Yu-Zhi Chueh

Modeling of symmetric composite right/left-handed coplanar waveguides with applications to compact bandpass filters

This study proposes an equivalent-circuit model for the composite right/left-handed (CRLH) coplanar waveguide (CPW) comprising the series interdigital capacitor and shunt meandering short-circuited stub inductor in symmetric configuration. The new technique for extracting the equivalent-circuit elements of the CRLH CPW, which include inductances, capacitances, and resistances to represent the left-handed, right-handed, and lossy characteristics, is developed based on the effective medium concept. The applications to the compact resonators and filters are presented to emphasize the unique features of the CRLH CPW. A novel CRLH CPW resonator with a 0/spl deg/ effective electrical length at resonance is proposed, which gives a 49.1% size reduction when compared with the conventional half-wavelength resonator at 5 GHz. Based on the zeroth-order CRLH CPW resonators, an inductively coupled two-pole bandpass filter with 5.4% 3-dB bandwidth and 2.7-dB insertion loss at 5 GHz is implemented, and it is 51.4% more compact than the conventional structure. A good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement demonstrates the effectiveness of the proposed modeling technique. To suppress the higher order harmonic spurious passbands, the electromagnetic-bandgap CPW structures are incorporated into the proposed CRLH CPW filter.

Broadband composite right/left-handed coplanar waveguide power splitters with arbitrary phase responses and balun and antenna applications

This study presents novel coplanar waveguide (CPW) power splitters comprising a CPW T-junction with outputs attached to phase-adjusting circuits, i.e., the composite right/left-handed (CRLH) CPW and the conventional CPW, to achieve a constant phase difference with arbitrary value over a wide bandwidth. To demonstrate the proposed technique, a 180/spl deg/ CRLH CPW power splitter with a phase error of less than 10/spl deg/ and a magnitude difference of below 1.5 dB within 2.4 to 5.22 GHz is experimentally demonstrated. Compared with the conventional 180/spl deg/ delay-line power splitter, the proposed structure possesses not only superior phase and magnitude performances but also a 37% size reduction. The equivalent circuit of the CRLH CPW, which represents the left-handed (LH), right-handed (RH), and lossy characteristics, is constructed and the results obtained are in good agreement with the full-wave simulation and measurement. Applications involving the wideband coplanar waveguide-to-coplanar stripline (CPW-to-CPS) transition and the tapered loop antenna are presented to stress the practicality of the 180/spl deg/ CRLH CPW power splitter. The 3-dB insertion loss bandwidth is measured as 98% for the case of a back-to-back CPW-to-CPS transition. The tapered loop antenna fed by the proposed transition achieves a measured 10-dB return loss bandwidth of 114%, and shows similar radiation patterns and 6-9 dBi antenna gain in its operating band.

Coplanar Waveguide Bandpass Filters With Compact Size and Wide Spurious-Free Stopband Using Electromagnetic Bandgap Resonators

This work presents a novel coplanar waveguide (CPW) bandpass filter (BPF) that uses electromagnetic bandgap (EBG) resonators to reduce the size and suppress the harmonic responses. The propagation characteristic of the EBG structure is investigated by its associated equivalent circuit model. Compared with the conventional half-wavelength resonator at 5GHz, the EBG resonator is 60.5 % more compact. Based on the EBG CPW resonators, the inductively-coupled two-pole BPF with 3.8% 3-dB bandwidth and 2-dB insertion loss at 5GHz is implemented. This structure generates a 59.6% reduction in size and suppresses a second harmonic passband when compared with a conventional filter. To eliminate the third harmonic response, the proposed EBG CPW BPF further incorporates two EBG structures into its input and output ports and has the merit of a small circuit area

Compact Ultra-Wideband Conductor-Backed Coplanar Waveguide Bandpass Filter With a Dual Band-Notched Response

This work presents a novel ultra-wideband (UWB) bandpass filter (BPF) based on a conductor-backed coplanar waveguide structure with tunable transmission zeros. The symmetrical UWB BPF, which consists of the broadside-coupled transitions and the stub resonators in double-layer configuration, achieves a UWB bandwidth with transmission zeros. For characterizing this structure, the equivalent-circuit model is established to realize a four-pole response with two transmission zeros located close to the passband edges. To eliminate the interference of the coexisting wireless local area network (WLAN) within the UWB spectrum, two slotlines are symmetrically arranged on the ground plane of UWB BPF to generate the band-notched frequencies at 5.2 and 5.8 GHz simultaneously. The proposed UWB BPFs have the advantages of compact size, low insertion loss, good selectivity, and flat group delay. All results obtained from the equivalent-circuit model and the full-wave simulation are verified by measurements.

