Seok-Gyu Choi

94 GHz MMIC single balanced mixer for FMCW radar sensor application

We present a 94 GHz MMIC single balanced mixer using the branch line couplers and 0.1 μm GaAs-based metamorphic high electron mobility transistors (MHEMTs) for FMCW radar sensor application. The mixer was designed in a resistive structure because of no drain bias and low DC currents. Two single ended mixers in the fabricated MMIC single balanced mixer share gate bias circuits. The fabricated mixer shows a conversion loss of 14.7 dB at 94 GHz, and the LO to RF isolation of 34.2 ~ 35.2 dB in LO frequency range of 93.675 ~ 94.275 GHz.

A Transceiver Module for FMCW Radar Sensors Using 94-GHz Dot-Type Schottky Diode Mixer

In this study, we fabricated a 94-GHz transceiver module for a millimeter-wave (MMW) frequency modulation continuous wave (FMCW) radar sensor. The transceiver modules consist of a waveguide voltage-controlled oscillator (VCO) and Rx module using a single balanced mixer. We designed a mixer with a conversion loss of 6.4 dB, without using an amplifier. Also, the waveguide VCO consisted of an InP Gunn diode, a varactor diode, two bias posts with LPF, and a Magic Tee for the MMW radar transceiver. The fabricated VCO has a tuning range of 1280 MHz by a varactor bias of 0~20 V, 1.69% linearity range of 680 MHz, and current consumption of 154 to 157 mA. The completed module has a good conversion loss of 10.6 dB with an LO power of 11.4 dBm at 94 GHz. With this RF and LO input power, the conversion loss was maintained between 10.2-11.5 dB in the RF frequency range of 93.67-94.95 GHz.

New Tuning Method for 94 GHz Waveguide Voltage Controlled Oscillator

We propose a simple, yet highly effective tuning method to increase the bandwidth of a waveguide voltage controlled oscillator (VCO) by applying controlled mechanical pressures to the packaged Gunn diode mounted in the waveguide cavity resonator. When we applied this method to a varactor-tuned, second-harmonic 94 GHz VCO, the bandwidth was doubled to 1 GHz with an output power over 14.8 dBm, which is suitable for frequency-modulated continuous-wave radar sensor applications.

Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar

In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.

Radio Frequency Characteristics of Multifinger 0.1 µm Metamorphic High-Electron-Mobility Transistors Depending on Number of Gate Fingers and Gate Width

We investigate the effects of the number of gate fingers (N) and gate width (W) on the high-frequency characteristics of 0.1 µm depletion-mode metamorphic high-electron-mobility transistors (MHEMTs). The extracted gate-to-source capacitance (Cgs), gate-to-drain capacitance (Cgd), intrinsic transconductance (gm,int), and drain conductance (Gds) are proportional to total gate width (wt), whereas intrinsic resistance (Ri) and source resistance (Rs) are inversely proportional to wt. Gate resistance (Rg) linearly increases at various slopes with non-zero gate resistances at zero gate width depending on N. The cutoff frequency ( fT) and maximum frequency of oscillation ( fmax) are calculated using a small-signal model and curve-fitting equations extracted from each small-signal parameter. fT is almost constant; however, fmax is a strong function of Rg1/2 and is affected by both N and wt. A large wt produces a low fmax; however, at a given wt, increasing the number of gate fingers is more efficient than increasing single gate width for maximizing the fmax.

V-band CPW balanced medium power amplifier for 60 GHz wireless LAN application

In this work, balanced medium power amplifiers for 60 GHz wireless LAN application were designed and fabricated. The single-ended and the balanced medium power amplifier on MIMIC technology were designed using 0.1/spl mu/m /spl Gamma/-gate GaAs PHEMT and CPW library. We compared the single-ended medium power amplifier on the balanced medium power amplifier of S-parameter and 1 dB gain compression point (P/sub 1dB/). From measurement, the single-ended and the balanced medium power amplifiers show S/sub 21/ gains of 13.14 dB and 12.8 dB, respectively, at 60 GHz. Also, we obtain P/sub 1dB/ of 5.9 dBm and 7.5 dBm at 60 GHz, respectively. The balanced medium power amplifier has better return losses and P/sub 1dB/ than those of the single-ended medium power amplifier within V-band region.

Development of Planar Schottky Diode on GaAs Substrate for Terahertz Applications

In this paper, we demonstrate the planar Schottky diode on GaAs substrate for terahertz applications. A nanoscale dot and T-shaped disk has been developed as the anode for terahertz Schottky diode. The low parasitic elements of the nanoscale anode with T-shaped disk yield high cutoff frequency characteristic. The fabricated Schottky diode with anode diameter of 500 nm has series resistance of 21 Ω, ideality factor of 1.32, junction capacitance of 8.03 fF, and cutoff frequency of 944 GHz.

Tuning characteristics of 94 GHz waveguide VCO

We have proposed a new tuning method of 94 GHz waveguide voltage controlled oscillator (VCO). We have designed and fabricated a varactor-tuned 94 GHz second harmonic VCO. We discuss a new method that a simple and effective tuning method increases greatly the bandwidth of the VCO with high output power and operating frequency simultaneously for the FMCW radar system by applying a controlled impact to the Gunn diode. The VCO employs a commercially available GaAs Gunn diode in packaged form and a GaAs Gunn diode mounted in a waveguide cavity. Also, we adapted MINTs GaAs Gunn diode.

Design and fabrication of MMW module for 94 GHz radar sensor applications

We present design and fabrication of a 94 GHz radar sensor module. The 94 GHz sensor module has four components including 94 GHz single balanced diode mixer part, waveguide VCO (voltage controlled oscillator) part, magic tee part and bias PCB part. The 94 GHz single balanced diode mixer is developed on Duroid RT 5880 substrate with DC 1346 Schottky diode. The mixer has advantage of good conversion loss at high LO power and isolation characteristic. 94 GHz single balanced diode mixer has advantage of comparatively easy fabrication. The waveguide VCO consist of GaAs Gunn diode, varactor diode, two-bias post and cavity. The waveguide VCO is operated at 94 GHz. The magic tee has four waveguide arm regions with standard WR-10 and divides output power from VCO. Transmission frequency of 94 GHz MMW sensor module is 93.607 ∼ 94.727 GHz. Bandwidth is 1.12 GHz. 2% linearity range is 680 MHz. Power is 11.03 ∼ 11.47 dBm. Conversion loss about −7 dB at IF 500 MHz

Fabrication of hyperabrupt GaAs varactor diode for W-band waveguide VCO

In this work, we fabricated a hyperabrupt varactor diode and W-band waveguide VCO using fabricated varactor diode. With the anode diameter of 90 µm, a maximum reverse breakdown voltage of 40 V at a leakage current of 30 µA, a maximum capacitance of 5.82 pF, and a minimum capacitance of 0.7 pF were obtained, resulting in a Cmax/Cmin ratio of 8.31. Fabricated VCO showed an excellent linearity of 1.6 % within 800 MHz. The bandwidth of the VCO was 1.165 GHz from 93.305 GHz to 94.47 GHz, and the output power was from 14.6 dBm to 15.42 dBm.