obtain a satisfactory antenna pattern with the simplest subreflector surface, the optimal number of B-spline patches are searched by particle swarm optimization (PSO). The shaping process is verified by compensating a 22-m Cassegrain antenna whose main reflector has 96 panels. The results are satisfactory and demonstrate the simplicity and effectiveness of the approach.

A Balanced Impulse Radiating Omnidirectional Ultrawideband Stacked Biconical Antenna

A compact symmetric discone antenna for the 3 GHz to 20 GHz frequency range is demonstrated. The antenna design is optimized for a good transient response with low angular dependency. This property reduces antenna distortions and simplifies antenna de-embedding. The design is based on the well-known biconical antenna, which has been radically enhanced with different geometric features. Far field modal analysis has been used for both the development and the verification of the concept that ensures a constant radiation pattern. A prototype of the balanced antenna with an improved feeding mechanism based on two separate discone antennas together with a three-port balun is also presented. Measurements in the time and in the frequency domain have been performed in order to characterize the antenna. Overall, the results show significantly improved impulse responses and input matching compared to a standard biconical antenna. Therefore, the new antenna is very well suited for advanced channel characterization, reference measurements, and system verifications.

The FEM–BIM approach using a mixed hexahedral finite element to model the electromagnetic and mechanical behavior of radiative microstrip antennas

This work is focused on the prediction of the impact of microstrip radiative antenna distortions on electromagnetic fields. In this way, a recent numerical tool, able to model the electromagnetic and mechanical behavior of a microstrip antenna, has been developed. Considering a weak coupling between electromagnetism and mechanical behavior, the mechanical equations are first solved. Then, from the mechanical strains results for the antenna, the electromagnetic fields are computed. To solve both problems, a 3D hexahedral finite element is used to discretize the structure, having both nodal mechanical and edges electromagnetic degrees of freedom. The weak electromagnetic formulation inducing integrals on an open infinite domain, a Boundary Integral Method (BIM) is used and applied to the strained structure. Three examples are considered. The simulations show that mechanical distortions can have major influence on the electromagnetic behavior of antennas.

Optical methods for formation of radiation patterns of phased array antennas

It is shown that architectural design principles based on application of photonics methods have prospects for the development of ultra-wideband and ultrashort-pulse radars. Transmitting and receiving systems with optical controllers based on dispersing fiber-optic prisms are considered. Design versions of a photoconductive antenna excited by picosecond optical pulses and a wideband photoelectronic pattern shaper on the basis of analog vector modulation are presented. A method for compensation of antenna distortion effects arising during transmission of an ultrashort pulse with the use of an optical shaping technique is described.

Characterization of system calibration parameters for high gain dual polarization satellite beacon diagnostics of ionospheric variations

[1] We present complementary methods for calibrating the dual-polarization feed of a ground-based tracking antenna used for ionospheric measurements. Several calibration parameters are defined which describe the state of the measurement equipment. These key parameters then form a transformational Mueller matrix which may be used to remove system bias in data received from known beacons. Several strategies are developed to quantify these time-dependent distortions for the Green Bank 140′ diameter antenna and receiver, although these methods could be applied to other similar systems. One approach quantifies the receiver biases in terms of amplitude and gain differentials. This is accomplished by measuring polarimetric differences between channels using a test signal with a known amplitude and phase. Due to variations over time periods on the scale of a beacon track, this procedure is most effective when the calibration signal is injected concurrently with the beacon measurements. To determine antenna feed distortion, including cross-polarization and ellipticity, data is recorded from an external celestial source. An example shows the effectiveness of this calibration technique by comparing calibrated data to data without correction. Error estimates of the calibration parameters in the example establish an upper bound of 0.22 TEC units for measurements at 150 MHz along track.

Polarimetric PALSAR Calibration

Polarimetric Phased-Array-type L-band Synthetic Aperture Radar (PALSAR) system parameters are assessed using data sets collected over several calibration sites. The data collected over the Amazonian rain forest help validate the hypothesis that Faraday rotation is zero near the equator. The analysis of the Amazonian forest data and the response of the corner reflectors deployed there during the PALSAR acquisitions lead to the conclusion that the antenna is highly isolated (better than -35 dB). These results are confirmed using the data collected over calibration sites located in Sweden and Canada. The 5-m-height corner reflector deployed at the Remningstorp (Sweden) calibration site by Chalmers University of Technology provides accurate measurement of antenna parameters and detection of a (2deg -3deg) Faraday rotation during day-time acquisitions, whereas no Faraday rotation was noted during night-time acquisitions. Small Faraday rotation angles (2deg-3deg) have been measured using acquisitions over the DLR Oberpfaffenhofen and the Ottawa calibration sites. The presence of small but still significant Faraday rotation (2deg-3deg) induces a corner reflector return at the cross-polarization HV and VH that should not be interpreted as the actual antenna crosstalk. These results show that the PALSAR antenna is highly isolated (better than -35 dB), and diagonal antenna distortion matrices (with zero crosstalk terms) can be used for accurate calibration of PALSAR polarimetric data.

