In this letter, a novel dual-mode bandpass balun filter is presented using a miniaturized cross-slotted patch resonator. This balun filter consists of a single slit-loaded patch etched by a pair of cross slots and a stepped-impedance open stub. An unbalanced input port is orthogonally arranged in-between two balanced output ports along the patch, and each feed line is connected to an additional stub for enhanced coupling. Due to the dual-mode characteristic of the patch resonator, two transmission poles can be easily constructed at both balanced passbands. Asymmetrical width and length of the cross-loaded slots perturb the field of the patch and excite two degenerate modes simultaneously, while the attached open-circuited stub provides an additional degree of freedom for performance tuning. Finally, two prototype balun filters are designed and fabricated at 3.48 and 1.80 GHz, respectively. Measured results achieve good filtering and balun performance and agree well with those from simulations. © 2011 IEEE.published_or_final_versio

Menzel, W

Sun, S

IEEE Microwave and Wireless Components Letters

In this letter, a novel dual-mode bandpass balun filter is presented using a miniaturized cross-slotted patch resonator. This balun filter consists of a single slit-loaded patch etched by a pair of cross slots and a stepped-impedance open stub. An unbalanced input port is orthogonally arranged in-between two balanced output ports along the patch, and each feed line is connected to an additional stub for enhanced coupling. Due to the dual-mode characteristic of the patch resonator, two transmission poles can be easily constructed at both balanced passbands. Asymmetrical width and length of the cross-loaded slots perturb the field of the patch and excite two degenerate modes simultaneously, while the attached open-circuited stub provides an additional degree of freedom for performance tuning. Finally, two prototype balun filters are designed and fabricated at 3.48 and 1.80 GHz, respectively. Measured results achieve good filtering and balun performance and agree well with those from simulations. © 2011 IEEE.link_to_subscribed_fulltex

