Even-odd Mode Method Research Articles

Compact Bandpass Filters Using Folded Quad-Mode Stub-Loaded Loop Resonators

Folded quad-mode stub-loaded loop resonators (QMSLLRs) are proposed for realizing both bandpass and dual-band bandpass filters with compact dimensions. The QMSLLR is a folded square loop loaded with four short stubs, providing structure symmetry in both transversal and longitudinal directions. Determined by the lengths of the loaded stubs, the four resonant frequencies as analyzed with even-odd mode method can be either distributed in one passband with equal space, or in two passbands with a guard band in between, for realizing a single-band bandpass filter or a dual-band bandpass filter, respectively. For both the input and output couplings, two perpendicular feeding lines are parallel coupled to the QMSLLR at one corner. The measure results prove that the structure is suitable for the design of a medium band or even narrow band bandpass filters with compact dimensions.

A Tunable Planar Balun with an Isolation Circuit Using Varactors Loaded Coupled Lines

In this paper, a frequency tunable planar balun composed of varactors loaded coupled lines (VL-CLs) is presented. By tuning the capacitances of the varactors, a wide frequency tuning range is obtained. Moreover, good impedance match, balanced output ports amplitude, and consistent output ports phase difference (PD) are maintained during the tuning. A detailed theoretical analysis using the signal flow diagram and the even-odd mode method is presented to clarify the characteristics of the proposed balun. To achieve ideal output matching and isolation for the proposed balun, a novel frequency tuned isolation circuit (IsC) is designed and connected to the balun. In theory, a frequency tuning range of 200% can be realized. In practice, due to the limited capacitances of the varactors, a prototype with a tunable frequency of 1.0 GHz ~ 2.0 GHz (66.7%) is designed, fabricated, and measured. The measured results show that more than21 dB of return loss (RL), 180° ± 1.8° of phase difference, 0.43 dB of amplitude imbalance (AP), and 22 dB of isolation are obtained at all tuning center frequencies, agreeing well with the simulated results.

AN IMPROVED DESIGN OF DUAL-BAND 3 DB 180° DIRECTIONAL COUPLER

A novel design concept of dual-band 180◦ hybrid ring coupler is presented in this paper. Coupler is a key element in front-end building blocks of wireless transceiver systems such as industrial systems and consumer electronic devices. The proposed design is realized by combining multiple arbitrary length transmission lines operating at two frequencies with one dual-band 180◦ phase shifter. The even-odd mode method is applied to derive the design equations for proposed dual-band 3dB 180◦ directional coupler. Based on the analysis, it is found that the realizable frequency ratio of the proposed coupler is very flexible (i.e., the ratio between the two operating frequencies). Moreover, the 180◦ phase shifter features arbitrary characteristic impedance (i.e., its characteristic impedance can be arbitrarily chosen), which further ensures the easy implementation of proposed structures. To prove the design concept, full-wave electromagnetic simulations are performed to design a dual-band ring hybrid coupler working at 0.9 and 1.98GHz. An experimental prototype is fabricated on Rogers RT/Duroid 5880 board. The measurement results match well with the theoretical and numerical ones.

Synthesis Design of Box-Section Bandpass Filter With Hybrid <formula formulatype="inline"><tex Notation="TeX">$\lambda/4$</tex> </formula> and Dual-Mode Resonators

In this letter, a box-section bandpass filter consisting of hybrid λ/4 and dual-mode resonators at X-band is presented. Compared with the conventional even-odd mode method, the dual-mode resonator in the proposed filter is equivalent to separate λ/2 and λ resonators. A generalized synthesis approach is firstly proposed with extensive discussions on designing asynchronously tuned resonators. One prototype centered at 8.65 GHz, with 0.9 GHz passband is fabricated. Measured results of this filter demonstrate very high single-sided selectivity with 40 dB skirt slope steepness of 1.98 and minimum in-band insertion loss of 1.43 dB.

