The consumer-level unmanned aerial vehicles (UAV) are small and an increasing treat to personal privacy and public security. Due to the small radar cross section (RCS) property and slow speed, it is difficult to detect UAVs by radar systems. This paper presents the design and analysis of the PLL-based synthesizer for passive or active UAV detection radar applications. The adaptive bandwidth of PLL ensures the loop stability to track exact frequency. In this design, the loop bandwidth is set around 400KHz with 8MHz reference clock. The integer N is programmed from 1 to 128, thereafter the inverse linear current in the charge pump is 64:1. Since the frequency operation ranges from 40MHz to 1.024GHz, the 8-bit end-of-counter (EOC) detector is a better solution for high-speed consideration. Based on a countdown counter configuration, the EOC detector detects the count state to reinitiate the counter to N and the cycle repeats. The PLL-based synthesizer is fabricated in a 90nm digital CMOS process with the core area of 0.24 x 0.47mm2. The core power consumption is 3.6mW from a 1V supply. The PLL-based synthesizer performs that the phase noise at 6MHz (or 8MHz) is below -100dBc/Hz, and below -110dBc/Hz at 12MHz (or 16MHz). The peak-to-peak tracking jitter at 240MHz is 7.2ns, and the RMS tracking jitter is 921ps. The overall settling time of the synthesizer is below 20μs, and the results guarantee the overall performance of the UAV detection radar.
Multiband cognitive radar systems, operating in a variety of frequency bands and combining the different channels into a joint system, can provide significant flexibility and capability to detect and track hostile targets. This paper proposes a multi-passband complex filter (MPCF) architecture and the related circuit design for a multiband cognitive radar system. By operating under the 5.8GHz UNII band, the sensing part detects the current usage of frequency bands from 5.15GHz to 5.825GHz and provides the information of unused channels. The multiband cognitive radar system uses the whole unused channels and eliminates the used channels by using an on-chip MPCF in order to be coexistent with the Wi-Fi standard. The MPCF filters out the unwanted channels and leave the wanted channels. It dynamically changes the bandwidth of frequency from 20MHz to 80MHz using the 0.18μm CMOS technology. The MPCF is composed of the combination of 5th-order Chebyshev low-pass filters and high-pass filters, and the overall inband ripple of the MPCF is 1.2dB. The consuming current is 21.7mA at 1.8V power supply and the 20MHz bandwidth noise is 55.5nV. The total harmonic distortion (THD) is 45dB at 25MHz and the adjacent channel rejection is 24dB. The result of the MPCF guarantees the performance requirements of the multiband cognitive radar system.
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