ANALYSIS AND DESIGN OF TWO LAYERED ULTRA WIDE BAND PASS FILTER WITH WIDE STOP BAND. D. Packiaraj

Transcription

1 A project Report submitted On ANALYSIS AND DESIGN OF TWO LAYERED ULTRA WIDE BAND PASS FILTER WITH WIDE STOP BAND by D. Packiaraj PhD Student Electrical Communication Engineering Indian Institute of Science Bangalore Under the guidance of Prof. K. J. Vinoy Electrical Communication Engineering Indian Institute of Science Bangalore

2 Contents Abstract 3 1. Introduction to UWB filters 4 2. Analysis UWB filter 6 3. Analysis UWB filter with Spur lines 7 4. Experimental Results 9 5. Conclusions 10 References 11 2

3 Abstract Design of an Ultra wide band (UWB) filter over 3.1GHz to 10.6GHz using broad side coupled lines and spur lines in microstrip medium suitable for UWB communications has been presented in this Project. Parameters of broad side coupled lines have been appropriately chosen to achieve ultra wide band response. Spur lines have been incorporated at the input and output feed lines of the filter to improve the stop band rejection characteristics of the filter. Filter has been analyzed based on circuit models and full wave simulations. Experimental results of the filter designed using the proposed structure has been verified against the results obtained from circuit models and full wave simulations. Results are satisfactorily matching. Stop band rejection of better than 20dB was obtained over 13GHz to 18.2GHz. Overall size of the filter is mm 3. 3

4 1. INTRODUCTION Ultra wide band (UWB) technology is gaining a lot of attention in applications such as medical imaging, through wall imaging and vehicular radar, etc due to its low power and high data rate features. U.S. Federal Communications Commission (FCC) allocated the unlicensed use of UWB devices for a variety of applications [1 3]. UWB Bandwidth will be contained between 3.1 and 10.6 GHz for the indoor and hand-held UWB systems. Various topologies of band pass filters with specified pass bands are therefore required to progress in UWB technology. Filters used in UWB systems need to operate over a wide instantaneous bandwidth of GHz with a constant group delay. Extensive work has been carried out to achieve ultra wide band characteristics in the filter performance. Ultra wide band filter based on quarter wavelength short circuited stubs has been demonstrated [4] as shown in Fig. 1. This has minimal number of vias and improved frequency bandwidth. Dual mode ring resonator with stepped impedance open circuited stubs is used to design ultra wide band filter in [5] as shown in Fig. 2. Stepped impedances are used to excite band stop response for achieving good rejection characteristics. The impedance ratio of the stubs controls the stop band region of the filter. As shown in Fig. 3, circular shaped ring resonator with stepped impedances and open circuit stub is used to implement UWB filter in [6]. Attenuation poles are controlled using stub and ring impedances. In [7], UWB filter using multiple mode resonators is designed and the filter structure is shown in Fig. 4. A quadruple-mode UWB filter with sharp out-ofband rejection is reported in [8]. Short circuited stubs are introduced as shown in Fig. 5, in the resonator to achieve transmission zeroes near the lower and upper cut-off frequencies of the filter to improve the rejection characteristics. Besides wide band operation, modern wireless systems need compact and high performance circuits for miniaturization. Multi-layer structure such as low temperature co-fired ceramic (LTCC) is the potential technology [9-11] for designing miniaturized circuits in multi-layered ceramic. Multilayer approach to design miniaturized passive components such as filters, couplers and baluns have been widely used. This project reports the design of a two layer compact ultra wide band filter which uses a set of broad side coupled lines and spur lines as shown in Fig. 6. Analysis of this filter is explained in Section II. In section III, measured results of the filter are compared against full wave simulation results for the validation. Section IV concludes this report. 4

5 Fig. 1. UWB filter using short circuited stubs Fig. 2. UWB filter using ring resonator and stepped impedance stubs Fig. 3. UWB filter using ring resonator with stepped impedances and stub Fig. 4. UWB filter using multiple mode resonators Fig. 5. UWB filter using quadruple mode resonators 5

6 Fig. 6. Proposed UWB filter. a) Top layer, b) Bottom layer 2. ANALYSIS OF UWB FILTER Fig. 1 shows the designed ultra wide band filter which operates over 3.1GHz to 10.6GHz. The filter is designed using broad side coupled lines and spur lines in two-layer structure. A floating conductor in the slot of the ground plane enhances coupling required for achieving broad band operation. Structural parameters of microstrip medium given in Table I are used for the design of filter. Coupled line model given in [12] is used to synthesize length of broad side coupled line L 1, substrate thickness h and width of coupled lines w. Band pass filter can be characterized using ABCD parameters, which are given by [12] where A = D = oe cotθ + e 1 1 oo cotθ 2 2 j + 2 (cotθ cotθ + cscθ cscθ ) oe oo oe oo e o e o B = 2 2 j C = 1 o = oe cscθ + cscθ 1 e oo o, θ e is even mode phase velocity and θ o is odd mode phase velocity. This basic element has two attenuation poles out of which one pole is located at DC while the other is located close to the upper stop band region of the filter. Bandwidth of the filter can be varied by varying broad side coupled line parameters. Required bandwidth can be achieved by properly choosing the value of w. For the present design, width w of 4.4 mm is chosen to get the desired response. Design parameters of the filter are given in Table II. Fig. 7 shows simulation results (1) (2) (3) 6

