Wideband beamspace adaptive array utilizing FIR fan filters for multibeam forming

Frequency invariant MVDR beamforming without filters and implementation using MIMO radar

“…It is to be noted that P , the number of weights to be adapted, is much less than the total number of sensors M × N and so it offers reduced complexity in adapting these weights in real time. Moreover, unlike [3], [8] and [9], the generation of the frequency invariant beams is achieved without tapped delayline filters. In [5], adaptive beamforming is also performed using the rectangular array without filters but it uses one weight per sensor.…”

“…Frequency invariant beamforming has been studied extensively because of the advantages it offers in terms of reduced complexity for adaptive beamforming [3], [8], [9], broadband DOA estimation and so forth [3], [11]. Generally frequency invariant beamforming needs filters at the sensor outputs to compensate for the frequency dependence of the beampattern.…”

A GSC employing two-dimensional frequency invariant filters

“…The resultant beamformer with such kind of coefficicnts will be frequency independent [41. IfH(ejn) is a lowpass filter [4], then signals from the directions around 0 will correspond to its passband. In this case, a main beam is formed pointing to the direction 0.…”

“…All these FIFs in the them to have a very low sidelobe level, which is different from thc beamspace processing method [4], where a low sidelobc level is required, resulting in a large dimcnsion of the FIFs and the requirement to increase the number of sensors. Moreover, in [4], the main dircction of a beam should ideally coincide with nulls (zero responses) of all other beams. As a result, the interfcrcncc cancellation capability is reduced comparing to the traditional GSC method.…”

“…To overcome this problem, several methods have been proposed, such as the use of adaptive pole-zero filters in [ l ] and subband adaptive methods [Z, 31. Another method is broadband beamspace adaptive arrays [4], where several frequency invariant beams are formed pointing to different directions by a fixed beamforming network with 0-7803-8545-4/04/$20.00 02004 IEEE 84 two-dimensional (2-D) filters; thereafter an adaptive filter is used to combine these beam outputs to form the desired output. Since both the number of beams and that of the selected beams are small, the total number of adaptive weights are greatly reduced compared to the tapped-delay line system.…”