A wavelength scaled array of Doubly-Mirrored Balanced Antipodal Vivaldi Antennas (Dm-BAVAs)

Abstract

IntroductionA wideband phased array with an aperture made of two distinct element periodicities, which effectively thin the array, is presented. The topology is based on a "quantized" version of the wavelenght-scaled aperture of [1], and [2]. This thinning method was used in conjunction with the Doubly-Mirrored Balanced Antipodal Vivaldi Antenna (Dm-BAVA) elements to substantially reduce the element (and T/R module) count of the array, while retaining good performance over the frequency range of 2-8 GHz (4:1 bandwidth). The use of modular Dm-BAVA elements is particularly beneficial in wavelength-scaled arrays because they allow easy assembly and appear to confine truncation effects to fewer elements around the discontinuities. The proposed structure offers a practical way to reduce the weight, cost and fabrication of large, wideband arrays. The majority of the studies in this paper were carried out using the full-wave domain decomposition finite element method (DD-FEM) [4]. This method is capable of quantifying truncation effects, the mutual coupling between the two array sections, and the far-field performance. The Wavelength Scaled ConceptIn a typical wideband array, the large ratio between the highest and lowest frequencies in the operating band results in a large disparity in the aperture's electrical size. As a result, the beamwidth at the high-frequency end could be unnecessarily narrow. To minimize this effect, and to save T /R modules, a frequency scaled structure illuminates only part of the array at the high frequencies, and illuminates the entire array at the low frequencies, as shown in Figure 1. The size of this illuminated part of the array can be tailored to yield a consistent electrical size over a large bandwidth, and therefore a consistent beamwidth and gain. The upper bound on the frequency band is dictated by the grating lobe onset frequencywhere 0 is the direction of the main lobe, c is the speed of light, and d is the element spacing along the scan direction. For elements operating only at the low frequency band, the grating lobe frequency can be reduced, allowing the element spacing to be increased substantially, while still fully illuminating the aperture.This array structure, depicted in Figure 1, populates 1/4 of the aperture with dense (d = 2cm) elements covering the 2-8 GHz frequency band, and the remaining 3/4 of the aperture with larger (d = 4cm) elements covering the 2-4 GHz band. This causes the electrical size of the array to be the same at frequencies one octave apart, which ensures smaller beamwidth variation over the full array bandwidth. To maintain 978-1-4244-3647-7/09/$25.00 ©2009 IEEE a constant power density across the aperture when operating at the low-frequency band, the voltage excitation of the 2-8 GHz elements must one-half of the 2-4 GHz elements. The Dm-BAVA ElementsEach Dm-BAVA [3] element consists of a vertical three layer stripline structure, where the outer ground layers form a pair of flared fins (shorted with vias), while the inner conductor is extended to for...

Analysis of wavelength-scaled array architectures via domain decomposition techniques for finite arrays

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A wavelength-scaled ultra-wide bandwidth array

“…If successful, this design study may lead to more affordable ultra-wide bandwidth arrays. In a related study, the University of Massachusetts, Amherst has been applying the concepts of wavelength-scaled array design to balanced-antipodal Vivaldi antennas [4]. This work is sponsored by the Office of Naval Research.…”