7 of UWB filter. The rejection is poor in the upper stop band region of the filter. Analytical calculations based on the above formulae are done in MATLAB. The calculated ABCD matrix is finally converted into scattering parameters. Table I. Structural Parameters of microstrip Substrate thickness h 0.787mm Substrate permiitivity ε r 2.17 Table II. Design Parameters of UWB filter without spur lines L 1 (mm) L 2 (mm) s o (mm) S 1 (mm) w(mm) w o (mm) mm Fig. 7. Simulation of GHz UWB filter without spur lines 3. ANALYSIS OF UWB FILTER WITH SPUR LINES Filter s stop band characteristics can be improved by incorporating the spur lines at the input and output sections of the filter as shown in Fig. 6. The length of the spur line shown in Fig. 8 is approximately quarter wavelength at the desired band stop frequency and can be calculated using [13] c L = (4) 4 ε f o where c is the velocity of the wave, f o is the band stop frequency and ε fo is the odd mode permittivity of the coupled lines having widths of w s and w o -w s -s p and gap s p. Spur line can be characterized using the following ABCD parameters A = cosθ e (5) fo B = j( oe sinθ + cosθ tanθ ) e oo e o 2 (6) 7

8 D = cosθ 2 j sin θ e C = e oo oe sinθ tanθ e oe o (7) (8) where, θ e is even mode phase velocity and θ o is odd mode phase velocity. Analytical results of spur lines having physical parameters given in Table III are calculated using the circuit model given in (5-8) and results are shown in Fig. 9. The band stop frequencies are chosen to be 14.2GHz, 15GHz, 17GHz and 17.8GHz for improving the rejection characteristics of the filter. Overall response of the filter obtained from both the analytical calculations (from MATLAB) and ADS simulations [14] is shown in Fig. 10. Results show that the embedded spur lines extended the stop band upto 18.2GHz with minimum rejection of 20dB. Fig. 8. Spur line Table III. Dimensions of band stop elements (spur lines, W s =0.4mm ) Spur line Overlap Length L (mm) Width W o (mm) Spacing s p (mm) Fig. 9. Analytical Results of individual spur lines 8

9 Fig. 10. Simulation results of UWB filter with extended stop band region. 4. EXPERIMENTAL RESULTS Fig. 11 shows the photograph of fabricated ultra wide band filter. Fig. 12 compares the experimental scattering parameters of the UWB filter against the results obtained from ADS simulator [14]. Results are satisfactorily matching each other. Results show that maximum insertion loss is 1dB and stop band attenuation is better than 20dB from 13GHz to 18.2GHz. Fig. 13 shows the measured group delay performance of the UWB filter and group delay is constant with ±0.02ns. Overall size of the filter is mm 3. Fig. 11. Assembled UWB filter. a)top layer 1, b)bottom layer 2. 9

10 Fig. 12. Measured S-Parameters of UWB filter Fig. 13. Measured group delay of UWB filter 5. CONCLUSIONS Analysis and design of UWB filter with wide stop band using broad side coupled lines and spur lines have been presented in this project. Spur lines have been used to improve the rejection characteristics of the filter. Proposed filter was analyzed using circuit models and full wave simulations. A filter operating from GHz has been designed and tested to verify the proposed filter configuration. Stop band rejection of better than 20dB is observed from 13 to 18.2GHz. 10

11 REFERENCES [1] Federal Communications Commission, Revision of part 15 of the commission s rules regarding ultra-wideband transmission systems, Tech. Rep., ET-Docket , FCC02 48, Apr [2] G. R. Aiello and G. D. Rogerson, Ultra-wideband wireless systems, IEEE Microw. Mag., vol. 4, no. 2, pp , Jun [3] L. Q. Yang and G. B. Giannakis, Ultra-wideband communications: an idea whose time has come, in IEEE Signal Process. Mag., vol. 21, Nov. 2004, pp [4] M. S. Razalli, A. Ismail and M. A. Mahdi, Novel compact microstrip ultra-wide band filter utilizing short-circuited stubs with less vias, Progress In Electromagnetics Research, PIER 88, , [5] Cheng-Ying Hsu, Chu-Yu Chen and Chuang-Hao Huang, A UWB filter using a dual-mode ring resonator with spurious pass band suppression, Microwave Journal, pp , Nov [6] H. Ishida and K. Araki, Design and Analysis of UWB band pass filter, IEEE Topical Conference on Wireless Communication Technology, Honolulu, Oct [7] L. Shu and S. Sun, Ultra-Wideband (UWB) band pass filters using multiple-mode resonator, IEEE Microw. Wireless Compon. Lett.,, vol. 11, No. 11, pp , Nov [8] S. W. Wong, L.. hu, Quadruple-Mode UWB band pass filter with improved out-of-band rejection, IEEE Microw. Wireless Compon. Lett.,, vol. 19, No. 3, pp , March [9] C.Q.Scrantom, Where we are and where we re going-ii, IEEE MTT-S IMS Dig., pp , [10] C. W. Tang, Harmonic-suppression LTCC filter with the step impedance quarter-wavelength open stub, IEEE Trans. Microwave Theory Tech., vol. 52, No. 2, pp , July [11] J.W.Sheen, LTCC-MLC duplexer for DCS-1800, IEEE Trans. Microwave Theory Tech., vol. 47, No. 9, pp , Sep [12] C. I. Mobbs and J. D. Rhodes, A Generalized Chebyshev Suspended Substrate Stripline Band pass filter, IEEE Trans. Microwave Theory Tech., vol. 31, No. 5, pp , May [13] C. Nguyen, C. Hsiah and D. W. Bale, Millimeter wave printed circuit spurline filters IEEE-S Digest, pp , [14] ADS Software Inc., 2009, 11