Qing-Xin Chu

A Compact Ultrawideband Antenna With 3.4/5.5 GHz Dual Band-Notched Characteristics

We propose a compact planar ultrawideband (UWB) antenna with 3.4/5.5 GHz dual band-notched characteristics. The antenna consists of a beveled rectangular metal patch and a 50 Omega coplanar waveguide (CPW) transmission line. By etching two nested C-shaped slots in the patch, band-rejected filtering properties in the WiMAX/WLAN bands are achieved. The proposed antenna is successfully simulated, designed, and measured showing broadband matched impedance, stable radiation patterns and constant gain. An equivalent circuit model of the proposed antenna is presented to discuss the mechanism of the dual band-notched UWB antenna. A UWB antenna and a single band-notched one are also provided for references.

A Compact Open-Loop Filter With Mixed Electric and Magnetic Coupling

A novel cascaded microstrip open-loop resonator filter with controllable electric and magnetic mixed coupling is presented to have one or more transmission zeros. For two coupled resonators, the coupled sides with the maximum magnetic field are combined with their open gaps with the maximum electric field, creating the electric and magnetic mixed coupling. By adjusting the distances between resonators and the positions of open gaps in a mixed coupled filter, the coupling coefficients can be changed, and controllable transmission zeros can be produced in the lower stopband, upper stopband, or both. Design and fabrication of the proposed second-and fourth-order filters show the advantages: such as a smaller number of resonators, higher rejection level, as well as asymmetrical response; moreover, the location of the transmission zeros can be precisely controlled.

A Compact Wideband MIMO Antenna With Two Novel Bent Slits

A compact wideband multiple-input- multiple-output (MIMO) antenna is presented. The MIMO antenna consists of two symmetric monopoles with edge-to-edge separation of nearly 0.083 λ0 at 2.5 GHz. Two novel bent slits are etched into the ground plane. At the lower frequencies, the bent slits can reduce the mutual coupling and have slight effect on the reflection coefficient. At the higher frequencies, the slits can be considered as slit antennas to widen the impedance bandwidth because the two slits are coupled fed by two 50-Ω microstrip lines, respectively. Two triangles are cut from the ground plane. In this way, the reflection coefficient and isolation of the two slit antennas can be improved. A bandwidth of 92.7% with |S11| ≤ -10 dB and |S21 | ≤ -18 dB from 2.4 to 6.55 GHz is achieved. In order to provide quantifications for the performance of the MIMO antenna in real-world usage conditions, the effects of human hand and head on the performance of the MIMO antenna are investigated. The results show that the MIMO antenna serving as a phone antenna can provide spatial and pattern diversity to combat multipath fading.

Design of Compact Tri-Band Bandpass Filters Using Assembled Resonators

A novel approach for designing tri-band bandpass filters with independently controllable center frequencies and improved stopband rejection characteristic is presented in this paper. The assembled resonator constructed by a stepped impedance resonator and a common half-wavelength resonator is employed to obtain tri-band response. The stepped impedance resonator is designed to operate at the first and third passbands and the other resonator is designed to operate at the second passband. Two kinds of filter configurations with cascaded and pseudointerdigital formats are proposed. Based on lossless lumped-element equivalent circuit, it is found that both filter structures can introduce transmission zeros between passbands. To verify the proposed approach, two filters are designed and fabricated, the measured results exhibit tri-band bandpass responses with high selectivity.

Compact Dual Band-Notched UWB MIMO Antenna With High Isolation

A compact dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation is designed on a FR4 substrate (27 × 30 × 0.8 mm3). To improve the input impedance matching and increase the isolation for the frequencies ≥ 4.0 GHz, the two antenna elements with compact size of 5.5 × 11 mm2 are connected to the two protruded ground parts, respectively. A 1/3 λ rectangular metal strip producing a 1.0 λ loop path with the corresponding antenna element is used to obtain the notched frequency from 5.15 to 5.85 GHz. For the rejected band of 3.30-3.70 GHz, a 1/4 λ open slot is etched into the radiator. Moreover, the two protruded ground parts are connected by a compact metal strip to reduce the mutual coupling for the band of 3.0-4.0 GHz. The simulated and measured results show a bandwidth with |S11| ≤ -10 dB, |S21| ≤ -20 dB and frequency ranged from 3.0 to 11.0 GHz excluding the two rejected bands, is achieved, and all the measured and calculated results show the proposed UWB MIMO antenna is a good candidate for UWB MIMO systems.

