Simulation of Post-ADC Digital Beam-Forming for Large Area Radar Receiver Arrays

Abstract

In order to provide instantaneous three-dimensional radar measurements spanning the entire vertical extent of the ionosphere, the planned EISCAT 3D incoherent scatter radar system includes multiple receive-only antenna arrays, situated at 90-280 km from the main transmit/receive site. These will employ band-pass sampling at ∼80 MHz, with the input signal spectrum contained in the 6 th Nyqvist zone. This paper presents simulations and methods used to investigate use of a post-ADC fractional-sample-delay (FSD) system necessary to perform true time-delay beamforming. To test the feasibility and limitations of the system an extensive simulation tool has been developed. The simulation system is implemented in matlab to provide cross-platform compatibility and can be applied to any similar system. Performance degrading aspects such as noise, jitter, bandwidth and resolution can be included in the simulations.The use of FIR-filters in the base-band of a band-pass sampled signal to apply true time-delay beam-forming is shown to be feasible.

A Measurement System for the Complex Far-Field of Physically Large Antenna Arrays Under Noisy Conditions Utilizing the Equivalent Electric Current Method

“…If the reference element is assumed to be unaffected by the environment the term will be known, with and given by (5). The only remaining unknowns are then the constants .…”

“…Assuming that there is a linear change of between time and , the state is related to the previous state with (18) where (19) where is the identity matrix and is the time between and . Further, the observations, at time can then be related to the state using (20) where is the noise and (21) where is given by (5). The Kalman filter uses the previous state and the observations to estimate the current state .…”

“…The maximum allowed timing error between any two antenna elements in the array has been found to be 160 ps [5]. The timing error is composed of jitter in the local oscillator and in the analog-to-digital converter (ADC), errors introduced in the clock distribution system, and changes in the phase of the far-field pattern of the antenna elements [6].…”

A Measurement System for the Position and Phase Errors of the Elements in an Antenna Array Subject to Mutual Coupling

“…Since the system will be multistatic and each antenna array will have narrow beams, it is crucial to have accurate control over the pointing direction and shape of the beam from the array. It has been found that the maximum acceptable delay error between any two antenna elements is 160 ps [6]. This limit includes all errors such as jitter in the local oscillator and in the analog-to-digital converter (ADC), errors introduced in the clock distribution system, changes in the phase of the far-field pattern of the antenna elements, and changes in the physical position of the antenna elements.…”