Ambiguity resolution in self-cohering arrays

Two approaches to resolving the phase ambiguity associated with phase multilateration of self-cohering antenna arrays are described and the probability of ambiguity error is derived for each approach. For the minimum least square error method an efficient computational technique is introduced which permits element position uncertainties as large as one wavelength in the presence of phase measurement errors in the order of one rad. The multiple frequency method permits element position uncertainties significantly larger than one wavelength, at some increase in bandwidth. The probability of ambiguity error is shown to be acceptably small if the root mean square (rms) phase measurement errors are in the order of 0.5 rad or smaller.     

Multi-beam synthesis with null constraints by phase control for antenna arrays of arbitrary geometry

A novel synthesis technique for antenna arrays of arbitrary geometry is proposed. Imposing equal excitation amplitudes and modifying only the excitation phases, the method is able to produce patterns endowed with multiple main lobes and nulls in assigned directions. The technique is quite simple and requires low CPU time     

Accurate DOA estimation using array antenna with arbitrary geometry

The so called universal steering vector (USV) whose locus is equivalent to the array element pattern is applied to the direction of arrival (DOA) estimation by multiple signal classification (MUSIC) algorithm. It is shown that if the USV which includes the effect of the mutual coupling between the array elements is used, the compensation for the received voltage to remove the effect of the mutual coupling is not required any more. The USV for array antennas with arbitrary geometry is derived and evaluated efficiently by using the method of moments (MoM) so that the DOA estimation can be performed accurately by using the array antenna with arbitrary geometry. Numerical examples of the DOA estimation by a dipole array antenna, and an antenna array composed of a monopole antenna and a planar inverted-F antenna (PIFA) mounted on a mobile handset are presented to demonstrate the effectiveness of the proposed method.     

Gain optimization for arbitrary antenna arrays subject to random fluctuations

A general procedure is formulated for the maximization of the expected directive gain for arbitrary antenna arrays whose excitation amplitudes and phases as well as element positions are subject to random errors. Correlations are allowed to exist between the random fluctuations, and the general formulation imposes no restrictions on either the magnitude or the probability distribution of the fluctuations. Numerical examples are given which illustrate the dependence of the expected gain, the main-beam radiation efficiency, the radiation pattern, and the optimum element excitations on the standard deviation and correlation distance of the parameter errors. It is shown that, in typical cases, the properly optimized array yields not only a higher directive gain and a higher mainbeam radiation efficiency but also a better radiation pattern than an array which is "optimized" under the assumption of no random errors.     

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.     

A generalized self-survey technique for self-cohering of large arrays

A technique is proposed for locating the elements of a flexible phased array sufficiently accurately to form high-quality beams. The technique requires beacon signal phase measurements and baseline measurements, but does not require the accurate beacon-location knowledge which is characteristic of radio navigation schemes. The effects of phase measurement errors and baseline measurement errors on array beam gain and pointing error are predicted and verified by experiments.     

Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

The effect of the mutual coupling between the array elements on the performance of the adaptive array antennas (AAA) is investigated when the actual received voltages which include the mutual coupling are directly used to estimate the weight vector based on the adaptive algorithm. The output signal-to-interference-noise ratio (SINR), the convergence of the adaptive algorithm and the synthesized pattern are evaluated to study the effect due to the existence of the mutual coupling. It is found that the mutual coupling affects the antenna adaptive gain, but does not affect the adaptive processing. It is also found that the mutual coupling does not always degrade the iterative convergence of the adaptive algorithm. It is proved that any invertible matrix for compensating the mutual coupling cannot improve the output SINR. It is also indicated that the radiation pattern can be correctly synthesized in the presence of the mutual coupling by introducing the universal steering vector (USV) whose element corresponds to the array element pattern.     

Optimum spatial processing in a noisy environment for arbitrary antenna arrays subject to random errors

A procedure is presented for the maximization of the expected signal-to-noise ratio improvement factor for arbitrary antenna arrays whose excitation amplitudes and phases, as well as element positions, are subject to random errors. In its general form, the formulation imposes no restrictions on either the probability distribution or the variance of the random errors. Correlations are allowed to exist between the random variations in array parameters, and the effect of system internal noise is considered. Computed results for a linear endfire array in a typical noise environment are given, illustrating the dependence of the signal-to-noise ratio improvement factor on the system internal noise; the system bandwidth; the amplitude, phase, and position errors; and the error correlation intervals. Typical expected power pattern functions are also plotted.     

Synthesis of linear antenna arrays

Synthesis of antenna arrays employing theL_{2}-norm as well as theL_{infty}-norm is discussed. The approximation in theL_{infty}-norm is obtained making use of Lawson's algorithm. A general iterative perturbation technique has been evolved for pattern synthesis for the case when the antenna currents alone are varied as web as for the case when both the antenna currents and the element positions are simultaneously varied. A few illustrative examples are given. The convergence of the iteration and the uniqueness of the solution are discussed.     