Verification of Polarimetric Calibration Method Including Faraday Rotation Compensation Using PALSAR Data

The spaceborne Phased Array L-band Synthetic Aperture Radar (PALSAR) needs polarimetric calibration in order for PALSAR data to be utilized for various applications such as geophysical analysis. In case of a PALSAR system using L-band, the Faraday rotation (FR) effect, which rotates the polarization plane of radio waves, becomes a problem when full-polarimetric observation data are used, such as target classification using polarization synthesis. Therefore, we need to estimate and remove both antenna distortion matrices and the FR effect. In this paper, we propose a polarimetric calibration method taking both channel imbalance and crosstalk of receiving and transmitting antennas and FR effect into consideration using two reference reflectors, namely, polarization preserving reflector and polarization rotating one. Then, we apply our calibration method to PALSAR data and derive antenna distortion matrices and FR angle simultaneously. Our calibration results show that the estimated antenna distortion matrices are almost equal to the calibration results from the Japan Aerospace Exploration Agency and that the estimated FR angle has a reasonable value.

Pulse shaping for cognitive ultra‐wideband communications

AbstractCognitive ultra‐wideband (C‐UWB) systems have recently received much attention because the huge bandwidth of ultra‐wideband (UWB) systems can better exploit the advantages of cognitive radio (CR) systems. Dynamic spectrum access (DSA) is a key technique in CR systems to implement dynamic spectrum change and can be easily implemented by changing the transmitted pulse shape in a C‐UWB communication system. In this paper, we propose an orthogonal expansion based pulse shaping method to implement DSA and to compensate for antenna distortion, which uses the orthogonal Hermite functions as the orthogonal basis. In order to eliminate the direct current (DC) component existing in even orthogonal Hermite functions and to reduce the computational complexity, two modified methods and a simplification procedure are also proposed. Our results indicate that the proposed orthogonal expansion based pulse shaping methods have a much lower computational complexity than the semi‐definite programming (SDP) method, while achieving a high power efficiency. Furthermore, we demonstrate that the distortion caused by the antenna effects can also be compensated during the pulse shaping process and a better signal‐to‐noise ratio (SNR) can thus be achieved. Therefore, the proposed method is very suitable for practical application in C‐UWB communications, in which the spectrum environment changes rapidly. Copyright © 2009 John Wiley & Sons, Ltd.

Ultrawideband Antenna Distortion Compensation

The radiation characteristics of ultrawideband (UWB) antennas vary with frequency, introducing directionally asymmetric bandwidth reduction and waveform dispersion. In this paper, we develop a simple technique to alleviate the distortion due to nonisotropically dispersive antennas, and use indoor channel measurements to verify its performance. The approach is based on multipath direction estimation and therefore involves antenna arrays. We show that antenna distortion can enhance sensor localization ambiguity and introduce errors in its estimate. Antenna compensation mitigates this effect, significantly improving the location estimation accuracy. We further demonstrate that antenna compensation helps reduce the small-scale fading artifacts that arise due to the antennas, thus reducing the channel spatial variability and delay spread. Our technique can also aid empirical channel characterization by providing antenna-independent propagation data.

Pulse shaping method to compensate for antenna distortion in ultra-wideband communications

In the ultra-wideband (UWB) communication systems, a critical spectral mask is released to restrict the allowable interference to other wireless devices by the Federal Communications Commission (FCC), and then some pulse shaping methods have been presented to fulfil the mask. However, most pulse shaping methods do not consider the antenna distortion which cannot be neglected in the UWB communication systems compared with the conventional systems. To this end, an orthogonal wavelet based pulse shaping method is proposed in this paper to integrate compensation of antenna distortion into pulse shaping. Simulation results show that the novel pulse shaping method can be used to achieve compensation for antenna distortion, optimization of transmission power spectrum, and simplification of the algorithm, as well as simple implementation of the pulse generator.

Beyond the Berry–Robnik regime: a random matrix study of tunneling effects

We consider the energy spectra of quantum Hamilton systems whose classical dynamics is of mixed type, i.e. regular for some initial conditions in the classical phase space and chaotic for the complementary initial conditions. In the strict semiclassical limit when the effective Planck constant ℏeff is sufficiently small the Berry–Robnik (BR) statistics applies, while at larger values of ℏeff (or smaller energies) one sees deviations from BR due to localization and tunneling effects. We derive a two-level random matrix model, which describes these effects and can be treated analytically in a closed form. The coupling between the regular and chaotic levels due to tunneling is assumed to be Gaussian distributed. This two-level model describes most of the features of matrices of large dimensions (here N = 1000), which we treat numerically, and is predicted to apply in mixed type systems at low energies. The proposed analytical level spacing distribution function has two parameters, the BR parameter ρ, characterizing the classical phase space, and the coupling (antenna distortion or tunneling) parameter σ between states. Localization effects so far are not included in our analysis except in the special case where ρ can be replaced by some effective ρeff.

