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A novel compact dual-mode circular-patch bandpass filter (BPF) with improved stopband performance is presented. A pair of square etched areas acting as a perturbation element on the circular-patch resonator is used in the proposed structure, so that the two split modes are coupled and the filter structure can be reduced. An open stub is attached at the input/output port in order to improve the stopband performance of the proposed BPF. The proposed BPF is demonstrated with a central frequency f0 = 2.17 GHz, insertion loss of −2 dB, a 3-dB bandwidth of 8%, and a rejection of −35 dB at the 2nd harmonic. The measured results of experimental filter show good agreement with the theoretical simulated results. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 203–206, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21123

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.

This paper describes the microstrip stepped-impedance resonator (SIR) bandpass filter with an over-coupling structure for the suppression of spurious response at twice the center frequency (2f0). In addition, the tapped I/O is used in the filter to create the extra transmission zeros to further improve stopband rejection. First, conventional approximate design formulas of microstrip SIR are also presented to predict the filter performance, and then the EM simulation is used to optimize the filter performance. The designed bandpass filters have a wide upper stopband with satisfactory attenuation levels. The experimental results of the two designed filters are in good agreement with the theoretical predictions and simulated results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 130–133, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20069

In this paper, we study the size effects of an H-shaped defected ground structure (DGS) cell upon the characteristic impedance of a microstrip line, by using a simple circuit-analysis method. An LC model of an equivalent circuit can represent the proposed H-shaped DGS cell. It is found that the characteristic impedance of a 50Ω microstrip line can be controlled easily in a wide range by using the H-shaped DGS cell. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 34–37, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20367

A stepped-impedance resonator (SIR) bandpass diplexer using over-coupling structures and tapped input/output (I/O) has been presented. The advantages of this construction are simple design and suppression of spurious response at twice the center frequency (2f0). The tapped I/O creates an extra transmission zero in each filter of the duplexer in order to improve stopband attenuation. The diplexer, designed at 0.9 and 1.8 GHz, is suitable for mobile communication and is easily fabricated in the packing surface. Experimental results of the designed duplexer are in good agreement with the theoretical predictions and simulated results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 79–82, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20215

A novel dual-mode bandpass filter using a microstrip triangular ring resonator with coupling stubs has been designed and tested. The basic configuration of this novel dual-mode filter is a triangular ring resonator. Quasi-L-shaped I/O arms used as coupling stubs for enhanced coupling are nonorthogonally and symmetrically separated on each corner of the triangular resonator, and a perturbation element is introduced within the resonator at a symmetrical location. The effects of the lengths of the coupling stubs and the width of the perturbation element are studied. New filters having narrower or wider bandwidth and transmission zeros are presented. The proposed filter responses are in good agreement with the simulations and experiments. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 512–515, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20519

Low temperature sintering and microwave dielectric properties of barium polytitanate (BaO–4TiO 2 ) ceramics prepared by means of polymeric precursor route based on the Pechini process were investigated. Pure and fine BaTi 4 O 9 powders with particle sizes of 100–200 nm were derived by thermal decomposition of amorphous gel precursor (above 750 °C). They formed single orthorhombic BaTi 4 O 9 phase and showed fine and well-dispersed by XRD and SEM observation. The high sintering ability of the prepared powders enabled the fabrication of dielectric ceramics at low sintering temperatures (1200–1300 °C). The well-sintered BaTi 4 O 9 ceramics with high relative densities (95%) were found to show excellent microwave dielectric properties compared to those prepared by conventional method at the same sintering temperature.

The effects of CuO, Bi2O3 and V2O5 additives (up to 3 wt.%) on the microstructures and the microwave dielectric properties of (Zr0.8Sn0.2)TiO4 ceramics are investigated. The sintering temperature of (Zr0.8Sn0.2)TiO4 ceramics with CuO, Bi2O3 and V2O5 additions can be effectively reduced from 1400 to 1300°C due to the liquid phase effects. The grain grows at lower sintering temperatures (1300°C) to 4.5–5.4 μm with CuO, Bi2O3 or V2O5 additions. The dielectric constants (er) are not significantly affected by various additives and ranged in 36–38. Small values (

(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.

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.

High-permittivity dielectric ceramic materials have been applied in the fabrication of a planar stepped-impedance resonator (SIR) microwave bandpass filter. The input/output ports of the filter are formed with transmission lines directly tapped to the resonators. The admittance matrix for the equivalent circuit of the filter has been derived and transformed to the scattering matrix to initially determine the required spec. Losses and other EM effects are taken into account to further modify the actual dimension of the designed filter. The designed structures are simulated using an IE3D simulator. Fabricated filters are measured by an HP8510B network analyzer. Sample results of the filter performances demonstrate responses in good agreement with the computer simulations. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 410–413, 2000.

