An efficient beamforming method using a combination of analog true time and digital delay

Abstract

In order to produce controllable deep zeroes in antenna patterns for signals with bandwidths comparable to antenna dimensions, beamforming by "true time delay" (TTD) has to be used. Normally, TTD is hard to achieve electrically for a big antenna array because it is hard to produce long delays without reducing the system bandwidth. The motivation. for this investigation is to see if, by combining digital and analog delays, a method can be found to produce long delays digitally and short delays with analog electric circuits without reducing system bandwidth. For all test cases, we found that a "fractional sample delay" (FSD) filter gives an improvement when taking the difference between two receiver channels in an antenna array. Our conclusion is therefore that this design can be used to improve the wideband performance for controllable zeroes in antenna patterns without using higher sample rates than normal; if the signal can be handled digitally, so can the time shifting. Depending on the physical dimensions of the sub antennas compared to the signal bandwidth, TTD may not even have to be used.