Amphenol RF Connector Training Course

Sept. 9, 2002

There are basic RF questions that should be asked before helping a customer choose a connector

However, first we should discuss

• Why is it necessary to ask these questions?

• The Sales Engineer must be able to speak to the customer and understand his needs

• A basic understanding of RF as it relates to helping the customer choose a connector is essential to accomplish this

• The Sales Engineer is the means by which this information is transmitted from the customer to the design engineer

• Clear, specific information leads to quick, correct designs

Understanding RF and how it relates to cable and connectors

1. Transmission Lines

2. Impedance

3. Frequency Range

4. Return Loss-VSWR

5. Insertion Loss

6. Passive Intermodulation Distortion

7. Power Handling-Voltage

8. Isolation-Crosstalk

9. RF Leakage

10. Cable Assembly

11. Amphenol RF Design Engineering Support and Capabilities

Connector Anatomy

• What is a Connector?• A connector is a device used to connect to cables or other devices through

which electromagnetic energy is transferred from one place to another• Body-Contact-Insulator

Body

ContactInsulator

Connector Anatomy

Lots of changes in a very short length

Mechanical rigidity

Hold Contacts in place

Prevent Insulator rotation or lateral movement

Adapt to different cable sizes

Transform between connector series

Creates many impedance variations or discontinuities in a very short distance

Reflections are important, Attenuation not as important

Connector Anatomy

Various Captivation Methods

Barbs

Grooves

Shoulders

Knurls

Staking

Connector Anatomy

Discontinuity Compensation Steps

Dielectric Support Bead

Contact BarbSlotted Contact

Cable Anatomy

• What is Cable?• Cable is a transmission line through which electromagnetic energy is

propagated and transferred from one place to another• Jacket-Braid-Shield-Dielectric-Center Conductor Conductor

Dielectric

Jacket

ShieldBraid

Cable Anatomy

No changes in a very long length

No impedance changes or discontinuities

Usually very few reflections, but Attenuation is important

Assistance on the Web

Amphenol RF Newsletter

Technical Questions: http://www.amphenolrf.com/rf_made_simple/techquestions.asp

VSWR Conversion Charts: http://www.amphenolrf.com/rf_made_simple/vswr.asp

Glossary: http://www.amphenolrf.com/rf_made_simple/glossary.asp

# 1. Transmission Line

• What is a transmission line?• A transmission line is a conduit by which electromagnetic energy is transferred

from one place to another• Coaxial Cable- Unbalanced Line: Center conductor surrounded by a

concentric dielectric and outer conductor-Most popular type of transmission line

# 1. Transmission Line

•What is a transmission line?•A transmission line is a conduit by which electromagnetic energy is transferred from one place to another

•Waveguide: Rectangular, Circular

# 1. Transmission Line

•What is a transmission line?•A transmission line is a conduit by which electromagnetic energy is transferred from one place to another

•Planar Transmission Line: Microstrip, Stripline, Coplanar waveguide are most common

# 1. Transmission Line

•What is a transmission line?•A transmission line is a conduit by which electromagnetic energy is transferred from one place to another

•Twin Line- balanced line: two parallel conductors separated by a dielectric

. .

# 1. Transmission Line

• The type of transmission line will determine the connector style

• Cable Connector-Coaxial Cable, Twin Line• Surface Mount Connector-Microstrip• Tab Launch Connector-Microstrip, Stripline, Coplanar• End Launch Connector-Microstrip, Coplanar• Pin Launch Connector-Microstrip, Stripline, Coplanar

# 2. Impedance

Ohm’s Law

# 2. Impedance

• What is the Characteristic Impedance?• The ratio of Voltage to Current at any point in a transmission line• A transmission line can be represented as shown, with the values of C. L,

R, and G determining the impedance

Coaxial Line Equivalent Circuit

# 2. Impedance

•50 and 75 Ohms are the most common impedances•Do not confuse impedance with LOSS: •A 50 ohm impedance does not have less loss than a 75 ohm impedance. It is not like resistance•Impedance is independent of the length of the cable or connector•Impedance is independent of frequency

•The Impedance will help determine the connector series•Some series are only one impedance: C, SC, HN, 7-16•Some series can be both 50 or 75 ohms: BNC, TNC, N

# 2. Impedance

•Impedance of Coaxial Cable: Zo=(138/(E))*log(D/d))= (L/C)•L=.0117*Log (D/d) uh/inch C=.614*E/Log (D/d) pf/inch

•Characteristic Impedance is determined by the geometry and dielectric constant of the transmission line

