• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.734-739
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• 2001

In this paper, the technique of analysis and optimization on the Passive intermodulation(PIM) in a filter using coaxial transmission resonator, is presented. The developed simulation technique can reduce PIM power without the degradation of the linear filter response, through the variation of filter dimensions. The increase of PIM in filter is depended on currents flowing through each resonator forming filter. The reduction of these currents therefore makes the reduction of PIM power.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.19-21
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• 2007

디지털용 Uncooled DFB 레이저 다이오드를 이용하여 광대역 아날로그 피드포워드 광송신기를 제작하였다. 광송신기의 상호변조왜곡 성분 및 잡음성분을 제거하기 위해 광 피드포워드 보상기법을 사용하였으며, 다중서비스를 위해 $2.05{\sim}2.60$ GHz(550 MHz)에서 상호 변조왜곡 성분이 10 dB 이상 억제되었고, 상대강도잡음은 1.5 dB 이상 억제되었다. 2.3 GHz 에서 3 차 상호변조왜곡성분이 21.3 dB, SFDR 이 7.11 dB 향상된 결과를 얻었다. 또한 단일 모드 광섬유 전송 실험을 통해 전송길이에 따른 3 차 상호변호 왜곡성분의 크기 변화를 확인하였다.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.115-119
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• 2017

Intermodulation distortion degrades the S/N(signal-to-noise) of the original signal and also affects the adjacent channels. Intermodulation distortion is mainly caused by the nonlinear characteristics of the power amplifier. If the power amplifier with nonlinear characteristics has a memory effect, the intermodulation distortions occurred in the power amplifier are generated in various and complex forms. The predistorter is used as a way to improve intermodulation distortions. In order to efficiently utilize the performance of the predistorter, the memory effect of the power amplifier must be reduced. In this paper, we describe the design method of bias circuit to reduce the memory effect in power amplifiers. To reduce the memory effect, the bias circuit must have a high impedance for the signal and a low impedance for the envelope(modulating signal) and the second harmonic component of the signal. To verify the performance of the bias circuit designed considering the memory effect, a power amplifier operating at 170 ~ 220MHz was designed and implemented. The designed bias circuit has a large impedance in the operating frequency band and low impedance in the envelope signal and the second harmonic of the signal. As a result of the performance measurement, it was found that the asymmetric intermodulation distortion component is improved by 3.7dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1394-1401
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• 2008

This work investigates the effects of vibration on the passive intermodulation distortion characteristics of base station antennas for 800 MHz CDMA mobile communication systems. In general, base station antennas are located at high positions such as on building rooftops or iron towers. Thus the antennas are always affected by random vibrations, coming from various natural environmental factors such as rain and wind, or from living environmental factors such as vehicles and trains passing by. The measured intermodulation distortion characteristics before and after vibration accelerated degradation test show that vibrations are indeed the main cause for the intermodulation distortion performances of such antennas. To minimize the effects of vibrations, a new antenna design isptoposed that has an improved tolerance for vibrations. Experimental results show that the proposed antenna design dramatically reduces the degradation of the intermodulation distortion more than 35 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.105
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• pp.129-133
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• 2006

In spite of the advantage of simple circuit, small size, and low price, predistortered power amplifier does not satisfy the IMD specification at low power range because of an IMD hump characteristic. To reduce the performance degradation by IMD hump, the method which is to control the operating point of amplifier according to its output power is presented. This method using envelope detection bias control is applied to the implemented class AB predistortered 16 W power amplifier. The measured result shows 10 dB improvement of $3^{rd}$ IMD performance in wide dynamic range of output power.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.741-749
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• 2003

In this paper, we investigated the degree of compensation for WDM channel signal distortion due to chromatic dispersion, self phase modulation(SPM) and cross phase modulation(XPM). The considered system is 120 Gbps (3${\times}$40 Gbps) intensity modulation direct detection(IM/DD) WDM transmission system with path-averaged intensity approximation(PAIA) mid-span spectral inversion(MSSI) as compensation method. This system have highly nonlinear dispersion shifted fiber(HNL-DSF) as nonlinear medium in optical phase conjugator(OPC). We use 1 dB eye opening peralty(EOP) in order to evaluate the characteristics of compensation for distorted WDM channels. We confirmed that improvement of transmission distance and performance is achieved by MSSI method to distorted long-haul IM/DD WDM channels due to chromatic dispersion, SPM and XPM. And in the aspect of compensation for distorted pulse due to XPM, the MSSI method is effective to IM/DD WDM transmission system with high fiber dispersion coefficient.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1201-1207
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• 2010

As the mobile services have been increased, the PIMD(Passive Inter-Modulation Distortion) as well as the active-IMD of the CDMA system should be considered for the design of base station antenna systems, because they have an interference of the neighboring base stations. In this paper, in order to reduce the nonlinearity of current caused by the local point contact, we have investigated an influence of the combination of nuts, contact torque(kgf.cm), and the contact area on the PIMD. We propose the improvement techniques of PIMD by investigating the effects of the distance of nuts, the contact area, and the type of nuts.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.12
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• pp.1684-1690
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• 2018

A new digital pre-distortion (DPD) technique for closely spaced dual-band signals is proposed. In the system under consideration, dual-band signals are amplified by a single broadband power amplifier (PA) at a transmitter. The PA output is distorted by cross-modulation between the two bands as well as their own inter-modulation distortion. Especially, if the two bands are placed in close proximity to each other, their spectral regrowths due to in-band intermodulation overlap with each other, which degrades DPD performance. To solve this problem, we propose a new DPD technique where the dual-band PA characteristics are estimated first, and then the DPD parameters are obtained from the estimated PA characteristics. By finding the DPD parameters through two steps, pre-distortion can perform well for the closely-spaced dual band signals. The proposed technique is verified through computer simulation. Simulation result shows that the proposed method performs better than the conventional method for closely-spaced dual band signals.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.92-96
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• 2003

In this paper, 30 W power Amplifier for IMT-2000 repeater was developed gain flatness and the third IMD (Intermodulation distortion) by Microwave absorber. The absorption ability of the absorber is measured up to -10 ㏈ and -4 ㏈ at 3.6 ㎓, 2.3 ㎓ band respectively. Non using absorber power amplifier has the gain over 57 ㏈, the gain flatness of ${\pm}$0.33 ㏈ and the third IMD of 27 ㏈c at 33.3 W output. Otherwise, using absorber power amplifier has the gain over 58㏈, the gain flatness of less than ${\pm}$0.9, the third IMD over 29 ㏈c at the same output power. As a result, the characteristic of the different type show improvement of 1 ㏈ in gain, 0.3 ㏈ in Gain flatness and 1.77 ㏈c in IMD.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.5
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• pp.33-39
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• 2008

We have experimentally demonstrated the transmission performance of a feedforward optical transmitter using an external light injection technique. The feedforward compensation method shows 31 dB intermodulation distortion suppression and 2.2 dB noise reduction. A high side-mode suppression ratio exceeding 35 dB of the wavelength of the locked Fabry-Perot laser diode was obtained over 12 nm ranges. The suppression characteristics of the intermodulation distortion for various wavelength differences and transmission lengths were measured and analyzed as the evaluation criteria for the system performance in WDM/SCM based radio-over-fiber systems.