Ultra wideband antenna array processing under spatial aliasing

摘要

Given a certain transmission frequency, Shannon spatial sampling limit de?nesan upper bound for the antenna element spacing. Beyond this bound, the exceededambiguity avoids correct estimation of the signal parameters (i.e., array manifoldcrossing). This spacing limit is inversely proportional to the frequency of transmis-sion. Therefore, to meet a wider spectral support, the element spacing should bedecreased. However, practical implementations of closely spaced elements result in adetrimental increase in electromagnetic mutual couplings among the sensors. Further-more, decreasing the spacing reduces the array angle resolution. In this dissertation,the problem of Direction of Arrival (DOA) estimation of broadband sources is ad-dressed when the element spacing of a Uniform Array Antenna (ULA) is inordinate.It is illustrated that one can resolve the aliasing ambiguity by utilizing the frequencydiversity of the broadband sources. An algorithm, based on Maximum LikelihoodEstimator (MLE), is proposed to estimate the transmitted data signal and the DOAof each source. In the sequel, a subspace-based algorithm is developed and the prob-lem of order estimation is discussed. The adopted signaling framework assumes asubband hopping transmission in order to resolve the problem of source associationsand system identi?cation. The proposed algorithms relax the stringent maximumelement-spacing constraint of the arrays pertinent to the upper-bound of frequencytransmission and suggest that, under some mild constraints, the element spacing can be conveniently increased. An approximate expression for the estimation error hasalso been developed to gauge the behavior of the proposed algorithms. Through con-?rmatory simulation, it is shown that the performance gain of the proposed setupis potentially signi?cant, speci?cally when the transmitters are closely spaced andunder low Signal to Noise Ratio (SNR), which makes it applicable to license-freecommunication.