Grating lobe suppression in phased arrays composed of identical or similar subarrays
The grating lobe suppression methods for non-equidistant array antennas composed of identical or similar subarrays are proposed. Subarrays have equidistant rectangular or triangular grid. The grating lobes of an antenna array are reduced due to the irregular arrangement of subarrays. The following methods are considered: relative shift of neighbor subarrays, arranging gaps between subarrays, using different element spacing in different subarrays, rotation of subarrays, and combination of these methods. The methods provide suppression of the grating lobes from −2.6 dB to −11 dB as compared to equidistant arrays while side lobes envelop grows slightly.
Grating lobe reduction in phased arrays with regular subarray architecture
Phase weighting at the subarray level alone causes grating lobes (GLs) in the far field pattern. In this paper, a technique for reducing GLs in phased arrays with regular subarray architectures is proposed. Two measures are used in this method. They are: (1) integrating a power divider with phase difference among output ports for each subarray, which controls the each subarray pattern has a different beam direction; (2) switching the subarrays on or off during scanning. The optimization of the beam directions of subarrays is carried out by using particle swarm optimization (PSO) algorithm. Numerical results show that the proposed approach can successfully suppress GLs while maintain the similar beamwidth (BW) with the filled array.
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.