Xubo Wei

Compact Printed UWB Diversity Slot Antenna With 5.5-GHz Band-Notched Characteristics

A novel compact printed ultrawideband (UWB) slot antenna for MIMO/diversity applications is presented in this letter. The antenna consists of two modified coplanar waveguides (CPWs) feeding staircase-shaped radiating elements for orthogonal radiation patterns, where a rectangle stub is placed at 45° between the CPW to ensure high isolations. By etching two split-ring resonator (SRR) slots on the radiators respectively, the band-notched property is achieved. Results show that this antenna meets a 10-dB impedance bandwidth and 15 dB isolation from 2.5 to 12 GHz, with a notched band at 5.5 GHz. The measurements of the radiation patterns and envelope correlation coefficient (ECC) denote that the antenna is suitable for multiple-input-multiple-output (MIMO)/diversity systems. Furthermore, it has a compact size of 48 × 48 mm2, which has been significantly reduced, and it is a good candidate for portable devices.

Compact Tri-Band Bandpass Filter Using Open Stub Loaded Tri-Section lambda/4 Stepped Impedance Resonator

A modified tri-mode λ/4 stepped impedance resonator (SIR) is proposed, in which a shunt open stub is loaded in the conventional λ/4 tri-section SIR. The resonant frequencies and frequency ratios can be properly controlled by adjusting the loaded open stub. A compact second-order tri-band bandpass filter (BPF) based on two coupled proposed open stub loaded λ/4 tri-section SIR is presented. A pair of transmission zeros (TZs) are generated at the lower and upper stopband of each passband for high selectivity and excellent band-to-band isolation. A tri-band BPF with the central frequencies of 1.92, 3.50, 5.75 GHz, and respective fractional bandwidths of 5.4%, 4.0%, and 2.4% is designed and fabricated. Measured results show good agreement with simulations. Moreover, the circuit only occupies 0.09 λg ×0.10 λg.

COMPACT MIXED-CROSS COUPLED BANDPASS FILTER WITH ENHANCED FREQUENCY SELECTIVITY

In this paper, a compact three-order mixed-cross coupled bandpass fllter (BPF) with enhanced frequency selectivity is proposed. Multiple transmission zeros (TZs) can be obtained near the passband for high frequency selectivity by introducing mixed-cross coupling between the nonadjacent resonators. The frequency-dependent mixed- cross coupling matrix of the proposed fllter is presented to explain the occurrence of the TZs caused by mixed-cross coupling. A new BPF centered at 2.7GHz with 11.5% fractional bandwidth has been designed and fabricated to verify the validity of the proposed method. The measurement result shows four flnite TZs in the stopband, located at 1.74GHz with 52.16dB rejection, 2.53GHz with 24.67dB rejection, 3.83GHz with 47.52dB rejection, and 7.75GHz with 54.83dB rejection, respectively. The circuit only occupies 6.2£7.6mm 2 .

COMPACT BANDPASS FILTER WITH MIXED ELECTRIC AND MAGNETIC (EM) COUPLING

A compact wide-band bandpass fllter (BPF) with high frequency selectivity using stepped impedance resonators (SIRs) is presented in this paper. The proposed BPF consists of four SIRs, which share a common grounded via-hole. To improve the frequency selectivity, multiple transmission zeros (TZs) are employed in the stopband by mixed electric/magnetic (EM) coupling. The novel fllter with 32.2% fractional bandwidth (FBW) has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The measured results show three flnite transmission zeros in the stopband, located at 2.47GHz, 5.26GHz, 9.39GHz, respectively. The circuit size of proposed BPF only occupies 3:10 £ 13:30mm 2 .

A compact printed filtering antenna with flat gain using annular slot and UIR

Design, fabrication and measurement of a filtering antenna are presented for WLAN / WIFI/ LTE communication systems in this paper. The filtering antenna consists of a feeding network, half-wavelength (λ/2) uniform impedance resonator (UIR) with a cambered structure and an annular slot. UIR with cambered structure is employed as the first stage resonator to improve the frequency selectivity in necessary passband. An annular slot etched on the back of substrate is excited by UIR through an inset coupling structure. The annular slot acts as a radiator as well as the last stage resonator. The inset coupling structure can be treated as the admittance inverter in the filter design. Compared to conventional antenna, the proposed filtering antenna has wide bandwidth, low cross polarization and good frequency skirt selectivity in passband. Measurement results show that the filtering antenna can operate at 2.5GHz with 550MHz, peak gain can be obtained to 1.2dBi, cross polarization can be suppressed to -30dB, respectively. The filtering antenna only occupies 0.23λg × 0.29λg.

