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Ching-Her Lee

Bio: Ching-Her Lee is an academic researcher from National Changhua University of Education. The author has contributed to research in topics: Passband & Microstrip. The author has an hindex of 16, co-authored 80 publications receiving 1209 citations. Previous affiliations of Ching-Her Lee include University of Education, Winneba.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the second-order tri-band bandpass filter (BPF) was designed using tri-section stepped-impedance resonators (TSSIRs) and the impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45 and 3.5 GHz.
Abstract: This letter presents a second-order tri-band bandpass filter (BPF) designed using tri-section stepped-impedance resonators (TSSIRs). The impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45, and 3.5 GHz. A cross-coupled configuration was arranged to sharpen the passband skirts. The newly designed tri-band BPF was verified by circuit implementation and very good agreement between the simulated and measured results was observed.

202 citations

Journal ArticleDOI
TL;DR: In this paper, a tri-band microstrip bandpass filter (BPF) is proposed to produce three passbands at the commercially practical frequencies through a single piece of filter circuitry.
Abstract: A new tri-band microstrip bandpass filter (BPF) is designed to produce three passbands at the commercially practical frequencies through a single piece of filter circuitry. The basic component used to build the proposed filter consists of two quarter-wavelength (lambda/4) stepped-impedance resonators (SIRs). One of the lambda/4 SIRs is designed to operate at 1.57 GHz and 5.25 GHz, and the other at 2.45 GHz. The feed positions for the two lambda/4 SIRs are carefully located to have the same distance from the via-hole ground and meanwhile to give the required external quality factors (Qe's). In such a way, the microstripline sections between the via-hole and each of the feed positions can be combined into one to simplify the filter structure, and to reduce the BPF circuit size. Performance of the newly designed tri-band BPF is verified by measured results

156 citations

Journal ArticleDOI
TL;DR: In this paper, a balanced dual-band band-pass filter (BPF) using four coupled bi-section halfwavelength (?/2) stepped-impedance resonators (SIRs) is presented.
Abstract: A new fourth-order balanced dual-band band-pass filter (BPF) designed using four coupled bi-section half-wavelength (?/2) stepped-impedance resonators (SIRs) is presented. To obtain the required differential-mode (DM) operation with suppressed common-mode (CM) transmission, the SIRs were designed to have the same odd-mode, but different even-mode, resonant frequencies. For that purpose, the two inner SIRs were loaded at the center with T-shaped open stubs of different dimensions so that their even-mode resonant frequencies are shifted away from those of the outer SIRs and that their odd-mode ones remain almost intact. For the fabricated prototype BPF, the measured minimum DM insertion losses for the first and second bands are 2.4 and 2.82 dB, respectively, whereas the measured CM insertion loss is larger than 25 dB in 1-7 GHz.

113 citations

Journal ArticleDOI
TL;DR: In this paper, a compact microstrip-fed slot antenna design is proposed, where multiple resonant frequencies are excited and merged to form a large enough 10-dB return loss bandwidth (measured from 3.1 to 11.45 GHz) for UWB applications.
Abstract: A novel compact microstrip-fed slot antenna design is proposed. By properly loading a notch to the open-ended T-shaped slot and extending a small section to the microstrip feed line, multiple resonant frequencies are excited and merged to form a large enough 10-dB return loss bandwidth (measured from 3.1 to 11.45 GHz) for ultrawideband (UWB) applications. The vital parameters of the proposed antenna are illustrated, and a prototype is constructed and experimentally studied. The measured results show good radiation patterns and stable signal transmission within the band of interest.

92 citations

Journal ArticleDOI
TL;DR: In this article, a new 5 GHz band-notched balanced ultra-wideband (UWB) bandpass filter (BPF) was designed using a stepped-impedance slotline multi-mode resonator (MMR).
Abstract: This letter presents a new 5 GHz band-notched balanced ultra-wideband (UWB) bandpass filter (BPF), which is designed using a stepped-impedance slotline multi-mode resonator (MMR). To obtain favorable uniform differential-mode (DM) response, a microstrip-to-slotline transition is used as the signal-feeding structure and the first three resonant modes of the slotline MMR are located in the UWB passband. Common-mode (CM) signal rejection is achieved by deploying the slotline MMR in such a way that the quarter-wavelength resonances occurring near the input and output sides of the resonator are well decoupled. Also featured in this design is the blocking of unwanted WLAN signals, which is achieved by loading the input feed-lines with a stepped-impedance microstrip stub to create a notch-band centered at 5.5 GHz. The designed BPF has a measured minimum DM insertion loss of 0.83 dB in the UWB passband, in which the measured CM suppression is larger than 18.85 dB.

