Lecture 12: Microstrip. ADS and LineCalc.whites.sdsmt.edu/classes/ee481/notes/481Lecture12.pdf · Lecture 12: Microstrip. ADS and LineCalc. ... In practical circuits there will often

Whites, EE 481/581 Lecture 12 Page 1 of 15

© 2016 Keith W. Whites

Lecture 12: Microstrip. ADS and LineCalc. One of the most widely used planar microwave circuit interconnections is microstrip. These are commonly formed by a strip conductor (land) on a dielectric substrate, which is backed by a ground plane (Fig. 3.25a):

rWd

t

We will often assume the land has zero thickness, t. In practical circuits there will often be metallic walls and covers to protect the circuit. We will ignore these effects, as does the text. Unlike stripline, a microstrip has more than one dielectric in which the EM fields are located (Fig 3.25b):

r

E

H

This presents a difficulty. Notice that if the field propagates as a TEM wave, then


0p

r

cv

But which r do we use? The answer is neither because there is actually no purely TEM wave on the microstrip, but something that closely approximates it called a “quasi-TEM” mode. At “lower frequencies,” this mode is almost exactly TEM. Conversely, when the frequency becomes too high, there are appreciable axial components of E and/or H making the mode no longer quasi-TEM. This property leads to dispersive behavior, among other effects. Numerical and other analysis have been performed on microstrip since approximately 1965. Some techniques, such as the method of moments, produce very accurate numerical solutions to equations derived directly from Maxwell’s equations and incorporate the exact cross-sectional geometry and materials of the microstrip. From these solutions, simple and quite accurate analytical expressions for 0Z , pv , etc. have been developed primarily by curve fitting. The result of these analyses is that at relatively “low” frequency, the wave propagates as a quasi-TEM mode with an effective relative permittivity, ,r e :


,

1 1 1

2 2 1 12r r

r ed W

(3.195),(1)

The phase velocity and phase constant, respectively, are:

0

,

p

r e

cv

(3.193),(2)

0 ,r ek (3.194),(3)

as for a typical TEM mode. In general, ,1 r e r (4)

The upper bound occurs if the entire space above the microstrip has the same permittivity as the substrate, while the lower bound occurs if in this situation the material is chosen to be free space. The characteristic impedance of the quasi-TEM mode on the microstrip can be approximated as

,

0

,

60 8ln 1

4

1201

1.393 0.667ln 1.444

r e

r e

d W W

W d d

Z W

dW W

d d

(3.196),(5)


Alternatively, given a desired 0Z and r , the necessary W d can be computed from (3.197) in the text, and given below. Again, (1) and (5) were obtained by curve fitting to numerically rigorous solutions. Equation (5) can be accurate to better than 1%.

Example N12.1. Design a 50- microstrip on Rogers RO4003C laminate with 1/2-oz copper and a standard thickness slightly less than 1 mm. Referring to the attached RO4003C data sheet from Rogers Corporation, we find that 3.38 0.05r and 0.032"d . We will ignore all losses (dielectric and metallic). What does “1/2-oz copper” mean? Referring to the attached technical bulletin from the Rogers Corporation, copper foil thickness is more accurately measured through an areal mass. The term “1/2-oz copper” actually means “1/2 oz of copper distributed over a 1-ft2 area.” For 1-oz copper, 34t m. For 2-oz copper, double this number and for ½-oz copper divide by 2.


We will use (3.197) to compute the required W d to achieve a 50- characteristic impedance:

2

82

2

2 1 0.611 ln 2 1 ln 1 0.39 2

2

A

A

r

r r

e W

e dW

WdB B B

d

(3.197),(6) To apply this equation, we first need to compute the constants A and B:

0 1 1 0.110.23

60 2 1r r

r r

ZA

1.376 (7)

0

377

2 r

BZ

6.442 (8)

Next, we will arbitrarily assume that 2W d and use the simpler equation in (6). We find that

1.376

2 1.376

82.317

2

W e

d e

.

Is this result less than 2? The answer is no. So, we need to recompute W d using the bottom equation in (6). We find here that 2.316W d , which is greater than 2 as assumed. So, with this result and 0.032"d , then 2.316 0.032"W

0.0741" .


A more common unit for width and thickness dimensions in microwave circuits is “mil” where

1 mil1

" 25.41000

m

Therefore,

74.1

0.0741" "1

4 1000

7 .W mils ( 1.88 mm).

This completes the design of the 50- microstrip.