Compact box-section bandpass filter with enhanced stopband characteristics

A compact bandpass filter (BPF) with enhanced stopband characteristics is presented in this paper. The proposed BPF consists of four improved stepped impedance resonators (SIRs), which implements into a box-section structure. To improve the frequency selectivity and the stopband characteristics, additional transmission zero (TZ) was introduced by mixed electric and magnetic (EM) coupling. A new filter with 31.2% fractional bandwidth (FBW) has been designed and fabricated to verify the validity of the proposed method. The filter has two transmission zeros, where TZ1 is located in 0.4 GHz with 78.7 dB rejection and TZ2 is located in 2.7 GHz with 50.2 dB rejection. Measured results are in good agreement with the electromagnetic simulation.

Preparation and Dielectric Properties of Cerium and Manganese Codoped Ba0.6Sr0.4TiO3 Ferroelectric Films

Cerium (Ce) and manganese (Mn) codoped Ba0.6Sr0.4TiO3 (BST) films were prepared by improved sol-gel method and the effect of preheating on their dielectric properties was investigated. X-ray diffraction (XRD) reveals that the films grow principally along (110) orientations and show cubic perovskite structures. Preheating corresponds to smaller FWHMs, stronger crystallization and larger grain sizes, and preheating with codoping corresponds to the smallest FWHM, the strongest crystallization and the largest grain size. The prepared film can show tunability of 55.7%, dielectric loss of 0.0074∼0.0175 and approximately 75 FOM, meeting the needs of tunable microwave applications.

Compact LTCC multilayer broadband power divider

In this paper, a compact and broadband Wilkinson power divider at 1–6GHz is presented. The device has been designed and fabricated based on optimized prototype circuit of lumped Wilkinson power divider, using the Low Temperature Co-fired Ceramics (LTCC) technology. By taking advantages of the three-dimensional layout capability of the LTCC substrate, the embedded lumped circuit elements of the proposed power divider are arranged vertically for size reduction, which features a compact size of 6mm×4.4 mm×1.3 mm.

Improved Mechanisms for Excellent Tunable Microwave Ce and Mn Codoped Ba0.6Sr0.4TiO3 Thin Films

Smooth and dense preheated cerium (Ce) and manganese (Mn) codoped barium strontium titanate (CeMn-BST) films with various thicknesses have been prepared by improved sol-gel method. Capacitance-voltage curves show that with increasing film thickness, combination of dielectric properties are significantly improved with optimized values of about 1300 moderate permittivity, less than 0.007 dielectric loss, more than 58% tunability and hence near 180 figure of merit (FOM) for eight-layer CeMn-BST film. The objective of this paper is to study the improved mechanisms for such excellent dielectric properties. XRD shows that the films layered-grow mainly along (110) orientation and exhibit ABO3 cubic perovskite structure. As film thickness increases, Ce3+ and/or Mn2+ ions are showing doping modes from donor doping to acceptor doping, the crystallization of films is enhancing, but the average grain sizes of the films show gradually decreased trend from about 45nm to 25nm in terms of the intensities of (110) diffraction peaks. AFM indicates that the films are getting smoother with smaller roughness with increasing thickness. XPS reveals that the films reveal decreased non-perovskite structure, element core levels and Fermi levels with increasing thickness. Leakage current densities are significantly decreased almost at two orders of magnitude with increasing thickness. Pure BST films are compared.

A Novelly Designed Ba0.6Sr0.4TiO3 Film with High Tunability and Low Dielectric Loss

Manganese (Mn) and yttrium (Y) alternately doped Ba0.6Sr0.4TiO3 (BST) films are novelly designed as MnBST/YBST/MnBST/YBST and prepared layer-after-layer on Pt wafer electrodes, and two films where one with the first layer preheated (1Mn/YBST) and the other with four layers preheated (4Mn/YBST) are focused on. XRD shows that two films grow along (110) orientation and reveal ABO3 cubic perovskite structures and donor doping, but 4Mn/YBST film shows larger average grain size. SEM demonstrates that 1Mn/YBST film is composed of one 630nm-thick layer with nodular microstructure and the other 570nm-thick surface layer with columnar microstructure, whereas 4Mn/YBST film is 670 nm thick with nodular microstructure. AFM shows that two films are smooth with no cracks, but 4Mn/YBST film is denser with smaller roughness. Two films show more than 55% high tunabilities, but 4Mn/YBST film also reveals low losses of 0.0062∼0.0156 and high figure of merit (FOM) of near 90 at -35V and 100 kHz, fully meeting the needs of tunable microwave applications.