Log-periodic Array Research Articles

A novel method for RCS reduction of the printed log-periodic dipole array

This paper devises a printed log-periodic Koch-dipole array (LPKDA) with low radar cross section (RCS) and proposes a novel wideband radar absorbing materials (RAM) with frequency selective surfaces. A wideband RAM is used as a ground plane of the LPKDA for in-band RCS reduction. The measurement result shows that the operating band is 6–12 GHz with a return loss higher than 10 dB and that the performance of radiation pattern of the antenna in the whole band is preserved. The RCS of the LPKDA with RAM can be reduced more than 28 dB at operating band by this method.

Periodicity of the input impedance of log-periodic array antennas

One way for an antenna to achieve an ultra-wideband (UWB) performance is to employ a log-periodic array (LPA), which usually involves many scaled elements cascaded one after another. If an LPA is infinite at both ends (infinitely small at one end and extended to infinitely large at the other end), it is obvious that the input impedance of the array is periodical over frequencies. However, for practical antennas, infinite LPAs have to be truncated. The purely periodical performance will not hold anymore. On the other hand, UWB LPA antennas are often very large in terms of the wavelength at the highest operating frequency, which makes numerical simulation very time consuming. The author presents a theoretical analysis of the periodicity of the input impedance of a general finite LPA. New periodicity formulas are verified by examples of the Eleven antenna - a folded dipole LPA, with simulated and measured data. By using the new periodicity formula, the input impedance of a large LPA antenna at higher frequencies can be predicted by its values at lower frequencies, which leads to an efficient calculation when a numerical simulation is employed, and helps to have an efficient design of large LPA antennas.

Optimization of Reflection Coefficient of Large Log-Periodic Array by Computing Only a Small Part of It

A new method is described in the paper to predict the reflection coefficient of a complete large log-periodic array (with large number of elements) from the computed performance of a small part of the array. The small part is referred to as the partial array. The method involves computing the embedded S-parameters between all the elements of this partial array and then using these S-parameters to predict the performance of the full array. As an example, the method has been applied to optimize the Eleven antenna for 2-13 GHz. The result of the optimization is that the reflection coefficient is improved significantly to be below -10 dB over the whole frequency band. The results have been verified by measurements.

Impedance Characteristics of Log Periodic Antenna

Log Periodic array Antenna is one of the most important and commercially used antennas for T.V. reception. It is used in VHF and UHF bands. Although the analysis of this antenna is reported in literature, the data of self impedance & mutual impedance is not fully available. But, this data is useful for the optimal design of the antenna. In view of this the array above is considered and the analysis is carried out in the present work. The computed data for Self-Impedance as a function of lengths of elements and frequency and the Mutual Impedance as a function of spacings of elements is presented.

On Conditions for Constant Radiation Characteristics for Log-Periodic Array Antennas

Wide frequency band antenna systems are required for many now and future applications, such as in radio astronomy and ultrawideband (UWB) technology. Constant radiation characteristics over a decade bandwidth are required for some of wide band applications, for example, feeds for reflector antennas in radio telescope. The log-periodic array antenna is one of the technologies for wideband antennas. In the present paper, an analysis on condition for constant radiation characteristics over wide bandwidth for a log-periodic array antenna is presented. From this condition, a guide rule for designing a wideband log-periodic array antenna is obtained. The Eleven antenna, a decade bandwidth log-periodic array antenna, is selected to illustrate the condition and verify the analysis in the paper.

Frequency reconfigurable log periodic patch array

A novel reconfigurable low profile log periodic patch array is presented. The patches are fed with a modulated meander line through aperture slots. A wideband mode from 7-10-GHz and three selected narrow band modes at 7.1, 8.2, and 9.4-GHz are demonstrated. The wideband to narrow band reconfiguration is realised by bridging the slot aperture, effectively deactivating the corresponding radiating element. Potentially the proposed method offers a very fine control of a narrow passband. Measured and simulated results with very good agreement are presented, thus verifying the proposed concept.

A Single-Layer Ultrawideband Microstrip Antenna

A single-layer microstrip antenna for ultrawideband (UWB) applications, in which an array of rectangular microstrip patches was arranged in the log-periodic way and proximity-coupled to the microstrip feeding line, is presented. In order to reduce the number of microstrip patches in the UWB log-periodic arrays, a large scale factor k = 1.1 was firstly reported and proved to be highly effective. Furthermore, instead of using an absorbing terminal loading, a novel loss-free compensating stub was proposed. Detailed parameters study was also presented for better understanding of the proposed antennas. The impedance bandwidth (measured VSWR < 2.5) of an example antenna with only 11 elements is from 2.26-6.85 GHz with a ratio of about 3.03:1. Both numerical and experimental results show that the proposed antenna has stable directional radiation patterns, very low-profile and low fabrication cost, which are suitable for various broadband applications.

