• ETRI Journal
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• v.26 no.6
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• pp.605-614
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• 2004

In this paper, we investigate array calibration algorithms to derive a further improved version for correcting antenna array errors and RF transceiver errors in CDMA smart antenna systems. The structure of a multi-channel RF transceiver with a digital calibration apparatus and its calibration techniques are presented, where we propose a new RF receiver calibration scheme to minimize interference of the calibration signal on the user signals. The calibration signal is injected into a multi-channel receiver through a calibration signal injector whose array response vector is controlled in order to have a low correlation with the antenna response vector of the receive signals. We suggest a model-based antenna array calibration to remove the antenna array errors including mutual coupling errors or to predict the element patterns from the array manifold measured at a small number of angles. Computer simulations and experiment results are shown to verify the calibration algorithms.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.2
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• pp.274-279
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• 2011

To increase the performance of mobile communication systems, base statations having beamforming function are released recently. For the proper beamforming function, it is required that each RF paths be calibrated periodically. However, the current calibration method has a problem when the base station is connected to a repeater. In this paper, we report the problem and propose a new calibration method to solve the problem.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.139-146
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• 2009

This paper presents an average internal loop-back antenna calibration method for array antenna in TDD(Time Division Duplex) systems. The proposed method calibrates the amplitude and the phase of RF systems using into mal coupler and switches without aids of external calibration systems. The average calibration scheme of the proposed method also increases reliability of calibration performance. Computer simulation demonstrates that the proposed method corrects beamforming angles of DOA estimation algorithm and BER performance in transmit power allocation scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.882-885
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• 2011

This paper presents testing and self-calibration of RF circuits using MEMS switches to identify process-related defects and out of specification circuits. We have developed a novel multi-tone dither test technique where the test stimulus is generated by modulating the RF carrier signal with a multi-tone signal generated using an Arbitrary Waveform Generator (AWG) with additive white Gaussian noise. This test stimulus is provided as input to the RF circuit and peak-to-average ratio (PAR) is measured at the output. For a faulty circuit, a significant difference is observed in the value of PAR as compared to a fault-free circuit. Simulation is performed for various circuit conditions such as fault-free as well as fault-induced and their corresponding PARs are stored in the look-up table. This testing and self-calibration technique is exhaustive and efficient for present-day communication systems.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.751-754
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• 2003

Metamorphic HEMTs (MHEMTs) have emerged as excellent challenges for the design and fabrication of high-speed HEMTs for millimeter-wave applications. Some of improvements result from improved mobility and larger conduction band discontinuity in the channel, leading to more efficient modulation doping, better confinement, and better device performance compared with pseudomorphic HEMTs. We have studied the calibration on the DC and RF characteristics of the MHEMT device using I $n_{0.53}$G $a_{0.47}$As/I $n_{0.52}$A1$_{0.48}$As modulation-doped heterostructure on the GaAs wafer. For the optimized device performance simulation, we calibrated the device performance of 0.1-${\mu}{\textrm}{m}$ $\Gamma$-gate MHEMT fabricated in our research center using the 2D ISE-DESSIS device simulator. With this calibrated parameter set, we have obtained very good reproducibility. The device simulation on the DC and RF characteristics exhibits good reproducibility for our 0.1-${\mu}{\textrm}{m}$ -gate MHEMT device compared with the measurements. We expect that our calibration result can help design over-100-GHz MHEMT devices for better device performance.ormance.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.859-864
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• 2010

In the next generation system, a study on realization of Multi-Core system is in progress for applying it in multi service network. Therefore some mobile systems are expected to be appeared. These systems can support WiBro, WCDMA, CDMA, etc with single terminal. These systems have to support various FA using broadband frequency and hand over to other service network. Especially, in the telecommunication system composed of cell, the transmit power can be interference at adjacent system, has effect on system channel capacity and cell size. In this paper, we improve the unstable transmit power caused by unsettled system operation, propose the RF(Radio Frequency) Calibration method which can use the transmit power stably even during hand over between heterogeneous networks causing unstable power change. Also we used proposed method and analysed used electricity of system during hand over between heterogeneous networks.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.25-27
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• 2010

This paper presents a gain and phase mismatch calibration technique for an image-reject RF receiver. The gain mismatch is calibrated by directly measuring the output signal amplitudes of two signal paths. The phase mismatch is calibrated by measuring the output amplitude of the final IF output at the image band. The calibration of the gain and phase mismatch is performed at power-up, and the normal operation of the RF receiver does not interfere with the mismatch calibration circuit. To verify the proposed technique, a 2.4-GHz Weaver image-reject receiver with the gain and phase mismatch calibration circuit is implemented in a 0.18-${\mu}m$ CMOS technology. The overall receiver achieves a voltage gain of 45 dB and a noise figure of 4.8 dB. The image rejection ratio(IRR) is improved from 31 dB to 59.76 dB even with 1 dB and $5^{\circ}$ mismatch in gain and phase, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1299-1308
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• 2007

In this paper, we propose the calibration method of monopulse slope to minimize the variation of angle estimate in frequency agile noncoherent monopulse system. We analyze the monopulse slope characteristics of antenna and RF receiver including the phase and gain imbalances of each receiving channel and present the calibration method to minimize the phase and gain imbalances of RF receiver channels including antenna. In addition, we present the calibration method using channel switching to minimize the gain imbalance of IF receiver channels. The measured average monopulse slope within the frequency bandwidth is -0.96, the maximum variation of angle estimate is similar to theoretical value, $0.15^{\circ}$ at ${\pm}2^{\circ}$ azimuth and $0.03^{\circ}$ at $0^{\circ}$ azimuth.

• Journal of electromagnetic engineering and science
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• v.15 no.3
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• pp.181-184
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• 2015

Evaluation of radiating radiofrequency fields from hand-held and body-mounted wireless communication devices to human bodies are conducted by measuring the specific absorption rate (SAR). The uncertainty of system validation and probe calibration in SAR measurement depend on the variation of RF power used for the validation and calibration. RF input power for system validation or probe calibration is controlled manually during the test process of the existing systems in the laboratories. Consequently, a long time is required to reach the stable power needed for testing that will cause less uncertainty. The standard uncertainty due to this power drift is typically 2.89%, which can be obtained by applying IEC 62209 in a normal operating condition. The principle of the Automatic Input Power Level Control System (AIPLC), which controls the equipment by a program that maintains a stable input power level, is suggested in this paper. The power drift is reduced to less than ${\pm}1.16dB$ by AIPLC, which reduces the standard uncertainty of power drift to 0.67%.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.47-52
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• 2002

It was virtually declared that measurement science must abandon the error analysis of measurement when ISO had published "Guide to Expression of uncertainty in Measurement" International inclination of measurement field in order to guarantee the traceability and confidence of measurement results discards the error concept and instead analyzes the measurement uncertainty. In this paper we establish a mathematical model of measurement and analyze all uncertainty factors as possible as for yielding the measurement uncertainty in the course of the calibration of RF multimeter using Transfer Standard, Thermal Voltage Converter We produce the expanded uncertainty by analyzing cable effects, correlation of thermocoupler and DC meter, DC source, RF source, attenuator, reflection coefficients and DUT.s and DUT.