ADS and LineCalc A considerable part of a microwave design engineer’s time is spent simulating the behavior of a circuit using computer tools. We will extensively use Advanced Design System (ADS) from Agilent Technologies in this course. ADS 2015 can be downloaded and run from your laptop, when on campus. One useful tool within ADS is LineCalc. Given the physical dimensions and material properties, LineCalc will accurately compute 0Z and ,r e for microstrip as well as for a large number of other planar waveguides. Conversely, it can synthesize a land width given the other parameters such as 0Z , d, t, r , and frequency. LineCalc uses accurate analysis techniques to make these calculations and can include the effect of losses, land thickness, the presence of side and top walls, etc. Also, LineCalc does not assume a TEM mode. Consequently, you may find at “high” frequencies that the microstrip becomes dispersive where 0Z and ,r e are functions of frequency.


The effective relative permittivity calculated by LineCalc is K_Eff = 2.692, as shown above. Compare this to the value predicted by the approximate expression (1)

,

1 1 1

2 2 1 12

3.38 1 3.38 1 12.666

2 2 321 12

73.24

r rr e

d W

LineCalc predicts W = 73.25 mil. Compare this to Example N12.1 where W = 74.1 mils was calculated using the accurate but approximate expression (3.197).







RO4000® hydrocarbon ceramic laminates are designed to offer superior high frequency performance and low cost circuit fabrication. The result is a low loss material which can be fabricated using standard epoxy/glass (FR-4) processes offered at competitive prices. The selection of laminates typically available to designers is signifi cantly reduced once operational frequencies increase to 500 MHz and above. RO4000 material possesses the properties needed by designers of RF microwave circuits and matching networks and controlled impedance transmission lines. Low dielectric loss allows RO4000 series material to be used in many applications where higher operating frequencies limit the use of conventional circuit board laminates. The temperature coeffi cient of dielectric constant is among the lowest of any circuit board material (Chart 1), and the dielectric constant is stable over a broad frequency range (Chart 2). This makes it an ideal substrate for broadband applications.RO4000 material’s thermal coeffi cient of expansion (CTE) provides several key benefi ts to the circuit designer. The expansion coeffi cient of RO4000 material is similar to that of copper which allows the material to exhibit excellent dimensional stability, a property needed for mixed dielectric multilayer boards constructions. The low Z-axis CTE of RO4000 laminates provides reliable plated through-hole quality, even in severe thermal shock applications. RO4000 series material has a Tg of >280°C (536°F) so its expansion characteristics remain stable over the entire range of circuit processing temperatures.RO4000 series laminates can easily be fabricated into printed circuit boards using standard FR-4 circuit board processing techniques. Unlike PTFE based high performance materials, RO4000 series laminates do not require specialized via preparation processes such as sodium etch. This material is a rigid, thermoset laminate that is capable of being processed by automated handling systems and scrubbing equipment used for copper surface preparation.RO4003™ laminates are currently offered in various confi gurations utilizing both 1080 and 1674 glass fabric styles, with all confi gurations meeting the same laminate electrical performance specifi cation. Specifi cally designed as a drop-in replacement for the RO4003C™ material, RO4350B™ laminates utilize RoHS compliant fl ame-retardant technology for applications requiring UL 94V-0 certifi cation. These materials conform to the requirements of IPC-4103, slash sheet /10 for RO4003C and /11 for RO4350B materials.

Data Sheet

RO4000® Series High Frequency Circuit Materials

The world runs better with Rogers.®

Advanced Circuit Materials

Advanced Circuit Materials Division100 S. Roosevelt Avenue

Chandler, AZ 85226Tel: 480-961-1382, Fax: 480-961-4533

www.rogerscorp.com

Features: Benefi ts:RO4000® materials are reinforced hydrocarbon/ceramic laminates

Designed for performance sensitive, high volume applications•

Low dielectric tolerance and low loss Excellent electrical performance• Allows applications wth higher operating frequencies• Ideal for broadband applications•

Stable electrical properties vs. frequency Controlled impedance transmission lines•

Lead-free process compatible No blistering or delamination•

Low Z-axis expansion Reliable plated through holes•

Low in-plane expansion coeffi cient Remains stable over an entire range of circuit processing temperatures•

Volume manufacturing process RO4000 laminates can be fabricated using stardard glass epoxy processes• Competitively priced•

