A Wide Scanning Array of Connected Bowtie Antennas Suitable for Integration in Composite Sandwich Structures With Monte-Carlo Tolerance Analysis

A low-profile and wide-scan phased-array antenna of connected cross-bowtie elements is proposed. The design goals and considerations are based on the applications requiring the integration of a large array antenna with composite sandwich structures, such as antennas on aircraft. In a very large array environment (modelled approximately as an infinite array), the main beam of the proposed antenna can be steered up to +/- 75 degrees at azimuth and +/- 15 degrees at elevation over bandwidths of 10% and 25% with active reflection coefficients below -10 dB and -5 dB, respectively. A Monte Carlo analysis of critical manufacturing and alignment tolerances shows the desired performance is achieved with the cumulative distribution probability over 80% under the uniformly distributed random combinations of the tolerances. Experimental results of a 7 x 7 element array prototype agree well with the simulations of this small-scale array case. The experiments show that this small-scale prototype is capable of steering the beam within the range of [-60 degrees, 60 degrees] at azimuth and [-15 degrees, 15 degrees] at elevation with the predicted performance satisfying the targeted application requirements and mechanical constraints. The achieved combination of the wide beam steering performance, relatively low antenna profile, and suitability of its feeding structure for sandwiched electro-mechanical integration makes this design unique with respect to the previously published results

A Wide Coverage S-Band Array with Dual Polarized Connected Bowtie Antenna Elements

A low profile dual-polarized bowtie antenna element is studied for an S-band (3 GHz) wide-scan application in a large-scale (nearly an infinitely large) uniformly excited phased array. The study shows that the array with such elements, when connected, is capable of scanning up to \ub175\ub0 at E-plane and \ub115\ub0 at H-plane for horizontal and vertical polarizations respectively. The bandwidth of the infinite array with such elements across these scan angles is 10% and 25% for the active reflection coefficient of −10 dB and −5 dB respectively

Load-Carrying Capacity of Steel Girders and Panels with Thin-Walled Trapezoidally Corrugated Webs

This thesis concerns the load-carrying capacity of steel girders and panels with thin-walled trapezoidally corrugated webs. Computer-based numerical methods are used as a tool and emphasis is placed on various parametric studies, covering geometric parameters, initial imperfections, material strain-hardening models, loading types and loading positions, and so forth. Trapezoidally corrugated steel panels are first considered. A B3-spline finite strip method is formulated and implemented for the analysis of elastic buckling of such panels. Various numerical experiments are made and compared with available laboratory tests. Geometric parameters with which a panel is able to achieve the highest elastic buckling load are identified. Simplified formul and interaction curves for predicting the elastic buckling load of such panels under shear, compression and combined loadings, are proposed. Steel girders with thin-walled trapezoidally corrugated webs are then considered. A non-linear finite element method is applied for the investigation of the load-carrying capacity and the buckling and post-buckling behaviour. Effects of large deflection and material non-linearity are taken into account. Material models of von Mises, either without strain-hardening (elastic-perfectly plastic) or with strain-hardening obeying Ramberg-Osgood\u27s equation, are assumed. In order to establish suitable non-linear finite element models for the analysis of girders with variable geometric parameters, several series of laboratory tests are numerically simulated up to an advanced post-buckling range. With those established non-linear finite element models a rather comprehensive parametric study is carried out. Based on numerical results, empirical formul that were proposed earlier for estimating the load-carrying capacity are examined. An improved empirical formula for predicting the ultimate strength of steel girders under patch loading is proposed. Suggestions for an optimal design of steel girders in shear and under patch loading are given

Load-Carrying Capacity of Steel Girders and Panels with Thin-Walled Trapezoidally Corrugated Webs

