The green low power networking potential of backscatter communication technology can be practically realized by efficiently using a multiantenna reader for tackling the hardware constraints of the underlying tags. We address this timely requirement by investigating the optimal transceiver designs for the multiantenna reader to maximize the minimum backscattered throughput among the single-antenna semi-passive tags. Novel analytical insights on the jointly-optimal precoding vector and detector matrix at the reader are also provided by exploring the asymptotically-optimal designs. Lastly, the numerical results corroborate the nontrivial analytical proposals and demonstrate a significant 47% increase in achievable common-backscattered-throughput among tags as compared to the relevant benchmarks.