# 2. Impedance

# 2. ImpedanceImpedance: The impedance of the connector generally must match that of the transmission line

Non-Constant 50, 75 ohm 50 ohm 75 ohmBNC Twinaxial BNC 7/16 1.6/5.6

UHF SMB C, SC, HN Type F

Twinaxial MCX Mini-UHF Type G

1.0/2.3 MMCX

TNC SMA

N

Outer Diameter Inner Diameter Dielectric Constant Impedance

.063 .020 2.0 50 Ohms

.063 .012 2.0 75 Ohms

.276 .120 1.0 50 Ohms

# 3. Frequency Range• Frequency is the number of electromagnetic waves that pass a given

point in 1 second• Hertz is the unit of frequency measurement• Generally, the RF performance of a connector degrades as the

frequency is increased (c=f)• Wavelength decreases, therefore smaller disruptions cause more problems

• Specifying the frequency will make it easier for the design engineer to optimize the performance

• Whenever possible, don’t specify a high frequency connector when a low frequency connector will work do the job

# 3. Frequency Range

• If a frequency range is not specified, then the connector will be designed to catalog specs and this could cause the design process to take a lot longer

• For example-A customer needs a new SMA to operate up to 12 Ghz. The catalog specifies 18 Ghz for some SMA connectors. If the connector is optimized for 18 Ghz, it will likely take a lot longer than necessary to design

• Give as much information about the application of the connector to the design engineer as possible

• Is it used in a high power, narrow frequency band amplifier?• Is it used in a band pass filter?

# 3. Frequency Range

Giga = 1,000,000,000 Billion

Mega = 1,000,000 Million

Kilo = 1,000 Thousand

Milli = 1/1000 One thousandth

Micro = 1/1,000,000 One millionth

Nano = 1/1,000,000,000 One billionth

Pico = 1/1,000,000,000,000 One trillionth

Some Typical Frequencies:

House current 60 Hz in the US (50 Hz in many other countries)

AM Radio 500 - 1500 kHz

Shortwave Radio 10 MHz

TV (channels 2-13) 60 - 250 MHz

Cellular Phone 824 - 894 MHz

Digital (PCS) Phone 1850 - 1990 MHz

Radar 6 - 26 GHz

Direct Broadcast Satellite (DBS) 12 GHz

Frequency Chart (GHz)

# 4. Return Loss or VSWR

• A measure of how much power is reflected Return Loss: The portion of a signal that is lost due to a reflection of

power at a line discontinuity. Return Loss is similar to VSWR and is generally preferred in the CATV industry to a VSWR specification

• VSWR: Acronym for Voltage Standing Wave Ratio. VSWR is the ratio of voltage applied to voltage reflected. It is the major factor contributing to the total signal efficiency of the connector.

• Best performance is achieved when the impedance of the cable and the connector are the same (matched)

# 4. Return Loss or VSWR• Reflections are created by deviations from the characteristic impedance caused by:

•variations in machining tolerances•Variations in the dielectric constants of insulators•transitions within the connector:

•transitioning from the cable size or stepping the connector from one line size to another line size

# 4. Return Loss or VSWR

• Reflection Coefficient is the basic measure of reflection: r=abs(Zo-Zl/Zo+Zl) where Zo is the characteristic impedance and Zl is the actual impedance

• Generally, this is the most important RF figure of merit for a connector

• VSWR=(1+r)/(1-r)• Return Loss=-20*log (r), in dB (decibels)• These are all the same thing, just expressed in different ways• Return Loss and VSWR are most commonly used

ComponentCable

Power transmittedinto componentIncident Power

Reflected Power

Return Loss = Ratio of reflected to incident power in dB

VSWR = Ratio of maximum to minimum electric field (Voltage)

Relative Magnitudes:Power Power Transmitted ReturnReflected into Component Loss VSWR

1% 99% 20 dB (1/100=10-2) 1.25

5% 95% 13 dB 1.58

10% 90% 10 dB (10/100=10-1) 1.95

50% 50% 3 dB 5.80

• Try to get a realistic idea of the Return Loss really required for a specific application

• Trying to design very low VSWR connectors, when not really needed, can take a long time and can add to the cost

dB Notation Increase Decibel (dB)of Signal Equivalent

1 = 100 = 0dB

2 = 100.3 = 3dB

10 = 101 = 10dB

20 = 101.3 = 13dB

100 = 102 = 20dB

1000 = 103 = 30dB

1/10 = 10-1 = -10dB

1/100 = 10-2 = -20dB

1/1000 = 10-3 = -30dB

Rather than say “The gain of the amplifier is 100 times”,

we say, “The gain is 20 decibels.”

