Scan Blindness Research Articles

Elimination of scan blindness in microstrip scanning array antennas using defected ground structure

In this paper, applying DGS to a linear six-element microstrip scanning array antenna, the blindness angle is removed. The method of moments is utilized in analyzing the proposed structure. The technique uses the band-stop characteristics of microstrip line filters to block the surface waves and reduce the coupling between elements that causes the blindness angle.

Elimination of Scan Blindness in Phased Array Antennas Using a Grounded-Dielectric EBG Material

In printed phased arrays, scan blindness occurs when the propagation constant of a Floquet mode coincides with that of a mode supported by the homogeneous substrate, resulting in large input mismatch and in a propagating mode with complex propagation constant. In our study we analyze the possibility to replace a standard homogeneous dielectric substrate with a grounded dielectric EBG substrate to eliminate scan blindness. We present here the main idea for the design, the dispersion diagrams of a dielectric EBG material with metallic patches to show that there are no surface modes (waves guided by the structure with real propagation constant), and the active reflection coefficient and input impedance for various frequencies. Furthermore, at a chosen operating frequency the active reflection coefficient for the phased case indicates that there is no scan blindness effect

Scan Blindness Phenomenon in Conformal Finite Phased Arrays of Printed Dipoles

Scan blindness phenomenon for finite phased arrays of printed dipoles on material coated, electrically large circular cylinders is investigated. Effects on the scan blindness mechanism of several array and supporting structure parameters, including curvature effects, are observed and discussed. A full-wave solution, based on a hybrid method of moments/Green's function technique in the spatial domain, is used to achieve the aforementioned goals. Numerical results show that the curvature affects the surface waves and hence the mutual coupling between array elements. As a result, the array current distribution of arrays mounted on coated cylinders are considerably different compared to similar arrays on planar platforms. Therefore, finite phased arrays of printed dipoles on coated cylinders show different behavior in terms of scan blindness phenomenon compared to their planar counterparts. Furthermore, this phenomenon is completely different for axially and circumferentially oriented printed dipoles on coated cylinders suggesting that particular element types might be important for cylindrical arrays.

Modelling and design of a finite dual-polarised notch phased-array antenna

The authors present the modelling and design procedure for a finite dual-polarised notch phased-array antenna which has a triangular lattice to obtain a widescan ability in the azimuth and elevation planes. The array antenna has orthogonal linear polarisations for transmitting and receiving, and the triangular element grid is achieved by 45° rotation of a square grid of notch elements in egg-crate configuration. A numerical waveguide simulator for the H-plane scan is modelled to eliminate scan blindness in the H-plane. A numerical model for the finite dual-polarised notch array is built to investigate the convergence of the active-element pattern (AEP) and the effects of the grating lobe according to array size. To verify the numerical results, a wideband active phased-array system was fabricated which consists of a 10×12×2 notch array, 8×8 transmit/receive modules and beam-forming networks. The scan patterns measured by near-field measurement show good agreement with the converged AEP for the finite array model and have widescan performance in the azimuth and elevation planes.

High-frequency Green's function for a semi-infinite array of electric dipoles on an infinite grounded stratified dielectric slab: part III $phase-matched wave interactions and numerical results

The particular effects of phase matching in interactions between different wave species and interaction mechanisms pertaining to the asymptotic Green's function for a semi-infinite phased array of parallel dipoles on an infinite grounded stratified dielectric slab are addressed. The two previous parts have lead to a grouping of certain asymptotic terms, which provides physically appealing interpretations of interacting wave processes that involve slab-modulated propagating (radiating) Floquet waves (FW), slab-guided leaky waves (LW), evanescent (nonradiating) FWs and surface waves (SW), together with their associated conical edge-coupled wave constituents. Special attention is now given to the role, in these wave interaction functions,of the difference between the propagating wave numbers (i.e., the degree of phase matching) that characterizes any pair of propagating FWs and LWs, and evanescent FWs and SWs. Cutoff transitions of FWs from the evanescent to the propagating regime are described also in terms of a second wave interaction function, structured similarly to the first. In connection with applications, the interaction between SWs and evanescent FWs, as well as FW transitions from evanescent to propagating, are discussed from the perspective of scan blindness in actual arrays. Various numerical studies highlight the role of phase matching in different problem scenarios.

