Min-Hung Weng

Low temperature sintering and microwave dielectric properties of Ba2Ti9O20 ceramics using glass additions

Abstract The effects of glass additions on the microwave dielectric properties and the microstructures of Ba 2 Ti 9 O 20 ceramics were investigated. The simple glasses B 2 O 3 and SiO 2 and the commercial glass PbO–B 2 O 3 –SiO 2 (PBS) were selected as liquid phase sintering aids to lower the sintering temperature of Ba 2 Ti 9 O 20 ceramics. With glass additions, the sintering temperatures can be effectively lowered. The dielectric properties of Ba 2 Ti 9 O 20 ceramics with glass additions are strongly dependent on the densification, the microstructure, and the reaction between glasses and ceramics. Ba 2 Ti 9 O 20 ceramics without glass addition sintered at 1380°C has a dielectric constant e r = 38.8, a quality factor Q = 7200 at 6.0 GHz, and a temperature coefficient of resonant frequency τ f = 4 ppm/°C. Among these glasses, 5 wt% B 2 O 3 added Ba 2 Ti 9 O 20 can be sintered to achieve theoretical densities of 96 and 95% at 1100 and 1200°C, and gives e r values of 36.5 and 36 together with Q values of 3200 and 6700 (at 6 GHz), respectively. Results of XRD analysis and scanning electron microscopy are also presented.

Low-Temperature Sintering of Microwave Dielectrics (Zn,Mg)TiO3

Dielectrics (Zn,Mg)TiO3, having a high dielectric constant and a near zero temperature coefficient of resonant frequency are promising materials for microwave applications. In this work, Bi2O3 was added to (Zn,Mg)TiO3 as a low-temperature-sintering dopant. The addition of Bi2O3 significantly improved the densification of (Zn,Mg)TiO3, which were densified below 1000°C. In addition, the decomposition temperature of (Zn,Mg)TiO3 increased as the magnesium substitution increased. Microwave dielectric properties of (Zn,Mg)TiO3 ceramics depend on crystalline structure. By properly adjusting the amount of magnesium, a small temperature coefficient of resonant frequency was obtained for (Zn,Mg)TiO3 dielectrics.

Novel compact microstrip interdigital bandstop filters

A novel compact microstrip interdigital band-stop filter is designed and implemented. The structure is similar to that of an interdigital capacitor. The input port and output ports are connected to form the bandstop characteristic. This proposed filter with microstrip interdigital geometry not only exhibits good bandstop characteristics and a tunable central frequency, but it also is easy to fabricate and integrate. The features of this microstrip interdigital bandstop filter are smaller than those of the conventional bandstop filter. Simulation results closely correspond to the experiments.

The effect of PbO loss on microwave dielectric properties of (Pb,Ca)(Zr,Ti)O3 ceramics

Abstract (Pb1−x,Cax)(Zr1−y,Tiy)O3 (PCZT) perovskite type ceramics exhibit microwave dielectric properties of high dielectric constant (er), high unloaded Q and small temperature coefficient of resonant frequency (τf). However, the sintering temperature was as high as 1450°C and the microstructure and dielectric properties were difficult to control due to high PbO volatility. In this paper, we report the effect of PbO loss on microstructure and microwave dielectric properties of PCZT ceramics. Suppression of PbO loss by B-site ion substitution in PCZT was also investigated.

Design of a Wide-Stopband Bandpass Filter by Using Different Feeding Positions of the I/O Ports

In this paper, a wide-stopband bandpass filter is presented. The proposed filter only used two stepped-impedance resonators (SIRs) with a simple electric-coupling structure to accomplish a wide-stopband response. The passband of the proposed filter is designed for global system for mobile communications (GSM) at 1.8 GHz. The spurious responses of the SIRs are suppressed by controlling the locations of the transmission zeros effectively. The measured results show the passband at 1.8 GHz with a low insertion loss 1.18 dB, and the 3 dB fractional bandwidth (FBW) of 14.1%. The rejection of the stopband is greater than 14 dB from 2.1 to 17.7 GHz, a stopband bandwidth of 9.8 times of the fundamental frequency. The measured result of the fabricated filter also shows a good agreement with the simulated result.

Spurious suppression of a microstrip filter using three types of rectangular PBG loops

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with arid without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stop-band; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.

Single Phase Ba2Ti9O20 Microwave Dielectric Ceramics Prepared by Low Temperature Liquid Phase Sintering

Microwave dielectric ceramics of Ba2Ti9O20 were prepared by adding PbO–B2O3–SiO2 (PBS) as a liquid phase sintering aid. With the addition of 5 wt% PBS, dense and single-phase Ba2Ti9O20 dielectric resonators could be fabricated at a sintering temperature below 1200°C. The microwave dielectric properties of PBS–Ba2Ti9O20 ceramics were found to depend upon the density, the amount of liquid phase and the sintering temperature. Although glass addition results in a decrease of the dielectric properties, the sintered PBS–Ba2Ti9O20 ceramics still exhibit much better dielectric properties than that of pure Ba2Ti9O20 ceramics at low sintering temperatures.

Design of the Fractal-Based Dual-Mode Bandpass Filter on Ultra Thin Liquid-Crystal-Polymer Substrate

In this paper, a novel miniature dual-mode bandpass filter based on modified Sierpinski fractal is proposed and realized on the ultra thin (100 μm) flexible liquid-crystal-polymer (LCP) substrate for wireless local area network (WLAN) IEEE 802.11a. The subwavelength property which leads to the miniature characteristic is investigated in this paper. We adopt the 3rd order Sierpinski geometry as the mainly dual-mode resonator to form a dual-mode filter. The measured result is in good agreement with the full-wave simulation result.

Design of a Compact CMOS Bandpass Filter for Passive Millimeter-Wave Imaging System Application

We proposed a novel method to realize a compact bandpass filter (BPF) using a standard CMOS process for a 35 GHz passive millimeter-wave (PMMW) imaging system. We first investigated the principal loss of low resistivity silicon substrate, which could be effectively reduced by adding a ground plane in bottom layer. In order to improve the inherent poor quality of the designed dual-mode BPF due to stacking less oxide layers, a novel design skill by adding a branch line in M3 layer was provided. A CMOS BPF with an insertion loss of 4 dB and good selectivity were realized in succeed.

A High Selectivity Dual-Band Filter Using Ring-Like Sir with Embedded Coupled Open Stubs Resonators

We present a design of dual-band bandpass filter (BPF) using a ring-like stepped-impedance-resonator (SIR) and embedded coupled open stubs for application to a wireless local area network (WLAN). The dual-passbands are created by optimally selecting the impedance ratio (K) and length ratio (u) in the resonant behavior of a conventional SIR. Without increasing the circuit size, the performance of the second passband can be enhanced by adding the coupled open stubs in the ring-like SIR. The proposed filter was designed and fabricated. The measured results have a return loss larger than 24 dB, a low insertion loss less than 1.3 dB, and a fractional bandwidth (FBW) of 15% at 2.4 GHz, as well as a return loss larger than 12 dB, a low insertion loss less than 2 dB, a FBW of 2% at 5.7 GHz, and transmission zeros at 2.09, 2.96, 5.44, and 6.11 GHz near the passband edges. It is verified that experimental results show a good agreement with the simulated results.