A Compact Dual-Band Bandpass Filter Using Meandering Stepped Impedance Resonators

This letter presents a miniaturized dual-band narrow bandpass filter (BPF) using meandering stepped impedance resonators (SIRs) with a new coupling scheme, which exhibited a size reduction of 50% compared with the traditional direct coupling structure at the same frequency, while the new structure can generate three transmission zeros in the insertion loss response. To validate the design and analysis, two dual-band BPFs centered at 2.4-GHz/5.2-GHz and 2.4-GHz/5.7-GHz for WLAN application were fabricated and measured. It is shown that the measured and simulated performances are in good agreement. The BPFs achieved insertion loss of less than 2 dB and return loss of greater than 16-dB in each band.

Design of UWB Bandpass Filter Using Stepped-Impedance Stub-Loaded Resonator

In this letter, an ultra-wideband (UWB) bandpass filter (BPF) using stepped-impedance stub-loaded resonator (SISLR) is presented. Characterized by theoretical analysis, the proposed SISLR is found to have the advantage of providing more degrees of freedom to adjust the resonant frequencies. Besides, two transmission zeros can be created at both lower and upper sides of the passband. Benefiting from these features, a UWB BPF is then investigated by incorporating this SISLR and two aperture-backed interdigital coupled-lines. Finally, this filter is built and tested. The simulated and measured results are in good agreement with each other, showing good wideband filtering performance with sharp rejection skirts outside the passband.

A Novel Crossed Resonator and Its Applications to Bandpass Filters

A novel open and short stubs loaded crossed resonator and its applications to cross-coupling filter and tri-band bandpass filters are presented in this paper. Based on the lossless transmission line model analysis, it is found that the first three resonance frequencies of the crossed resonator can be conveniently controlled. Benefiting from this feature, the resonator can be utilized to design not only a cascaded triplet (CT) filter, but also a tri-band bandpass filter. The tri-band filter offers two tunable passbands and one fixed passband. The first and third passband frequencies can be tuned effectively by changing the lengths of the stubs. To demonstrate these applications, a CT filter and two tri-band bandpass filters using a crossed resonator are implemented. The experiments verify the theoretical predictions and simulations.

Novel UWB Bandpass Filter Using Stub-Loaded Multiple-Mode Resonator

Novel compact ultra-wideband (UWB) bandpass filter (BPF) using stub-loaded multiple-mode resonator (MMR) is presented in this letter. The MMR is constructed by loading three open stubs in a uniform-impedance resonator, i.e., one stepped-impedance stub at the center and two uniform-impedance stubs at the symmetrical side locations. Five modes, including two odd modes and three even modes, could be designed within UWB band, and two transmission zeros generated by the stepped-impedance stub improve the passband selectivity greatly. The letter shows modal resonant frequencies against the step-impedance-stub-loaded parameters, which can control the even modes flexibly, while the odd modes remain the same. A compact planar UWB BPF is simulated, fabricated and measured. The simulated and measured results are in good agreement and show good in-band filtering performance and sharp selectivity.

Design of Compact Dual-Wideband Antenna With Assembled Monopoles

A coplanar waveguide (CPW)-fed dual-wideband antenna formed by a triangular monopole and a U-shaped monopole is presented. The antenna can generate two wide bands centered at about 2.5 GHz and 5 GHz to cover all the 2.4/5.2/5.8 GHz WLAN bands and the 2.5/3.5/5.5 WiMAX bands. Furthermore, the antenna has a simple planar structure and occupies a small size of about 28 X 33 mm2, including the finite ground CPW feeding mechanism. Good dipole-like radiation characteristics over the operating bands are obtained.