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.
Shaping of flat-topped element patterns in a planar array of circular waveguides using a multilayered disk structure. I. Theory and numerical modeling
An infinite planar array of stepped circular waveguides radiating through a multilayered disk structure, which is arranged above the waveguide apertures in order to shape the flat-topped element patterns, is analyzed. The analysis is based on modal representations for the fields in the partial regions and for the currents on the disks with subsequent application of the mode-matching method and Galerkin's method for determining the modal coefficients used in the calculation of the array characteristics. The application of the algorithm is demonstrated by an array design that provides flat-topped element patterns of /spl plusmn/20/spl deg/ width in the main planes within a 5.6% frequency band. Outside the indicated band, the disk structure can cause sharp dips in the element patterns at the broadside, and some features of this effect are discussed.
The relation between the clay content and certain physical properties of a soil
A simple experimental method has been described for measuring certain physical constants of soil, using small brass boxes into which soil passing a sieve of 100 meshes to the inch has been packed by hand. The quantities determined are: (1) The weight of unit volume (100 c.c.s.) of air-dry soil, or the apparent specific gravity. (2) Amount of water taken up by unit weight of soil. (3) Pore space. (4) Specific gravity of the soil. (5) The volume expansion of unit volume (100 c.c.) of soil when saturated. The results for one soil only are given, and discussed, to illustrate the method. With the co-operation of the Science Masters Association it is being applied to a number of soils by various schools. The particular soil used was obtained in six depths as follows: 0–6–12″, 12–18″, 18–24″, 2–3′, 3–4′, and the above constants were determined on each depth. It was shown that (1) and (4) varied inversely with the percentage of clay in the soil, while (2), (3), and (5) varied directly with the clay percentage. The effect on the constants of the larger quantities of organic, matter present in the top two layers of soil was, weight for weight, approximately equal to that of the clay, except in the volume expansion results where the effect if any was within experimental error. It is possible that the fraction fine silt II, whose upper limit of diameter is ·005 mm., has similar effects to the clay fraction.