Tunable Composite Right/Left-Handed Delay Line with Large Group Delay for an FMCW Radar Transmitter

Abstract

This paper presents a tunable composite right/left-handed (CRLH) delay line for a delay line discriminator that linearizes modulated frequency sweep in a frequency modulated continuous wave (FMCW) radar transmitter. The tunable delay line consists of 8 cascaded unit cells with series varactor diodes and shunt inductors. The reverse bias voltage of the varactor diode controlled the group delay through its junction capacitance. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Ⅰ. IntroductionMany studies over the past 10 years have focused on various delay lines such as surface acoustic wave (SAW), magnetostatic wave (MSW), and composite right/lefthanded (CRLH) delay lines [1]. These delay lines have been used in many applications; for example, in time or phase synchronization when designing linear power amplifiers [2], and in phased array antennas where the antenna feeding lines are adjusted to control the antenna beam direction and directivity [3]. Another major application is as a delay line discriminator, which finds the instantaneous frequency of a received signal by mixing the received signal and its time-delayed signal through a known delay line, followed by low-pass filtering of the mixed output [4]. This paper presents a tunable group delay line for a delay line discriminator that is a control circuit used to linearize the modulated frequency sweep of an FMCW radar transmitter [5]. A fabricated delay line has a CR-LH transmission line configuration and uses varactor diodes in series in order to obtain sufficient tunable group delay to linearize a VCO output signal with an inherently nonlinear frequency sweep characteristic. A design frequency of 250 MHz and a group delay variation of ≤5 % within the frequency sweep bandwidth were chosen according to the specifications of a 24 GHz FM-CW radar transmitter and frequency dividing ratios of the phase-locked loop (PLL) of the transmitter.Previous studies have investigated nonlinear CRLH transmission lines with varactor diodes; however, the group delay results in these studies are so small that it is difficult to utilize them in the delay line discriminator of an FMCW radar transmitter. One of the recently reported group delays is approximately 2 ns [6], which is still a relatively small value when compared with the group delay of more than 8 ns in the present work. The design and simulation results of the tunable CRLH delay line are presented next, followed by the fabrication and measured results. Ⅱ. Design and SimulationIn general, a tunable CRLH transmission line is composed of right-handed (RH) and left-handed (LH) transmission lines. The RH transmission line, which consists of a series L and shunt C, corresponds to a conventional transmission line; whereas the LH transmission line, with a series C ...

A new RF interference cancellation using a novel 3-pole bandstop resonator designed using tapped CRLH T-line model

“…9 shows the setup used for testing the cancellation performance using the new bandstop resonator. Where the phase of path (1) and path (2) are matched at 680 MHz as shown in Fig. 10.…”

“…Over the past few years, many novel microwave devices were developed using CRLH-T lines. Examples include: Wideband tunable phase shifters for distortion cancellation in power amplifiers [1]; compact antennas; filters; and tunable large delay lines [2].…”