Microstrip Filter Design

Transcription

1 Practical Aspects of Microwave Filter Design and Realization IMS 5 Workshop-WMB Microstrip Filter Design Jia-Sheng Hong Heriot-Watt University Edinburgh, UK

2 Outline Introduction Design considerations Design examples Summary 2

3 Introduction- Driving forces Recent development of microstrip filters has been driven by applications - Wireless communications Wireless sensor/radar systems. Driven by technologies - High temperature superconducting Micromachining LTCC Ferroelectric. 3

4 Introduction- Microstrip Filter Publications 2 Total 6+ in recent years Search from IEEE Xplore N u m b e r Year 4

5 Design Considerations- Topologies l l 2 l n l n+ W C Y s W W W 2 W L s 2 l 2 l 4 l 6 l l 3 l 5 l 7 W 2 C 2 C 4 W n s n L 4 Z L 3 L 5 Z L L 2 C 6 W n W n+ s n+ W n+ Y W W 2 W 3 W n l g/4 l g /4 C L C L2 C L3 C Ln- C Ln l l 2 l 3 l n q 2 3 n- n n+ l h l 2h l 3h l 4h l 5h Y t Y Y n Y t q t l v l 3v l 5v s s 2 s 3 s 4 s 5 W Y A Y A s,2 s 2,3 s n-,n l 2v l 4v ~ λ/4 ~ λ/4 ~ λ /4 ~ λ/4 Via hole grounding 5

6 Design Considerations- Topologies The choice of a topology depends on Characteristics of filters, such as chebyshev or elliptic Bandwidth Size Power handling 6

7 Design Considerations- Substrates The choice of a substrate depends on Size Higher-order modes Surface wave effects Implementations couplings, line/spacing tolerances, Dielectric loss Temperature stability Power handling dielectric strength (breakdown), thermal conductivity 7

8 Design Considerations- Higher-order modes Keep operating frequencies below the cutoff frequency of the st higher-order mode, c fc = ε ( 2 W +.8h) r Cutoff frequency f c (GHz) W =. mm ε r = 3 ε r = 6.5 ε r =.8 Cutoff frequency f c (GHz) ε r =.8 W=.5 mm W=. mm W=.5 mm Substrate thickness h (mm) Substrate thickness h (mm) 8

9 Design Considerations- Surface waves Keep operating frequencies below the threat frequency of the lowest surface wave mode, f s = c tan ε 2πh r r ε at which the surface mode couples strongly to the dominant mode of microstrip because the phase velocities of the two modes are close. Threat frequency f s (GHz) Substrate thickness h (mm) ε r = 3 ε r = 6.5 ε r =.8 9

10 Design Considerations- Losses There are three major losses in a microstrip resonator: Conductor loss Q c h 377Ω π λ Rs Dielectric loss Q d tanδ Radiation loss Q u = Q c + Q d + Q r

11 Design Considerations- Power handling Peak power handling capability when the breakdown occurs in substrate P p V 2Z 2 o c V o is the maximum breakdown voltage of the substrate Z c is the characteristic impedance of the microstrip Narrower band filters result in higher electric field density, leading to a lower peak power handling

12 Design Considerations- Temperature effect Temperature characteristic of a microstrip half-wavelength resonator on RT/Duroid substrate with ε r =.2, h =.27 mm Copper CTE (coefficient of thermal expansion) = 7 ppm/ o C Substrate CTE = 24 ppm/ o C Substrate TCK (thermal coefficient of ε r ) = 425 ppm/ o C At 23 o C f = MHz f = At 73 o C for copper CTE only f = 928. MHz f =.7 MHz At 73 o C for substrate thickness CTE only f = MHz f =. MHz At 73 o C for substrate TCK only f = MHz f = 9.6 MHz At 73 o C (consider all) f = MHz f = 8. MHz Frequency variation versus temperature is mainly due to dielectric constant change vs temperature 2

