A method to detect people in multiple locations using a multiple-input and multiple-output (MIMO) frequency-modulated continuous wave (FMCW) radar system is proposed. A 2-D range-angle map is estimated by digital beamforming with virtual receiver arrays obtained via the operation of time-division multiplexing (TDM) MIMO radar. Phase variations due to human vital signs and movements allow the identification of people from stationary clutter in the range-angle map. To improve the sensitivity of phase-based human detection, a curve-length (CL) method that estimates the length of the I/Q signal trajectory is proposed. The proposed method can overcome the codomain limitation of a conventional method through its use of the standard deviation of phase variations. Measurements show that the method improves the signal-to-clutter ratio (SCR) by 10 dB compared with that when using the conventional approach.

A 28-GHz fully differential four-channel beamforming front-end IC with variable gain phase shifters (VGPSs) is presented, of which orthogonal phase and gain control is achieved in a single block using the proposed dual-vector synthesis technique. This greatly reduces chip size, power consumption, and calibration complexity. The antenna switch embedded in the front-end matching network minimizes degradation of the transmitter (TX) efficiency and receiver (RX) noise figure. The multi-mode power amplifier (PA) with a built-in linearizer is presented to have high efficiency and linearity for all power modes, which reduces power consumption during gain control. Also, a differential four-way power divider and an single pole double throw (SPDT) switch are introduced in the common path, which has a small chip size and a low insertion loss. By adopting differential structures for all components in the four-channel IC, the effect of parasitic grounding inductances due to bonding and package is minimized. Thanks to the proposed dual-vector VGPS, the rms gain error of 0.21 dB and the peak phase variation of ±1.7° are achieved during phase control and gain control, respectively, without any calibration. The four-channel front-end IC also achieves rms phase error of only 1.4° during the simultaneous phase and gain control without any calibration. It has a TX OP1dB of 13.3 dBm and the highest linear output power of 7.2 dBm with 400-MHz 64-QAM fifth-generation (5G) new radio (NR) signals with 9.6-dB peak-to-average power ratio (PAPR). Also, this article presents a 64-element brick-type phased array antenna using four-channel core chips. It shows a high effective isotropic radiated power (EIRP) of 54.4 dBm at 28 GHz. An over-the-air link is demonstrated with a competitive data rate of 4 Gb/s using 64-QAM waveforms over all scan angles at a distance of 100 m.

A Ka-band variable-gain phase shifter (VGPS) using a multi-vector summation method is proposed, which represents both phase and amplitude by summing the I and Q signals of multiple vectors. The VGPS has an orthogonal phase and gain control function with a wide gain-control dynamic range because it is designed to keep the input and output impedances almost constant regardless of the control states. It shows a measured RMS phase error of 2.9 ° during 17.3 dB gain control and that of 3.5 ° during simultaneous 17.3 dB gain and 360 ° phase control without any calibration from 30 to 32.5 GHz. The measured average insertion loss ranges from -4 to -2.8 dB from 28 to 33 GHz. It is implemented in a 65-nm RF CMOS process with the size of 0.21 mm ² excluding pads.

A Ka-band CMOS cascode power amplifier (PA) linearized with a cold-FET-based interstage matching network is presented, which is designed in a 65-nm CMOS process. Since it is difficult to make a cascode PA matched to the optimum output and input impedances at high frequencies, a matching network has to be introduced at the node between the common-source (CS) and common-gate (CG) stages. The cold-FET-based matching network improves the linearity and the input and output impedance matchings, which is analyzed and optimized with its simple model. It makes the PA have gain expansion and phase lag with the power, which allows the PA to have less amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) distortions. In addition, it improves the return losses of the PA by making the impedances for power matching and conjugate matching located closely. The implemented PA achieves the peak power-added efficiency (PAE) of 38.2% and the saturated output power (Psat) of 17.1 dBm at 31 GHz while occupying the chip area of 0.16 mm². It is also shown that the OP1,dB is improved by 1.7 dB, and the AM-PM distortion is reduced to only 1.1° due to the linearization technique. It is tested with 64-quadrature amplitude modulation (QAM) signals, which has a 400-MHz channel bandwidth (BW) and a 9.7-dB peak-to-average power ratio (PAPR). It achieves average output powers of 9.6/7.7 dBm with error vector magnitudes (EVMs) of -25/-30 dB for 64-QAM OFDM signals, efficiencies of 17.7%/12%, and the adjacent channel leakage ratio (ACLR) of -28.2/-32.8 dBc, respectively.

A collocated phased-subarray multiple-input and multiple-output (MIMO) radar system that reduces the number of MIMO channels to implement a large antenna array is proposed. Both the transmitter (TX) and receiver (RX) arrays are divided into phased subarrays, which consist of several RF beamforming antenna elements. Each phased subarray is exploited as an MIMO channel. To estimate the angular information of targets, a hybrid beamforming technique that incorporates RF beamforming of the phased subarrays and digital beamforming of the MIMO virtual array is used. Antenna configurations of the phased-subarray MIMO radar and the corresponding virtual array are also presented. A space between the TX phased subarrays larger than one TX subarray aperture is introduced to facilitate the larger antenna aperture. Because this involves unwanted overall grating lobes, a grating lobe cancellation method is proposed using sum and difference RF subarray beams. This provides a higher angular resolution with the same number of antenna elements. The proposed phased-subarray MIMO radar concept with the corresponding grating lobe cancellation method is demonstrated by implementing a 60-GHz 16-element phased-subarray 2 ${\times }$ 2 MIMO frequency-modulated continuous-wave (FMCW) radar system.