Microwave phase comparators for large antenna arrays

Three instruments are described which are useful in equalizing path lengths in large antenna arrays. With each instrument the difference in length between two paths is measured directly, thereby avoiding many of the difficulties in measuring very long paths. A gas discharge tube, used as a modulated reflector, is placed at each of two antenna elements of an array. A null in the detected modulation occurs when the paths leading to the reflectors are equalized in length. The accuracy, limited by instability of the discharge tubes, is about3degin phase at a wavelength of 10 cm. With the most sensitive instrument, this accuracy is maintained when there is a two-way loss of as much as 100 dB between each reflector and the receiver terminal of the array.     

Arbitrary footprint patterns from planar arrays with complexexcitations

Elliott and Stern's (1990) method for synthesising shaped patterns using a circular or elliptical planar aperture or array with a complex excitation distribution is generalised to allow the synthesis of footprints of arbitrary shape. The use of complex excitations allows a given footprint to be synthesised using a smaller array than with real excitations. The procedure is illustrated by synthesising a square footprint using an array with a rectangular grid     

A voltage-matching method for feeding antenna arrays

A method for feeding antenna arrays is presented. Each element of the array is connected with transmission line sections. The first two sections are connected to a common point where the voltage from both sections is the same. The common point is connected with a new transmission line which is also doing the same with the third section. The procedure is continued until the last common point will be connected to a single source. A formulation for the antenna currents as a function of the frequency is also given. Some examples show the applicability of the method     

Synthesis of antenna arrays with shaped-beam patterns

A method for the synthesis of the amplitude-phase distribution of an antenna array, which uses embedded element patterns, is developed. In the general case, the method ensures formation of an arbitrary shaped-beam pattern. Features of the synthesis of shaped-beam patterns of antenna arrays with elliptical polarization and vector patterns are considered. The numerical analysis of the synthesis method, which is performed for an array of rectangular waveguides with vector patterns, confirms the efficiency of the proposed approach.     

A very large antenna for the 1.8 MHz band

This article describes a large 1.8 MHz antenna system that generates significantly more forward gain than that produced by commonly-used phased-vertical arrays. It provides coverage of all four azimuthal quadrants, along with a choice of four elevation angles, which may be selected at the turn of a switch     

A new method for obtaining antenna gain from backscattermeasurements

A method is presented for determining the gain of an antenna from analysis of backscatter data of the antenna. This approach is different from those which have been presented in the past because it accounts for the presence of resonances which can occur in the antenna during a backscatter measurement. In particular, this type of resonance appears in the backscatter measurement of symmetric reflector antennas. This technique is applied to determine the gain of a Ka-band Cassegrain antenna and an X-band prime focus-fed antenna     

Design of planar arrays to obtain efficient footprint patterns withan arbitrary footprint boundary

An antenna pattern synthesis technique is presented that permits the design of planar antenna arrays with footprint patterns of a specified boundary. This technique is applicable to planar arrays of a wide variety of grid structures and can produce patterns with controlled ripple and sidelobe levels. The approach involves two steps: the first consists in stretching the pure real-continuous aperture (an extension of circular Taylor distributions, developed by Elliott and Stern [1990]) into a distribution with a boundary that is inversely proportional to the flat-top beamwidth; the second is the minimization of a cost function (the square of the difference between the resulting power pattern and the desired one) using the Fletcher-Powell method. A square footprint, produced by a rectangular grid (obtained by sampling this distribution) with the corner elements appropriately removed, is presented as an illustration of the method     

Synthesis of antenna patterns of circular arc arrays

A new method is described for the synthesis of antenna patterns of circular are arrays. The method is based on the application of the simulated annealing technique to achieve the excitations of elements for a desired radiation pattern. Design specifications include sidelobe level, beamwidth, control of nulls, and other parameters such as the dynamic range of excitations     

A short design method for nonuniformly spaced antenna arrays

A design method is presented for symmetrical nonuniformly spaced linear arrays. Element positions are easily found if one element position is given. Instead of restricting the cosine functions in the array factor, a constraint is placed upon the arguments of the cosine functions. For an array of2Nelements, one obtainsN - 1equations inNunknowns, which can be solved sequentially instead of simultaneously. The array designs are not optimum, but the simplicity of this method will allow arrays to be designed quickly. These arrays could inturn be used as preliminary steps toward more rigorous studies.     

