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 ...

This paper proposes a method for minimizing the inductor current ripple of a DC–DC converter in a two-stage power conversion system consisting of a grid-connected PWM converter and an interleaved multiphase three-level DC–DC converter. To reduce the output voltage ripple, the three-level DC–DC converter is configured in parallel and operated interleaved. However, a circulating current generated by the interleaved operation increases the inductor current ripple of each DC–DC converter and causes system loss and inductor saturation. In this paper, the inductor and output current ripple of the interleaved three-phase three-level DC–DC converter is mathematically analyzed and the effect of the DC–DC converter’s duty ratio and output voltage on each current ripple is described. Based on this analysis, a method is proposed for controlling the optimal DC link voltage through the PWM converter, so that the DC–DC converter is controlled with the duty ratio that minimizes the inductor current ripple. The simulation and experimental results under various operating conditions are presented to verify the feasibility of the proposed control method.

In this paper, we design, fabricate and measure two kinds of high-frequency packages for K-band CMOS FMCW radar chips using RF via structures. The packages are fabricated with the conventional PCB process and LTCC process. The design centering of the packages is performed at 24 GHz and impedance variation caused by the wire bonding and RF via structure is fully evaluated using 3D electromagnetic simulation. The RF via structure with characteristic impedance of 50 Ω is used to reduce impedance mismatch loss. Two kinds of test packages with back-to-back connected RF paths are fabricated and measured for the design verification of the PCB-based package and LTCC package. Their measured results show an insertion loss of less than 0.4 dB at 24 GHz and less than 0.5 dB for 20～29 GHz. The measured return loss is less than -13 dB for the PCB-based package and less than -15 dB for the LTCC package in the frequency band, but the return loss of the package itself is predicted to be better than that of the test package by about 5 dB, because the ripples of the back-to-back connection typically degrade the return loss by 5 dB or more.