Scan impedance of RSW microstrip antennas in a finite array

Scan impedances of finite reduced surface wave (RSW) arrays are studied. Center element scan impedances of linear arrays and two-dimensional (2-D) square lattice arrays are calculated and compared with those of conventional microstrip arrays. Results show that compared with conventional microstrip arrays, broadside scan impedance of RSW arrays has less variation and converges much faster when the array size increases. Scan performance of the linear and 2-D square lattice RSW arrays are also studied. Results show that the RSW array can avoid the scan blindness (when the array spacing is greater than 0.5/spl lambda//sub 0/) and the scan impedance has much less variation than that of conventional microstrip array with the same array spacing. However, due to the size limitation of RSW elements, the grating lobes cannot be avoided. Hence, the scan region is limited to about 20/spl deg/ (with 0.75/spl lambda//sub 0/ array spacing). Compared with conventional microstrip arrays with 0.5/spl lambda//sub 0/ array spacing, the results show no favor to RSW arrays.

Scan Blindness Free Phased Array Design Using PBG Materials

Scan blindness occurs for phased arrays when propagation constants of Floquet modes (space harmonics) coincide with those of surface waves supported by the array structure. In this paper, we studied the possibility of using photonic band-gap (PBG) substrate to eliminate scan blindness. A specially designed printed PBG substrate can suppress surface wave propagation inside its bandgap range, therefore it can be used to eliminate scan blindness. In this paper, we presented a method of moments (MoM) analysis of the scan properties of dipole arrays on PBG substrates with ominidirectional bandgap(s). We found that scan blindness is completely eliminated. The elimination of scan blindness makes PBG materials very attractive in phased array design.

Elimination of scan blindness in phased array of microstrip patches using electromagnetic bandgap materials

Electromagnetic bandgap (EBG) material is applied in the design of a phased array of rectangular microstrip patches. The surface-waves could be suppressed by the frequency bandgap and, therefore, the scan blindness could be eliminated. A high-impedance surface is chosen as EBG structure, and the numerical simulation is performed by periodic Green's functions plus the moment method. Both the bandgap curve of the EBG structure and the scan characteristics of the phased arrays have been calculated. The elimination of scan blindness is observed.

Magneto optical technique for beam steering by ferrite based patch arrays

An improved technique is presented to scan a beam of a phased antenna array on a ferrite substrate through use of time delays instead of phase shifts provided by nonlinear transmission lines coupled to elements of the array. A coplanar transmission line loaded with a varactor diode when subjected to varied optical illumination offers bias dependent time delays to the elements of the arrays over a wide range of tunable operating frequencies at lower UHF without scan blindness effect. This method results in a broadband ferrite based phased antenna array with reduced weight, loss and complexity of the integrated system. This technique has proved to have a special application potential in case of beam steering by ferrite based microstrip antenna arrays at lower UHF (800 MHz-2 GHz).

Full and partial crosswalls between unit cells of endfire slotline arrays

Endfire slotline antenna arrays, also known as Vivaldi notch arrays, may be used to build broad-band phased arrays with wide scanning capabilities. However, scan blindnesses may render the phased array unusable over portions of its intended operating frequency range and scan volume. One such scan blindness occurs in the E-plane of single polarized arrays and can be predicted by a simple formula. By inserting full and partial crosswalls between unit cells of the array, this blindness can be moved to higher frequencies, moved toward endfire, or totally eliminated. Arrays with upper crosswalls exhibit another type of scan blindness. This scan blindness can he utilized to reduce far-out sidelobes of a limited-scan array.

A class of E-plane scan blindnesses in single-polarized arrays of tapered-slot antennas with a ground plane

A simple model has been postulated for predicting the existence and location of a class of E-plane scan blindnesses in single-polarized arrays of tapered-slot antennas. The blindnesses of interest occur in arrays that have H-plane element spacing greater than /spl lambda//sub 0//2. A simple dispersion relation is easily evaluated to obtain accurate estimates of the locations of scan blindnesses. The postulated model is not completely rigorous, but (i) it correctly models the dominant effects for this class of scan blindnesses, (ii) it has a simple physical interpretation, and (iii) the formula can be evaluated so easily that array designers can readily choose array parameters that prevent this type of blindness or they can determine if proposed or existing designs are likely to exhibit this scan blindness.

