Beamwidth of phased arrays

A formula is developed for estimating the far-field beamwidth of an arbitrary narrow-beam phased array of identical isotropic elements at a single frequency. Equations are developed for the effects of errors in the estimated positions of the array elements.     

Nonlinearities in digital manifold phased arrays

In digital beamforming (DBF), the phase shifter is functionally replaced with a receiver and digital phase rotation. A Taylor series expansion of mixer nonlinearities is used to generate receiver intermodulation spectrums respective of the element position and the iso-Doppler wavefront directions of signal arrival across the array. The dominant intermodulation distortion at each element experiences linear phase errors across the array proportional to the harmonic number and the desired steering direction phase gradient. The array distortion signals are reduced relative to the desired signal by the array factor sidelobe isolation when desired collimation directions exceed a few beamwidths of scan off the array normal vector. The result of the nonlinear down conversion analysis is extended to inphase and quadrature imbalances and batch manufacturing tolerances for element receivers.     

Design of thinned phased arrays

A new method for determining the element position in a phased array is presented, only one array factor being calculated in each step. It is thereby possible to design larger arrays than can be designed using other methods.     

Voltage-controlled ferroelectric lens phased arrays

A new concept for phased arrays is proposed using a voltage-controlled ferroelectric lens. The ferroelectric lens concept uniquely incorporates bulk phase shifting-the array does not contain individual phase shifters-using ferroelectric material. This will reduce the number of phase shifters from (n×m) to (n+m), where n is the number of columns and m is the number of rows in a phased array. The number of phase shifter drivers and phase shifter controls is also significantly reduced by using row-column beam steering. Thus, the ferroelectric lens concept can potentially lead to low-cost phased arrays. This paper presents the ferroelectric lens concept, theoretical analysis and design, and experimental results. The results indicate that the ferroelectric lens concept is viable and sound. Various phased-array configurations using ferroelectric lens are included. A discussion on ferroelectric materials is included along with information on a US Department of Defense program to improve ferroelectric materials     

Practical failure compensation in active phased arrays

A practical failure compensation technique for active phased arrays is presented. It is suitable for real-time applications and is applicable to any distribution of the failures across the array. It is independent of the external signal environment and is capable of achieving substantial performance improvement across broad selectable angular sectors at the expense of some additional performance degradation in other less important sectors     

Feed region modes in dipole phased arrays

Feed region modes are derived for a class of dipole phased arrays. The dipole and its balun are a linearly polarized version of the perimeter array radar (PAR) antenna element, and are modeled in strip-line geometry. Knowledge of the feed region modes is essential in determining the influence of supports on the element scan performance, and should shed light on the formation of blind spots in dipole arrays. It is shown that for practical spacings, the balanced strip-line feed structure supports a propagating transverse magnetic (TM) mode in addition to two transverse electromagnetic (TEM) modes. The propagation constant of this mode is scan dependent, and under inappropriate conditions its cutoff occurs before the onset of the grating lobe. Pending further analysis, it is conjectured that this mode cutoff may cause blind spots which limit the array scan coverage.     

A flat-feed technique for phased arrays

A recently developed phased-array feed configuration offering significant advantages over the conventional space, corporate, and series feed techniques is described. This technique, referred to as the "flat feed," allows power division for monopulse sum and difference pattern illumination functions in a feed depth of less than a half-wavelength with low loss. The technique used to extract energy from the power divider, which consists in part of a radial transmission line, results, in its simplest configuration, in a circular grid of antenna elements. Relations governing the circular grid array geometry design are derived which relate the angular locations of attenuated grating lobes to the spacing between the rings of radiating elements. ExperimentalS-band hardware, built to prove the feed technique, is described. It includes a multimode launcher with measured coupling between circular wavegulde sum (TM_{01}) and difference (TE_{11}) modes of less than -37 dB; a seven-ring 1:195 radial power divider measured across a 10-percent band to have insertion loss of 0.1 dB and rms phase and amplitude deviations of less than3.5degand 0.47 dB; a 144-element array whose measured sum and difference beam radiation patterns are compared with calculated patterns for scan angles out to60degand whose sum port VSWR, measured across a 10-percent band, was under 1.8:1 with the array steered to broadside, and under 1.5:1 for other scan angles out to60deg.     

