Falin Liu

Compressive Sensing for Fast Analysis of Wide-Angle Monostatic Scattering Problems

The method of moments (MOM) is used in conjugation with the compressive sensing (CS) to efficiently analyze the electromagnetic scattering problems over a wide incident angle. A new incident source is formed based on CS theory, in which much information from different incident angle is included. By solving the integral equations under this new incident source, one can obtain the measurements of the induced currents without calculating the problems with a finer angle increment. Finally, the orthogonal matching pursuit technique (OMP) is used to recover the real induced currents. Numerical simulations for differently shaped objects are presented to validate the effectiveness of the proposed method.

A new impedance match method in serial chireix combiner

In this paper, we analyze the impedances seen by each amplifier under the active load pulling in Chireix combiner. We derive the analytical expressions for the impedances and prove them in Agilent ADS software. From these expressions, we propose an impedance match method to improve the efficiency of the Chireix impedance using LoadPull simulation in ADS.

SIW-Slot-Fed Thin Beam-Squint-Free Fabry-Pérot Cavity Antenna With Low Backlobe Levels

The substrate integrated waveguide (SIW)-slot feeding structure is introduced in a fully substrate-integrated thin Fabry-Pérot cavity (FPC) antenna to achieve the boresight radiation free of beam squint and with low backward radiation levels. Single longitudinal slot symmetrically cut onto the broadwall (the ground plane of the FPC) of the SIW is proposed to feed the FPC antenna in order to point maximum radiation at boresight and avoid frequency-dependent beam squint caused by conventional asymmetrically edge-fed feeding patch. The beam-squint variation of 11.3 ° along with the edge-fed patch feed is significantly reduced to 0.3 ° within the operating bandwidth of 9.8-10.1 GHz using the proposed SIW-slot feed. The comparison of the radiation performance shows the proposed SIW-slot-fed FPC antenna suitable for integrated circuits.

Novel Tag Anti-Collision Algorithm with Adaptive Grouping

For RFID tags, a Novel Tag Anti-collision Algorithm with Grouping (TAAG) is proposed. It divides tags into groups and adopts a deterministic method to identify tags within group. TAAG estimates the total number of tags in systems from group identifying result and then adjusts the grouping method accordingly. The performance of the proposed TAAG algorithm is compared with the conventional tag anti-collision algorithms by simulation experiments. According to both the analysis and simulation result, the proposed algorithm shows better performance in terms of throughput, total slots used to identify and total cycles.

A Unified Approach to the Analysis of a Category of H-Plane Discontinuities

Based on the mode matching method, the generalized scattering parameters including the fundamental and higher order modes (multi-modes) are obtained for the discontinuity interface of a category of waveguide H-plane discontinuities. Then by using a general port-connection order-decrease method raised by the author, the whole discontinuity including the two interfaces and the intermediate part of finite length or zero length (as is the case for very thin inductive windows or irises) can be combined into one network, and the generalized scattering parameters of this network can be obtained from which the scattering parameters of the fundamental mode can be extracted. If needed, the equivalent circuit parameters can be calculated directly from the scattering parameters. Examples are given to show the validity and versatility of this new method for dielectric filled waveguide, inductive iris and/or window, E-plane metal and/or finline insert, and even the offset E-plane finline insert, etc.. Multiple inserts, windows and irises can also be analysed.

A random demodulation based reduced sampling rate method for wideband digital predistortion

The linearization performance of the traditional wideband digital predistortion (DPD) is seriously limited by the analog-to-digital converter (ADC) sampling rate in the feedback path. In this paper, a random demodulation based reduced sampling rate (RDRS) method is proposed to model and linearize the broadband power amplifiers (PAs). Compared with the existing spectrum extrapolation method, the proposed method can further reduce the sampling rate, but still maintain good performances. The simulation results demonstrate that the proposed method is well suitable for the ultra wideband digital predistortion.

A Novel Dual-Band Controllable Bandpass Filter Based on Fan-Shaped Substrate Integrated Waveguide

A compact dual-band bandpass filter with controllable center frequencies based on the 90° fan-shaped substrate integrated waveguide resonator (FSSIWR) is first proposed in this letter. Dual-band response is achieved by the fundamental mode (TM101 mode) and high mode (TM201 mode) of the FSSIWR, respectively. In this design, two pairs of the posts are loaded at the 45° direction of FSSIWRs, which produce perturbation to adjust the center frequency of the first passband. In order to control the second-passband center frequency, the complementary split-ring resonators (CSRRs) are etched on the surface of the resonator. The etched CSRRs can not only adjust the second-passband center frequency by changing the locations of the CSSRs but also produce a transmission zero (TZ) in the upper stopband of the second-passband. In addition, other five TZs are obtained by introducing source–load coupling, which highly improve the frequency selectivity. Finally, the proposed filter is fabricated and measured. The measured results agree well with the simulated ones.

Robust and fast iterative algorithm based on Levenberg-Marquardt and spectral extrapolation for wideband digital predistortion of RF power amplifiers

The analog-to-digital converter (ADC) is one of the most expensive components in an RF transmitter, conventional digital predistortion (DPD) could be seriously limited in dealing with the wideband feedback signals. Modern wireless communication systems are requiring higher data rate and wider bandwidth, a more powerful linearization technique is required. In this paper, we propose a robust iterative DPD coefficients extraction algorithm based on Levenberg-Marquardt algorithm and spectral extrapolation. By applying this method, the speed of ADC can be reduced significantly and thus save the cost. Experimental results demonstrate that the proposed method is numerically stable and more suitable for iteration than the damped Gauss-Newton method mentioned in [7].

An easily implementable structure for broadband high efficiency Class-J power amplifier

This paper presents a new and easily implementable structure in the design of Class-J power amplifiers (PA) for obtaining high efficiency in wide band, based on the closed form equations for the needed impedances, on a large-signal transistor model to estimate the devices output parasitic elements and on the idea of design space. The new structure can be realized with only three sections of microstrip lines to match the fundamental and the second harmonic impedances, simultaneously. The designed amplifier using the proposed structure shows a broadband performance of greater than 60% PAE, the gain of more than 10dB and almost 40dBm output power with a 0.5-0.9GHz (57%) bandwidth. Realization of the design has confirmed the value of the idea of design space and shows the proposed structures potential to implement the Class-J PA.

Compact balanced bandpass filter with the fractal defected structures

In this letter, the fractal defected structure (FDS) is firstly used to design miniaturized balanced bandpass filter (BPF). A novel quarter-mode substrate integrated waveguide resonator (QMSIWR) with etched symmetrical FDSs is presented, which has a lower resonate frequency ( f0) and acceptable unloaded quality (Qu) at TE201 mode. Based on this novel resonator and eighth-mode substrate integrated waveguide resonator (EMSIWR) with etched the FDS, a compact balanced BPF with a reduced size over 72.5% is designed, which can implement one transmission zero (TZ) on each side of the differential-mode (DM) passband by using cross-coupling technology. Meanwhile, the common-mode (CM) signal is suppressed below −23.6 dB in the DM passband. The measured results agree well with the simulated ones.