Keun-Kwan Ryu

Ring Hybrid Balun with Good Amplitude and Phase Balance

We present a ring hybrid balun with additional two lambda/4 short stubs, which offers excellent amplitude and phase balance characteristic. In the proposed scheme, the phase and amplitude imbalance essentially occurred in the conventional ring hybrid is alleviated by a lambda/4 shorted stub and the second stub with a series resistor respectively. The measured data shows that phase imbalance is less than 2.5deg and magnitude imbalance is less than 0.2 dB over a 1.75-2.25 GHz.

MMIC HEMT switch for switch matrix of satellite communication system

A MMIC (monolithic microwave integrated circuit) switch chip using InGaAs/GaAs p-HEMT process has been developed for switch matrix of satellite communication system. This absorptive type MMIC switch has good reflection coefficients performances of input and output ports at both on and off-states. A quarter wavelength impedance transformer is realized with lumped elements of MIM capacitor and spiral inductor for 3GHz band to reduce the chip size. The MMIC switch covers the range of 3.2/spl sim/3.6GHz. According to the on-wafer measurement, the fabricated MMIC switch with miniature size of 1.6mm/spl times/1.3mm demonstrates insertion loss below 2dB, isolation above 56.8dB, respectively, and the performance coincides with simulation results.

Push-Push Voltage Controlled Dielectric Resonator Oscillator Using a Broadside Coupler

A push-push voltage controlled dielectric resonator oscillator (VCDRO) with a modified frequency tuning structure using broadside couplers is investigated. The push-push VCDRO designed at 16 GHz is manufactured using a low temperature cofired ceramic (LTCC) technology to reduce the circuit size. The frequency tuning structure using a broadside coupler is embedded in a layer of the A6 substrate by using the LTCC process. Experimental results show that the fundamental and third harmonics are suppressed above 15 dBc and 30 dBc, respectively, and the phase noise of push-push VCDRO is -97.5 dBc/Hz at an offset frequency of 100 kHz from the carrier. The proposed frequency tuning structure has a tuning range of 4.46 MHz over a control voltage of 1?11 V. This push-push VCDRO has a miniature size of 15 mm×15 mm. The proposed design and fabrication techniques for a push-push oscillator seem to be applicable in many space and commercial VCDRO products.

LNA topologies for RX carrier aggregation

Performance of the low-noise amplifier (LNA) determines the sensitivity, impedance matching (reflection), and other critical parameters of the receiver. Carrier aggregation (CA) in LTE-Advanced and upcoming 5G requires the LNA to support multiple-outputs without degrading its dynamic range (DR) performance and thus requires the architectural changes. In this paper, several LNA topologies are presented which can support RX carrier aggregation. Each topology is meticulously characterized in its performance. Simulation results reveal that the cascode divert-switch and cascode-shutoff in common-source configuration shows comparable performance to the legacy operation.

Reduced Hybrid Ring Coupler Using Surface Micromachining Technology for 94-GHz MMIC Applications

In this study, we developed a reduced 94 GHz hybrid ring coupler on a GaAs substrate in order to demonstrate the possibility of the integration of various passive components and MMICs in the millimeter-wave range. To reduce the size of the hybrid ring coupler, we used multiple open stubs on the inside of the ring structure. The chip size of the reduced hybrid ring coupler with multiple open stubs was decreased by 62% compared with the area of the hybrid ring coupler without open stubs. Performance in terms of the loss, isolation, and phase difference characteristics exhibited no significant change after the use of the multiple open stubs on the inside of the ring structure. The reduced hybrid ring coupler showed excellent coupling loss of 3.87±0.33 dB and transmission loss of 3.77±0.72 dB in the measured frequency range of 90–100 GHz. The isolation and reflection were −48 dB and −32 dB at 94 GHz, respectively. The phase differences between two output ports were 180°±1° at 94 GHz.

Design of a 94-GHz Single Balanced Mixer Using Planar Schottky Diodes with a Nano-Dot Structure on a GaAs Substrate

In this paper, we develop a 94-㎓ single balanced mixer with low conversion loss using planar Schottky diodes on a GaAs substrate. The GaAs Schottky diode has a nanoscale anode with a T-shaped disk that can yield high cutoff frequency characteristics. The fabricated Schottky diode with an anode diameter of 500 ㎚ has a series resistance of 21 Ω, an ideality factor of 1.32, a junction capacitance of 8.03 fF, and a cutoff frequency of 944 GHz. Based on this technology, a 94-㎓ single balanced mixer was constructed. The fabricated mixer shows an average conversion loss of -7.58 ㏈ at an RF frequency of 92.5 ㎓ to 95 ㎓ and an IF frequency of 500 ㎒ with an LO power of 7 ㏈m. The RF-to-LO isolation characteristics were greater than -32 ㏈. These values are considered to be attributed to superior Schottky diode characteristics.

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.

A 94-GHz Phased Array Antenna Using a Log-Periodic Antenna on a GaAs Substrate

A 94-GHz phased array antenna using a log-periodic antenna has been developed on a GaAs substrate. The developed phased array antenna comprises four log-periodic antennas, a phase shifter, and a Wilkinson power divider. This antenna was fabricated using the standard microwave monolithic integrated circuit (MMIC) process including an air bridge for unipolar circuit implementations on the same GaAs substrate. The total chip size of the fabricated phased array antenna is 4.8 mm × 4.5 mm. Measurement results showed that the fabricated phased array antenna had a very wide band performance from 80 GHz to 110 GHz with return loss characteristics better than -10 dB. In the center frequency of 94 GHz, the fabricated phased array antenna showed a return loss of -16 dB and a gain of 4.43 dBi. The developed antenna is expected to be widely applied in many applications at W-band frequency.

A 4W GaAs Power Amplifier MMIC for Ku-band Satellite Communication Applications

In this paper, we demonstrated a 4W power amplifier monolithic microwave integrated circuit (MMIC) for Ku-band satellite communication applications. The used device technology relies on 0.25mm GaAs pseudomorphic high electron mobility transistor (PHEMT) process. The 4W power amplifier MMIC has linear gain of over 30 dB and saturated output power of over 36.1 dBm in the frequency range of 13.75 GHz ~ 14.5 GHz. Power added efficiency (PAE) is over 30 %.

High Performance W-band VCO for FMCW Applications

In this paper, we reported on a high performance waveguide VCO(voltage controlled oscillator) for FMCW applications. The waveguide VCO consists of a GaAs Gunn diode, a varactor diode, and two bias posts with low pass filter(LPF). The cavity is designed for fundamental mode at 47 GHz and operated at second harmonic of 94 GHz center frequency. The developed waveguide VCO has 1.095 GHz bandwidth, 590 MHz linearity with 1.69% and output power from 14.86 to 15.93 dBm. The phase noise is under -95 dBc/Hz at 1 MHz offset.