13 Design Examples- Open-loop filters () a ( b) ( c ) ( d) From: Jia-Sheng Hong and M.J.Lancaster, Microstrip Filters for RF/Microwave Applications, John Wiley & Sons. Inc. New York, 2 3

14 Design Examples- Open-loop filters Specifications: Center frequency 985MHz Fractional Bandwidth.359% 4dB-Rejection Bandwidth Passband Return loss 25.5MHz 2dB Design parameters for an 8-pole 8 filter: M M M,2 3,4 3,6 = M = M 7,8 5,6 =.752 =.844 =.5375 M M 2,3 4,5 = M 6,7 =.723 =.663 Q ei = Q eo =

15 Design Examples- Open-loop filters Realisation On RT/Duroid substrate with a relative dielectric constant of.8 and a thickness of.27mm. Each resonator has a size of 6 by 6 mm. -5 Insertion/Return Loss (db) Insertion Loss (db) Insertion loss Return loss Frequency (MHz) Frequency (MHz) 5

16 Design Examples- Open-loop filters Realisation 2 On RT/Duroid substrate with a relative dielectric constant of.8 and a thickness of.27mm 6

17 Design Examples- Trisection open-loop filters Midband or centre frequency : 95MHz Bandwidth of pass band : 4MHz Return loss in the pass band : < 2dB Rejection : > 2dB for frequencies 95MHz f f Q 2 M M ei 2 3 = f 3 = MHz = MHz = Q eo = M = =.4753 = Magnitude (db) -2-3 S 2-4 S On RT/Duroid substrate with a relative dielectric constant of.8 and a thickness of.27mm Frequency (MHz) Measured response 7

18 Design Examples- Trisection open-loop filters Midband or centre frequency : 9MHz Bandwidth of pass band : 4MHz Return loss in the pass band : < 2dB Rejection : > 35dB for frequencies 843MHz f f Q 2 M M ei 2 3 = f 3 = MHz = MHz = Q eo = M = =.95 = Magnitude (db) S 2 S On RT/Duroid substrate with a relative dielectric constant of.8 and a thickness of.27mm Frequency (MHz) Measured response 8

19 Design Examples- Trisection open-loop filters -2 Insertion Loss (db) case case 2 case 3 case 4 Insertion Loss (db) Measured wideband response Frequency (MHz) Experimental results on extra transmission zeros, where case to 4 indicate the increase of direct coupling between the two feed lines. Frequency (GHz) 9

20 Design Examples- Multi-layer layer filters Common Ground Plane Dielectric Substrate Electric Coupling Aperture Magnetic Coupling Aperture I/O Ports Microstrip Open-Loop Resonator 2

21 Design Examples- Multi-layer layer filters Transmission/Return Loss (db) - Q u = Chebyshev -5 Elliptic Linear Phase Frequency (MHz) (a) Group Delay (ns) 35 3 Q u = Chebyshev Elliptic 5 Linear Phase Frequency (MHz) (b) 2

22 Design Examples- Multi-layer layer filters Experimental results Transmission (db) Transmission (db) Transmission (db) Group delay (ns) Frequency (MHz) Frequency (MHz) (a) Group delay (ns) Frequency (MHz) Frequency (MHz) (b) Group delay (ns) Frequency (MHz) Frequency (MHz) (c) 22

23 Design Examples- Slow-wave wave filters Capacitively loaded line resonator Microstrip slow wave resonator (I) d d I I 2 Z, a ba V C/2 L C/2 L V 2 w 2 w a L Wa= mm, w=2 mm, w2=3 mm, d=6 mm on RT/Duroid 6 L 2 w Frequency (GHz) f f f / f f / f Frequency (GHz) f f f / f f / f Loading capacitance (pf) Open-stub length, L (mm) 23

24 Design Examples- Slow-wave wave filters Centre Frequency : 335 MHz 3dB Bandwidth : 3 MHz passband Loss : 3dB Max. Min. stopband rejection : D.C. to 253 MHz 6dB 457 to 265 MHz 6dB 265 to 3 MHz 3dB 6dB Bandwidth : 2 MHz Max. On RT/Duroid 6 substrate 24

