A highly-integrated reconfigurable Ka-band receiver in a 90-nm CMOS technology is proposed for the applications of satellite wireless communications, remote sensing of atmospheric conditions, and detection of space debris. The proposed receiver can be reconfigured to support active-receiver and passivereceiver modes. At the active-detection mode, it works as a direct-conversion coherent receiver for highspeed and global-coverage satellite communications. Measured conversion gain of 45.2 dB, noise figure of 7.6 dB, and output 1-dB compression point of -6.8 dBm can be acquired at 35 GHz while only consuming 54.4 mW from a 1.2-V supply. As switched to the passive-detection mode, it can potentially operate as a noncoherent radiometer to sense atmospheric conditions which are employed to dynamically compensate the atmospheric attenuation to mitigate the fading effects. This enables the satellite communication systems to establish reliable links. Moreover, the proposed passive receiver can be utilized to detect the space debris. Collisions can be avoided and hence satellite lifetime can be enhanced. Experimental results show that the proposed receiver at the passive-detection mode exhibits voltage responsivity of 1.2 GV/W and noise equivalent power (NEP) of 2.1 aW/Hz 0.5 at 35 GHz. The power dissipation is only 49.6 mW from a supply voltage of 1.2 V. To the best of the authors' knowledge, the proposed receiver owns the highest responsivity and the lowest NEP at Ka-band reported thus far. It is also the first receiver capable of being reconfigured to support active-detection and passive-detection modes according to different application scenarios.INDEX TERMS Reconfigurable, Ka-band, CMOS, active receiver, passive receiver, satellite communications, radiometer, effect of fading, space debris.