A new design method is proposed for the power or shaped beam pattern synthesis problem of narrowband conformal arrays, where only the magnitude response is specified. The proposed method iteratively linearizes the non-convex power pattern function to obtain a convex subproblem in the design variables, which can be solved optimally using second-order cone programming (SOCP). In addition, a wide variety of magnitude constraints such as non-convex lower bound magnitude constraints can be incorporated. An efficient technique for determining a reasonably good initial guess to the problem is also proposed to further improve the reliability of the method. Computer simulations show that the initial guesses so obtained converge to satisfactory solutions while satisfying various prescribed magnitude constraints. Design results show that the performance of the proposed method is comparable to the optimal solution previously obtained for uniform linear arrays with isotropic elements. Moreover, we show by means of examples that the proposed method is also applicable to general non-convex power pattern synthesis problems involving arbitrary array geometries, arbitrary polarization characteristics and mutual coupling effect.

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Pattern Synthesis of Narrowband Conformal Arrays Using Iterative Second-Order Cone Programming

Despite their potential and promising advantages over classical planar arrays, conformal arrays also present many challenges to the antenna designer, including varying element normal due to curvature, serious cross-polarisation effect, limited operational bandwidth and so on. A uniform method for the element polarised pattern transformation of arbitrary 3D conformal arrays is presented based on Euler rotation. A space-time-polarisation filter structure is proposed for the pattern synthesis of conformal array, in which the finite impulse response (FIR) filters assigned to every element are used to acquire the frequency-invariant array pattern and the element polarisation diversity in array global coordinates is used to depress the cross-polarisation level. The optimal weight vector is obtained by alternating projection method. The alternating projection method is a powerful and attractive method for the pattern synthesis in that it requires relatively smaller amount of computation burden and a wide variety of desirable constraints can be freely implemented in a -visible- way, which is usually impossible for other optimisation method. The pattern synthesis method proposed has established a unified frame for the frequency-invariant and low cross-polarisation pattern synthesis of conformal array. Simulation results are provided to demonstrate the effectiveness and behaviour of the proposed method.

Frequency-invariant pattern synthesis of conformal array antenna with low cross-polarisation

The radiation characteristics of a wideband conformal end-fire antenna array mounted on a large conducting cylinder are investigated in this communication. By employing balanced Vivaldi antenna element, the antenna array has ultra-wide bandwidth, low cross-polarization levels, and wide 3 dB beam-width. It is shown that using a larger antenna height, shorter distance away from the edge of a hollow conducting cylinder, and bigger slant angle of antenna element leads to better end-fire radiation performances. Measured radiation patterns are compared with simulated values and a good agreement is observed. A radome-antenna system is also studied and it is found that the antenna has a larger beam-pointing angle in the H-plane owing to the electromagnetic waves reflected from a dielectric radome surface, while retaining its symmetric pattern in the E-plane. These findings may provide useful insights and guidelines for the design of large radome-antenna systems mounted a cylindrical platform.

A Wideband Conformal End-Fire Antenna Array Mounted on a Large Conducting Cylinder

This thesis studies several topics within the area of antennas and propagation from a signal processing perspective. However, theory and methods from electromagnetics and communications have also been used, contributing to an interdisciplinary character of the thesis. Several physical models are derived in the thesis that describes the wireless communications channel and several novel antennas. On the basis of these models, it is investigated how multiple antennas may be employed to increasing the capacity of future wireless communication systems. Furthermore, several aspects of using antenna arrays for finding the directions of arrival of electromagnetic waves, with applications in radar and acoustic sonar, are studied. An often neglected issue when employing several antennas is that the elements affect each other through mutual coupling. By deriving expressions for the mutual coupling, the achievable direction finding performance is analyzed for this case. It is found that if the coupling is known, the effects on direction finding are small and can even increase performance in some cases. Similar results are also obtained when examining the capacity of communication systems employing multiple closely spaced antennas at both the transmitter and receiver. To evaluate the performance of communication systems, a spatio-temporal channel model is proposed that is based on electromagnetic scattering and fundamental physics. By using a dyad notation and concepts from rough surface scattering, a compact formulation of the channel model is obtained. System models are then derived that employs multiple antennas at both the transmitter and receiver, so called Multi-Input Multi-Output (MIMO) systems. The polarization properties of the channel as well as those of the antennas are also included in the model, allowing for studies of different antenna arrangements. Two novel antenna solutions are proposed that can be used as diversity receivers in MIMO systems or when performing high-resolution direction finding. By exciting higher order modes of biconical or microstrip antennas, several directionally dependent radiation patterns are obtained. Different patterns can also be obtained by employing parasitic elements. It is found that these antennas, the multimode and switched parasitic antenna, offer performance comparable to that of an antenna array.

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Antennas and Propagation from a Signal Processing Perspective

The research in the paper puts forward a novel method for synthesizing conformal arrays and optimizing low cross-polarizations including the efiects of elements mutual coupling and mounted platform. Starting from the far-fleld superposition principle, an e-cient approach with active element pattern technique is proposed to calculate the far-fleld patterns. A coordinate transform is used to create polarization quantities, and a general process for the element polarized pattern transformation is proposed. The two numerical examples are proposed, and the desired sidelobe levels and low cross- polarizations are optimized. Numerical results indicate the proposed method is valid.

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An Arbitrary Conformal Array Pattern Synthesis Method That Include Mutual Coupling and Platform Effects

Discusses various uses of rotation matrices. The author has used rotation matrices to find the patterns with elements in a conformal array that requires one to rotate not only the direction, but the polarization directions, as well. A second useful thing to do with rotation matrices is to analytically rotate objects in space. In computer graphics, it may be neccessary to rotate the object. Many computer graphics texts have useful discussions of object rotations using rotation matrices. A third related use of rotation matrices is to understand antenna positioners. One can describe the rotations of a positioner by rotation matrices, and calculate the effects of rotation not only on the directing of the antenna, but on the polarization directions, as well.

T. Milligan

Papers

More applications of Euler rotation angles