Typical Applications:Cellular Base Station Antennas and Power Amplifi ers•

RF Identifi cation Tags•

Automotive Radar and Sensors•

LNB’s for Direct Broadcast Satellites•

0.000

-0.200

-0.400

-0.600

-0.800

-1.000

-1.200

-1.400

-1.600 0 2 4 6 8 10 12 14 16 18

dB

/In

ch

F requency, GHz

RO3003 PTFE Woven Glass RO4003 RO4350 BT Glass BT/Epoxy FR4Epoxy/PPO

Chart 2: RO4000 Series MaterialsDielectric Constant vs. Frequency

Chart 3: Microstrip Insertion Loss(0.030” Dielectric Thickness)

Property Typical Value Direction Units Condition Test MethodRO4003C RO4350B

Dielectric Constant, εr(Process specifi cation) 3.38 ± 0.05 (1) 3.48 ± 0.05 Z -- 10 GHz/23°C

IPC-TM-6502.5.5.5

(2)Clamped Stripline

(3) Dielectric Constant, εr (Recommended for use in circuit design) 3.55 3.66 Z -- FSR/23°C

IPC-TM-6502.5.5.6

Full Sheet Resonance

Dissipation Factor tan, δ 0.00270.0021

0.00370.0031 Z -- 10 GHz/23°C

2.5 GHz/23°CIPC-TM-650

2.5.5.5

Thermal Coeffi cient of εr +40 +50 Z ppm/°C -50°C to 150°C IPC-TM-6502.5.5.5

Volume Resistivity 1.7 X 1010 1.2 X 1010 MΩ•cm COND A IPC-TM-6502.5.17.1

Surface Resistivity 4.2 X 109 5.7 X 109 MΩ COND A IPC-TM-6502.5.17.1

Electrical Strength 31.2(780)

31.2(780) Z KV/mm

(V/mil)0.51mm(0.020”)

IPC-TM-6502.5.6.2

Tensile Modulus 26,889(3900)

11,473(1664) Y MPa

(kpsi) RT ASTM D638

Tensile Strength 141(20.4)

175(25.4) Y MPa

(kpsi) RT ASTM D638

Flexural Strength 276(40)

255(37)

MPa(kpsi)

IPC-TM-6502.4.4

Dimensional Stability <0.3 <0.5 X,Y mm/m(mils/inch)

after etch+E2/150°C

IPC-TM-6502.4.39A

Coeffi cient of Thermal Expansion

111446

141635

XYZ

ppm/°C -55 to 288°C IPC-TM-6502.1.41

Tg >280 >280 °C DSC A IPC-TM-6502.4.24

Td 425 390 °C TGA ASTM D3850Thermal Conductivity 0.71 0.69 W/m/°K 80°C ASTM C518

Moisture Absorption 0.06 0.06 %48 hrs immersion 0.060” sample

Temperature 50°CASTM D570

Density 1.79 1.86 gm/cm3 23°C ASTM D792

Copper Peel Strength 1.05(6.0)

0.88(5.0)

N/mm(pli)

after solder fl oat1 oz. EDC Foil

IPC-TM-6502.4.8

Flammability N/A (4)V-0 UL 94Lead-Free Process Compatible Yes Yes

(1) Dielectric constant typical value does not apply to 0.004” (0.101mm) laminates. Dielectric constant specifi cation value for 0.004” RO4350B material is 3.33 ± 0.05.

(2) The IPC clamped stripline method can potentially lower the actual dielectric constant due to presence of airgaps between the laminates under test and the resonator card. Dielectric constant in practice may be higher than the values listed.

(3) The design Dk is an average number from several different tested lots of material and on the most common thickness/s. If more detailed information is required please contact Rogers Corporation. Refer to Rogers’ technical paper “Dielectric Properties of High Frequency Materials” available at http://www.rogerscorp.com/acm

(4) ** Note on 94V-0 ** RO4350B LoPro™ laminates do not share the same UL designation as standard RO4350B laminates. A separate UL qualifi cation may be necessary.

Typical values are a representation of an average value for the population of the property. For specifi cation values contact Rogers Corporation.

RO4000 LoPro laminate uses a modifi ed version of RO4000 resin system to bond reverse treated foil. Values shown above are RO4000 laminates with out the addition of the LoPro resin. For double-sided board, the LoPro foil results in a thickness increase of approximately 0.0007” (0.018mm) and the DK is approxi-mately 2.4. Therefore, effective Dk is highly dependent on core thickness.

Prolonged exposure in an oxidative environment may cause changes to the dielectric properties of hydrocarbon based materials. The rate of change increases at higher temperatures and is highly dependent on the circuit design. Although Rogers’ high frequency materials have been used successfully in innumerable applications and reports of oxidation resulting in performance problems are extremely rare, Rogers recommends that the customer evaluate each material and design combination to determine fi tness for use over the entire life of the end product.