A pseudo-interdigital stepped impedance resonator (SIR) bandpass filter (BPF) using tapped I/O is designed and fabricated. By using a pseudo-interdigital structure and the SIR, the proposed BPF gains advantages of compactness and high selectivity. In this paper, the first and second spurious responses are shifted to higher than 3f0 (the designed center frequency) due to the SIR effect and the effect of using the tapped I/O, and fast passband-edge attenuation is obtained as a result of the transmission zeros in the passband edge created by interstage coupling. The experimental results of the fabricated filter show good agreement with the simulation results. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 462–464, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21200

In this paper, a microstrip parallel-coupled bandpass filter based on electromagnetic bandgap (EBG) structures to achieve spurious suppression is presented. The EBG loops of the middle layer add an extra stopband-rejection mode to the 2nd and 3rd harmonics of the filter with attenuation losses of over than −30 dB, without affecting the center frequency and insertion loss of the originally designed filter. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 575–577, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20700

A tapped-line stepped-impedance resonator band-pass filter was implemented using a low temperature cofired multilayer-ceramic structure. By constructing a multilayer structure, a compact band-pass filter was realized. Moreover, the multilayer structure demonstrated an extra cross-coupling effect that produced extra transmission zeros in the stopband and, hence, realized a highly steep passband skirt. The center frequency of the fabricated band-pass filter was 6.075 GHz and the 3 dB fractional bandwidth was 18%. The measured insertion loss and return loss of the filter were -0.31 dB and -28 dB, respectively. The measured response of the fabricated band-pass filter was in good agreement with simulated results.

A novel dual-mode band-pass filter with a cross-shaped resonator and three ring resonators has been designed and implemented. The proposed structure is different from the conventional dual-mode band-pass filter. The designed dual-mode band-pass filter has a very sharp attenuation rate by two transmission zeros, and high spurious suppression by the band-stop effect of the three ring resonators. The experiments show good agreement with the simulations. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 177–179, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20412

A microstrip triangular-patch dual-mode filter using quasi-fork recessed tapped I/O is designed and fabricated. The proposed filter uses quasi-fork recessed tapped I/O for enhanced coupling and dual-mode excitation. The filter characteristics, which are influenced by the recessed depth and gap size between the feed line and the triangular-patch resonator, is studied. The central frequency of 4.19 GHz, insertion loss S21 of −1.26 dB, and 3-dB bandwidth of 26.5% are measured, and the three attenuation poles have deep insertion losses of −36.8 dB at 2.72 GHz, −44.6 dB at 3.06 GHz, and −49 dB at 5.56 GHz, respectively. The proposed filters demonstrate good agreement between the experiment and simulation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 99–101, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20388

By using high-permittivity dielectrics, bandpass filters can be miniaturized. A hairpin-line filter based on high-permittivity dielectrics is proposed in this study. Ba2Ti9O20, with high dielectric constant, low loss, and stable temperature is available for the dielectric resonator and is adopted as a material in the fabrication of high-permittivity ceramic substrates. A tape-casting technique is employed to produce thin and flat Ba2Ti9O20-based ceramic substrates. The center frequency of the fabricated bandpass filter is 5.75 GHz and the bandwidth is 742 MHz. The measured insertion and return losses of the filter are −1.34 and −12 dB, respectively. The measured response of the fabricated filter is in agreement with the simulated results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 164–166, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20408

A miniaturized multilayer hairpin bandpass filter using tapped-line I/O with tunable transmission zeros is designed and implemented. This structure provides additional cross-coupling between two layers, as well as the coupling effect on the same layer. The designed filter demonstrates superior passband characteristics with a central frequency f0= 2.39 GHz, insertion loss S21= −1.45 dB and a return loss S11= −32 dB. Moreover, by combining with two layers and tapped-line I/O structure, the filter produces two tunable transmission zeros at 2.8 GHz with −48 dB and 3.2 GHz with −43-dB rejection that the typical elliptic function response can be easily. Experimental results of the fabricated filter measured by network analyzer agree well with the simulation results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 53–55, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20044

This paper presents the improved stopband of a novel dual-mode bandpass filter (BPF) using an etched H-shaped defected ground structure (DGS) at 2 GHz. The wide-stopband characteristic results from the rejection-band resonant characteristic of the DGS in the harmonic frequency of the dual-mode BPF. The proposed BPF is designed and fabricated with the following frequency characteristics: central frequency f0 = 2 GHz, 3-dB bandwidth of 3%, and wide stopband from 2.5 to 5 GHz at −40 dB. The measured results of the fabricated filter show good agreement with the simulation results. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 247–249, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20600