SYNTHESIS OF TRIPLE-BAND AND QUAD-BAND BANDPASS FILTERS USING LUMPED-ELEMENT COPLANAR WAVEGUIDE RESONATORS

This paper develops a novel design method for synthesizing the multi-passband filter with high flexibility in various passband location and fractional bandwidth. Using the proposed compensation technology in the equivalent circuit of multi-passband resonator, the cutoff frequencies and matching property in passband regions can be improved. Tripleand quad-band bandpass filters operating in both wireless local area network (WLAN) 802.11 a/b/g and worldwide interoperability for microwave access (WiMAX) systems are presented to verify the design method. The lumped-element coplanar waveguide stub fabricated by the split-ring resonator is established to realize filter with compact size. All the measured, full-wave simulated and equivalent-circuit modeled results illustrate a good agreement among them, which validates the multi-passband design methodology and shows the advantages of DC elimination and deep rejection between each passband.

Design of Composite Right/Left-Handed Coplanar-Waveguide Bandpass and Dual-Passband Filters

The design and implementation of novel coplanar-waveguide (CPW) bandpass and dual-passband filters that consist of the composite right/left-handed short-circuited stubs are proposed. In contrast to the conventional short-circuited stub, whose input impedance repeats every half-wavelength, the composite right/left-handed CPW stub combines the phase-lead composite right/left-handed CPW and the phase-lag uniform CPW to achieve the arbitrary resonant frequencies with compact size. The equivalent bandpass and dual-passband LC resonators are established by investigating the frequency responses of the composite right/left-handed CPW stubs. The composite right/left-handed CPW bandpass filter is 62.5% more compact than the conventional quarter-wavelength shunt-stub CPW bandpass filter. The composite right/left-handed CPW dual-passband filter, which possesses the sharp rejection between the two asymmetric passbands, is also developed. The synthesis procedures of the composite right/left-handed CPW bandpass and dual-passband filters are successfully validated by measurement and full-wave simulation

A Novel Triple-Band Microstrip Branch-Line Coupler With Arbitrary Operating Frequencies

This letter presents a novel microstrip branch-line coupler operating in three frequency bands. The design methodology of the triple-band branch-line coupler is established by using a compensation technique to improve the matching property within each passband region. The proposed coupler with compact size is realized by folded microstrip open-circuited and short-circuited stubs. The measured, full-wave simulated and equivalent-circuit modeled results illustrate good agreement among them, which validates the design method and shows the advantages of deep rejection between each operating frequency, and the dc grounded input and output ports.

Asymmetric Dual-Passband Coplanar Waveguide Filters Using Periodic Composite Right/Left-Handed and Quarter-Wavelength Stubs

A novel dual-passband coplanar waveguide (CPW) filter periodically loaded with the composite right/left-handed (CRLH) short-circuited stubs and the quarter-wavelength open-circuited stubs in asymmetric configuration is presented. The unit-cell equivalent circuit of the periodic structure in conjunction with Floquets theorem is employed to find the propagation characteristics of passband and stopband regions. Unlike the conventional quarter-wavelength transmission-line inverter suitable only for a narrow frequency range, the dual-band inverter is adopted in the dual-passband filter to achieve a better frequency response within two operating bands. The performance of the 2.4/5.8-GHz third-order CRLH CPW dual-passband filter with 52% and 23% bandwidths is measured and validated by full-wave simulation. Two arbitrary passband regions are presented and the stopband within the passbands can be controlled by varying the length of open-circuited stub, supporting the flexibility and compactness of the proposed dual-passband filter

Broadband and strong coupling metamaterial-based cavity resonator using artificial magnetic surfaces

This study proposes a novel metamaterial-based cavity with a strong coupling effect between the transmitting and receiving devices. It is compact in size and the field distribution is uniform inside the cavity, which is realized by combining four artificial magnetic conductor surfaces at the four sidewalls and two metal palates at the top and bottom walls. The AMC consisting of a periodic array of square patches printed on the metal-backed double-layer dielectric substrate without connecting vias to enhance its operating bandwidth. Two monopole-type antennas are used as the transmitting and receiving terminals to examine the transmission property. The measured insertion loss of the metamaterial-based with different receiving positions are 1.06 dB, 2.26 dB, 2.02 dB, and 0.6 dB for position A, B, C, and D, respectively. The fabrication and measurement of the metamaterial-based cavity are demonstrated to validate its broad bandwidth and compact size.

Novel compact metamaterial-based cavity resonator with broad bandwidth

Metamaterials have attracted considerable interest among scientists and engineers owing to their interesting electromagnetic properties not observed in naturally occurring materials [1]. As a kind of metamaterial, the artificial magnetic conductor (AMC) [2]-[4] is composed of the periodic metal arrays on a metal-backed dielectric substrate. Such a structure functions as a perfect magnetic conductor (PMC) with the capability of presenting a near-zero reflection phase for a wave normally incident to the surface. Among the numerous applications that these AMC structures can be found, they include ground plane of antennas [2], cavity antennas [3], and quasi-TEM waveguides [4].