INLINE TE 01δ MODE DIELECTRIC-RESONATOR FIL- TERS WITH CONTROLLABLE TRANSMISSION ZERO FOR WIRELESS BASE STATIONS

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1 Prgress In Electrmagnetics Research Letters, Vl. 38, 11 11, 213 INLINE TE 1δ MODE DIELECTRIC-RESONATOR FIL- TERS WITH CONTROLLABLE TRANSMISSION ZERO FOR WIRELESS BASE STATIONS Xia Ouyang * and B-Yng Wang Cmmunicatin Center, Guangzhu Pwer Supply Bureau, China Suthern Pwer Grid C., Ltd., 2 Tianhe Nan Er Rd., Tianhe District, Guangzhu, Guangdng 5162, China Abstract A methd t cntrl the transmissin zer f TE 1δ mde dielectric-resnatr (DR) filters fr wireless base statins is prpsed. Instead f using flder structures, dedicated cupling prbes, r extra cavities, as required by cnventinal techniques, transmissin zers are realized. The feeding prbes, extended alng ring dielectric resnatrs, are used t excite the TE 1δ mde and intrduce transmissin zers. By rtating the angle f feeding psitin, transmissin zers can be shifted t the lwer r the upper stpband. Thus, TE 1δ mde dielectric resnatr filters with quasi-elliptic respnses are realized with nly iris cupling cmpnents. Based n this methd, furth-rder inline TE 1δ mde DR filters with different respnses are designed and fabricated. Measured results cnfirm the predicted perfrmance. 1. INTRODUCTION The raid expansin f wireless cmmunicatins has significantly increased the demands fr high-perfrmance micrwave filters [1 3]. Due t the advantages f lw lss, small size, and superir temperature stability, dielectric resnatr filters are widely used in varius cmmunicatin systems [4 7]. T imprve TE 1δ mde DR filters, crss-cupling is the mst cmmn way [8]. At least three mre DRs must be utilized t realize transmissin zers, which are prduced by crss-cupling. Fr size reductin, multi-mde dielectric resnatrs are utilized t design crss-cupling DR filters [9 11]. Dualmde resnatrs allw fr the realizatin f cmpact inline structures Received 2 January 213, Accepted 12 March 213, Scheduled 13 March 213 * Crrespnding authr: Xia Ouyang (yx.scut@gmail.cm).

2 12 Ouyang and Wang and have been extensively used fr satellite applicatins t halve the number f physical cavities f a filter structure [12, 13]. Pseud-elliptic respnses can be easily btained by realizing direct- and crss-cupling amng the mdes f adjacent resnatrs. Hwever the crss-cupling, using flded structures, dedicated cuplings, r extra cavities, will make the design prcedures cmplex. A cnfiguratin f TE 1δ singlemde filter having inline structure and pseud-elliptic respnse has been recently intrduced in [14]. Changing the rientatin f selected dielectric resnatrs can alter the cupling mde between resnatrs. Sequential cupling between adjacent resnatrs and crss cupling between nn-adjacent resnatrs are cntrlled by metallic rds and waveguide steps. Using multiple methds t cntrl the crss- and direct-cupling will increase the cmplexity f design prcedures. In this paper, we present an inline cnfiguratin fr TE 1δ mde dielectric resnatr filters characterized by simple and cmpact structures and imprved perfrmance. By changing the angles f the feeding psitins, transmissin zers can be selected in the upper r lwer stpband. Transmissin zers can be generated in inline TE 1δ mde dielectric resnatr filters by crss-cupling starting frm surce r lad. Thus, quasi-elliptic respnses can be realized in TE 1δ mde DR cavities filters. Cmpared t the cnventinal crss-cupling TE 1δ mde DR filters, the prpsed TE 1δ mde DR filters have simple design prcedures and high selectivity. By using this methd, we design and fabricate furth-rder TE 1δ mde DR filters with symmetric, asymmetric and withut transmissin zers respnses. All designed filters are realized by cupling iris, which can depend n engineering needs. The measured results are identical with the simulated results, which demnstrate the validity f the prpsed methd. 2. TRANSMISSION ZERO REALIZED IN TE 1δ MODE DR FILTERS The electric and magnetic field distributins f TE 1δ mde dielectric resnatr are illustrated in Figure 1. The TE 1δ mde dielectric resnatr cavity has a circular electric field distributin, as well as a circular electric current distributin. The magnetic field is strngest n the axis f the dielectric resnatr disk and at sufficient distance utside the disk. The field resembles that f an axial magnetic diple. TE 1δ mde dielectric resnatr cavity filters are cmmnly excited by prbe feeding structures. On the iris between DR cavities, the directin f the magnetic field vertically pints upward r dwnward. S the prblem f the first cavity can be treated in such a way that the secnd cavity is replaced