25 Design Examples- Slow-wave wave filters Transmission (db) mm.5mm Substrate: ε r =.8 h=.27mm Frequency (GHz) 25

26 Design Examples- Dual-mode filters Type I dual-mode resonator D.84λg π D λ g 2 C L L 2 C 2 () a () b D λ g π D λ 4 g D < λ g 4 Mode Mode 2 ( c ) () d () e 26

27 Design Examples- Dual-mode filters 6 mm - Port d x d Amplitude (db) S 2 S Port 2 d =2 mm on RT/Duroid 6 substrate Frequency (GHz) 2.5% bandwidth at.58 GHz 27

28 Design Examples- Dual-mode filters 2 mm Port mm Port 2 On RT/Duroid 6 substrate Centred at 82 MHz 28

29 Design Examples- Dual-mode filters Type II dual-mode resonator a, 3 a Y a a, X a a, Z E Electric Field Mode Mode Equilateral triangular microstrip patch resonator 29

30 Design Examples- Dual-mode filters w b L J, J,3 C 3 INPUT J,3 OUTPUT a 2 L 2 J,2 J 2,3 C 2 Circuit model (No coupling between the two modes) Magnitude (db) S (Theory) S 2 (Theory) S (EM) Frequency response Frequency (GHz) S 2 (EM) (a = 5 mm and b =.25 mm on a.27mm thick dielectric substrate with a relative dielectric constant of.8) 3

31 Design Examples- Dual-mode filters w b Magnitude (db) S (Theory) S 2 (Theory) S (Simulation) a -6-7 S 2 (Simulation) a = 5 mm and b = 4 mm on a.27mm thick dielectric substrate with a relative dielectric constant of.8 Frequency (GHz) Frequency response 3

32 Design Examples- Dual-mode filters Four-pole dual-mode filters On a substrate with a relative constant of.8 and a thickness of.27 mm 32

33 Design Examples- Dual-mode reject filters s W l g Magnitude (db) S S 2 a Single dual-mode resonator Frequency (GHz) PORT 2 PORT 2 The details to be presented in another session (WE4C) at IMS25 33

34 Design Examples- Extract-pole filters L s = z in C s z in J= L=C s C=L s l λ g /4 l 2 s z in l 3 λ g /2 34

35 Design Examples- Extract-pole filters On RT/Duroid 6 substrate EM simulated performance 35

36 Design Examples- Extract-pole filters On RT/Duroid 6 substrate 36

37 Design Examples- CQ filters PORT PORT 2 db 8 pole 5MHz wideband S2 response 65K S Start:.88 GHz Stop: 2.2 GHz Another 8-pole filter of this type with group delay equalisation will be presented in THF session at IMS25 37

38 Design Examples- CQT filters PORT PORT 2 db S S2 db S GHz db Start:.96 GHz Stop:.985 GHz 38

39 Design Examples- Wideband filters Optimum stub bandpass or pseudo highpass 2θ c 2θ c Unit: mm y = y,2 y n-,n y = y y 2 y n- θ c Short-circuited stub of electrical length θ c y n Via hole grounding 5 On substrate: ε r = 2.2, h =.57 mm θ c π/2 π θ c π 3π/2 θ - S 2 Amplitude (db) S 2-5 S f c (π/θ c )f c From: Jia-Sheng Hong and M.J.Lancaster, Microstrip Filters for RF/Microwave Applications, John Wiley & Sons. Inc. New York, 2 f Frequency (GHz) EM simulated performance 39

40 Summary Microstrip filter designs involve a number of considerations, including careful choice of topologies and substrates. Some design examples of new topologies with advanced filtering characteristics have been described, including Open-loop resonator filters Multilayer filters Slow-wave wave filters Dual-mode filters Extract pole, Trisection, CQ and CQT filters Optimum wideband stub filters Driven by applications and emerging device technologies, many new and advanced microstrip filters have been developed and their designs are available in open literatures. 4