1. Microwave Integrated Circuits (MIC)
Microwave circuits exist in three different forms:
Discrete circuit
Packaged diodes/transistors mounted in coaxial and waveguide assemblies. Devices can usually be removed from the assembly and replaced
Hybrid MIC
Diodes/transistors, resonators, capacitors, circulators, … are fabricated separately on most appropriate material and then mounted into the microstrip circuit and connected with bond wires
MMIC
Diodes/transistors, resistors, capacitors, microstrip,…all fabricated simultaneously, including their interconnections, in semiconductor chip
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2. Advantages and Disadvantages of HMIC
1- Each component can be designed for optimal performance:
 Each transistor can be made of the best material.
 Other devices can be made of the most appropriate material.
 The lowest loss microwave components can be made by choosing the optimal microstrip substrate.
2- It has high power capability since the high power generating elements can be optimally heat-sinked
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3. 4- Special-purpose devices for each function are not required.
3- Standard diodes and transistors can be used and made to perform different functions by using different circuit design.
4- Special-purpose devices for each function are not required.
5- Trimming adjustments are possible
6- The most economical approach when small quantities, up to several hundred, of the circuits are required.
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4. Disadvantages:
1- Wire bonds cause reliability problems. Each circuit element that is not part of the microstrip assembly must be attached to the microstrip by a wire bond.
2- The number of devices that can be included is limited by the economics of mounting the devices onto the circuit and attaching them by a wire bonds. The circuit is usually limited to a few dozen compartments.
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5. Advantages and Disadvantages of MMICs
1- Minimal mismatches and minimal signal delay
2- There are no wire bond reliability problems
3- Up to thousands of devices can be fabricated at one time into a single MMIC.
4- It is the least expensive approach when large quantities are to be fabricated.
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6. Disadvantages:
1- Performance compromised, since the optimal materials cannot be used for each circuit element.
2- Power capability is lower because good heat transfer materials cannot be used
3- Trimming adjustments are difficult or impossible.
4- Unfavorable device-to-chip area ratio in the semiconductor material.
5- Tooling is prohibitively expensive for small quantities of MMIC.
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7. Materials used for MIC
The basic materials for fabricating MICs, in general are divided into four categories:
1- Substrate materials sapphire, alumina, ferrite/garnet, silicon, RT/duroid, quartz, GaAs, Inp, etc.,
2- Conductor materials-copper, gold, silver, aluminum, etc.
3- Dielectric films SiO, SiO2,…etc
4- Resistive films- Nichrome (cNiCr), tantalum (Ta)
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8. Substrate Materials:
1- The cost of the substrate must be justifiable for the application
2. Is the technology to be thin- or thick film?
3- The choice of thickness and permittivity determines the achievable impedance range and the usable frequency range.
4- There should be low loss tangent for negligible dielectric loss
5- The substrate surface finish should be good (~ 0.1 mm), with relative freedom from voids, to keep conductor loss low and yet maintain good metal-film adhesion
6- There should be good mechanical strength and thermal conductivity.
7- No deformation should be occur during processing of circuit
8- A substrates with sufficient size are for the particular application and complexity should be available
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9. The desirable properties:
Conductor Materials:
High conductivity, low temperature coefficient of resistance, low RF resistance, good adhesion, good etch- ability and solder-ability, and be easy to deposit.
Dielectric Material:
Used as insulators for capacitors, protective layer for active devices, and insulating layer for passive circuits.
The desirable properties:
Reproducibility, high breakdown voltage, low loss tangent, and the ability to under go processing without developing pin holes
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10. Sheet sensitivities in the range of 10 to 2000 W/square
Resistive Films:
Required for fabricating resistors for terminations, attenuators, and for bias networks.
The properties required for resistive material are: Good stability, low temperature coefficient of resistively
Sheet sensitivities in the range of 10 to 2000 W/square
1% accuracy is achievable
The creation of these resistive films demands additional processes of deposition and etching beyond those of the thin-film metallization. This complexity may be obviated by bonding directly chip resistors onto the conducting pattern (ex. using surface mount).