3 Prgress In Electrmagnetics Research Letters, Vl. 38, Magnetic field Electric field Vlume current Figure 1. The field distributins f a TE 1δ mde dielectric resnatr cavity. Prt_2 Prt_1 Prt_ Prt_1 Gap Prt_2 27 (a) Prt_1 (b) Figure 2. (a) A single TE 1δ mde dielectric resnatr cavity excited by a prbe and a wave-prt. (b) Overlk f the single TE 1δ mde dielectric resnatr cavity excited by a prbe and a wave-prt. by a wave-prt, as shwn in Figure 2(a). In ding s, the prblem will be simplified. A planar view f Figure 2(a) is shwn in Figure 2(b), where θ is the angle f feeding psitin f the prbe. Figure 3 shws the E-M simulated respnses f the structure shwn in Figure 2 with different angles θ f feeding psitins. The E-M simulatin in this paper is carried ut by HFSS. It is seen that there is a transmissin zer f z near the TE 1δ mde resnance. The transmissin zer variatin rules are as fllws: 1. When θ < 18, the transmissin zer is lcated at the left side f the resnance and shifts leftward with the increase f θ. 2. When θ > 18, the transmissin zer is lcated at the right side f the resnance and als shifts leftward with the increase f θ. 3. When θ = 18, there is n transmissin zer existed. The mde peratin ccurring fr a feeding angle f 27 can be described by EM simulatin f the electric field distributin shwn in

4 14 Ouyang and Wang Figure 4(a). The input r utput excites the resnant TE 1δ mde at the first and last resnatrs, respectively. The iris is cupled t the prbe by means f the evanescent TE 1 mde. When the feeding angle is changed t 18, the directin f electric field wuld be changed t rthgnal rientatin at iris, as shwn in Figure 4(b). Because there is n hrizntal part f electric field thrugh the iris, it is hard t excite nn-adjacent dielectric resnatr fr a feeding angle f 18. Thus, the transmissin zer wuld vanish under such cnditin. In high-rder TE 1δ DR filters, the shifted transmissin zers are changed by the cupling frm surce/lad t the nn-adjacent resnatr, which is a gd realizatin f Macchirarella s thery [15]. Figure 5 summarizes the psitins f transmissin zers with different angles θ f feeding S 21 (db) Variatin Tendency 6 deg 9 deg 12 deg 15 deg 18 deg 21 deg 24 deg 27 deg 3 deg Figure 3. E-M simulated respnses f the structure in Figure 2 with different angles f feeding psitin. TE1 Prt_2 Prt_1 18 Prt_2 Prt_1 (a) 27 y x Figure 4. (a) The electric field distributin fr a feeding angle f 27 degree. (b) The electric field distributin fr a feeding angle f 18 degree. (b) y x

5 Prgress In Electrmagnetics Research Letters, Vl. 38, Transmissin Zer (GHz) TE 1δ mde regin Simuluated Result Angles f feeding psitin (Degree) Figure 5. Variatin f transmissin zer f z versus angles f feeding psitin. 193mm 18 (a) (b) mm 9 (c) Figure 6. Tp view f three fur-ple dielectric resnatr filter cnfiguratins. psitin. The shadwed zne means the field distributins f dielectric resnatr are still the TE 1δ mde. It is pssible t achieve the transmissin zer in the range 1.7 t 2.1 GHz fr a center frequency f apprximately GHz.

6 16 Ouyang and Wang 3. THREE CONFIGURATIONS OF FOUR-POLE BANDPASS FILTER Frm the abve analysis we can knw that, the cntrl f the angles f feeding psitin can shift the transmissin zers. In the fllwing, design examples are presented using the prpsed filter cnfiguratin. Figure 6 presents three pssible dielectric resnatr filter cnfiguratins. The resulting filter tplgy, cmmnly referred t as triplet, is diagrammed in Figure 7. S L Figure 7. Tplgy f the surce and lad multi-resnatr cuplings inline cnfiguratin filters Filter withut Transmissin Zer In the first example, the filter cnfiguratin in Figure 6(a) is used t realize a fur-ple filter withut transmissin zer. T design a filter that has a center frequency 1.84 GHz,.5-dB insertin lss bandwidth 21 MHz. The input and utput feeding angle are 18 degree, s that the cupling frm surce (r the lad) t the secnd resnatr des nt exist. Thus, n transmissin zer exists near the passband Filter with Asymmetric Transmissin Zers The next filter example has the same center frequency and bandwidth. The angle f utput feeding psitin is rtated t 9 degree. S a negative cupling fr a triplet sectin had been realized with inline cnfiguratin. The triplet sectin starting frm lad t the last tw resnatrs intrduced a transmissin zer near the passband Filter with Symmetric Transmissin Zers In the last example, the filter cnfiguratin in Figure 6(c) is used t realize a fur-ple filter with tw transmissin zers near its passband. In cnfiguratin (c), the input (left) angle f feeding psitin is 9 degree while the utput angle f feeding psitin is 27 degree. The negative cupling frm the input t the first tw resnatrs generates a transmissin zer belw its passband. Meanwhile, the psitive cupling

