Sang-Kyu Lim

The design of a temperature-stable stepped-impedance resonator using composite ceramic materials

The authors present a method to design a coaxial ceramic resonator, whose resonance frequency is unchanged with temperature, using a material with a positive temperature coefficient of resonant frequency (/spl tau//sub f/) and a negative /spl tau//sub f/ material. From the resonance conditions according to temperature variation, the length to be filled with each material is calculated to minimize the resonance frequency shift with temperature change. As an example, Ba(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/ and CaZrO/sub 3/ are selected in this work, and their lengths are obtained at various resonant frequencies. The temperature dependence of the resonant frequency of this resonator is simulated.

The microwave dielectric properties of xTiO2(1−x)CeO2 ceramics

The xTiO2(1−x)CeO2 system was investigated and its dielectric properties were measured. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. CeO2 was measured to have dielectric constant er=24, Q*f=57,000 and τf=−104 ppm/°C. TiO2 has er=93, Q*f=10,000 and τf=350 ppm/°C. xTiO2(1−x)CeO2 system has the dielectric properties as follows: 32<er<74, 25,000<Q*f<43,000 and −100<τf<300. It is the temperature-stable material that is achieved. A series of new xTiO2(1−x)CeO2 dielectric materials were synthesized. Its dielectric characteristics(er, Q*f and τf) are intermediate between TiO2 and CeO2. It is found that the ceramic in the xTiO2(1−x)CeO2 system has excellent dielectric characteristics at microwave frequencies.

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na1/2Ln1/2)TiO3> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (τf) (where Ln represents a lanthanide: La+3, Pr+3, Nd+3 and Sm+3). On the other hand, MgTiO3 ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO3-(1 − x)(Na1/2 Ln1/2) TiO3. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO3 and Na1/2 Ln1/2)TiO3 phases. Its dielectric characteristics (Q*f, temperature coefficient and dielectric constant) are intermediate between (Na1/2 Ln1/2) TiO3 and MgTiO3 and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.

Design and RF characteristics of traveling-wave electrodes for high-speed lithium niobate optical modulators

Various types of traveling-wave electrodes for a high-speed LiNbO/sub 3/ optical intensity modulator were fabricated and characterized from the viewpoints of the characteristic impedance, the effective refractive index and an attenuation constant, which were extracted from measurements in the time domain and the frequency domain. The effects of trenching the SiO/sub 2/ buffer layer on electrical properties were examined. In this work the maximum value of the optical 3 dB modulation bandwidth, calculated by experimental results, was 18 GHz, and it is suggested that optical/RF phase velocity matching and the impedance matching can be achieved, and thus a higher value of the optical 3 dB modulation bandwidth can be obtained.

Improvement of sintering condition and dielectric characteristics of (Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramics with addition of Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/ ceramics

We report the effects of the addition of PFW on the decrease of the sintering temperature and the improvement of dielectric properties at microwave frequencies of the PCZ ceramic system. It was found that an addition of Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/ promotes the grain growth, the solid solution between the Pb-based perovskite and the Ca-based perovskite and a decrease of the sintering temperature. We found that 0.05Pb(Fe/sub 2/3/W/sub 1/3/)O/sub 3/-0.95(Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramic can be sintered at less than 1250/spl deg/C. The dielectric properties of this compound are better than those of the (Pb/sub x/Ca/sub 1-x/)ZrO/sub 3/ ceramic system.

Low temperature sintered ceramics in ZnO-RO/sub 2/-TiO/sub 2/-Nb/sub 2/O/sub 5/(R=Sn,Zr,Ce) ceramic system with FeVO/sub 4/ addition

In the present study, a new microwave dielectric ceramic is reported that is based on ZnO-TiO/sub 2/-Nb/sub 2/O/sub 5/ systems. The dielectric properties at microwave frequencies of ZnO-RO/sub 2/-TiO/sub 2/-Nb/sub 2/O/sub 5/ (R=Sn,Zr,Ce) ceramic systems with FeVO/sub 4/ addition were characterized.