Rapid near-field antenna testing via arrays of modulated scatteringprobes

Key results are summarized of efforts to significantly reduce the near-field measurement time by utilizing one- or two-dimensional arrays of modulated scattering probes in lieu of the single probe ordinarily used in conventional near-field measurement techniques. Results of analytical, numerical, and experimental investigations show that the modulated-scattering technique (MST) using arrays of hundreds or even thousands of modulated scattering probes can be used to map the complex near-field of antennas or scatterers in a few seconds or minutes. The results also strongly indicate that classical (nonmodulated) receiving/transmitting arrays can be adapted for rapid near-field data collection. Major factors affecting the accuracy and speed of probe arrays for near-field measurement are delineated and discussed. Experimental results obtained using laboratory prototype MST systems are also presented and discussed     

MoM快速全波分析微带天线阵

微带天线及其阵列有着十分广泛的应用,对它们的精确分析也越来越引起人们的重视.首先采用混合位积分方程的MoM在空域建立全波分析模型,然后采用离散复镜像求解空域格林函数,从而提高了计算效率.三角形网格剖分计算目标也使得本文方法更适合分析复杂结构.同时,又将自适应的有理逼近和MoM结合,用于分析微带天线的宽频带特性和单站RCS,计算效率进一步提高.几个典型实例的数值结果表明了本文方法的有效性.     

New calibration method for large aerial arrays

A method for adjusting large multielement, aerial arrays is described. Calibrating signals are transmitted to the array elements in each direction in turn along a ring transmission line. With this procedure, gain and phase shift can be compared between elements without determining the length or attenuation of the calibration-signal feeder.     

Synthesis method of series-fed microstrip antenna arrays

A method for non-uniformly spaced series-fed rectangular microstrip array synthesis is given. By this approach the problem of patch array design turns out to be slot array synthesis. The resulting equivalent configuration gives the necessary parameters for the microstrip array geometry. Applications on Taylor, Bayliss and shaped-beam patterns show the validity of the method     

A semiblind method for transmit antenna arrays in CDMA systems

Using a transmit antenna array (TAA), the downlink beamforming is able to improve the performance of wireless communication systems. We propose a semiblind downlink beamforming method based on channel reciprocity of the wireless channels for code-division multiple-access (CDMA) systems equipped with TAA. In the proposed semiblind method, it is shown that the feedback delay can result in performance degradation under a time-varying fading channel environment. Hence, the performance of the semiblind method is satisfactory only when the maximum Doppler frequency is low or the feedback delay is not significant. To overcome this difficulty, the channel prediction is considered. Using the channel predictor, the semiblind method can provide a reasonable performance for a moderate maximum Doppler frequency (about a few hundred hertz). For theoretical performance analysis, upper, and lower bounds of the bit error probability under a fading channel environment are derived     

Beamforming and interference canceling with very large wideband arrays

Future radio telescopes are envisioned to be beamforming arrays containing hundreds to millions of elements distributed over thousands of km/sup 2/, with bandwidths that are 10% or more of the RF center frequency. It is awkward to analyze such systems using traditional narrowband beamforming theory. This paper presents a frequency-domain model that includes relevant features such as true time delay, distributed Doppler effects, and nonideal instrumental frequency response. Conventional beamforming - i.e., maximizing the gain in a certain direction subject to no other constraints - is analyzed in the context of the model. A simple method for suppressing interference in the beamformer output is also analyzed. In this method, a second beam is formed in the direction of the interference and subtracted from the output of the desired beam. Although the concept is sound, two problems are identified. First is the potential for partial or complete canceling of the desired source, along with the interference. The second problem is coloring of the noise spectrum, which may thwart the detection of weak spectral features. These problems are shown to be closely related to the array geometry, and some workarounds are suggested.     

Forming flat-topped element patterns in antenna arrays of two-mode waveguides

The results of numerical simulation are presented for an array of two-mode slot-coupled parallel plate waveguides excited by TEM modes through dominant mode waveguides and two-step junctions. It is shown that flat-topped element patterns formed by this simple structure are no worse than those of a known array with power dividers and directional couplers.<>     

Synthesis of antenna arrays radiation patterns on random geometry cylinders

Synthesis algorithm for gain-phase radiation patterns formed by linear electrical vibrators antenna arrays located on random geometry cylinders is discussed. The results of numerical calculations are presented.     

Optimization techniques for antenna arrays

Various techniques for optimizing the performance indices of antenna arrays are discussed. In particular, methods for maximizing array directivity and signal-to-noise power ratio are reviewed. These performance indices are expressible as a ratio of two Hermitian forms, which has a certain special property to enable the facile determination of both its maximum value and the conditions under which this maximum is attained. Special maximization procedures by excitation amplitude and phase adjustments, by spacing perturbation, by phase adjustments only, and by a coordinate transformation with constraints on the array pattern are examined. For wire antennas the method of moments using a subsectioning technique can be applied to obtain numerical answers which include mutual-coupling effects. Methods for considering large arrays and for the maximization of power gain are indicated.