7 Prgress In Electrmagnetics Research Letters, Vl. 38, S-parameters (db) S 21 S 11 Cnfiguratin (a) -1 Cnfiguratin (b) Cnfiguratin (c) Figure 8. Simulated results f three fur-ple dielectric resnatr filter cnfiguratins. S-parameters (db) S 21 S Figure 9. Cupling matrix respnse f the designed filter. frm the utput t the last tw resnatrs creates a transmissin zer abve its passband. Three crrespnding respnses are shwn in Figure FILTER DESIGN EXAMPLES A fur-ple TE 1δ mde DR filters with a passband ripple f.36 db, a center frequency at 1.86 GHz, and a bandwidth f 2 MHz, and tw stpband transmissin zers lcated at and 1.93 GHz is designed. Accrding t the tplgy f Figure 7, the filtering functin is described by the fllwing nrmalized cupling matrix M = The cupling matrix respnse is shwn in Figure 9. The HFSS simulated and measured results are shwn in Figure 1, alng with the cupling matrix respnse: the agreement between the curves validates the filter tplgy used t describe the structure. As shwn in Figure 11, the filter has a.5 db insertin lss bandwidth frm GHz t GHz. Transmissin zers, created by input and utput cavities, are at and 1.93 GHz. The fluctuatin f the in-band grup delay is less than 8.6 ns. Figure 12 illustrates the prperties f the input and utput cavities, which effectively prves that they create tw transmissin zers fr this filter.

8 18 Ouyang and Wang T demnstrate that the transmissin zers f the fabricated filter are tunable, we alternate the angle f utput feeding psitin. The filtering functin is described by the fllwing cupling matric M = The cupling matrix respnse is shwn in Figure 13. Because f tw transmissin zers at and 1.77 GHz, a much higher rejectin level f the lwer stpband can be btained, as shwn in Figure 14. S-parameters (db) S 21 S 11-7 Measurement -8 E-M Simulatin -9 C-M Simulatin Figure 1. Measurement f the prpsed dielectric resnatr filter. Insertin lss (db) Grup Delay (db) E-M Simulatin -2. Measurement (a) (b) E-M Simulatin Measurement Figure 11. Measurement f the prpsed DR filter. (a) Passband insertin lsses. (b) Grup delay. S 21 (db) Leftside DR Cavity Rightside DR Cavity Filter Simulatin Figure 12. Cntributins f the input and utput cavities. S-parameters (db) S 21 S Figure 13. Cupling matrix respnse f the designed filter.

9 Prgress In Electrmagnetics Research Letters, Vl. 38, S-parameters (db) Measurement E-M Simulatin C-M Simulatin Figure 14. The input and utput create tw same transmissin zers at the lwer stpband. Figure 15. Phtgraphs f manufactured fur-ple DR filter. The phtgraphs f the designed and fabricated furth-rder TE 1δ mde DR filters are given in Figure CONCLUSION A methd t design cntrllable transmissin zers in inline TE 1δ mde DR filter was prpsed. Firstly, the transmissin zer in inline DR cavity filter has been analyzed. Rtating the angle f feeding psitin, transmissin zer can be shifted t the lwer r the upper stpband. Based n this methd, quasi-elliptic TE 1δ mde DR filters are realized by nly iris cupling cmpnents. Furth-rder TE 1δ mde DR filters with asymmetric, symmetric and withut transmissin zers respnses are designed and fabricated. The simulated and measured results prve the effectiveness f the prpsed methd. REFERENCES 1. Ku, J. -T. and S. -W. Lai, New dual-band bandpass filter with wide upper rejectin band, Prgress In Electrmagnetics Research, Vl. 123, , Weng, M.-H., S.-K. Liu, H.-W. Wu, and C.-H. Hung, Stpbandextended balanced filters using bth λ/4 and λ/2 SIRs with cmmn-mde suppressin and imprved passband selectivity, Prgress In Electrmagnetics Research, Vl. 128, , 212.

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