Publications

Detailed Information

A STUDY ON WALL-CLUTTER REJECTION TECHNIQUES FOR THROUGH-THE-WALL FMCW RADAR APPLICATIONS : 벽투과 FMCW 레이다를 위한 벽클러터 제거 기법에 관한 연구

Cited 0 time in Web of Science Cited 0 time in Scopus
Authors

김병준

Advisor
남상욱
Major
공과대학 전기·컴퓨터공학부
Issue Date
2017-02
Publisher
서울대학교 대학원
Keywords
Frequency-modulated continuous-wave (FMCW) radarlow-order high-pass filter (HPF)phase controllerTwo phase-locked loops (PLL)wall-clutter rejection
Description
학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 남상욱.
Abstract
This thesis proposes novel wall-clutter rejection techniques and frequency-modulated continuous-wave (FMCW) radar architectures for through-the-wall radar applications. In the through-the-wall radar applications, wall-cutter rejection is very important because the wall-clutter requires high dynamic range of receiver and analog-to-digital converter (ADC). Wideband FMCW radars are good candidates for a high-resolution wall-penetrating detection radar because they can achieve high dynamic range by using a range-gating filter at intermediate frequency or baseband to fully eliminate wall-clutter. However, homodyne FMCW radars require a very high-order high-pass filter (HPF) to fully eliminate wall-clutter when a target is located behind and in close proximity to the wall.
In this thesis, we first investigate a delay-line technique. The inserted delay-line decreases the time-gap between the received signal and the chirp signal. Therefore, the beat-frequencies of the target and wall are shifted to lower frequencies, and the ratio of pass-band to stop-band frequency is increased. As a result, the low-order HPF meets the filter specification. A design methodology and an example for short-range target is provided in this thesis. And the validity of this technique has been verified with a system simulation.
Even though, the delay-line technique allows the low-order HPF can fully attenuate the wall-clutter, the delay-line in an RF signal path or LO signal path cause several problems: 1) A conventional long delay-line makes considerable signal loss at a high frequency such as X-band or Ka-band
2) The line-loss also introduces amplitude modulation due to the loss, depending on frequency. Therefore, amplitude modulation increases as radar bandwidth increases, representing a particular problem for high-resolution radar. This amplitude modulation can lead to large side-lobes near a target-beat-frequency
3) The delay-line requires a large area single-layer substrate or a multi-layer substrate with additional process or expensive process, such as surface acoustic wave (SAW) process to produce a long delay
4) It is difficult to achieve a controllable delay, from a short delay to a long delay, with a fine time-resolution. It requires abundant delay-lines, control circuits, and loss-compensate circuits, resulting in a bulky system.
Therefore, we propose a novel FMCW radar architecture that employs two phase-locked loops (PLL) and a phase controller. One PLL generates a chirp signal for transmitting (TX chirp) while the other PLL generates a chirp signal for mixing at the mixer (LO chirp). The PLLs share a reference clock, but the transmitter PLL input path includes a digital phase-controller. When a digital phase control function is activated, the controller advances the reference clock as a half-period by generating one more edge and inversing the following edges. Each reference clock is divided by two and compared to the corresponding PLLs feedback clock. When the phase controller invokes a half-period advance, the transmitter PLL starts tracking. After some cycles, the PLL locks onto the advanced clock, producing a corresponding advanced time in the TX chirp. By repeating this process (advance reference, PLL tracking and PLL locking), it is theoretically possible to produce an infinite time-difference. In practice, due to the finite period of the TX chirp and the LO chirp, the maximum time-difference is limited. This method solves all of the above problems: It does not result in any loss in RF or LO signals, nor produce any amplitude modulation including wideband FMCW radars
does not require greatly increased volume
and permits infinite time-delay with fine time-resolution. This method allows a low-order HPF to highly attenuate wall-clutter and also decouples the relationship between the walls distance and the HPFs cut-off frequency. The proposed radar was implemented and measured. The wall was located at 1.5 m and the target was located at 3 m at the middle of the room. The measured results show a second-order HPF attenuates by more than 20 dB for the wall-beat-frequency signal while it does not attenuate the target-beat-frequency signal. The proposed radar is highly appropriate for wall-penetrating detection applications.
Language
English
URI
https://hdl.handle.net/10371/119276
Files in This Item:
Appears in Collections:

Altmetrics

Item View & Download Count

  • mendeley

Items in S-Space are protected by copyright, with all rights reserved, unless otherwise indicated.

Share