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Title Novel dual-mode balun bandpass filters using single cross-slotted patch resonatorAuthor(s) Sun, S; Menzel, WCitation IEEE Microwave and Wireless Components Letters, 2011, v. 21 n.8, p. 415-417Issued Date 2011URL http://hdl.handle.net/10722/139263Rights©2011 IEEE. Personal use of this material is permitted. However,permission to reprint/republish this material for advertising orpromotional purposes or for creating new collective works forresale or redistribution to servers or lists, or to reuse anycopyrighted component of this work in other works must beobtained from the IEEE.IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 21, NO. 8, AUGUST 2011 415Novel Dual-Mode Balun Bandpass Filters UsingSingle Cross-Slotted Patch ResonatorSheng Sun, Member, IEEE, and Wolfgang Menzel, Fellow, IEEEAbstract—In this letter, a novel dual-mode bandpass balun filteris presented using a miniaturized cross-slotted patch resonator.This balun filter consists of a single slit-loaded patch etched bya pair of cross slots and a stepped-impedance open stub. Anunbalanced input port is orthogonally arranged in-between twobalanced output ports along the patch, and each feed line isconnected to an additional stub for enhanced coupling. Due to thedual-mode characteristic of the patch resonator, two transmissionpoles can be easily constructed at both balanced passbands. Asym-metrical width and length of the cross-loaded slots perturb thefield of the patch and excite two degenerate modes simultaneously,while the attached open-circuited stub provides an additionaldegree of freedom for performance tuning. Finally, two prototypebalun filters are designed and fabricated at 3.48 and 1.80 GHz,respectively. Measured results achieve good filtering and balunperformance and agree well with those from simulations.Index Terms—Balun bandpass filter (BPF), balanced filter,cross-slotted patch, dual-mode resonator.I. INTRODUCTIONT ODAY, integration, compact size, and low cost are highlydesirable for RF and microwave integrated circuits inmodern wireless systems. As two key components, both balunand filter play important roles in the design of RF front-endmodules. Directly cascading a balun and a filter offers an intu-itive solution for the balanced-to-unbalanced signal conversionwith filtering selection. However, this proposal always suffersfrom high insertion loss and large size due to the linear sum oftwo separate circuit topologies.To overcome these problems, an idea of integrating these twodevices has been proposed to reduce the loss and circuit size[1], [2]. That means an integrated device can provide not onlya frequency-band selection as a filter, but also a balanced-to-unbalanced conversion as a balun. By using low-temperatureco-fired ceramic (LTCC) technology, a balun and a filter wereconnected in series and considered as a chip-type multi-func-tional device [1]. Because of multilayer configurations, theseLTCC-based balun filters have compact sizes, but the structureand design procedure is very complicated. Based on the tradi-tional Marchand balun, the filtering function can also be intro-Manuscript received February 16, 2011; revised April 29, 2011; acceptedMay 13, 2011. Date of publication July 08, 2011; date of current version Au-gust 10, 2011. This work was supported in part by the Alexander von HumboldtFoundation, Germany.S. Sun is with the Department of Electrical and Electronic Engineering, TheUniversity of Hong Kong, Hong Kong, China (e-mail: sunsheng@ieee.org).W. Menzel is with the Institute of Microwave Techniques, University of Ulm,Ulm 89069, Germany (e-mail: wolfgang.menzel@uni-ulm.de).Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LMWC.2011.2158535duced by involving lumped capacitors [2]. However, the circuithas large size and requires many via holes due to the multipleuse of short-circuited coupled lines. In [3], smaller size can beachieved by implementing shorter multi-coupled lines on LTCCsubstrate. Nevertheless, more shunt lumped capacitors have tobe added into the multilayer structure and make the design morecomplicated. On the other hand, a symmetrical four-port bal-anced-to-balanced bandpass filter (BPF) can be converted to athree-port balun filter with one of the ports being opened [4].In this letter, we present a dual-mode balun BPF using across-slotted patch resonator. The concept of dual-mode balunfilter was initially proposed in [5] and modified in [6] using asingle ring resonator. Due to the excitation of two degeneratemodes, two-pole transmission characteristic can be realized onboth of two balanced outputs. To reduce the size and radiationloss, dual-mode filters using cross-slotted