The information in this data sheet is intended to assist you in designing with Rogers’ circuit material laminates. It is not intended to and does not create any warranties express or implied, including any warranty of merchantability or fi tness for a particular purpose or that the results shown on this data sheet will be achieved by a user for a particular purpose. The user should determine the suitability of Rogers’ circuit material laminates for each application.

Prolonged exposure in an oxidative environment may cause changes to the dielectric properties of hydrocarbon based materi-als. The rate of change increases at higher temperatures and is highly dependent on the circuit design. Although Rogers’ high frequency materials have been used successfully in innumerable applications and reports of oxidation resulting in performance problems are extremely rare, Rogers recommends that the customer evaluate each material and design combination to deter-mine fi tness for use over the entire life of the end product.

These commodities, technology and software are exported from the United States in accordance with the Export Administration regulations. Diversion contrary to U.S. law prohibited.

LoPro, RO4000, RO4003, RO4350, RO4350B and RO4003C are licensed trademarks of Rogers Corporation.The world runs better with Rogers. and the Rogers’ logo are licensed trademarks of Rogers Corporation.

© 1995, 1996, 1997, 1999, 2002, 2005, 2006, 2007, 2010 Rogers Corporation, Printed in U.S.A., All rights reserved.

Revised 05/2010 0891-0110-0.5CCPublication #92-004

CONTACT INFORMATION:

USA: Rogers Advanced Circuit Materials, ISO 9002 certifi ed Tel: 480-961-1382 Fax: 480-961-4533Belgium: Rogers - BVBA Belgium Tel: 32-9-2353611 Fax: 32-9-2353658Japan: Rogers Japan Inc. Tel: 81-3-5200-2700 Fax: 81-3-5200-0571Taiwan: Rogers Taiwan Inc. Tel: 886-2-86609056 Fax: 886-2-86609057Korea: Rogers Korea Inc. Tel: 82-31-716-6112 Fax: 82-31-716-6208Singapore: Rogers Technologies Singapore Inc. Tel: 65-747-3521 Fax: 65-747-7425China: Rogers (Shanghai) International Trading Co., Ltd (Shanghai Offi ce) Tel: 86-21-62175599 Fax: 86-21-62677913China: Rogers (Shanghai) International Trading Co., Ltd (Beijing Offi ce) Tel: 86-10-5820-7667 Fax: 86-10-5820-7997China: Rogers International Trading Co., Ltd (Shenzhen Offi ce) Tel: 86-755-8236-6060 Fax: 86-755-8236-6123

World Class PerformanceRogers Corporation (NYSE:ROG), headquartered in Rogers, Conn., is a global technology leader in the development and manu-facture of high performance, specialty material-based products for a variety of applications in diverse markets including: portable communications, communications infrastructure, computer and offi ce equipment, consumer products, ground transportation, aerospace and defense. In an ever-changing world, where product design and manufacturing often take place on different sides of the planet, Rogers has the global reach to meet customer needs. Rogers operates facilities in the United States, Europe and Asia. The world runs better with Rogers.®

Standard Thickness Standard Panel Size Standard Copper CladdingRO4003C: 0.008” (0.203mm), 0.012 (0.305mm), 0.016” (0.406mm), 0.020” (0.508mm) 0.032” (0.813mm), 0.060” (1.524mm)RO4350B:*0.004” (0.101mm), 0.0066” (0.168mm) 0.010” (0.254mm), 0.0133” (0.338mm), 0.0166” (0.422mm), 0.020”(0.508mm), 0.030” (0.762mm), 0.060” (1.524mm)

Material clad with LoPro foil add .0007” (0.018mm) to dielectric thickeness

12” X 18” (305 X457 mm)24” X 18” (610 X 457 mm)24” X 36” (610 X 915 mm)48” X 36” (1.224 m X 915 mm)

*0. 004” material in not available in panel sizes larger than 24”x18” (610 X 457mm).

½ oz. (17μm), 1 oz. (35μm) and2 oz. (70μm) electrodeposited copper foil.LoPro Reverse Treated EDC for PIM Sensitive Applications: ½ oz (17mm), 1 oz (35 μm)

Note: LoPro EDC foil adds .00035” to the panel thickness per side.

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Lecture 12: Microstrip. ADS and LineCalc.whites.sdsmt.edu/classes/ee481/notes/481Lecture12.pdf · Lecture 12: Microstrip. ADS and LineCalc. ... In practical circuits there will often