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A planar monopole antenna is designed for ultra‐wideband applications. A novel feeding structure is proposed to improve the impedance bandwidth. Promising performances are achieved, including wide impedance bandwidth, flat gain, and omnidirectional radiation patterns. Two kinds of band‐notched structure extended from the proposed antenna are designed and verified. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 899–902, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24265

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For a compact range (CR), the near-field angular spectrum can be obtained by making an inverse Fourier transform of its aperture spatial near field. The characteristics of the aperture design have been carried by the aperture near-field angular spectrum. The direct wave and edge-diffracted waves from the aperture can be separated and distinguished clearly in the angular domain. Therefore, the CR performance can be evaluated and improved accordingly. In this paper, based on the aperture field convolution method and plane wave spectrum (PWS) theory, near-field angular spectrums for different apertures have been computed. The general criteria for the CR aperture design have been discussed. The selections of the whole aperture shape, the serration height, the serration base length, the serration number, and the serration shape (including isosceles and right-angled triangles) have been compared. At last, the near fields of an optimized serrated-edge aperture and an original circular aperture in different transverse planes have been computed and compared. The width and height of the apertures are all 30 wavelengths in free space. In order to suppress the sidelobes, a Chebyshev window with dB sidelobes has been adopted in the spatial-angular transform.Index Terms-Aperture antennas, compact range (CR), convolution, near fields, plane wave spectrum (PWS), spectrum analysis.

Based on swept frequency RCS measurement system, low density foam column and proper data processing procedure, the resonance curves of conducting spheres with RCS below −32.95 dBsm are achieved in a single reflector Compact Antenna Test Range (CATR), with the measurement errors less than 1.0 dB over most of the measurement frequencies. Nine spheres down to −49.01 dBsm are clearly imaged with Range-Doppler (R-D) method and pointwise vector background subtraction technique.