(A) 24 GHz ISM band pulse radar with an improved range resolution for short-range applications

Abstract

An approach to improve the range resolution of a 24 GHz ISM band pulse radar is presented for auto-motive short-range radars. The resolution of the range profile is improved by applying the regularized least squares (RLS) method to a discrete baseband signal at the receiver. For a 24 GHz ISM band pulse radar adopting a RLS method, a triangular pulse is identified as the optimal pulse shape under the regulations and in terms of cost effectiveness, and MATLAB simulations based on the least absolute shrinkage and selection operator (LASSO) algorithm are conducted. To resolve multiple adjacent pulses with a constant false alarm rate, the additional threshold values and the required signal-to-noise ratio (SNR) are derived. An improved range resolution at a given false-alarm rate is achieved and verified by measuring a radar test module. To implement a 24 GHz ISM band pulse radar module, a simple and tunable pulse-generator and a linear up-conversion mixer are proposed and implemented in a 0.13-μm CMOS technology. In the proposed pulse-generator, which consists of V-I converters and charge pumps, by applying tunable input signals to the V-I converters, the amount of currents flowing through the charge pumps can be controlled without requiring the current source switching, and thus the switching noise can be avoided. Implemented in a 0.13-μm CMOS technology, measured tuning ranges of pulse-width and -amplitude are 12.7-28.5 ns and 15.0-216.1 $mV_{pp}$, respectively, while dissipating 4.5 mW from a 1.5-V supply. In the proposed mixer, the double-balanced Gil-bert-cell topology is employed with a low-distortion transconductance stage which combines voltage feedback and adaptive biasing schemes. The proposed adaptive biasing circuit improves the linearity of the transconductance stage by providing an additional bias current when IF input signals exceed the current-limited linear input range. The mixer showed a conversion gain of -1.9 dB and output 1-dB compression point of 0.3 dBm for the IF, LO, and RF frequency ranges of 10.0-314.7 MHz, 18.9-29.0 GHz, and 23.4-29.2 GHz, respectively, while dissipating 22.8 and 16.5 mW for the mixer and the LO buffer, respectively, from a 1.5-V supply. To verify the proposed 24 GHz ISM band pulse radar adopting the RLS method, two trihedral corner reflectors were used as test targets, and measurements were conducted in a radio anechoic chamber to avoid clutter signals. Baseband echo signals at the receiver output were measured and processed by an oscilloscope and MATLAB simulation, respectively. The simulated and measured values of the required SNR ratio were 20.5 and 21.1 dB, respectively, for two-target detection with a range resolution of 30 cm, at the detection and false alarm probabilities of 0.9 and $10^{-3}$, respectively.