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11. Microwave Engineering/ Passive Microwave Components

12. Planar and Uniplanar Transmission lines
Microstrip TL Coplanar Wave-Guide (CPW)
Slot line
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13. Material er Tan d Ther. Cond. Tmax during Fab. W/inoC (Co)
Teflon ×
fiberglass
Epsilam ×
Alumina 10 1×
Beryllia 6 2×
Ferrite 15 2×
Silicon ×
GaAs ×
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14. Microstrip Circuit elements commonly used in HMIC
The components that can be fabricated as part of the microstrip transmission line are:
Matching stubs and transformers
Directional couplers
Combiners and dividers
Resonators
Filters
Inductors and capacitors
Thin film resistors
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15. Typical spiral inductor and interdigitated capacitor
Coupled line filter
Hybrid coupler
Branch line coupler
Microstrip coupler
Typical spiral inductor and interdigitated capacitor
Loop inductor
High impedance transmission line inductor
Figure: Microstrip elements used in HMIC
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16. Components Added After Microstrip Fabrication
The MIC Components that are fabricated separately and added to the microstrip circuits are:
Bond wire
Chip resistor
Chip capacitors
Dielectric resonators
Circulators
Diodes and transistors
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17. Chip capacitor and resistor
Bond wires
Dielectric resonator
Chip capacitor and resistor
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18. Microwave Engineering/ Passive Microwave Components

19. Passive microwave components include: Combiners & Dividers
Passive Microwave Components (PMC) (The circuits that does not contain any active device such as diode or transistor) PMC are used extensively in any microwave communication system
Passive microwave components include:
Combiners & Dividers
Phase shifters
Filters
Terminations & attenuators
Switches
Couplers
Isolators & Circulators
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20. Terminations
Absorb all the power at the end of transmission line in order to terminate a microwave equipment without allowing the power to escape into surroundings or to be reflected back into the equipment.
Termination can be found in the form of:
 Waveguide,
 Coaxial line
 Microstrip
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21. Some Types of Terminations
In waveguide form it contains a tapered absorber, usually consisting of a carbon-impregnated dielectric material that absorbs the microwave power
Some Types of Terminations
8.2 – 12.4 GHz handles 75 watts
GHz7 - 10
watt300
Important specifications:
 SWR (or S11)
 Power-handling capability
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22. Coaxial terminations 50 W N-type 50 W SMA 75 W BNC High power 50 W)
Strip Line Load
100 W
High power 50 W)
GHzDC- 3 Type C Cwwat600
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23. Attenuators Used to adjust the power level of microwave signals.
Attenuators Types:
 Fixed (Pads)
 Mechanically adjustable
 Electronically Controlled
Coaxial attenuators cover the frequency range from dc to 18 GHz, and they can have any value of attenuation. Typical values are 3, 6 10, and 20 dB.
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24. Fixed coaxial attenuator
Coaxial Attenuators
3 dB 1 W DC- 2 GHz
N-Type
Fixed coaxial attenuator
The lossy material extending from the center to the outer conductor and along the center conductor. This lossy material forms a resistive T, which absorbs some of the microwave power without reflecting any type
30 dB 100 W DC- 21GHz
N-Type QC
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25. Mechanical variable attenuator
8.2 – 12.4 GHz dB
A van of absorbing material inserted into the waveguide through a slot on the broad wall. The greater the penetration of the vane the greater the attenuation. The dial can be calibrated in dB
12.4 – 18 GHz dB
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26. Achieved with PIN diodes Will be covered in active circuits
Electronically variable attenuator
Achieved with PIN diodes
Will be covered in active circuits
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27. Switches
Direct s microwave power from one transmission line to another or turns microwave power on and off. Switches can be mechanically or electronically. Here we discuss some types of mechanical switchs. Electronically switches will be introduced in active devices section.
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28. Directional Couplers
Directional couplers sample the power traveling in only one direction down a transmission line. Pi Po Pc
Pwrong
Important specifications:
 Coupling Factor (dB) C = 10 log Pi/Pc
How much of the input power is sampled
 Insertion Loss IL = 10 log Pi/Po
Specify the output power relative to the input power
 Directivity D = 10 log Pc/Pwrong
No coupler is perfect i.e Pwrong  0
 Isolation I = 10 log Pi/Pwrong
= D + C dB
The amount of power sampled in the wrong direction
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29. Typical values are 3, 6, 10, 20, 30, 40, and 50 dB
Directional coupler can also be used as an attenuator and to measure the reflected power from a mismatch
lg/4
Coupled power
Input power
Output power
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30. Coupling Loss vs Coupling Factor
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31. Directional Coupler Signal Paths
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32. Wave guide coupler Coaxial and microstrip coupler
High power
High directivity
limited in BW
Wide band
Poor directivity
Limited power
Waveguid coupler
Coaxial coupler
D is not critical for sampling microwave power
D is extremely important for a return loss measurement, to measure the small power reflected from the mismatch.
Microstrip coupler
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33. Microwave Engineering/ Passive Microwave Components

34. 3-dB Quadrature Hybrid (Hybrid Coupler)2
(Input)
(output)
(Isolated) 3 1 4
The 3-dB quadrature hybrids are used as components, in almost every RF System, such as:
 Power combiners and dividers De(modulators)
 Balanced Mixers  Image rejection mixers
 Balanced amplifiers  Feed network in antenna arrays
With all ports matched, power entering port 1 is divided between ports 2 and 3, with 90o phase shift between these outputs. No power is coupled to port 4. Ports 1 and 4 as well as ports 2 and 3 are isolated.
