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AGU: Radio Science

 

Keywords

  • digital beamforming
  • incoherent scatter radar
  • simulation

Index Terms

  • Radio Science: Ionospheric physics
  • Ionosphere: Instruments and techniques
  • Radio Science: Radar atmospheric physics
  • Radio Science: Instruments and techniques
Abstract
Cited By (0)
 

Abstract

RADIO SCIENCE, VOL. 45, RS3001, 12 PP., 2010
doi:10.1029/2008RS004124

Simulation of post-ADC digital beamforming for large aperture array radars

G. Johansson

CSEE, Luleå University of Technology, Luleå, Sweden

J. Borg

CSEE, Luleå University of Technology, Luleå, Sweden

J. Johansson

CSEE, Luleå University of Technology, Luleå, Sweden

M. Lundberg Nordenvaad

CSEE, Luleå University of Technology, Luleå, Sweden

G. Wannberg

Swedish Institute of Space Physics, Kiruna, Sweden

This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.

Received 20 December 2008; accepted 10 December 2009; published 5 May 2010.

Citation: Johansson, G., J. Borg, J. Johansson, M. Lundberg Nordenvaad, and G. Wannberg (2010), Simulation of post-ADC digital beamforming for large aperture array radars, Radio Sci., 45, RS3001, doi:10.1029/2008RS004124.

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