A Channel-Based Statistical Approach to Antenna Performance in UWB Communications

An analysis of the joint antenna-channel problem in ultrawideband communications is carried out in order to provide tools for the performance evaluation of antennas while taking into account the system architecture and the radio link scenarios. Owing to the stochastic character of channels and of antenna close environment, a statistical approach to the problem based on discrete channel models is favored. The distinction between gain and dispersion effects is highlighted, both in a nondirectional and in a fully directional channel model. It is shown that antenna distortion generally has a small effect, but for coherent pulse detection it provides an extra gain in dense multipath channels with respect to ideal antennas and low density channels

Transient radiation from an unloaded, finite dipole antenna in a borehole: Experimental and numerical results

Dipole antennas in boreholes are used for tomographic imaging or electromagnetic well logging. A cylindrically layered structure within the borehole will change the radiation characteristics of a dipole antenna. Our objective is to understand the effects of the borehole structure upon the impedance, waveform distortion, and directivity patterns of a dipole antenna. We use a finite-difference, time-domain (FDTD) technique to simulate borehole-antenna radiation, while the geometry of both the dipole and the borehole are modeled with a subgrid technique. The simulated input impedances are verified by experimental results. Both the water-filled and the air-filled boreholes distort the radiated wavefronts, waveforms, and resonant frequencies relative to the same characteristics of a dipole in homogeneous media. A water-filled borehole lowers the first resonant frequency, while an air-filled borehole raises it. At high frequencies, the antenna in the water-filled borehole exhibits radiation side lobes. The borehole effects for water- and air-filled boreholes differ and should not be neglected for borehole antenna design.

STATIC SHAPE CONTROL OF FORCE-INDUCED INFINITESIMAL DEFORMATIONS SUPERIMPOSED ON LARGE DEFORMATIONS OF THERMOELASTIC BODIES

The present paper is concerned with the geometrically nonlinear static theory of anisotropic thermoelastic solids and structures. We consider infinitesimal incremental deformations superimposed on a given state of possibly large strain, the latter being called the intermediate state. Our goal is to derive a distribution of incremental thermal actuation stresses, which, when applied to the intermediate state together with a given set of incremental body forces and surface tractions, give zero incremental displacements everywhere in the body under consideration. This problem belongs to the field of static shape control, a notion originally introduced by Haftka and Adelman, who developed a procedure for determining temperatures in control elements to minimize the infinitesimal distortion of a large space antenna from its original shape. The present paper is concerned with the extension of shape control to infinitesimal force-induced static distortions from a large pre-deformation. Referring to the intermediate configuration as the reference configuration, we show that, in order to compensate the incremental force-induced deformations everywhere within the body, the incremental thermal actuation stress tensor must be equal to any statically admissible incremental first-order Piola–Kirchhoff stress tensor, a relation that is derived under the assumption that the intermediate state is infinitesimally superstable. We also discuss under which conditions it is possible to work with an isotropic thermal actuation stress. Finally, we present a formulation for shape control of infinitesimal deflections superimposed on a state of possibly large deflections of a slender beam.

Improving radiation-pattern distortion of a patch antenna having a finite ground plane

This paper presents a very useful and yet simple method of improving the radiation-pattern distortion of a patch antenna having a finite ground plane. The improvement can be achieved by cutting out the edges of the finite ground plane. This produces a phase shift between the induced equivalent magnetic currents on the edges, thereby causing cancellation in the diffracted fields. We numerically and experimentally examined the effects for some typical patch antennas and confirmed that the ripples in the copolar E plane pattern could be eliminated by using this approach.

Calibration of a distorted towed array using a propagation operator

In this paper, a new method for array shape calibration is presented. This method can be applied to any antenna distortion, it does not require any a priori knowledge about the sources, and it is relatively simple to implement. A number of unknown remote point sources, propagating plane waves, are required to implement this method. An equal number of sensors having known relative positions are used as a geometric reference. The method relies on a propagation operator, called the propagator, which can be estimated from the cross spectral matrix of the received signals through a simple least-square process. The performances of the proposed method are illustrated through simulations by showing how good accuracy in source bearing estimation, by both the classical beamforming method and MUSIC, can be recovered when the array shape is estimated.