Kuo-Sheng Chin

Compact Dual-Band Branch-Line and Rat-Race Couplers With Stepped-Impedance-Stub Lines

This study constructs stepped-impedance-stub lines for a dual-band branch-line coupler design with improved design flexibility. The proposed structure demonstrates dual-band performance and a compact size due to additional stepped-impedance stubs to branches. The developed synthesis method has two degrees of freedom which can be exploited to miniaturize circuit size and/or replace impractical impedances with more realizable ones. Observations also show the advantage of a wide-range realizable frequency ratio of dual bands. The current work fabricates three experimental dual-band branch-line couplers, including a two-section coupler, and achieves a size reduction up to 21.7%, compared with conventional structures. The measured results validate good dual-band performance at 2.4/5.8 GHz with enhanced bandwidths up to 21% and 12%, respectively. This research also successfully applies the proposed circuit to synthesize a dual-band rat-race coupler.

Compact Dual-Band Bandstop Filters Using Stepped-Impedance Resonators

This work presents a compact dual-band bandstop filter (DBBSF) that features two controllable stopbands at desired frequencies. Stepped-impedance resonators are utilized to realize the dual-stopband characteristics, and reduce size. The synthesis method is developed. An experimental circuit is fabricated and evaluated to validate the design concept. Measurements correlate well with the simulation results, and the size is 12.6% less than that of a standard DBBSF.

Dual-Wideband Bandpass Filter Using Short-Circuited Stepped-Impedance Resonators

A compact dual-wideband bandpass filter featuring two controllable passbands is presented and experimentally validated. The proposed filter uses shorted stepped-impedance resonators to achieve dual-wideband bandpass capability and to minimum size. Design curves are given for the filter design. It is found that the frequency ratio of the second to first band has a wide achievable range. An experimental circuit is fabricated and evaluated to validate the design concept. The measurement results correlated well with the simulation results.

New formulas for synthesizing microstrip bandpass filters with relatively wide bandwidths

New formulas are proposed for designing wideband parallel-coupled microstrip bandpass filters with improved prediction of bandwidth. When a fractional bandwidth /spl Delta/ is required, a correction /spl theta/=(/spl pi//2)(1/spl plusmn//spl Delta//2) is incorporated into the formulation for determining the dimensions of each coupled stage. Two filters with /spl Delta/=50% are designed and fabricated to show the improvement. The measurement shows a very good agreement with the simulation.

MINIATURIZED MICROSTRIP DUAL-BAND BANDSTOP FILTERS USING TRI-SECTION STEPPED-IMPEDANCE RESONATORS

A novel circuit structure of dual-band bandstop fllters is proposed in this paper. This structure comprises two shunt-connected tri-section stepped impedance resonators with a transmission line in between. Theoretical analysis and design procedures are described. The derived synthesis equations have two degrees of freedom which provide more design ∞exibility in fllter synthesis. Notably, three advantages of the proposed fllter structure lie in the fact of its increased nonuniform impedances, resulting in a compact size, wide range of realizable frequency ratio, and more realizable impedances. Three experimental dual-band bandstop fllters with various frequency ratios were fabricated to demonstrate the feasibility of the new fllter structure.

Wideband LTCC 60-GHz Antenna Array With a Dual-Resonant Slot and Patch Structure

This paper presents a wideband 60-GHz antenna array with a dual-resonant slot-patch structure. A multilayered low-temperature co-fired ceramic substrate was used for antenna fabrication. A half-wavelength resonant slot was designed with a backed substrate-integrated waveguide (SIW) cavity to enhance the front radiation. The inverted microstrip center-fed structure was designed for easy signal excitation and superior impedance matching. A parasitic patch was also applied to enhance for bandwidth and gain enhancement. The effects of the SIW cavity-backed slot antenna with and without parasitic patches were empirically examined. The simulated results show that adding parasitic patches increased the resonance of the poles and improved antenna gain by 1.85 dB and bandwidth by 9%. A 2 × 2 dual-resonant slot-patch antenna array was designed to further enhance the gain and bandwidth. The equipment setup for on-chip measurements of gain and radiation patterns was established. The measured S11 showed a wide bandwidth of 23%. The measured gain for the four-element antenna array was 9 dBi with slight fluctuations over the 57-64-GHz frequency range.

