Thick-film multilayer microwave circuits offer advantages over single-layer circuits for wireless applications. Multilayer circuits allow for strong broadside coupling between conductors on different layers, eliminating the need for fine gaps. This makes them well-suited for thick-film printing technology. Examples discussed include directional couplers and DC blocks fabricated using a multilayer approach that demonstrated improved performance compared to single-layer designs. Thick-film technology is particularly applicable for implementing multilayer microwave circuits due to enabling higher density integration and close coupling between conductors.

1. Thick-Film Multilayer Microwave
Circuits for Wireless Applications
By
Kavindra krishna
Research Scholar
AMU
Department of Electronics Engineering AMU
1

2. CONTENTS
 Introduction
 Thick-film technology
 Significance of line losses
 Single layer microwave circuits
 Multilayer microwave circuits
 Summary
2

3. INTRODUCTON
3

4. Typical frequencies for wireless application :
Current mobile : 0.9GHz - 2GHz
3G systems : 2.5GHz
Bluetooth : 2.5GHz
GPS : 12.6GHz
LMDS : 24GHz and 40GHz
Automotive : 77GHz
4

5. LMDS
(Local Multi Point Distribution Services)
5

6. Driving forces created by the wireless market:
 lower cost
 higher performance
 greater functionality
 increased packing density
6

7. Microstrip: basic microwave interconnection
structure
It provides one free surface on which solid state device can be placed.
7

8. Summary of key material requirements at RF:
Conductors: - low bulk resistivity
- good surface finish (low surface roughness)
- high line/space resolution
- good temperature stability
Dielectrics: - low loss tangent (<10-2)
- good surface finish
- precisely defined r (stable with frequency)
- isotropic r
- consistent substrate thickness
- low Tf (< 50 ppm/oC)
8

9. THICK-FILM TECHNOLOGY
9

10. Thick-Film Technology
Advantages:
Low Cost
Feasibility for mass production
Adequate quality at microwave frequencies
Potential for multi-layer circuit structures
Difficulty:
Fabrication of fine line and gaps: limited
quality by direct screen printing
10

11. Standard range of materials is used:
CONDUCTORS: - gold
- silver
- copper
DIELECTRICS: - ceramic (alumina)
- green tape (LTCC)
- thick-film pastes
- laminates
Plus photoimageable conductors and dielectrics.
11

12. Fine lines < 25 micron with 1 micron
precision
High density, 4 micron thick conductor
High conductivity - 95% of bulk
96% Al
50m lines
Photodefined conductors
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13. Losses in Thick-Film Technology
• Skin effect: at RF and microwave frequencies current tends to
flow only in the surface of a conductor.
• Skin depth (): depth of penetration at which the magnitude
of the current has decreased to 1/e of the surface value.
• Effect due to loss tangent on line : - this effect is shown in
figure [1] on next slide.
• Effect due to surface roughness:-the roughness on surface
creates a loss,shown in figure [2]


f
1

13

14. Figure [1]-Effect of loss tangent on line
14

15. 0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 10 20 30 40 50
Frequency (GHz)
Lineloss(dB/mm)
RGH=0.5
RGH=0.2
RGH=0.1
RGH=0
Figure [2]-Effect of surface roughness
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16. 0%
20%
40%
60%
80%
100%
Line
Loss
(%)
8 20 32 44
Frequency (GHz)
Bulk Conductor Loss Loss due to Surface Roughness Dielectric Loss
16

17. 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Line
Loss
(%)
Al LTCC
Different Material (evaluated at 2GHz)
Bulk Conductor Loss Loss due to Surface Roughness Dielectric Loss
17

18. LTCC TECHNOLOGY
• LTCC technology is a well-established technology
• Reliability established in the automotive market
• Advantages for high frequency applications:
• parallel processing ( reduced cost)
• precisely defined parameters
• high performance conductors
• potential for multi-layer structures
• high interconnect density
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19. LTCC TECHNOLOGY
For Microwave applications:-
•  LTCC can meet the physical and electrical
performance demanded at frequencies above
1GHz.
• Increases in material and circuit production are
reflected in lower costs: LTCC is now comparable
to other technologies.
• Significant space savings when compared to other
technologies.
19

20. SINGLE-LAYER
MICROWAVE CIRCUITS
20

21. Single-layer microstrip circuits:
 all conductors in a single layer
 coupling between conductors achieved
through edge or end proximity (across
narrow gaps)
Problem:
 difficult to fabricate (cheaply in production)
fine gaps, possibly  10m
21

22. End-coupled
filter
Directional
coupler
Examples of single-layer microstrip circuits
22

23. MULTI-LAYER MICROWAVE CIRCUITS
23

24. Multilayer Microwave Circuits:
 conductors stacked on different layers
 conductors separated by dielectric layers
 allows for (strong) broadside coupling
 eliminated need for fine gaps
 registration between layers not as difficult to
achieve as narrow gaps
technique well-suited to thick-film print technology
 also suitable for LTCC technology
24

25. 3 Isolated port
Direct port 4
Ground plane
H
h1
εr
W1
W2
εr1
1
2 Coupled port
l
S
Main substrate
Thick-film dielectric layer
Input port
Multilayer
configuration
25

26. Thick-film technology is particularly suitable for the
implementation of multilayer circuits:
 higher packing density
 integration of antenna
 close coupling between conductors
Circuit examples:
 DC block
 Directional coupler
26

27. Directional Coupler
• Directional coupler under multi -
Layer concept and single layer
concept.
27

28. Measured result of 2dB directional
coupler under multi layer concept
28

29. Microstrip DC Block
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30. Multi layer DC Block
30

31. 0
0.4
0.8
1.2
1.6
2
1 2 3 4 5 6 7 8 9 10 11 12
Frequency (GHz)
InsertionLoss(dB)
Measured performance of multilayer DC block
31

32. Multi Layer Microwave Receiver
• All blocks processed independently.
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33. Comparison
• The variation in noise figure is reduced as compare to single layer fabrication.
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34. SUMMARY
 Thick-film technology provides a viable fabrication
process for wireless circuits at microwave frequencies
 Multilayer microwave circuits can offer enhanced
performance for coupled-line circuits
 Photoimageable thick-film materials extend the usable
frequency range to mm-wavelengths
34