82 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, the second-order tri-band bandpass filter (BPF) was designed using tri-section stepped-impedance resonators (TSSIRs) and the impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45 and 3.5 GHz.
Abstract: This letter presents a second-order tri-band bandpass filter (BPF) designed using tri-section stepped-impedance resonators (TSSIRs). The impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45, and 3.5 GHz. A cross-coupled configuration was arranged to sharpen the passband skirts. The newly designed tri-band BPF was verified by circuit implementation and very good agreement between the simulated and measured results was observed.

202 citations

Journal ArticleDOI
TL;DR: In this paper, a new approach is proposed to reject certain bands within the passband of an ultra-wideband planar monopole antenna, which utilizes a mushroom-type electromagnetic-bandgap (EBG) structure.
Abstract: A new approach is proposed to reject certain bands within the passband of an ultra-wideband planar monopole antenna. The proposed approach that utilizes a mushroom-type electromagnetic-bandgap (EBG) structure is proven to be an effective way for band-notched designs. The approach has many advantages, such as notch-frequency tunability, notch-band width controllable capacity, efficient dual-notch design, and stable radiation patterns. Several design examples using conventional mushroom-type EBG and edge-located vias mushroom-type EBG are presented. The examples exhibit good bandstop characteristics to reject the wireless local-area network interference bands (5.2- and 5.8-GHz bands). Besides, the causes that lead to the discrepancies between the simulations and measurements are discussed.

180 citations

Journal ArticleDOI
TL;DR: In this paper, complementary split-ring resonators (CSRRs) are used to suppress the common mode in microstrip differential transmission lines, where the differential signals are not affected.
Abstract: This paper is focused on the application of complementary split-ring resonators (CSRRs) to the suppression of the common (even) mode in microstrip differential transmission lines. By periodically and symmetrically etching CSRRs in the ground plane of microstrip differential lines, the common mode can be efficiently suppressed over a wide band whereas the differential signals are not affected. Throughout the paper, we present and discuss the principle for the selective common-mode suppression, the circuit model of the structure (including the models under even- and odd-mode excitation), the strategies for bandwidth enhancement of the rejected common mode, and a methodology for common-mode filter design. On the basis of the dispersion relation for the common mode, it is shown that the maximum achievable rejection bandwidth can be estimated. Finally, theory is validated by designing and measuring a differential line and a balanced bandpass filter with common-mode suppression, where double-slit CSRRs (DS-CSRRs) are used in order to enhance the common-mode rejection bandwidth. Due to the presence of DS-CSRRs, the balanced filter exhibits more than 40 dB of common-mode rejection within a 34% bandwidth around the filter pass band.

146 citations

Journal ArticleDOI
TL;DR: In this paper, a tri-band bandpass filter using short and open stubs loaded resonators is presented, the first and third passband frequencies can be flexibly controlled by tuning the lengths of the stubs, whereas the second passband frequency is fixed.
Abstract: A tri-band bandpass filter using short and open stubs loaded resonators is presented. The first and the third passband frequencies of the tri-band filter can be flexibly controlled by tuning the lengths of the stubs, whereas the second passband frequency is fixed. A tri-band filter has been implemented with four transmission zeros, the filter has good tri-passband performance at 1.57, 2.4, 3.5 GHz measured results agree well with simulated ones.

146 citations

Journal ArticleDOI
TL;DR: In this paper, a triple-band bandpass filter with two transmission poles in each passband is proposed using three pairs of degenerate modes in a ring resonator, where four open-circuited stubs are attached symmetrically along the ring and they are treated as perturbation elements to split the two second-order degenerate mode, resulting in a two-pole second passband.
Abstract: In this paper, a class of triple-band bandpass filters with two transmission poles in each passband is proposed using three pairs of degenerate modes in a ring resonator. In order to provide a physical insight into the resonance movements, the equivalent lumped circuits are firstly developed, where two transmission poles in the first and third passbands can be distinctly tracked as a function of port separation angle. Under the choice of 135° and 45° port separations along a ring, four open-circuited stubs are attached symmetrically along the ring and they are treated as perturbation elements to split the two second-order degenerate modes, resulting in a two-pole second passband. To verify the proposed design concept, two filter prototypes on a single microstrip ring resonator are finally designed, fabricated, and measured. The three pairs of transmission poles are achieved in all three passbands, as demonstrated and verified in simulated and measured results.

136 citations