Design of an extremely miniaturized branch-line coupler

In this paper, a new size-reduction approach for branch-line coupler is introduced which uses parallel end-shorted coupled lines with lumped capacitors. The characteristic of the new design was analyzed using even-odd mode method, and simulated on HFSS before fabricated on the FR4 epoxy glass cloth copper-clad plat (CCL) PCB substrate at center frequency of 1 GHz. The electrical length of transmission line was reduced to 15 degrees, therefore the size of branch-line coupler was largely reduced approximately maintaining the same characteristic around the stable center frequency. The insertion loss of the branch-line coupler filter was ?4.39 dB. The size of the overall hybrid is 20 mm × 20 mm. Measurements results were well agreed with the simulated ones.

Design of Microwave Baluns With Flexible Structures

In this letter, two types (Type-I and Type-II) of microwave baluns with generalized structures are presented. Different from the conventional transmission-line-based baluns where λ/2 transmission lines or λ/4 microstrip lines are used, the proposed baluns are constructed by transmission lines with arbitrary electrical lengths. Both of the two types of baluns are designed based on a symmetric four-port structure with one of the ports open-ended. Even-odd mode method is applied to analyze the performance of these baluns. Specifically, for the Type-I design, a symmetrical impedance transformer is employed to realize the desired flexible balun function. For the Type-II design, an asymmetric impedance transforming network is applied, and a compact size is achieved. Analytical design equations have been derived for both designs. Based on these equations, two different baluns (Type-I and Type-II) have been designed, fabricated and measured. The measurement results match well with the theoretical analysis, which practically proves the design theory.

A Varactor Based 90$^{\circ}$ Directional Coupler With Tunable Coupling Ratios and Reconfigurable Responses

In this paper, a symmetric four-port microwave varactor based 90 ° directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. By applying suitable biasing voltages to the varactors, the power-dividing ratios between the two output ports (i.e., port 2 and port 3) of the coupler can be easily controlled. Moreover, it is found that the realizable power ratio using the proposed structure is very flexible (it could be extremely large or small). Therefore, under the special case when the coupling ratio is tuned to be 1, the proposed coupler is reconfigured to be a crossover. Good isolation and return-loss performance have been maintained for different power-dividing ratios. To theoretically analyze the proposed device, closed-form design equations are derived using the even-odd mode method. Based on these analytical equations, an experimental prototype working at 1 GHz is designed, fabricated, and characterized. The measurement results match well with the simulation and theoretical results, validating the proposed design theory.

A QUASI-ELLIPTIC MICROSTRIP BANDPASS FILTER USING MODIFIED ANTI-PARALLEL COUPLED-LINE

A novel band-pass fllter (BPF) with lower and upper stopband zeros is proposed. The fllter mainly consists of two antisymmetric modifled anti-parallel coupled-lines and double pairs of transmission lines. Compared with the traditional anti-parallel coupled-line, the new fllter has a better performance at both pass band and stop band. On the basis of even-odd mode method and network theory, the fllter has been analyzed in detail. In addition, a simple method to create transmission zeros is investigated, which is beneflcial for controlling the stopband zeros. The proposed fllter is implemented on RT/Duroid 4350 substrate. Measured results show low insertion loss of less than 1.6dB in the pass band and good suppressing of more than 22dB in the lower stop band. Measured results show a good agreement with simulated results.

A novel dual‐band balun using branch‐lines with open stubs

AbstractThis letter presents a novel dual‐band balun using the branch‐line configuration. We establish design equations for dual‐band balun based on the even‐odd mode method. The proposed circuit operates at 2.45 GHz and 5.25 GHz. The single‐ended power is divided differentially at the balanced ports. The insertion losses (S21 and S31) show around −2.7 dB to −4.3 dB at the two different frequencies. The phase difference between the balanced ports shows maximum 3° deviation from 180°. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 642–644, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24996

A Tapped Stepped-Impedance Balun With Dual-Band Operations

This letter presents the design of a dual-band balun using tapped stubs and stepped-impedance structures. By adjusting the impedances of the tapped stubs properly, the two output signals of the balun are out-of-phase at the two operating frequencies which is essential for the balun operation. Meanwhile, the stepped-impedance structure is designed to satisfy the dual-band matching condition at the input port. Closed form design equations are derived using the even-odd mode method. Based on these equations, a microstrip balun on Rogers' duroid/RT 5880 substrate operating at 2.45 GHz/5.25 GHz is designed, fabricated, and measured. The measurement results verify the dual-band operations of the balun. Finally, the impedance transformation property of the proposed dual-band balun is discussed.