Q.-X. Chu

Dual-Band Circularly Polarized Stacked Square Microstrip Antenna with Small Frequency Ratio

A probe-fed stacked square microstrip antenna for dual-band circularly polarized (CP) applications is presented. By properly selecting two square patches in the proposed design and loading a chip-resistance along the centerline of each square patch, dual-band CP radiation with small frequency ratio can be achieved. In order to prevent the second operating frequency from shifting to higher band which is resulted from a small air-gap between two substrates, an additional patch is introduced. Compared with conventional stacked dual-band CP antennas, the proposed antenna can achieve a smaller frequency ratio and has a larger tolerance of processing as well. Details of the proposed antenna design and experimental results for the dual-band CP performances are presented and discussed.

A modified two-section UWB Wilkinson power divider

A novel Wilkinson power divider with modification of the traditional two-section Wilkinson power divider by adding one open stub on each branch is proposed. This design method is validated by building a divider working in the UWB band (3.1 GHz - 10.6 GHz). It is better in performance, but is about 10% smaller than the traditional three-section power divider and spares one resistor. The simulation and measurement results of the modified divider show equal power split, a good insertion loss of less than 1.1 dB, a good return loss of all ports of less than - 10 dB, and a good isolation is less than -11 dB over the UWB band.

A Compact Band-Notched UWB Antenna with Controllable Notched Bandwidths by Using Coupled Slots

A compact coplanar waveguide fed (CPW-FED) ultrawideband (UWB) antenna with controllable notched bandwidths for WLAN bands ranging from 5.3 GHz to 5.7 GHz is proposed and implemented. The proposed antenna consists of part of a circular patch and two modified ground planes. Two upper half-wavelength C-shaped slots and another lower half-wavelength C-shaped slot are coupled separately to form a band rejection. The simulation and measurement show that the proposed antenna achieves a well-matched broadband impedance of 3.1–10.6 GHz (|S11| < –10 dB), except the rejection bandwidths of 5.3–5.7 GHz for the centre band of WLAN (|S11| > –5 dB). Moreover, the notched bandwidths can be controlled by adjusting the coupling distances of the corresponding slots. The antenna is successfully designed, simulated and measured with broadband matched impedance and near omnidirectional radiation patterns.

A Novel Compact UWB Power Divider for Spatial Power Combining

A novel ultra wideband (UWB) power divider applied in spatial power combining is proposed, which combines a tapered transmission line and 1-to-2 power dividers to realize a 1-to-4 power-dividing function. The simulated and measured results reveal a good agreement. The magnitudes of insertion loss are approximately equal, and phases are almost the same, so the proposed structure is used to design a passive spatial power combiner. The return loss of the spatial power combiner is below –15 dB on the whole, and insertion loss is between –0.9 ∼ 0 dB.

Design of a compact UWB Wilkinson power divider

In this paper, a Wilkinson power divider operating over an ultra wide frequency band (3.1 to 10.6 GHz) is presented. The proposed power divider consists of two branches of impedance transformer, each of which consists of two sections of transmission line with different characteristic impedance and different length. And a resistor is set between the two sections. The simulated and experimental results of the developed divider are presented and show good agreement.

Compact Ultra-Wideband Slot Antenna with Stepped Slots

In this paper, a compact ultra-wideband (UWB) slot antenna with two stepped slots is presented. The overall dimension of the antenna is as small as 15 × 25 × 0.8 mm3. The measured impedance bandwidth defined by voltage-standing wave ratios (VWSR) < 2 is from 3.1 to more than 11 GHz. The proposed antenna exhibits a nearly omni-directional radiation pattern, stable gain and constant group delay in the UWB band. Due to the advantages of compact size and simple structure, the proposed antenna is very suitable for various portable UWB systems.

Compact broadband microstrip rat-race couplers using microstrip/slotline phase inverters for arbitrary power-dividing ratios

Compact broadband microstrip rat-race couplers using microstrip/slotline phase inverters are proposed. A wide range of power-dividing ratio ( ) is achieved by varying the impedance ratio of the transmission lines, while the dual-band impedance matching characteristic with frequency ratio ( ) is obtained by varying the impedances of the transmission lines only. For verification, a rat-race coupler with power-dividing ratio of and operating at 1.0/2.5 GHz is designed, fabricated, and measured. The measured results are in good agreement with the simulated ones. The measured results show a bandwidth of 120% with better than 10-dB return loss and 31-dB isolation from 0.69 to 2.74 GHz.

Design of Dual-Band CT Filter with Sourceload Coupling

A dual-band filter consisting of two cascaded triplet (CT) units is presented in this paper. Two sets of λ /4 resonators are employed to construct the CT unit. The utilization of λ /4 resonators not only makes the filter compact, but also allows the inductive cross coupling to be realized conveniently. This results in a transmission zero of finite frequency on the high side of each passband. The bandwidth of each passband can be tuned independently by adjusting the coupling via hole. The source-load coupling is also proposed to introduce two tunable transmission zeros, which can improve the selectivity of the filter. A trial dual-band filter is designed and measured, and the filter centered at 2.45 and 5.25 GHz occupies an area of only 33 × 15 mm2. Measured results show that a rejection level of 20 dB up to more than four times the first passband frequency can be obtained.

A Compact Dual-Band Mimo Antenna of Mobile Phone

A compact dual-band multiple-input-multiple-output (MIMO) antenna is presented. The MIMO antenna consists of two orthogonal elements with edge-to-edge separation of nearly 0.047λ0 at 2.0 GHz, and the element is two-strip structure which can help to improve the impedance matching and isolation. Result shows a dual-band of 76% from 1.62 to 3.6 GHz and 28.5% from 4.44 to 5.92 GHz. The MIMO antenna has strong robust property to the nearby conducting elements, and that is an advantage over the conventional MIMO antennas. The mean effective gain (MEG), radiation efficiency, correlation coefficient, and effective diversity gain (EDG) are calculated to evaluate the diversity performance of the MIMO antenna. To provide quantifications for the performance of the MIMO antenna in real-world usage condition, effects of human hand and head on radiation efficiency and total radiated power (TRP) are investigated. The results indicate the antenna serving as a phone antenna can provide spatial and pattern diversity to combat multipath fading.

A Compact Bandpass Filter with Source-Load Coupling by Using Short-Circuited Coupled Lines Between Ports

A compact filter with a T-shaped resonator and short-circuited coupled lines between two ports is presented. The frequency response of filter has four extra controllable transmission zeros in the stopband because of the multiple signal transmission paths and controllable source-load coupling strength. The positions of the transmission zeros in the stopband are controllable by adjusting the length of coupled lines. At the same time, the center frequency and bandwidth are both not changed. The bandwidth of filter can be adjusted by the different lengths of short-circuited stub of T-shaped resonator. In addition, the second harmonic is suppressed. Good skirt selectivity and controllable stopband characteristics can be achieved simultaneously.