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35. The most important parameters of the hybrid are
Isolation between isolated ports
SWR at the input ports
Phase difference between the two coupled ports
Insertion loss between the input and the coupled ports
The [S] matrix is
0 j j j
j 0 -1
[S] = 2
Small size coupler
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36. The 0o/180o hybrid coupler is preferred in some applications, namely,
(2) 180o Hybrid Ring:
The 0o/180o hybrid coupler is preferred in some applications, namely,
 Mixers
 Modulators
 Isolated power splitters since the isolation between its input ports may be independent of the value of the two balanced impedance loads. 1 2 3 4
lg/4
3lg/4
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37. [S] = 2 The [S] matrix is 0 1 1 0 1 0 0 - 1 1 0 0 1 0 -1 1 0 -j
[S] = 2
Some Small size couplers configurations
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38. Combiners and Dividers
Combiners are used to combine two or more transmission lines into one transmission line. They can also be used to divide the microwave signal from one transmission line into two transmission lines
The T- Junction Power Dividers (simplest configuration)
E-plane waveguide T
Microstrip T-junction
H-plane waveguide T
Lossless junctions
Can not be matched simultaneously at all ports
No isolation between the two input lines
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39. Resistive Divider
Matching T-junctions is possible if a lossy components is inserted in series to all branches at the junction
Dissipate half of the supplied power and the two output ports may not be isolated
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40. Wlikinson Power divider
Wilkinson power divider, is a wide band circuit (2:1 or more), can be matched at all ports and lossless when the output ports are matched. It can also be designed to give arbitrary power division. This divider is often made in microstrip or stripline form.
In-phase Wilkinson divider
Isolation is achieved between ports by terminating resistors. Any unequal mismatch or out-of-phase condition that would couple power from one line to the other is attenuated by the resistor.
Disadvantages:
The termination must be mounted inside the coupler, which limits its power handling capability
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41. Multi-channel Combiner
Lossy
Very little selectivity
Small size
Wide band
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42. Magic-T
The 180o hybrid can also be implemented in waveguide form as shown in the Figure. The waveguide magic-T hybrid junction has terminal properties similar to those of the ring hybrid. In practice, tuning posts irises are often used for matching. 4 3 2 1
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43. It is a type of quadrature coupler (90o phase shift between 2 and 3)
The Lange coupler
Tight coupling 3 or 6 dB
Wide band (as high as 4:1)
It is a type of quadrature coupler (90o phase shift between 2 and 3)
Lines are very narrow
Bonding wires are needed 4 2
l/4 1 3
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44. Phase Shifters
Microwave signals are characterized by amplitude and phase. The amplitude is controlled with amplifiers and attenuators. The phase can be controlled by phase shifters. Phase shifters like attenuators, can be mechanically or electronically adjustable
Mechanically adjustable phase shifters
It is a line stretchers. The phase shift can be adjusted by changing the signal path.
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45. Isolators and Circulators
0 0
1 0
An isolator allows microwaves to pass in one direction but not the other, so it has unidirectional transmission characteristics. This isolating effect is achieved with ferrites
Isolators are usually used to protect high power microwave sources from possible reflection that may cause source damage. It can also be used in place of matching networks.
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46. Low insertion loss in the normal or forward path
The most important specifications for isolators are the isolation which is the insertion loss in the reverse direction and the forward insertion loss. The isolation should be high and the insertion loss should be low. Typical values are 20 dB for isolation and 0.5 dB for insertion loss.
Purpose of Isolator
Low insertion loss in the normal or forward path
High isolation in the reverse path
Uses
Circulators providing input and output isolation for a one port amplifier
Isolator minimizing the pulling effect of an oscillator
Isolator reducing the power reflected back to a mixer
Reduce VSWR interactions between RF components
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47. Circulator Isolators are not a broadband as attenuators
Circulator route microwave signals from one port of the device to another. For example, a microwave signal entering port 1 is directed out of the circulator at port 2. A signal entering port 2 is routed to leave the circulator at port 3 and does not get back into port 1. A signal entering port 3 does not get into port 2, but goes out through port 1. The S matrix of an ideal circulator is
[S] = 1 2 3
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48. The important specifications of a circulator are the insertion loss, which is the loss of signal as it travels in the direction that it is supposed to go, and the directivity, which is the loss in the signal as it travel in the wrong direction. Insertion loss is typically 0.5 dB and the directivity is 20 dB. Circulator enable the use of one antenna for both transmitter and receiver of communication system.
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49. Microwave Engineering/ Passive Microwave Components