Infinite phased arrays of cavity-backed patches

An analysis of the radiation properties of infinite phased arrays of probe-fed circular microstrip patches backed by circular cavities using a rigorous Green's function/Galerkin's method is presented. The effect of substrate thickness on both scan volume and bandwidth performance is considered. Results are compared to those of infinite arrays of conventional probe-fed circular patch antennas     

Optical technique for broadbanding phased arrays

An optical method for broadbanding a phased array is considered. A narrow band feed-through aperture lens comprised of pick-up elements, radiating elements, and360degtype phase shifters is fed by a small feed array with an intervening passive lens. The lens has fixed frequency-sensitive properties. The feed array has variable time delay compensators which are selected in accordance with the desired scan angle in the far field. Using geometrical optics, design formulas are derived that relate bandwidth and scan angle to the minimum number of variable time delayers. To demonstrate performance, diffraction theory is used to calculate patterns, sidelobe levels, and efficiencies as a function of bandwidth and scan angle out to50degscan for several aperture sizes. In the worst cases, the optical system provides somewhat less gain than the comparable constrained subarray antenna; however, it always provides much better sidelobe levels.     

Optimum tilt for elevation-scanned phased arrays

It is shown that, subject to certain restrictions, the optimum tilt angle can be calculated as a function of only the highest beam elevation angle. The term optimum means the condition that the antenna gain at the horizon is maximum. The restrictions are that the antenna be operated outside the grating-lobe regime for all required scan angles and that scan angles greater than 60° off broadside by avoided to allow useful operation of the radar system (considering antenna impedance match, sidelobes, gain, and beam width). It is assumed that the antenna, in principle, can be impedance matched to any elevation angle, leaving the match at broadside as a special case, without particular advantages. The results indicate that for most practical requirements (high-beam elevation between 45° and 70 °) the optimum tilt angle should be around 20° to 30°     

Collimation of row-and-column steered phased arrays

An optically fed phased array must be provided with a means of collimation as well as with a beam steering function. The same phase shifters which are used to steer the beam can be used to collimate the beam. The use of row-and-column phase commands, while greatly simplifying the beam steering function over that required for commanding individual elements, precludes the attainment of exact collimation. A consequent phase error across the aperture results in a loss of antenna gain. For a given order of approximation to the collimation function, the minimization of the gain loss is a valid criterion for completely specifying all the parameters of the approximate collimation function. The gain loss incurred can then be determined. This paper develops the equations necessary to specify any order of approximation to the collimation function and the expression for the gain loss. Examples illustrate the differences between first- and second-order approximations and the effect of another parameter (f/D) on the gain loss of a typical antenna system.     

Quadruple ridge-loaded circular waveguide phased arrays

An equivalent circuit representation of quadruple ridge-loaded waveguide arrays is presented which is useful for synthesis and optimization of array performance. The validity of this technique has been verified by simulator measurement.     

Microstrip stacked strip element phased arrays

The frequency and scan performance of E-plane scanned, ideal probe-excited, broadband stacked strip element phased arrays are numerically investigated. Results indicate a 1.85:1 bandwidth over a 45° E-plane scan range. The results clarify the operative physical phenomena and lead to an iterative element synthesis in the array environment     

A method for removing blindness in phased arrays

In periodic phased arrays, due to the mutual coupling effect, there is a sharp dip in radiation at a certain scan angle, thus causing the so-called blindness phenomenon. It is shown that by using random (or other aperiodic) arrays, this adverse effect can be almost completely removed.     

Difference pattern synthesis in small planar phased arrays

A pattern synthesis technique for low sidelobe arbitrarily scanned difference beams in small planar phased arrays is presented. The approach is based on adaptive array theory and is the development of a technique used for radiation pattern synthesis in linear arrays. The method has been applied to measured element pattern data from a small planar array, which includes the effects of pattern corruption by mutual coupling. The successful synthesis of low sidelobe difference beams is demonstrated, with arbitrary difference plane and scan angle     

Grating-lobe suppression in phased arrays by subarray rotation

A method of suppressing grating lobes in a uniform planar array is presented. In this method, the array is divided into equal sub-arrays which are physically rotated with respect to each other by specified angles. As a result, the grating lobes, which remain at the same angular distance from the main beam, are multiplied in number by the number of subarrays while their amplitude is divided by the same number. Spacing within each subarray still remains uniform. Only at the subarray boundaries do different spacings occur.     

Finite phased arrays of rectangular microstrip patches

Finite phased arrays of rectangular microstrip patch antennas are analyzed. Reflection coefficient magnitudes, element patterns and efficiency (based on power lost to surface waves) are calculated for various sized arrays on substrates of practical interest and are compared with previous infinite array solutions. Measured element patterns and mutual coupling data for a small array are presented and compared with calculations.