Chung-I G. Hsu

Tri-Band Bandpass Filter With Sharp Passband Skirts Designed Using Tri-Section SIRs

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.

Design of Circularly Polarized Annular-Ring Slot Antennas Fed by a Double-Bent Microstripline

A novel design of a circularly polarized annular-ring slot antenna is discussed. The circular polarization is attained through a newly proposed double-bent microstripline that feeds the antenna at two different positions. Several structural parameters were experimentally studied with care to establish a design procedure, which was subsequently drawn into a design flow chart. Validation was carried out using the antennas designed at 3.5 and 1.59 GHz. The measured 3-dB axial-ratio bandwidth (ARBW) for the former is 10.5% and for the latter, 10.0%, which is larger than the 8.5% 3-dB ARBW required by an Inmarsat application.

Band-Notched Balanced UWB BPF With Stepped-Impedance Slotline Multi-Mode Resonator

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.

Dual-Band Balanced BPF Using λ/4 Stepped-Impedance Resonators and Folded Feed Lines

This paper presents a second-order dual-band balanced bandpass filter (BPF) designed using bi-section quarter-wavelength (λ/4) stepped-impedance resonators (SIRs) and folded feed lines. The first two modes of the λ/4 SIRs are designed to resonate in the designated 2.4- and 5.2-GHz WLAN bands. High-impedance folded transmission-line sections are inserted in series with the feed lines to improve the overall impedance matching at the input/output ports, so that the signal transmission can be enhanced. In addition, the feed lines and λ/4 SIRs are properly arranged to form an all-stop-like coupling configuration for common-mode operation. For the first (second) operating band of interest, the fabricated balanced BPF printed on an FR4 substrate was measured to have a minimum differential-mode insertion loss of 3.03 dB (4.3 dB) and a minimum common-mode rejection level of as high as 15.7 dB (22.3 dB).

Tri-band microstrip BPF design using tri-section SIRs

In this paper, a new second-order tri-band BPF is proposed and designed using open-stub-embedded TSSIRs. The three operating bands are chosen to be commercially practical, with their center frequencies being 1.57 GHz (GPS LI), 2.45 GHz (ISM), and 3.5 GHz (WiMAX), respectively. The 0deg feed and the embedded open stubs are implemented in the designed tri-band BPF to produce transmission zeros at appropriate frequencies for improving passband selectivity and stopband rejection. In addition, the TSSIRs are bent into rectangular shape to reduce the circuit size; their end sections are designed in an anti-parallel fashion to produce an extra zero. The proposed tri-band BPF will first be simulated by using HFSS (a full-wave electromagnetic simulator) and then verified by measured data. The filter design and the obtained results are presented.

Balanced Dual-Band BPF using only Equal-Electric-Length SIRs for Common-Mode Suppression

This paper presents a new balanced dual-band bandpass filter (BPF) designed for 2.4/5.2 GHz wireless local area networks (WLANs). Because adopted in the BPF are only bi-section equal-electric-length stepped-impedance resonators (SIRs), whose dimensions can be determined using analytic formulas, the BPF can be easily and efficiently designed. The inner SIRs are designed to resonate only at the odd-mode resonant frequencies of the input and output SIRs but not at the even-mode ones. This leads to well-behaved differential-mode (DM) transmission and excellent common-mode (CM) suppression for the BPF. Simulated and measured results are found to agree quite well to each other. The measured minimum DM insertion losses in the two passbands are 2.1 and 2.54 dB, whereas the measured CM rejections are higher than 33 dB in the frequency range from 1 to 7 GHz.

Design of balanced and balun diplexers using stepped-impedance slot-line resonators

A balanced diplexer and a balun diplexer, both designed for the two channels of 2.45-GHz WLAN and 3.55-GHz WiMAX, are proposed with high common-mode (CM) suppression and differential-mode (DM) isolation in this paper. For the balanced diplexer, balanced BPFs for the two desired channels were first designed using stepped-impedance slot-line resonators (SISLRs). Through two T-junctions, the two BPFs were subsequently combined to form a three-balanced-port diplexer having six single-ended ports. Such a balanced diplexer can be easily converted into a balun diplexer with one single-ended and two balanced ports. For that purpose, one of the T-junctions and its associated two feeding lines are removed, and the feeding lines connected to the other T-junction are modified. For both diplexers, the measured CM suppressions (DM isolations) are larger than 54.3 (39.5), 52.2 (44.5), and 40.7 (38.7) dB, respectively, in the lower channel, the upper channel, and the displayed frequency range of 1–6 GHz. A satisfactory agreement has been validated between the simulated and measured results.

Balanced Wideband Filtering Planar Inverted-F Antenna Design

A balanced wideband (WB) planar inverted-F antenna (PIFA) integrated with a balanced WB bandpass filter (BPF) is presented in this letter. Due to circuit symmetry, the balanced patch PIFA does not need a grounded via hole for its shorting strip, rendering the PIFA easy to fabricate. The balanced WB BPF that is added in front of the balanced PIFA serves to improve the differential-mode (DM) passband selectivity and upper stopband rejection and meanwhile to increase the common-mode (CM) rejection. In terms of the passband selectivity defined by the ratio of 20-dB bandwidth to the 3-dB bandwidth in the DM return-loss response, the simulated WB filtering PIFAs selectivity is increased from 0.6 to 0.86 after the WB BPF is integrated. In addition, high CM suppression was observed with a maximum return loss of 2.37 dB within the DM passband.

Design of Band-Notched UWB BPF with Very Wide Upper Stopband Using Combined λ/4 TSSIR

In this paper, a new band-notched UWB BPF with a very wide upper stopband is designed using a λ/4-type multi-mode resonator (MMR). The proposed MMR, being formed by combining two identical λ/4 tri-section stepped-impedance resonators (TSSIRs) in a structure-shared fashion, exhibits both λ/4 and embedded λ/2 types of resonance with a relatively smaller circuit size. By properly locating the first four resonant modes of the MMR and the coupling peaks of the input/output parallel-coupled lines, a five-transmission-pole UWB BPF is realized with a favorable uniform in-band UWB response. Besides the good UWB performance, a 5-GHz notched band is created by embedding in the output feed line a T-shape lumped-element bandstop structure to reject the influence from WLAN signals. Also, a very wide upper stopband is achieved by implementing a compact bandstop filter structure in the input feed line together with the properly located transmission zeros generated by the input/output interdigital-coupled lines and the second harmonic of the T-shape bandstop structure. A prototype of the proposed UWB BPF was fabricated and measured for performance verification. The measured results show a return loss of higher than 10 dB, a minimum insertion loss of 0.41 dB, and a group delay variation of less than 0.11 ns in the UWB passband except the notch. The notched band has a 3-dB bandwidth of 18%. The measured upper-end –20-dB stopband ranges from 11.94 to 30.56 GHz, with a bandwidth of 18.62 GHz.

Balanced dual-band diplexer design using microstrip and slot-line resonators

A balanced dual-band diplexer formed using hybrid microstrip and slot-line structure is proposed with good common-mode (CM) suppression in this paper. The balanced dual-band diplexer was constructed by combining two dual-band bandpass filters (BPFs) operating at 1.92/5.25 GHz and 2.45/5.8 GHz, respectively, through T-junctions. The incompleteness of the slot-line resonator results from the open-boundary condition along the symmetry plane in CM operation is employed to effectively suppress the CM signals. A prototype of the proposed balanced dual-band diplexer was implemented and measured with a differential-mode isolation of higher than 38.8 (33.4) dB and a CM suppression of larger than 22.9 (22.4) dB in the frequency range of 1-8 GHz.