LTCC Multilayered Substrate-Integrated Waveguide Filter With Enhanced Frequency Selectivity for System-in-Package Applications

This paper presents a cross-coupled bandpass filter with stacked substrate-integrated waveguide cavities on low-temperature cofired ceramic substrates. The proposed filter has a local multipoint distribution service band with a novel same-side-feed input/output structure. Conventionally, a cross-coupled structure generates only a single pair of transmission zeros. The proposed filter can generate two pairs of transmission zeros beside the passband, thereby providing an excellent cutoff rate in the stopband and improved frequency selectivity. The additional pair of transmission zeros is created by the same-side-feed structure, which constructs an additional source-load coupling path without increasing the circuit size. A multipath coupling diagram is used to illustrate the conformation of the second pair of transmission zeros and predict its behavior. The experimental filter exhibits responses centered at 27.95 GHz with an insertion loss of -2.8 dB, and a bandwidth of 9%. Two pairs of transmission zeros (at 26.3 and 29.6 GHz, and at 23.2 and 37 GHz) around the passband were obtained, achieving excellent selectivity and a wide stopband.

A Low-Profile Frequency Selective Surface With Controllable Triband Characteristics

A novel compact low-profile frequency selective surface (FSS) with controllable triband characteristics is presented. The proposed FSS consists of a stacked periodic array of square loops and complementary apertures, respectively centered within a wire grid and an aperture grid, which can create three transmission poles and two transmission zeros. Controllable triband performance is achieved, allowing the FSS to transmit the signal at 4 GHz while reflecting the signals at 6 and 9.5 GHz. Due to the compact and low-profile structure, the designed FSS has a reduced sensitivity to the incident angle compared to traditional triband FSSs. An equivalent circuit model is proposed for predicting and analyzing the frequency characteristics of this structure. For demonstration, a prototype of the proposed FSS is fabricated and measured. Good agreement between the simulated and measured results is observed.

Differential-Fed Patch Antenna Arrays With Low Cross Polarization and Wide Bandwidths

In this letter, two differential-fed Ku-band 2 × 2 patch antenna arrays with low cross polarization and wide bandwidths were developed using multilayer printed circuit board (PCB) technology. The patch elements in Design I were fed differentially, whereas the patches in Design II were single-ended. However, Design II is differential if the array is considered as a whole. The experimental demonstration revealed that Design I achieved a 10-dB impedance bandwidth of 15.3%. The measured gain was 10.41 dBi at 12.62 GHz with low cross polarization of -17.5 dB in the E-plane and -20.2 dB in the H-plane. Design II exhibited a 10-dB impedance bandwidth of 12.8%. The measured gain was 12.32 dBi at 13 GHz with cross polarization of -17.7 and -17 dB in the E-plane and H-plane, respectively. Design II achieves performance levels similar to that of Design I, but comprises a simple and compact feed network.

28-GHz patch antenna arrays with PCB and LTCC substrates

Ka-band spectrum is relatively abundant and therefore attractive for services of satellite communication, targeting radar, and wireless broadband access technologies. However, Ka-band patch antenna is difficult in realization because the accurate manufacturing is indeed a challenge in obtaining excellent antenna performance at such high frequencies. This study develops three patch antenna arrays for operation at 28 GHz. Two of the three patch arrays with 2×2 and 4×1 patches, respectively, are realized on microwave printed circuit boards (PCBs). The experimental PCB patch arrays have bandwidths up to 5.7% and gains up to 13 dBi. Another 2×2 stacked-patch antenna array is fabricated with low temperature co-fired ceramic (LTCC) technology for further bandwidth enhancement. This LTCC stacked-patch array comprises a novel opposite-side feeding structure to prevent any electrical effect on the parasitic patch. A measured gain of 10.35 dBi and a wide bandwidth of 10.1% (26.75–29.6 GHz) are achieved.