A parameter study of Vivaldi notch-antenna arrays demonstrates that the wide-band performance of these antennas can be improved systematically. Stripline-fed Vivaldi antennas are comprised of: (1) a stripline-to-slotline transition; (2) a stripline stub and a slotline cavity; and (3) a tapered slot. The impedances of the slotline cavity and the tapered slot radiator combine at the transition to yield an equivalent series impedance on the feedline. The stripline stub can be represented by a series reactance. The resistance and reactance of the antenna impedance yield insights into the effects of various design parameters. In particular, it is found that the minimum operating frequency can be lowered primarily by increasing the antenna resistance through a change of design parameters. However, beyond a limit for each design parameter, the in-band performance begins to deteriorate. Plots of antenna impedance versus frequency for several parameter variations have been obtained by using a full wave method of moments analysis of infinite arrays. These plots provide a means for designers to systematically improve array performance with bandwidths in excess of 6:1 having been achieved.

A parameter study of stripline-fed Vivaldi notch-antenna arrays

A near object detection (NOD) system includes a plurality of sensors, each of the sensors for providing detection coverage in a predetermined coverage zone and each of the sensors including a transmit antenna for transmitting a first RF signal, a receive antenna for receiving a second RF signal and means for sharing information between each of the plurality of sensors in the NOD system.

Near object detection system

In this letter, a modified antipodal Vivaldi antenna is presented. A novel tapered slot edge (TSE) structure is employed in this design. The proposed TSE has the capacity to extend the low-end bandwidth limitation and improve the radiation characteristics in the lower frequencies. A prototype of the modified antenna is fabricated and experimentally studied as well. The measured results show reasonable agreement with the simulated ones that validate the design procedure and confirm the benefits of the modification.

A Miniaturized Antipodal Vivaldi Antenna With Improved Radiation Characteristics

We discuss how forward scattering can he characterized in terms of an equivalent blockage width, and a relation between this and the bistatic scattering width is derived. Then, we show how cylinders such as struts and masts can be constructed to reduce their blockage widths. Thereby, when the cylinders are mounted in front of an antenna, the sidelobes and losses caused by the blockage will be reduced. For thin metal cylinders the blockage width reduction is obtained by giving its cross section an oblong shape and, in addition (for the TM case), by coating the outer metal surface with dielectric material to obtain a hard boundary condition. For thick cylinders, the reduced scattering is obtained by designing them as dielectric-filled parallel plate waveguides with the outer surfaces of the plates coated in the same way as for the thin struts. Dual-polarized performance is obtained in both cases by strip loading the outer surfaces. The performance of both the thin and the thick struts have limited frequency bandwidth. Both computed and measured results are presented; the computations being done with the moment method. The designs are based on the concept of soft and hard surfaces in electromagnetics, and the results can be regarded as a proof of the existence of hard surfaces for electromagnetic waves. The study considers reduction of forward scattering which also will give a reduction of the total integrated power of the scattered field over all directions-even backward.

Reduction of forward scattering from cylindrical objects using hard surfaces

A radar detection process includes computing a derivative of an FFT output signal to detect an object within a specified detection zone. In one embodiment, a zero crossing in the second derivative of the FFT output signal indicates the presence of an object. The range of the object is determined as a function of the frequency at which the zero crossing occurs. Also described is a detection table containing indicators of the presence or absence of an object within a respective radar beam and processing cycle. At least two such indicators are combined in order to detect the presence of an object within the detection zone.

Radar detection method and apparatus

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays Catastrophic effects such as scan blindness are accurately predicted A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented >

Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

In a symmetrical reflector antenna the feed system and its support struts block the aperture and thereby deteriorate the radiation characteristics. Simple design curves are presented for the efficiency reduction, the sidelobe levels, and the cross polarization caused by strut blockage. The results are obtained from an analytical study that includes the induced field ratio (IFR) of the struts. The most significant IFR values for struts with circular cross section are calculated and plotted in a way which makes them easy to use as design curves. The use of the design curves is demonstrated by an example. >

Losses, sidelobes, and cross polarization caused by feed-support struts in reflector antennas: design curves

The concepts of artificially hard and soft surfaces are interpreted in terms of the plane-wave reflection properties of the surfaces, in particular the reflection phase angles for two orthogonal polarizations. Numerical results are presented for two types of nearly hard surfaces. The first is a surface with longitudinally oriented and dielectrically filled corrugations. The second is a surface with longitudinally oriented strips on a grounded dielectric substrate. Neither of the two realizations is ideally hard in the strictest sense of the concept, but a good approximation can be achieved over a limited bandwidth. The numerical results demonstrate how various geometrical parameters affect the behavior of the surfaces. One important result is that the strip-loaded surface is the most favorable with respect to bandwidth. Another is that the strip-loaded surface can be made arbitrarily thin, though at the expense of bandwidth. >

J.A. Aas

Papers

Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

Losses, sidelobes, and cross polarization caused by feed-support struts in reflector antennas: design curves

Plane-wave reflection properties of two artificially hard surfaces