A novel bandpass filter using tapered PBG cells is designed and implemented. With the tapered PBG structure inserted between the top layer of two hairpin resonators with symmetric feed-line tapping and a ground-plane bottom layer, the passband characteristics are excited and, moreover, a transmission zero on the higher passband edge is produced. The novel bandpass filter using tapered PBG cells demonstrates the frequency characteristics with a central frequency f0 = 2.9 GHz, a 3-dB bandwidth (FBW) of 9%, and insertion loss S21 of −2.8 dB. Good agreement between the experimental and simulation results is obtained. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 66–68, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20048

A stepped impedance resonator (SIR) low-pass filter using defect ground structure (DGS), which has high isolation and compact size, is proposed. The proposed defect ground structure (DGS) provides excellent cutoff and stopband characteristics for improving the stopband rejection and the attenuation rate of the bandpass edge. In order to illustrate the improved performance, we compare the conventional low-pass filter and the proposed novel low-pass filter with DGS. The measurement results of the fabricated low-pass filter show excellent agreement with the theoretical results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 382–384, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20477

A microstrip coupled-line filter with a multilayer structure is designed and implemented. This structure provides additional overlapped coupling and cross coupling between two layers, except for the coupling effect on the same layer. The designed filter demonstrates the frequency characteristics with central frequency f0 = 2.4 GHz, return loss S11 = −12.2 dB, and insertion loss S21 = −2.49 dB. Moreover, it is found that, due to a transmission zero occurring at 3.14 GHz with −45-dB rejection, a typical elliptic-function response can be easily obtained by the proposed structure. Experimental results of the fabricated filter measured by using a network analyzer agree well with the simulation results. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 493–495, 2003

Small size and rapid attenuation rate are two important factors in the selection of bandpass filters for practical applications. This paper describes a monoblock and modified Chebyshev-type bandpass filter with an attenuation pole in the lower stopband. The equivalent circuit consists of resonators, and series capacitance is presented to predict the filter performance. The series capacitance is made directly by an appropriate choice of the electrode pattern. Since no additional lumped element is needed, the designed filter shows a simple structure. Also, a compact monoblock bandpass filter using high-permittivity ceramics of (Ba,Sr)O–Sm2O3–4.7TiO2 is fabricated. Experimental results of the fabricated filter measured by an HP8510B network analyzer verify the expected effect. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 400–402, 2002.

A miniature monoblock bandpass filter with combline-type, quarter-wavelength, and capacitive coupling is investigated. The coupling analysis and equivalent circuit consist of the transmission lines, and lumped elements are presented to predict the filter performance. A filter design technique based on the results of the equivalent-circuit parameters is described. A miniature monoblock bandpass filter using (Zr0.8, Sn0.2)TiO4 ceramics is fabricated at a center frequency of 1600 MHz. Excellent experimental results of the fabricated filter measured by an HP8510B network analyzer verify the design specification. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 95–97, 2001.

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.

The Nano powder and microwave dielectric properties of zirconium tin titanate (Zr0.8Sn0.2TiO4, ZST) ceramics prepared by sol–gel process were investigated. Pure and fine ZST powders with particle sizes of 10–20 nm were derived by thermal decomposition of an amorphous gel precursor at about 700°C. They formed a single orthorhombic ZST phase and appeared fine and well-dispersed in both scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). The high sintering ability of the prepared powders enabled the fabrication of dielectric ceramics at low sintering temperatures (1250–1300°C). The well-sintered ZST ceramics with high relative densities (96%) showed excellent microwave dielectric properties compared with those prepared by a conventional method at the same sintering temperature.

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.

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.

The microwave dielectric properties and the microstructures of (1-x)BiNbO4-x BiTaO4 ceramics (x=0, 0.15, 0.2, 0.4, and 0.6) doped with 0.5 wt% CuO are investigated. Ta is substituted for Nb in order to adjust the temperature coefficient of the resonant frequency (τf) and improve the quality factor (Q). All BiNb(1-x)Ta x O4 compositions can be sintered to achieve a 96% theoretical density below 960°C. The sintering temperatures of BiNb(1-x)Ta x O4 increase with increasing of x values. The dielectric constants (ε r) of all compositions saturate at 44–45 in spite of the Ta content. Q×f values of 13000–22000 (GHz) are obtained for all compositions when the sintering temperatures are in the range of 920–940°C. By increasing the amount of the doped Ta, the temperature coefficient of the resonant frequency τf can be adjusted from a positive value of +15 ppm/°C to a negative value of -30 ppm/°C. The BiNb(1-x)Ta x O4 ceramics can be applied to multilayer microwave devices with low sintering temperatures.