This thesis concerns the load-carrying capacity of steel girders and panels with thin-walled trapezoidally corrugated webs. Computer-based numerical methods are used as a tool and emphasis is placed on various parametric studies, covering geometric parameters, initial imperfections, material strain-hardening models, loading types and loading positions, and so forth.<p /> Trapezoidally corrugated steel panels are first considered. A B3-spline finite strip method is formulated and implemented for the analysis of elastic buckling of such panels. Various numerical experiments are made and compared with available laboratory tests. Geometric parameters with which a panel is able to achieve the highest elastic buckling load are identified. Simplified formul and interaction curves for predicting the elastic buckling load of such panels under shear, compression and combined loadings, are proposed.<p /> Steel girders with thin-walled trapezoidally corrugated webs are then considered. A non-linear finite element method is applied for the investigation of the load-carrying capacity and the buckling and post-buckling behaviour. Effects of large deflection and material non-linearity are taken into account. Material models of von Mises, either without strain-hardening (elastic-perfectly plastic) or with strain-hardening obeying Ramberg-Osgood's equation, are assumed. In order to establish suitable non-linear finite element models for the analysis of girders with variable geometric parameters, several series of laboratory tests are numerically simulated up to an advanced post-buckling range. With those established non-linear finite element models a rather comprehensive parametric study is carried out. Based on numerical results, empirical formul that were proposed earlier for estimating the load-carrying capacity are examined. An improved empirical formula for predicting the ultimate strength of steel girders under patch loading is proposed. Suggestions for an optimal design of steel girders in shear and under patch loading are given

SMART SKIN FOR AEW AIRCRAFT

A multifunctional fuselage structure has been developed. It provides the structural integrity necessary for smaller aircraft and permits the transmission of high-power microwave radiation characteristics for long-range surveillance radars. In particular, the solution permits a straightforward integration and allows for a curvature that improves buckling performance. A 700 mm 7 700 mm fuselage demonstrator was manufactured to verify its performance via measurements. The demonstrator exhibits good antenna performance (good RF coupling and good radiation beam shape) as well as good stiffness and load-carrying capability. It also performed well in vibration tests showing low dynamic response which is useful in dynamic environments

Edge Truncation Effects in a Wide-Scan Phased Array of Connected Bowtie Antenna Elements

Edge truncation effects are critical when designing a phased array, as these can lead to the variation of the active antenna impedance and radiation pattern between individual array elements. This paper investigates edge truncation effects in an array of connected Bowtie antenna elements that has been initially designed through an infinite array approach. This design represents a novel implementation of the connected-array concept that offers a wide-scan performance with up to \ub1 80 degrees scan range in the E-plane (in the infinite array). The goal of this study is to estimate the minimum size of a realistic finite array of such connected Bowtie antennas

Integration of Airborne Early Warning Radar Platforms on Aircraft

The need for a long-range and complete Air Picture has long since motivated the presence of airborne early warning (AEW) radar platforms. Later developments, such as stealth and advancing threats at low altitudes or hypersonic speeds have nothing but reinforce the need for increased-performance AEW. However, the high costs for the platform, integration, and operations restrict the number of platforms to a point where these high-value assets become sensitive to preemptive actions by an adversary. Therefore, SAAB has within the NFFP7 framework launched a series of studies aiming at smaller, adapted, and cost-efficient unmanned AEW platforms with extreme endurance. Thus, the aerodynamic performance of the carrier plus radar must be optimized, which implies that the projected area of the radar must be minimized. In this project, we study the possibility of integrating the antenna layer in the fuselage structure of the aircraft, thus gaining (i) body width and (ii) a more optimal wet geometry

A Wide-Scanning Array Antenna of Connected Vertical Bowtie Elements Structurally Integrated Within an Aircraft Fuselage

A low-profile, wide-scanning phased-array antenna of vertical bowtie elements fully integrated with a structurally efficient radome and ribs of an aircraft fuselage is proposed in this article. The array is designed to simultaneously fulfil the electrical requirements of an airborne antenna sensor and the mechanical requirements of a load-carrying aircraft fuselage. The array antenna is capable of steering the beam up to\ua0\ub180 degrees in the azimuth plane over a 20% bandwidth (2.4–3 GHz) with the active reflection coefficient (\ua0Γact\ua0) below −10 dB in an infinite array environment. Experimental results of a\ua016 716\ua0element array demonstrator agree well with the simulation results. The\ua016 716\ua0array antenna is capable of steering the beam up to\ua0\ub160 degrees and\ua0\ub175 degrees with the bandwidth of 20% and 10%, respectively, at\ua0Γact≤−10\ua0dB. The array antenna also achieved good stiffness and performed well in the vibration loads of commercial transport aircraft