In practical implementations, physical-layer key generation (PKG) encounters the bottlenecks of imperfect channel reciprocity, nearby attack, and high temporal auto-correlation. Existing One-Band Multiple-Antenna Loop-bAck key generation (OB-MALA) schemes try to address these challenges through establishing bi-directional channels via echoing rotated received signals. However, we find that OB-MALA schemes can be vulnerable to a multiply-divide (MD) attack, as they echo the received signals through the same band with the pilot signals. To overcome this deficiency, we propose a new method, named Two-Band Multiple-Antenna Loop-bAck key generation (TB-MALA), which exploits two separate bands for pilot transmission and echo reception. The TB-MALA is proved to be robust to the imperfect channel reciprocity caused by radio frequency (RF) front-ends and can resist both the nearby attack and the MD attack. It also reduces the auto-correlation of effective channels with the help of a rotation matrix. The secret key rate of TB-MALA is analyzed and the closed-form of a lower bound is derived for the worst case. Numerical results demonstrate that the proposed TB-MALA protects against these attacks and achieves performance comparable to the ideal case with the perfect reciprocity of RF front-ends. It can thus be used to form a robust, fast, and secure key generation in a multiple-input and multiple-output (MIMO) system.