A Low-Cost and Complexity Multibeam RF Transmit Beamformer for Wideband LFM Radar

This letter presents a simple and efficient multibeam radio-frequency (RF) beamformer for wideband linear frequency modulation waveform transmission. A time-varying weighting method instead of the true time delay technique is proposed. The process of beamforming weighting is implemented by quadrature modulators in the transmit (TX) path. As the RF operation frequency changes, the modulating phase-shift coefficients in baseband vary in time series. Since this beamformer is easy to perform at the element level, the simultaneous and independent TX multiple beamforming has become achievable. Moreover, the quality of the output signal and the process of wideband equalization among multiple channels are considered. The channel imbalances over a broad frequency range are compensated by time-varying predistortion coefficients. To validate the practical feasibility of this method, a prototype system with four-element antenna array is designed and tested. Single-beam and simultaneous two-beam patterns steering between ± 30° over 500 MHz at the center frequency 2.45 GHz have been demonstrated experimentally.