Yan-Fu Bai

Design of Compact Quad-Frequency Impedance Transformer Using Two-Section Coupled Line

This paper presents a compact quad-frequency impedance transformer that is composed of a two-section coupled line to achieve ideal impedance matching at three arbitrary frequencies and a related frequency. The exact closed-form equations and design procedures are given based on strict theoretical analysis. After demonstrating the bandwidth performance and symmetry properties of different impedance transform ratios, we fabricated a circuit to show the validity of practical applications. Good agreement between the measured data and anticipated results is achieved.

Smart antenna design for GPS/GLONASS anti-jamming using adaptive beamforming

Smart antenna has the advantage of suppressing jamming in spatial region and improving signal to Interference plus Noise Ratio (SINR) of receive signals, thus it is recognized as the promising technologies and indispensable anti-jamming methods. This paper presents a practical design of smart antenna system for GPS/GLONASS anti-jamming base on adaptive beam-forming. It firstly introduces the basic concepts and principles of the smart antenna, provides the structure of the system, analyses and discusses each component, then designs a anti-jamming smart antenna for GPS and GLONASS, ultimately realizes a flexible hardware platform base on the technology of digital signal processor (DSP), field-programmable gate arrays (FPGA), and software defined radio (SDR).

Planar Dual-Frequency Power Divider using Umbrella-Shaped Resonator

In this paper, a new planar dual-frequency power divider based on umbrella-shaped dual-mode resonator is presented. The topology of the circuit, different from conventional Wilkinson power divider, is the couple lines and resonators instead of the transmission lines. It can provide not only dual band, but also direct current (DC) block characteristic and compact size, which fits for microwave intergraded circuit application. The proposed structure is analyzed and simulated. To certify the validity of the technique, two proposed power dividers are fabricated and measured at 1.85/4.85 GHz and 1.57/3.5 GHz. Good experimental performances at both frequencies are obtained, which are in good agreement with the simulated results.

A wide stopband CPW low pass filter using quarter wavelength stepped impedance resonators

A novel wide stopband coplanar waveguide (CPW) low pass filter (LPF) using quarter wavelength stepped impedance resonators (SIR) is presented. The bandstop characteristics of the quarter wavelength short circuited stubs SIR are demonstrated. By cascading three tapered quarter wavelength short circuited stubs SIR and a CPW spurline resonator, the fabricated low pass filter has sharp rejection with cutoff frequency of 3.5 GHz, and deep attenuation from 3.7 GHz to 11 GHz lower than −24 dB. Good agreement between simulated and measured results is demonstrated.

Compact electronically tunable microstrip dual-band filter using stub-loaded SIRs

A compact electronically tunable dual-bandpass filter (BPF) with harmonic suppression is investigated in this paper. The BPF is composed of a step-impedance resonator, a T-stub with a varactor diode and a filtering network. The second passband can be independently tuned by varying the bias voltage across the varactor, whereas the first passband is fixed. The proposed filter exhibits wide stopband due to the introduction of the filtering network suppressing harmonics. A prototype of a tunable dual-band BPF, in which the second passband is tuned from 1.58 to 2.21 GHz and the first passband is fixed at 0.98 GHz, is designed and fabricated. The simulated and measured results are in good agreement with each other.

A tri-band Wilkinson power divider using step-impedance resonator

A novel planar tri-band power divider using step-impedance resonator with band-pass response is proposed in this paper. The topology of the circuit, different from conventional Wilkinson power divider, is the couple lines and resonators instead of the transmission lines. It can provide good isolation, good amplitude balance simultaneously at three arbitrary frequencies and direct current (DC) block characteristic. The proposed structure is analyzed and simulated. The validity of the design is demonstrated by experimental results on a 930/2300/3600 MHz power divider.

Small Printed Ultra-Wideband Antenna with an Inverted F-Slotted Ground

A novel printed antenna having a frequency band notched function for UWB application is proposed and studied. With a pair of inverted-F-shaped slots introduced around the microstrip line on the ground and inserting a semicircle-rectangle radiating element, the designed antenna satisfies the VSWR requirement of less than 2.0 in the frequency band between 2.9 GHz–11.15 GHz while showing the band rejection performance in the frequency band from 4.96 GHz to 6.03 GHz. The experiment results and characteristics of the proposed antenna are shown in this paper.

Compact tunable dual-band filter using SIRs without extra blocking capacitances

A tunable dual-band microstrip filter using step-impedance resonators with harmonic suppression and compact size is presented in this paper. The second passband frequency of the filter can be flexibly controlled by tuning the bias voltage across the varactor whereas the first passband frequency is fixed. The structure is composed of couple lines and capacitive-loaded stepped-impedance resonator to provide frequency tunability and folded to reduce the size of the filter. The coupling scheme applied in this paper helps to reduce insertion loss and eliminate parasitic parameters, which is due to that extra blocking capacitances that are needless compared with the conventional coupling structure. To certify the validity, a prototype dual-band filter is designed, fabricated, and measured. The measured results show good agreement with the simulated ones.

Dual Passband Filter Using Hybrid Microstrip Split Ring Resonators and Coplanar Waveguide Quarter Wavelength Resonators

A novel dual passband filter using hybrid microstrip split ring resonators and coplanar wavelength (CPW) quarter wavelength resonators is presented. An equivalent RLC circuit model is presented, and its corresponding parameters are also extracted from the theoretical analysis. The proposed dual passband filter has two passbands with the center frequencies of 2.44 GHz and 3.5 GHz. Good agreement among equivalent circuit (EC), electromagnetic (EM) simulated and measured results is demonstrated.

Dual-band power divider with high frequency-ratio

A compact dual-frequency power divider for large frequency-ratio (greater than 3) applications is proposed in this paper. The topology of the power divider is two-section transmission-line transformers and combing of parallel R and series LC as the isolation network which are provide enough isolation at two arbitrary frequencies. Furthermore, based on even and odd mode analysis and transmission line theory, the close-form design equations are derived. Finally, the proposed power divider is fabricated and measured at 1 GHz/4 GHz to certify the validity of the design. Both theoretical and simulated results are obtained, which are good agreement with the measured results.