# 5. Insertion Loss

• Insertion Loss is expressed in dB, and is a measure of the total loss of power going through a device

• IL = -20*log (Pout/Pin)• Includes losses due to reflection (usually the dominant factor unless the Return

Loss is very low <-26 dB), plus losses due to the dielectric and metal conductors (Attenuation)

• Long Cable assembly-Connector insertion loss not usually significant• Short cable assembly- Connector insertion loss can be significant

• Typically, connector insertion loss is very small (.1-.25 dB)

# 5. Insertion Loss

•As frequencies increase, the insertion loss increases (as a square law function (P=E^2/Z)

•Most of the electromagnetic energy (current) travels through the conductors in a circumferential ring

•Most of it in center conductor, but there is some impact from outer conductor

•Current flow is restricted to the surface layer or “skin” of the conductor

• Approximately 98% of the current density travels within 4.6 skin depths

# 5. Insertion Loss

• The length of the connector and the materials chosen will impact the insertion loss

• shorter is better• Plate the conductors with a high conductivity material

• Nickel-Inexpensive, hard material with good conductivity, but high relative permeability resulting in higher insertion loss

• Gold-Hard material and an excellent conductor, but expensive• Silver-Excellent conductor, less expensive than gold, better

permeability than nickel, but softer, and tarnishes• Stainless Steel-Rugged material for small connectors such as SMA,

but steel has high relative permeability

# 5. Insertion Loss

# 6. Passive Intermodulation Distortion• Not well known until mid 1990’s

• Primarily concern to satellite, microwave relay industries

• Modern Frequency plans

• High Power levels

• Sensitive Receivers

• Spurious Signals created by non-linear mixing of 2 or more

frequencies in a passive device

• Active PIM-generated by amplifiers-is reduced by filtering

• Passive PIM-filtering not possible

• Common to many channels

• Must be low PIM designs

# 6. Passive Intermodulation Distortion

• Spurious Signals created by non-linear mixing of 2 or more

frequencies in a passive device

• PIM products fall in receive (uplink) band

• Block Channels

• 3rd order generally greatest amplitude

• 5th and 7th may be of concern

• fIM = mf1 +/- nf2

• (2f1-f2), where m = 2 and n = 1 is a 3rd order product

# 6. Passive Intermodulation Distortion

F1 = 930 Mhz and F2 = 955 Mhz, then Fim = 905 Mhz

# 6. Passive Intermodulation DistortionBase Station Antenna Systems

•Simplex-

•Most prone to PIM effects

•Most economical

•Duplex

•Less Prone to PIM

•More expensive

•Cross Polarization

•Least PIM susceptible

•May require more space

# 6. Passive Intermodulation Distortion

•dBm-measure of power relative to 1 milliwatt

•dBc-measure of dB below a specified carrier level

•+43 dBm input

•PIM: -120 dBm

•Spec: -163 dBc

•Common Spec is -143 to -163 dBc (-100 to -120 dBm)

# 6. Passive Intermodulation Distortion• Causes of PIM

• Poor Contact Junctions-Non linear rectifying

• Solder outer-Solder inner- over molded design are best

• Most stable

• Ferromagnetic materials-Non-linear hysteresis

• No Nickel, Stainless Steel

• Contamination

• Types of Connectors

• 7-16 DIN

• Type N

• TNC-Occasionally

• Never use Bayonet (BNC) or Push on styles

# 7. Power Handling Capability

• There are 2 types of power handling (expressed in watts) that must be considered

• Average Power• Peak Power

• Average Power-the input power to a cable/connector which will produce a maximum safe center conductor temperature under steady state conditions when terminated with a matched load. A safe center conductor temperature is one that will not melt the dielectric

# 7. Power Handling Capability

• Average Power is inversely proportional to frequency and must be derated accordingly

• Average Power=Power Rating @ 1 Mhz/ (Frequency in Mhz)

• Connectors generally have higher power ratings than the cable to which they are attached

• They have metal shell-cables have braids covered by plastic jackets• They can be attached to bulkheads which help dissipate heat• They usually have lower attenuation per unit length due to air

sections within the connector

# 7. Power Handling Capability

• Peak Power-is limited by the voltage rating of the connector. The peak power is determined by the equation V^2/Z where V=the peak voltage rating and Z is the characteristic impedance

• Peak Power is not a function of frequency• Peak Power is an inverse function of VSWR and modulation schemes

and must be derated• Peak and Average Power are functions of altitude and must be derated

accordingly• Maximum power ratings will always be the lesser of the

cable/connector combination

Max. Operating Voltage (volts) Used to determine Peak Power Ratings

# 8. Isolation-Crosstalk

• Isolation and Crosstalk are used interchangeably• They are a measure of how much signal is picked up by an adjacent

line• Ganged style connectors on PC boards• Harnessed or “parallel run” cable assemblies

• They are measured in dB and usually range from –60 to –100 dB• If frequency increases or the length of the lines increase, crosstalk gets

worse• If the distance between the lines increases, crosstalk gets better

# 8. Isolation-Crosstalk

There will be significant crosstalk between the lines on this ganged connector unless some precautions (such as shielding) are taken

Question # 9. RF-Leakage

• RF Leakage is a measure of how much signal leaks out from a connector in dB at both the interface and at the cable entry