Improving the scan performance of probe-fed microstrip patch arrays on high dielectric constant substrates

This paper presents a thorough investigation into the use of E-plane parasitic elements to remove scan blindness in probe-fed microstrip patch phased arrays using a rigorous full-wave analysis. It is shown that the addition of an E-plane parasitic element in the unit cell of the array can enhance the impedance scanning range; however, the parasitic element must be resonating. As a consequence of this, the method of scan blindness removal is only suited to microstrip patch arrays mounted on high dielectric constant material. A novel configuration incorporating a varactor diode to reduce the significant reactive nature of the input impedance at large scan angles is introduced which further improves the scanning potential of the parasitic element array. A further modification to the unit cell is proposed which allows the array to operate over a broad frequency range. For all the configurations considered, comparisons of active reflection coefficient, scan impedance behavior, efficiency, and cross-polarization levels are presented. >

Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described. The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas. Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method. Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays. Catastrophic effects such as scan blindness are accurately predicted. A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented. >

Scan performance of infinite arrays of microstrip patch elements loaded with varactor diodes

The analysis and scanning characteristics of an infinite array of rectangular microstrip patches each loaded with a varactor diode is presented. The analysis is based on full-wave moment method theory and uses attachment modes to accurately model the current through the feed and the diode. The effect of the biased varactor diode on the scan performance is presented, and it is shown that the impedance mismatch caused by a scan blindness can be eliminated. Other characteristics are also given such as: the active element gain, the efficiency of each loaded microstrip element, and the level of cross polarization generated by the loading of the patch. The effect of the diode biasing level as well as the position of the diode on each radiating element on these scan characteristics is also considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Extension of the E-plane scanning range in large microstrip arrays by substrate modification

The effect of the substrate structure modification on the E-plane scanning performance in large microstrip arrays is studied with the aid of a two-dimensional model. The goal is to alleviate scan blindness effects. The finite-element method of lines is used to solve the electromagnetic equations, thus demonstrating its applicability to open, periodic structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scanning characteristics of infinite arrays of printed antenna subarrays

The analysis and scanning characteristics of several different types of infinite arrays composed of subarrayed printed dipole and microstrip patch elements are presented. The analysis is based on full-wave moment method theory, and includes mutual coupling between elements in the subarray as well as between subarrays. The effect of subarraying on scan blindness is demonstrated for arrays using two-element subarrays of printed dipoles and microstrip patches. Results are also given for the amount of power radiated in grating lobes. The effect of a subarray composed of one driven element and one parasitic element, and the use of a four-element synchronous subarray of microstrip patches to generate circular polarization are also considered. Data are given for impedance mismatch, power radiated into grating lobes, and the axial ratio; both square and rectangular patches area considered. Results are also shown for an infinite array of seven-element hexagonal subarrays of printed dipoles, and it is found that the large spacing between subarrays leads to a limited scan range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Antenna designer's notebook-approximate location of scan-blindness angle in printed phased arrays

An approximate equation for the computation of scan blindness in the E-plane of a printed phased array is given. The scan blindness occurs before the onset of the grating lobe, requiring the recalculation of the element spacing to keep the scan blindness out of the required scanned area. As an example, the case of an infinite array of printed radiators designed for a maximum scan angle of 30 degrees in the E-plane and a maximum scan angle of 45 degrees in the H-plane is considered. >

Performance of an infinite array of monopoles in a grounded dielectric slab

A full-wave solution is presented for the problem of an infinite array of vertical monopoles embedded in a grounded dielectric sheet. Calculated results are compared with experimental data from waveguide simulators for er = 1 (air) and er = 2.5 (acrylic) cases. Scan blindness is observed for the dielectric loaded case, and a grating lobe diagram augmented with surface wave circles is used to explain this phenomenon.

Nonreciprocity and scan blindness in phased arrays using balanced-fed radiators

It is shown that scanning an array of balanced wire or patch type radiators in their <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> -plane can destroy the radiators' dual probe symmetry. This loss of symmetry can cause the radiator's unit cell "scattering matrix" to be nonreciprocal, where in this scattering matrix each of the radiator's dual probes is now considered as a separate input port. This breaking of radiator symmetry can result in scan blindness when the radiator is fed by a reactive power divider balun. This effect is illustrated by a numerical example using balanced-fed patch radiators.

Analysis of finite phased arrays of printed dipoles

The problem of a finite array of printed dipoles is treated, and results are presented in the form of reflection coefficient magnitudes, element patterns, and efficiency (based on power lost to surface waves). Various sized arrays are considered, and are compared with infinite array solutions. The excitation of surface waves is discussed in relation to the scan blindness phenomenon and the transition to an infinite array. Techniques for computational efficiency are also presented.