Major features and system-level design considerations for 3-D array apertures with hemispherical coverage are presented. First, an ideal 3-D dome-like hemispherical aperture is simulated using physical optics. Second, 3-D smooth aperture shape is approximated by several planar facets each presenting identical 2-D aperture arrays. Optimal division of hemispherical field of view into sectors of regards with similar maximum angular scan extent is discussed along with optimization of major electrical features of planar array facets, their number and total component count.
Subarray modules are introduced for face arrays used to create 3-D aperture antenna systems. Several representative topologies and major electrical features are reviewed for beam-forming networks of subarray modules. Major performance measures such as Gain to Temperature ratio (G/T) are discussed. Three key components are identified and their impact on G/T is studied using circuit models.
Some elements of the modern ground penetrating radar (GPR) determine its performance factor, resolution and depth of sounding. There are impulse transmitter, ultra-wide-band receiver as well as transmitting and receiver antennas. Improvement of the GPR's parameters is usually achieved by modernization of receiving circuits, antenna design, decreasing of input noises and using of complex computational algorithms for on-line and post-processing. As active element for impulse generation are widely used step recovery diodes (SRDs) or avalanche transistors. However such devices can not generate nanosecond pulses up to some hundreds volts on the antenna terminal. This work is devoted to application of drift step recovery didoes (DSRDs) in GPR transmitter design. Current drive circuit based on charge DSRD model has been computed and optimized. Investigation results for pulse generator characterized by peak power up to 5 kW and rise times as small as 2 nanosecond (ns) are reported. Application abilities of commercial power rectifier diodes in the DSRD mode are shown. Transmitter based on DSRD can operate with low impedance antennas, high repetition rate and efficiency.
This paper deals with the application of ultra-wide band time- domain subsurface radars, equipped with special signal processing techniques, to realize non-invasive image testing of the building walls' internal structure that are made with brick, stone, concrete, reinforced concrete and other construction materials. There are two normally associated problems, qualitative and quantitative, considered. Limitations and shortcomings of radar imaging, due to inherent physical features as well as signal processing improving the quality of radar images, are discussed. Actual field data are used to illustrate applications of subsurface radar for non- destructive testing of walls' internal regions.