Xuehui Guan

Synthesis of dual-band bandpass filters using successive frequency transformations and circuit conversions

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype low-pass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series resonators, and is thereby easy to be realized by using conventional distributed elements. A dual-band BPF with center frequencies of 1.8GHz and 2.4GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate the proposed theory.

A Novel Compact Ultra-Wideband Bandpass Filter Using a Microstrip Stepped-Impedance Four-Modes Resonator

A novel compact ultra-wideband (UWB) bandpass filter (BPF) using a microstrip stepped-impedance four-modes resonator is developed in this paper. By controlling the resonant frequencies of the first four modes of the resonator, we get four transmission poles within the passband of the filter. Moreover, by enhancing the coupling between the resonator and the input/output feed lines, we obtain two additional transmission poles. As a consequence, we realize a UWB bandpass filter that has six transmission poles in its passband, although only one resonator is utilized. A design method, based on network analysis and optimization in the z-domain, is established to determine the circuit and geometrical parameters of the filter. The measured filtering characteristics of the filter show good agreement with the theoretical predictions and satisfy well the Federal Communications Commissions indoor limit.

A compact UWB bandpass filter using two-section open-circuited stubs to realize transmission zeros

A design of a compact ultra-wideband (UWB) bandpass filter is presented in this paper. The filter is synthesized by a modified theory using Z-transform technique. In order to get sharp attenuations of the filter, shunt two-section open-circuited stubs are employed to produce transmission zeros in the lower and upper stopbans. A 3-degree UWB filter is designed and implemented in the form of microstrip lines, and the measured characteristics show good agreement with the theoretical and simulated results.

Compact and High-Isolation Diplexer Using Dual-Mode Stub-Loaded Resonators

A novel compact microstrip diplexer for UMTS and WCDMA system is proposed in this letter. The diplexer is mainly composed of three dual-mode stub-loaded microstrip resonators. Two resonant modes of a stub-loaded resonator work together with one mode produced by the common stub-loaded resonator to form a passband or operating band of the proposed diplexer. Extensive study is then conducted on coupling scheme involved in various parts of the diplexer. In particular, the resonance of a resonator is employed to create a desired transmission zero in the stopband, thus improving the isolation between two passbands. The proposed diplexer is in final fabricated and measured. A good agreement between EM simulated and measured results evidently validates the proposed methodology.

Compact Diplexer Using Slotline Stepped Impedance Resonator

In this letter, a compact diplexer is implemented by using slotline hairpin stepped impedance resonator (SIR) in ground plane. Two sets of slotline SIR with different dimensions are designed to resonate at different frequencies for the diplexer operation. Also, the SIR can provide a degree of freedom to improve the out-of-band rejection by properly tuning its geometrical parameter ratio. Besides, microstrip-slotline transition is used to split the signal to two channels without extra matching circuits and thereby economizes the circuit size. Finally, good agreement between measurement and simulation is achieved.

Synthesis and realization of novel ultra-wideband bandpass filters using 3/4 wavelength parallel-coupled line resonators

In this paper, a novel synthesis theory is proposed to design ultra-wideband (UWB) bandpass filters using 3lambda0/4 (lambda0 is the wavelength at central frequency of the filter) parallel-coupled line resonators. By using the first two resonant modes of the 3lambda0/4 parallel-coupled line resonators, this kind of UWB BPF can achieve a wide bandwidth larger than 100%. In order to alleviate the requirement on fabrication precision, aperture-enhanced coupled lines are introduced in the filter. A three-degree UWB filter with a midband frequency of 6.85 GHz is synthesized, simulated and fabricated. Measured results indicate that the filter is low loss in the passband, and the attenuations in the lower and upper stopbands satisfy the indoor limit issued by the Federal Communications Commission (FCC).

Compact and High Selectivity Tri-Band Bandpass Filter Using Multimode Stepped-Impedance Resonator

In this letter, a miniaturized tri-band bandpass filter (BPF) using a multimode stepped-impedance resonator (SIR) with a 0 ° tapped-feed structure is presented. The odd- and even-mode fundamental resonant frequencies and the first high-order resonant frequencies of the SIR are utilized to generate dual-mode dual-band response and the tapped side-coupled feed-lines construct an additional passband avoiding occupying extra size. Owing to the 0 ° tapped-feed structure and the intrinsic characteristics of the SIR, multiple transmission zeros are created to improve the selectivity of the filter. The bands of the designed tri-band BPF are located at 1.57 GHz (GPS application), 3.5 GHz (WiMAX application) and 5.8 GHz (WLAN application). Good agreement between the simulated and the measured results is observed.

Dual-Band Superconducting Bandpass Filter Using Embedded Split Ring Resonator

In this paper, a superconducting YBa2Cu3Oy (YBCO) filter employs two sets of octagonal half-wavelength split ring resonators, which are designed to generate two passbands with compact size. The center frequency of the lower passband can be tuned by the outer resonators with loading spirals, and the center frequency of the upper passband can be adjusted by the inner resonators with interdigital structure. Both of them provide sufficient degrees of freedom to control the center frequencies and fractional bandwidths of the two passbands, independently. In addition, a pair of side-coupled stubs is applied to control the bandwidth of the lower passband whereas the interdigital structure is used to adjust the coupling strength between the inner split ring resonator (SRR). Based on the above-mentioned design methodology, a dual-band superconducting elliptic-function-response bandpass filter operating at 2.45 and 3.5 GHz is proposed in this paper. Simulated results show that the insertion losses in both passbands are less than 0.05 dB. Four transmission zeros are created close to the passband edges, resulting in high skirt selectivity. For fabrication, high-Tc superconducting YBCO films are deposited on double-side-polished 0.5-mm-thick MgO substrates. The overall size of this filter is 12.1 × 8.4 mm (about 0.25 × 0.17 λg, where λg is the guided wavelength at the center frequency of the first passband).

Compact Dual-Band Bandpass Filter Using Quadruple-Mode Square Ring Loaded Resonator (SRLR)

A compact quadruple-mode square ring loaded resonator (SRLR) is proposed in this letter. Distinct mode splitting characteristics of the quadruple-mode SRLR are investigated and explained by using even- and odd-mode analysis. It results to excite four resonant modes which are applied to produce two pairs of transmission poles for dual-band bandpass filter (BPF) design. Based on the unique characteristics of the proposed SRLR, a miniaturized dual-band BPF operating at 2.45 GHz and 5.20 GHz for WLAN applications was designed and fabricated. Multiple transmission zeros are generated to improve the selectivity of the filter. Measurements are in good agreement with the simulations. Also, the circuit size occupies only 0.11λg×0.23λg, where λg is the guided wavelength at the center frequency of the first passband.

A Novel Millimeter-Wave Ultra-Wideband Bandpass Filter Using Microstrip Dual-Mode Ring Resonators Loaded with Open Tuning Stubs of Different Lengths

In this paper, a millimeter-wave ultra-wideband (UWB) bandpass filter is developed by cascading two microstrip dual-mode ring resonators loaded with lambda0/4 and 3lambda0/4 open tuning stubs, respectively. The ring resonators are analyzed by using the even-and odd-mode method, and closed-form formulas are derived to facilitate the design of transmission zeros of these resonators. The filter has a midband frequency of 25.5 GHz and a 3-dB bandwidth of 5 GHz (20%). Due to the multiple transmission zeros produced in both the lower and upper stopbands, the filter exhibits sharp attenuations near the passband and very wide stopbands. Over 13-35 GHz, the Federal Communications Commissions indoor limit is satisfied quite well.