Tae-Jong Baek

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.

Hybrid ring coupler for W-band MMIC applications using MEMS technology

The hybrid ring coupler was designed and fabricated on a GaAs substrate using surface micromachining techniques, which adopted dielectric-supported air-gapped microstrip line (DAML) structure. The fabrication process of DAML is compatible with the standard monolithic microwave integrated circuit (MMIC) techniques, and the hybrid ring coupler can be simply integrated into a plane-structural MMIC. The fabricated hybrid ring coupler shows wideband characteristics of the coupling loss of 3.57 /spl plusmn/ 0.22dB and the transmission loss of 3.80 /spl plusmn/ 0.08dB across the measured frequency range of 85 to 105GHz. The isolation characteristics and output phase differences are -34dB and 180/spl plusmn/1/spl deg/, at 94GHz, respectively.

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.

Fabrication of new micromachined transmission line with dielectric posts for millimeter-wave applications

This paper describes a new GaAs-based surface-micromachined microstrip line supported by dielectric posts and with an air gap between the signal line and the ground metal. This new type of dielectric post and air-gapped microstripline (DAML) structure was developed using surface micromachining techniques to provide an easy means of air-bridge connection between the signal lines and to achieve low losses in the millimeter-wave frequency band with a wide impedance range. Each DAML is fabricated with a length of 5 mm. By elevating the signal lines from the substrate using micromachining technology, the substrate dielectric loss can be reduced. Compared with conventional microstrip transmission lines, which show over 10 dB cm−1 loss, the loss of a DAML can be reduced to 1.1 dB cm−1 at 50 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.

The Fabrication of the Low Loss Transmission Line and Low Pass Filter using Surface Microelectromechanical Systems Technology

In this study, we first fabricated a new GaAs-based dielectric-supported air-gap microstrip lines (DAMLs) by the surface microelectromechanical systems (MEMS) technology, and then fabricated the low-pass filter (LPF) for the Ka-band using those DAMLs. We elevated the signal lines from the surface in order to reduce the substrate dielectric loss and to obtain low losses at the millimeter-wave frequency band with a wide impedance range. We fabricated LPFs with DAMLs for Ka-bands, and we were able to reduce the insertion loss of LPFs by reducing the dielectric loss of the DAMLs. Miniaturization is essential for integrating LPFs with active devices, so we fabricated a LPF with the slot on the ground metal to reduce the size of the LPF. We compared the characteristics of the LPF with a slot and the LPF without the slot.

3-D 94 GHz single balanced mixer for low conversion loss with ring coupler by DAML

A 94 GHz single balanced mixer in 3-dimension was successfully fabricated. The GaAs-based low loss transmission lines, dielectric-supported air-gapped microstrip lines (DAMLs), have been developed using surface micromachining technology, and the DAML-based hybrid ring coupler is successively fabricated. We have developed the high-performance 94 GHz single balanced active mixer using hybrid ring coupler with 70 nm gate length MHEMT. The mixer showed the conversion loss of 2.5 dB ~ 2.8 dB and isolation characteristics less than −30 dB, in the range of 93.65 GHz ~ 94.25 GHz. These results are the best performances demonstrated from a 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.

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.

A 94 GHz diode mixer for low LO power operation

For low LO power and broadband characteristics of the mixer, an antipodal fin-line to microstrip transition for operation in the 94 GHz frequency has been designed and characterized. Back to back transitions fabricated on soft substrates have been measured and simulated to verify their behavior. A single balanced fin-line mixer was designed and fabricated. In the mixer, a wideband fin-line to coplanar waveguide 180/spl deg/ balun and low pass filter were used. Conversion loss is less than 10 dB at LO power of 6 dBm.