  In this paper, we investigate a radio frequency (RF) lens-embedded massive
multiple-input multiple-output (MIMO) system and evaluate the system
performance of limited feedback by utilizing a technique for generating a
suitable codebook for the system. We fabricate an RF lens that operates on a 77
GHz (mmWave) band. Experimental results show a proper value of amplitude gain
and an appropriate focusing property. In addition, using a simple numerical
technique--beam propagation method (BPM)--we estimate the power profile of the
RF lens and verify its accordance with experimental results. We also design a
codebook--multi-variance codebook quantization (MVCQ)--for limited feedback by
considering the characteristics of the RF lens antenna for massive MIMO
systems. Numerical results confirm that the proposed system shows significant
performance enhancement over a conventional massive MIMO system without an RF
lens.
