Hao-Jia Lin

A Tunable Bandpass Filter with Switchable Bandwidth

A novel bandpass filter with tunable center frequency and switchable bandwidth is presented in this paper. This work is devoted to demonstrate a new approach to tune bandwidth of filters by changing the size of perturbation patch of dual-mode resonator. The proposed filter mainly consists of a dual-mode ring resonator, four varactor diodes and a pin diode. The center frequency could be conveniently tuned from 1.25 GHz to 1.45 GHz, and the fractional bandwidth can be tuned in two discrete states 8% and 12%, respectively. Comparison of the measured and simulated results shows good agreement about center frequency and bandwidth.

A Dual Passband Filter using Hybrid Microstrip Open Loop Resonators and Coplanar Waveguide Slotline Resonators

A novel dual passband filter using hybrid microstrip open loop resonators and coplanar waveguide (CPW) slotline resonators is proposed. With the CPW feeding structure, the center frequencies and 3-dB fractional bandwidth (FBW) can be achieved relatively independently. The external quality factor and coupling coefficient of the resonators are obtained. The proposed dual passband filter has center frequencies of 2.44 GHz and 3.5 GHz, which could be appropriately used for wireless local area networks (WLAN) and WiMax. Good agreement between simulated and measured results is demonstrated.

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).

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.

Analysis and design of broadband microstrip patch antenna with a pair of double cross-shaped slots

A novel method of designing broadband microstrip antenna is proposed in this paper. By embedding a pair of Cross-shaped slots placed close to the non-radiating edges of a microstrip patch and adding an air layer between the substrate and the ground, the broadband character can be achieved. Whats more, the formulas for calculating the two resonant frequencies have been experimentally deduced. Employing the method and the formulas, a antenna with a pair of double cross-shaped is designed. The measured bandwidth of 15.2% is achieved with small sizes, and the good radiation characteristic for operating frequencies within the impedance bandwidth is also observed.

Design of a Dual-Frequency Retrodirective Array

A dual-frequency retrodirective array is proposed. By using two separated antenna arrays and double balanced passive mixers, the proposed system can achieve dual-frequency retrodirectivity in a bidirectional way. The low-frequency interrogating signal can be retransmitted at the high frequency, and it can also work in a reverse order. The proposed array has the advantages of low cost and high isolation between interrogating and retransmitting signals. The bidirectional characteristic can make it very useful in the two-way communication system. A four-element prototype is designed and fabricated. Measured results show good retrodirective performance.

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.

A wide stopband branch-line coupler using defected ground structure

This paper presents a novel branch-line coupler which has a wide stopband characteristic with attenuation 30 dB from 4 GHz to 8 GHz using defected ground structure (DGS). The conventional branch-line coupler suffers from the presence of spurious response at odd harmonics of the operating frequency. The proposed coupler adopts the two symmetrical dumbbell DGS under the input and output feed lines to suppress the harmonic components. To verify the proposed structure, both simulated results of the conventional and proposed branch-line coupler are presented. It demonstrates that the proposed structure has a high harmonic suppression. Moreover, it produces a much wider passband bandwidth compared with the conventional coupler design. The measured results show good agreement with the simulated results.

Open loop resonator bandpass filter with wide stopband using spurlines and microstrip stubs

This paper presents a new microstrip open loop resonator bandpass filter (BPF) for wireless local area networks (WLAN) with wide stopband response. The proposed BPF is composed of a pair of half-wavelength open loop resonators and two additional resonators operating at the center frequency of 2.44 GHz. Two novel resonators consisted of asymmetrical spurlines and quarter-wavelength open-circuited stubs are adopted at the input/output (I/O) feed lines to improve its stopband performance. For the outband spurious respond suppression, its upper stopband attenuation loss is lower than −20 dB from 2.6 GHz to 10 GHz, without affecting the center frequency and insertion loss. Good agreement between simulated and measured results.

Design of compact planar three-way dual-band power divider using defected ground structure

In this paper, a novel compact planar three-way dual-band power divider using defected ground structure (DGS) is proposed. Based on this method, the power divider is reduced half of its original size. And it achieves a good performance. To verify the validity, a 915/2400 MHz power divider is fabricated, which could be applied in radio frequency identification (RFID) system. The experimental results show good agreement with the simulated responses.