patch resonators weredeveloped in [7], [8]. As the slot length is increased, the route ofthe electric current on the patch is bent and extended. Then, theresonant frequency can be shifted down, and the size can be re-duced accordingly. In [9], two such patch resonators have beenstacked to make a balun filter, where each resonator producedtwo modes for each balanced passband. However, an additionalconductor plane was inserted between two patch resonators andincreased the design complexity and cost accordingly. There-fore, the objective of this work is to design a balun filter usinga single patch resonator. By etching the patch with asymmet-rical-cross slots, two degenerate modes can be excited and cou-pled to each other at both balanced output ports. Finally, twopatch balun filters with and without shielding box are designedand verified experimentally.II. PROPOSED BALUN FILTERSFig. 1 depicts the schematic of this proposed balun BPF.A pair of asymmetrical-crossed slots, ended with a stepped-impedance-shape and T-shape slots, is formed on a square patchresonator with four slits at its four sides. An open-circuitedstepped-impedance shaped stub is installed at the enlarged slitand provides an additional degree of freedom for performanceadjustment by controlling the transmission zeros. Compared tothe two-port dual-mode BPF with only port 1 and 2, a third port(port 3) is added to another side of the patch. Since both port2 and 3 are placed face-to-face at the orthogonal plane with re-spect to port 1, a half-wavelength electrical length is naturallyformed between them and offers an 180 phase difference forthe two balanced outputs. Each feed line is connected to a cou-pling stub inserted into slits in order to provide an enhanced cou-pling degree. Fig. 2 shows the size-vectored current densities onthe conducting surface of the patches at 3.48 GHz. The current1531-1309/$26.00 © 2011 IEEE416 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 21, NO. 8, AUGUST 2011Fig. 1. Physical layout of the designed balun BPF.(a) (b)Fig. 2. Current distributions of the (a) symmetrical and (b) asymmetrical cross-slotted patches.flow path on the patch is significantly distorted and extended bythe pair of symmetrical-crossed slots, where the electrically ex-tended and oppositely oriented current densities along the slotslead to a reduction of the size and radiation loss. In particular,the current distributions around port 2 and 3 are also symmet-rical, which implies that the two degenerate modes at two outputports can be excited by sharing the asymmetrical perturbations,as shown in Fig. 2(b).Similar to the operation principle of the inner corner-cut per-turbation along a ring resonator [10], the effective inductiveloading between input port 1 and output port 3 is larger thanthe other one between port 1 and 2, due to wider etching at theend of the stepped-impedance-shape slot. That means two trans-mission zeros can be only observed at the transmission path be-tween input port 1 and output port 2. Fig. 3 displays the fre-quency responses with varied slot and stub sizes. By adjustingthese perturbation elements, the dual-mode behavior with twotransmission zeros can be well controlled to obtain both bal-anced in-band and out-band responses. In order to provide aninsight of the quality of a balun filter, the associated mixed-modeparameters, e.g., differential and common modes, can be deter-mined from the standard three-port -parameters as [11](1)(2)The simulated transmission responses of the differentialand common modes are shown in Fig. 4, wherea bandpass performance is observed in differential excitation.According to the definitions in (1) and (2), the intersectionFig. 3. Frequency responses with varied slot sizes (  and  ) and stub lengths( and  ).Fig. 4. Transmission responses of differential and common modes.points between and are corresponding to the trans-mission zeros in as appeared in Fig. 3. On the other hand,20 dB suppression of the common mode has been achievedover the whole simulated frequency range.III. IMPLEMENTATION AND MEASUREMENTTo verify the performance of the aforementioned balun fil-ters, a balun filter, namely, balun-filter A, has been designedat 3.48 GHz. Fig. 5(a) shows the frequency responses of theproposed balun-filter A and Fig. 5(b) shows the amplitude andphase differences of the two balanced ports. The measured min-imum insertion and maximum return losses are dBand 23.1 dB, respectively. The measured amplitude imbalanceand phase difference between the two balanced ports are within0.5 dB and , respectively, over the passband from 3.45to 3.51 GHz. Fig. 5(c) shows the simulated loss factors againstfrequency. We can note that the main loss is mainly contributedfrom the metallic conductor, while the substrate loss is compa-rable with the radiation loss. In order to further reduce the con-ductor and radiation losses, the balun-filter B is designed withwider strip width at 1.8 GHz, and shielded within an aluminumbox. The inset of Fig. 6 illustrates the photograph of this fab-ricated circuit. A good agreement between the simulated andmeasured mixed-mode S-parameters is achieved and shown inFig. 