Impedance matrix of a folded dipole pair under eleven configuration

A new decade wideband antenna, the Eleven antenna, has been developed during the last years. The basic configuration of Eleven antenna is two parallel dipoles separated by half wavelength above the ground plane, which is referred to as the eleven configuration. In order to cascade the dipoles in log-periodic array for obtaining wideband performance, folded dipoles are often used. The input impedance of shorted folded dipole in free space has been analysed by using two-mode method: a transmission line mode and an antenna mode. In the present study, the impedance matrix of a pair of folded dipoles as a two-port network under the eleven configuration will be analysed by including the mutual coupling among elements of folded dipoles into the two-mode method. As veri. cation, an Eleven antenna with one pair of folded dipoles has been analysed by the present method, modelled in a commercial software - CST MS and manufactured. The results by using the present method agree well with the measured and simulated one.

DESIGN AND SIMULATION OF CIRCULAR ARRAYS OF TRAPEZOIDAL-TOOTH LOG-PERIODIC ANTENNAS VIA GENETIC OPTIMIZATION

Circular arrays of log-periodic (LP) antennas are designed and their operational properties are investigated in a sophisticated simulation environment that is based on the recent advances in computational electromagnetics. Due to the complicated structures of the trapezoidal-tooth array elements and the overall array configuration, their analytical treatments are prohibitively difficult. Therefore, the simulation results presented in this paper are essential for their analysis and design. We present the design of a threeelement LP array showing broadband characteristics. The directive gain is stabilized in the operation band using optimization by genetic algorithms. We demonstrate that the optimization procedure can also be used to provide beam-steering ability to LP arrays.

Modeling and synthesis of circular‐sectoral arrays of log‐periodic antennas using multilevel fast multipole algorithm and genetic algorithms

Circular‐sectoral arrays of log‐periodic (LP) antennas are presented for frequency‐independent operation and beam‐steering capability. Specifically, nonplanar trapezoidal tooth LP antennas are considered in a circular array configuration, where closely spaced antennas occupy a sector of the circle. Electromagnetic interactions of the array elements, each of which is a complicated LP antenna structure, are rigorously computed with the multilevel fast multipole algorithm (MLFMA). Genetic algorithms (GAs) are also employed in combination with MLFMA for synthesis and design purposes. By optimizing the excitations of the array elements via GAs, beam‐steering ability is achieved in addition to the broadband (nearly frequency‐independent) characteristics of the designed arrays. Computational results are presented to demonstrate the important properties of LP arrays.

CPW-fed log-periodic dumb-bell slot antenna array

A coplanar waveguide (CPW) fed log-periodic dumb-bell slot antenna array is presented. Due to the log-periodic structure and dumb-bell slot, the proposed antenna operates as a frequency independent antenna. The antenna is printed on a substrate with a single metal layer and therefore is easily constructed. The measured return loss and radiation patterns are also included.

Quasi-Periodicity in global solar radio flux at metric wavelengths during Noise Storms

We present observational results from studying the quasi-periodicities in global solar radio flux during periods of enhanced noise storm activity, over durations of ∼ 4 hr a day (`intra-day' variations), observed at 77.5 MHz with the newly commissioned log-periodic array tracking system at the Gauribidanur Radio Observatory. Positional information on the storm centers was obtained with the radio imaging data from the Nan\c cay Radio Heliograph (NRH), while their active region counterparts on the photosphere (and the overlying chromosphere ) were located from the Hα images of the Big Bear Solar Observatory. The quasi-periodicity in flux was found to be 110 min, with the fluctuation in flux being 3(±1.5) solar flux units (s.f.u.). The results of such pulsations are interpreted qualitatively as evidence for coronal seismology.

Log-periodic slot antenna array

Wideband operation of a microstrip-fed slot antenna is achieved by arranging the slots in a log-periodic manner. A nine-element log-periodic microstrip slot antenna array operating in the X-band is designed using the finite-difference time-domain method (FDTD). The FDTD results are verified by measurements, and a bandwidth of about 33% is attained. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 24–27, 2000.

