Ching-Her Lee

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.

Compact Slot Antenna for UWB Applications

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.

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).

Planar UWB Antenna with 5 GHz Band Rejection Switching Function at Ground Plane

The design of an octagonal-shaped microstrip-fed planar monopole antenna for ultrawideband (UWB) operation is studied. Two inverted T-shaped slits are embedded on the ground plane to allow band rejection characteristic from 5 to 6GHz (for VSWR < 2). To enable switching capability for this band rejection function, a PIN diode is connected to each slit via a specifled chip inductor that will be further investigated. Several prototypes were constructed and the measured results show that the proposed antenna can provide an operating bandwidth from 3.07 to 10.7GHz, except for the rejected band. Simulation analyses are also carried out to validate the experimental results.

MMR-based Band-notched UWB Bandpass Filter Design

A new band-notched ultra-wideband (UWB) bandpass filter (BPF) with an improved upper stopband is designed using a multi-mode resonator (MMR). The MMR, being a modified version of a common tri-section stepped-impedance resonator (TSSIR), is split at its two open ends with the input/output feed lines sandwiched in between to form an interdigital parallel-coupled configuration that results in stronger coupling. In addition, an extended coupling length in the second section of the TSSIR is featured to provide further coupling and impedance-matching tuning. With such a design strategy, coupling gaps of no smaller than 0.1 mm was achieved to obtain the required UWB response. In this design, the first five resonant modes of the MMR and the coupling peaks of the input/output parallel-coupled lines are properly located in the UWB passband to achieve a uniform in-band transmission response. Also, the spur lines and open-circuited stubs are implemented in the MMR to create a 5-GHz notched band and to broaden the upper stopband, respectively. The designed UWB BPF, which being verified by measurement, shows a very good UWB performance. The measured in-band minimum insertion loss and maximum group delay variation except those in the notched band are 0.45 dB and 0.05 ns, respectively, and the upper-end −20-dB stopband bandwidth is about 5.35 GHz. The created notched band is centered at 5.69 GHz with a maximum insertion loss of 37.2 dB and a 3-dB notch bandwidth of 18%.

Dual-Band Meander Monopole Antenna for WLAN Operation in Laptop Computer

A very small-size (10 × 6 × 0.4 mm ) uniplanar meandered monopole antenna that is fed by a 50-Ω mini-coaxial cable for laptop computer applications is proposed. To achieve dual-band 2.4/5-GHz wireless local area network (WLAN) operation, a protruded tuning stub is introduced into the meandered monopole structure. The achieved 10-dB bandwidths of the lower and upper operating bands in free-space condition are 12% (2360-2660 MHz) and 20% (4870-5960 MHz), respectively. Further experimental studies are also conducted by mounting the proposed antenna onto an actual laptop computer that works as the host platform.

Multi-Band Printed Internal Monopole Antenna for Mobile Handset Applications

An internal multi-band CPW-fed monopole antenna designed for mobile handset applications is proposed. By embedding an open-ended slot and two parallel slits in the ground plane and radiating element, respectively, a triple-band operation measured along VSWR 3 : 1 that is able to cover the wireless applications such as GSM, DCS, PCS, UMTS, WLAN, and WiMAX can be achieved for this antenna. Furthermore, good radiation patterns and stable gain variation are measured over these bands of interest.

Balanced Single- and Dual-Band BPFs Using Ring Resonators

This paper presents new balanced single- and dual-band bandpass fllters (BPFs), both of which are constructed using two ring resonators. For each BPF, open-circuited stubs are added to one of the two resonators so that the transmitted common-mode (CM) signals can be attenuated, and source-load coupling is established so that two transmission zeros are generated near the edges of each desired difierential-mode (DM) passband to sharpen the passband selectivity. The measurement agrees well with the simulation. For the single-band BPF, the measured minimum DM insertion loss is 1.4dB in the DM passband, in which the CM suppression is larger than 41.6dB. For the dual-band BPF, the minimum DM insertion losses are 1 and 1.35dB in the flrst and second passbands, respectively, in which the CM rejections are larger than 29 and 22dB.

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.