PA calibration in TDMA antenna arrays

The behavior of a 5.2-GHz transmit antenna array in time division multiple acess operation is investigated, where the power amplifiers are only switched on during the data bursts. Using monolithically integrated power amplifiers, two thermal time-constants are found, associated with gain and phase changes that alter the antenna pattern. In this letter, the correlation of these changes between multiple channels is experimentally studied to derive guidelines for the calibration of such an array. It is found that changes within the typical burst duration are well correlated and no time-dependent calibration is needed. Thermal changes linked to a second time-constant lead to a calibration error.     

Potential direction-finding accuracy of systems with antenna arrays configured as a set of an arbitrary number of rings

Configurations of antenna arrays for direction-finding systems in the form of a set of concentric circumferences are considered. An estimate of the potential accuracy of the measured bearing, which was obtained using the Cramer-Rao lower bound, is proposed. It is shown that in the case of antenna-feeder systems with antennas distributed uniformly over each circle, the potential accuracy is independent of the direction from which the received signal arrives.     

Effects of coupling accumulation in antenna arrays

Mutual coupling between antenna elements in a phased array causes array performance to vary with scan angle. Large impedance mismatch and radiation loss can occur in certain critical directions for which the steering phase advances match the antenna coupling delays. At these critical scan angles, many coupling contributions add inphase to produce a large impedance mismatch and minimum radiation from the array. Several different phased arrays have exhibited scanning "blind" regions that appear to be a consequence of coupling accumulation. A large, flat, homogeneous antenna array is analyzed, and a relationship is found between the critical scan angles and phase of the mutual coupling coefficients. Extensive measurements on arrays of horn antennas have shown radiation minima that correlate with coupling phase measurements and with theory.     

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.     

Periodic receiving broad-band antenna arrays

The principle of the periodic receiving antenna array composed of arbitrary antenna units has been developed. A generalization of the well-known principle of log-periodic antennas is presented and applied also to antenna units formed by the system of dipoles with active networks. This reveals the potentialities for the exploitation of this principle in the miniaturization of directional antenna systems.     

A new quasi-Yagi antenna for planar active antenna arrays

In this paper, a novel broadband planar antenna based on the classic Yagi-Uda dipole antenna is presented, and its usefulness as an array antenna is explored. This “quasi-Yagi” antenna is realized on a high dielectric-constant substrate, and is completely compatible with microstrip circuitry and solid-state devices. This antenna achieves a measured 48% frequency bandwidth for voltage standing-wave ratio <2, better than a 12-dB front-to-back ratio, smaller than -15 dB cross polarization, and 3-5-dBi absolute gain. Mutual coupling of the antenna in an array environment is investigated. Finally, three simple arrays are presented, demonstrating the usefulness of the antenna as an array element. This novel antenna should find wide application in wireless communication systems, power combining, phased arrays, and active arrays, as well as millimeter-wave imaging arrays     

一种对任意线阵天线的主波束赋形方法

基于自适应天线阵理论,给出了一种用于任意线阵天线的主波束赋形算法.该方法通过迭代获得一组最优权值,用来减小加权赋形方向图和期望方向图在主波束上的差别,同时将旁瓣电平降低到期望值.一些算例充分说明了这种算法的有效性.该算法可以有效的控制主波束方向、宽度、形状和旁瓣电平.     

Ray analysis of conformal antenna arrays

The aperture design of conformal arrays is predicated on the knowledge of the element patterns and coupling coefficients in a mutually coupled environment. For equispaced identical slits on a perfectly conducting cylinder, a previous analysis has utilized the modal theory of periodic structures to simplify the calculations. Modal procedures are rather difficult to apply when the array surface has a more general, though rotationally symmetric and separable, shape; they become practically inapplicable when the surface is nonseparable. These difficulties may be overcome by recourse to the geometrical theory of diffraction and utilization of surface rays whose properties are determined from an appropriately defined local environment on the array surface. Depending on the problem under consideration, the local environment may involve either the unperforated array surface or a surface with periodic loading. It is shown how the surface ray technique can be applied to the analysis of mutual coupling in full ring arrays and finite arrays on a circular cylinder, and in nonperiodic or almost periodic arrays on surfaces of variable curvature. For finite arrays, a theoretical model leading to a representation of finiteness effects in terms of multiple scattering of surface rays of the periodic array structure between the edge discontinuities is confirmed by independently calculated numerical results. Although the demonstrations in this paper are confined to two-dimensional geometries, the procedure is applicable also to three-dimensional configurations.     

Wavenumber support regions for arbitrary arrays

We set out a procedure for defining the region of wavenumber support relevant for maximum entropy spectral estimation of a noise field incident on a planar array. We consider first linear, nonequispaced arrays, and argue that the problem of defining a region of wavenumber support is only well-posed when either position uncertainty for the array elements is postulated, or phase uncertainty in the measurement of the signals at the array elements is postulated, or one acknowledges that a polar diagram that is almost periodic defines an aliasing frequency in virtually the same way as a polar diagram which is periodic. For planar arrays, the region of wavenumber support can be approximately circular but in general has to be defined with reference to the particular array.Work supported by Australian Department of Defence.