6. The obtained insertion loss of the differential mode isabout 1.45 dB, while the suppression of the common mode isbetter than 20 dB. Table I compares measured 3-dB bandwidthsSUN AND MENZEL: NOVEL DUAL-MODE BALUN BANDPASS FILTERS USING SINGLE CROSS-SLOTTED PATCH RESONATOR 417Fig. 5. Simulated and measured results of the designed balun-filter A. (a) -Magnitudes. (b) Amplitude imbalance and phase balance. Dimensions:               	                            ~~    .All are in mm. Material:     and thickness    	 mm,    ~~	   	   S/m. (c) Simulated loss factors againstfrequency. EM simulator: Advanced Design System 2009.and minimum insertion losses for published and our prototypebalun filters.IV. CONCLUSIONIn this letter, we present a dual-mode balun BPF using only asingle cross-slotted patch resonator. By adjusting the sizes of theasymmetrical-crossed slots and the embedded stub, a two-polefiltering responses can be easily obtained in the passbands at twobalanced outputs. Moreover, the losses are further reduced withthe help of the shielding metal box and the wider strip width.REFERENCES[1] L. K. Yeung and K.-L. Wu, “An LTCC balanced-to-unbalanced ex-tracted-pole bandpass filter with complex load,” IEEE Trans. Microw.Theory Tech., vol. 54, no. 4, pp. 1512–1518, Apr. 2006.[2] R. Kravchenko, K. Markov, D. Orlenko, G. Sevskiy, and P. Heide, “Im-plementation of a miniaturized lumped-distributed balun in balancedfiltering for wireless applications,” in Proc. 35th Eur. Microw. Conf.,Oct. 2005, pp. 1303–1306.[3] C.-L. Tsai and Y.-S. Lin, “Analysis and design of new single-to-bal-anced multicoupled line bandpass filters using low-temperatureco-fired ceramictechnology,” IEEE Trans. Microw. Theory Tech., vol.56, no. 12, pp. 2902–2912, Dec. 2008.Fig. 6. Transmission responses of differential and common modes for balun-filter B with shielding box (	      S/m). Inset: Photographof the fabricated shielded balun BPF. Dimensions:                                              	. All are in mm. Material:    and thickness     mm,     .TABLE ICOMPARISONS AMONG PUBLISHED AND OUR PROTOTYPE BALUN FILTERS[4] C.-H. Wu, C.-H. Wang, S.-Y. Chen, and C. H. Chen, “Balanced-to-unbalanced bandpass filters and the antenna application,” IEEE Trans.Microw. Theory Tech., vol. 56, no. 11, pp. 2474–2482, Nov. 2008.[5] E.-Y. Jung and H.-Y. Hwang, “A balun-BPF using a dual-mode ringresonator,” IEEE Microw. Wireless Compon. Lett., vol. 17, no. 9, pp.652–654, Sep. 2007.[6] P. Cheong, T.-S. Lv, W.-W. Choi, and K.-W. Tam, “Compactmicrostripsquare-loop dual-mode balun-bandpass filter with simul-taneous spurious response suppression and differential performanceimprovement,” IEEE Microw. Wireless Compon. Lett., vol. 21, no. 2,pp. 77–79, Feb. 2011.[7] L. Zhu, P.-M. Wecowski, and K. Wu, “New planar dual-mode filterusing cross-slotted patch resonator for simultaneous size and lossreduction,” IEEE Trans. Microw. Theory Tech., vol. 47, no. 5, pp.650–654, May 1999.[8] L. Zhu, B. C. Tan, and S. J. Quek, “Miniaturized dual-mode bandpassfilter using inductively loaded cross-slotted patch resonator,” IEEE Mi-crow. Wireless Compon. Lett., vol. 15, no. 1, pp. 22–24, Jan. 2005.[9] J. X. Chen, C. Y. Cheung, and Q. Xue, “Integrated bandpass filter balunbased on double-sided parallel-strip line with an inserted conductorplane,” in Proc. Asia-Pacific Microw. Conf., Dec. 2007, pp. 701–704.[10] A. Gorur, “Description of coupling between degenerate modes of adualmode microstrip loop resonator using a novel perturbation arange-ment andits dual-mode bandpass filter applications,” IEEE Trans. Mi-crow. Theory Tech., vol. 52, no. 2, pp. 671–677, Feb. 2004.[11] W. R. Eisenstadt, B. Stengel, and B. M. Thompson, Microwave Dif-ferential Circuit Design Using Mixed-Mode S-Parameters. Norwood,MA: Artech House, 2006, pp. 153–192.

Novel dual-mode balun bandpass filters using single cross-slotted patch resonator

Sheng Sun

Wolfgang Menzel

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Novel Dual-Mode Balun Bandpass Filters Using Single Cross-Slotted Patch Resonator

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Novel dual-mode balun bandpass filters using single cross-slotted patch resonator

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