Pareto Genetic Algorithm Based Optimization of Log-Periodic Monopole Arrays Mounted On Realistic Platforms

A three-objective Pareto genetic algorithm is applied to the design of practical impedance-modulated feeds for log-periodic monopole arrays (LPMAs) mounted on arbitrary structures. Traditional design techniques do not permit the synthesis of feed structures for arrays on complex grounding structures. The multimodality of the search space of the feed-network design parameters precludes the use of standard gradient-search methods. The use of Pareto genetic algorithms allows for the study of tradeoffs between competing performance goals, and permits the generation of a database of feed designs that represent optimal performance tradeoffs from which one can select a posteriori. Numerical results are presented for the design of an LPMA mounted on a realistic wing.

NASA B-757 HIRF test series low power on-the-ground tests

The data acquisition phase of a program intended to provide data for the validation of computational, analytical and experimental techniques for the assessment of electromagnetic effects in commercial transports, for the checkout of instrumentation for following test programs, and for the support of protection engineering of airborne systems has been completed. The initial phase involved on-the-ground electromagnetic measurements. Measurements were made of the fields coupled into the aircraft interior and signals induced in select structures and equipment under controlled illumination by RF fields. A characterization of the ground was also performed to permit ground effects to be included in forthcoming computer modeling exercises. A series of fly-by experiments were conducted in early 1995 in which the NASA B-757 was flown in the vicinity of a Voice of America station (/spl sim/25 MHz), a fixed transmitter driving a log periodic array (172 MHz), and an ASRF radar at Wallops Island (430 MHz). In this paper, the overall test program is defined with particular attention to the on-the-ground portion. The test rationale, test layout, and samples of the data are described. Samples of some inferences from the data that will be useful in protection engineering and EM effects mitigation will also be presented.

Log-periodic array of dual-feed microstrip patch antennas

The dual-feed microstrip patch antenna is presented. This new radiator has broadband match and unidirectional azimuth pattern, desirable characteristics for use in broadband endfire arrays. Design, construction, and experimental results (realized gain, input impedance and far-field patterns) are given for a log-periodic array of dual-feed patches. An array with only ten elements has been demonstrated to operate at nearly constant gain over a 2:1 frequency band with a voltage standing-wave ratio (VSWR) of less than 2:1.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation Characteristics of Linear Log-Periodic Dipole Array Antennas Placed Near a Lossy Ground

The radiation properties of linear log-periodic dipole array antennas placed near a finite conductivity earth is investigated analytically. A method of moment solution is developed to solve the integral equation associated with the log periodic antenna array. The effect of finite ground conductivity is taken into account by using the appropriate Green's function which is derived from the well known Sommerfeld solution of the finite conductivity semi-infinite space. Piecewise sinusoidal pulse functions are employed as describing and testing functions. In computing the mutual impedance matrix elements, Sommerfeld type integrals are encountered which are computed by applying a numerically efficient technique. After computing the current distributions on the dipole elements of the log-periodic array the far field of the antenna is computed by employing the stationary phase integration technique. Several type log-periodic dipole arrays placed near a finite conductivity ground are computed. The effects of condu...

Microstrip log-periodic antenna array with endfire beam

Endfire action with a very wide-bandwidth, low-profile antenna array has not yet been achieved. After showing that a conventional microstrip log-periodic array cannot be successfully scanned from broadside to endfire, a new configuration involving quarter-wavelength shorted patches is described. First-order theory indicates that good endfire action should be possible, and this is confirmed by preliminary measurements on an array designed for a 25% bandwidth. Radiation pattern control is seen to be the most critical performance parameter.

Multioctave bandwidth log-periodic microstrip antenna array

The application of the log-periodic technique to the series-fed electromagnetically coupled overlaidpatch array allows antennas with flat conformal characteristics and wide bandwidths to be obtained. A k-β analysis of this and other microstrip array types indicate that the microstrip patch is not an optimum element for log-periodic arrays and that direct connection will result in arrays having a limited bandwidth. The addition of series capacitance to the patch equivalent circuit, implemented by electromagnetic coupling, allows an optimum to be approached. Log-periodic overlaid patch array design and measured results for an array with a 4:1 bandwidth are presented. These, together with a transmission-line analysis, indicate the array-design trade offs available and that the ultimate bandwidth is limited primarily by changes in the input return loss and radiation pattern due to the use of uniform thickness substrates.

Log-periodic flat short-circuited dipole array with a squinted beam

A new class of microstrip travelling wave antenna of large bandwidth is described. The log-periodic array is composed of flat short-circuited half dipoles acting at quarter-wave resonance and fed in series by means of a high characteristic impedance microstrip line. A model has been constructed and tested. A large squinted main beam is obtained between 0.75 and 4.5 GHz. The constant experimental radioelectric properties are in good agreement with the theoretical predictions.