• As frequency increases, the leakage gets worse• Typical RF Leakage values range from –40 dB for Push-On types to

-90 dB for threaded styles on Semi Rigid cables• Generally not a big concern except if epoxy captivation is used

#10: Is the connector used on a cable assembly

• 2 connectors separated by a distance on a cable• At specific frequencies, all of the reflections can add up

(both connectors and cable)• When specifying a connector for a cable assembly, the cable

assembly requirements must be known• Catalog connectors, even if performance levels meet MIL Spec

requirements, may not be able to perform to the cable assembly specifications

#10: Is the connector used on a cable assembly

• Calculate the total worst case VSWR by multiplying all of the VSWR’s: For example- The cable assembly specification is 1.45 maximum

• 1st connector VSWR=1.25• 2nd connector VSWR=1.15• Cable VSWR=1.05• Total worst case VSWR=1.25*1.15*1.05=1.51

• Choosing a catalog BNC connector with a VSWR=1.25 and a catalog SMA connector with a VSWR of 1.15 obviously won’t work. Special connectors are needed.

#10: Is the connector used on a cable assembly

#11: How can Amphenol RF adequately support the design and development of high performance, RF

connectors?• RF Design Capabilities

• ANSOFT High Frequency Structure Simulator

• Test Capabilities-Design Verification

• Network Analyzers• PIM Test Capabilities

RF Simulation Capability• ANSOFT 3D High Frequency Structure Simulator

• Model any Geometry

• No Frequency Limitation

• S Parameter Analysis

• Return Loss, VSWR, Insertion Loss etc.

• Radiated Power

• E Field Plots

• Time Domain Analysis

• Optimization Capability

RF Simulation Capability• The connector is designed using standard RF practices and 2D linear analysis

programs for “ballpark” performance

• Calculate impedances within the connector

• Calculate nominal compensation steps within the connector

• Draw the problem in HFSS-import from PRO-E: IGES (3D), or DXF (2D)File

• Assign the materials

• Set the ports and boundary conditions (symmetry)

• Solve

• Analyze frequency and time domain plots

RF Simulation Capability

Draw the RF Model from the Mechanical drawing

RF Simulation Capability

Plot the desired S Parameters

RF Simulation Capability

View Time Domain response to determine the location of impedance mismatch

RF Simulation Capability

•All design changes are made on the computer (No

samples made until the design is optimized)

•Simulations in a matter of minutes, or hours at most

•Numerous iterations in a matter of hours or days

•Final modifications (if needed) made after testing

Surface Mount Connector on Microstrip

Connector has excellent Return Loss (-35 to –40 dB)

When mounted on board, performance deteriorates (-20 dB) due to the mismatch at the launch

Customer must supply board

characteristics:

1. Thickness

2. Trace width

3. Material (dielectric constant)

4. Transmission line type (i.e.. Microstrip, stripline)

Surface Mount Connector on MicrostripInitial simulation results

Return Loss Insertion Loss

Surface Mount Connector on Microstrip

.010 wide .015 wide .022 wide

Modify launch area to reduce the negative (capacitive)

discontinuity at the launch area

Time Domain

Capacitance due to launch

Surface Mount Connector on Microstrip

Able to achieve a significant improvement in Return Loss and Insertion Loss by modifying the launch area

Return Loss Insertion Loss

Final Return Loss

Final Insertion Loss

Antenna Isolation Board

• Design Capabilities are not limited to connectors• Can model and simulate entire assemblies• Example:

• MCX angle PC connector on a capacitively coupled microstrip board

• 4” of RG-316 cable• Straight MCX connector and angle MCX PC connector on ends of

cable

919-101P-51SX

4” RG-316/U

47pf, 4000 V, capacitor

Board, Top View

.115 wide trace

.063 thick, FR4

Antenna Isolation Board

919-134C-51P1X

919-119J-51AX

47 pf Cap, 4000 V, capacitor

Ground PlaneBoard, Bottom View

Antenna Isolation Board

Return Loss

Insertion Loss

Spec: -15 dB Return Loss and -1.5 dB Insertion Loss at 900 Mhz

Antenna Isolation Board (Simulated vs. actual test results)

Example: Angle Plug for LMR400 Cable VSWR Improvement

Contact too close to body

5 mm Diameter too small (35 ohm impedance)

ANSOFT HFSS Model

Initial VSWR

Angle Plug for LMR400 Cable VSWR Improvement

Recommended Design Changes

1. Remove Chamfer at solder post on contact

2. Increase 5mm diameter to 6.3 mm diameter on Body

ANSOFT Model

Increase diameter to 6.3 mm

Remove chamfer and shorten contact by 1.25 mm

Final improved VSWR

Test Capability-S Parameters

• State of the art Network Analyzers• HP 8510: 26.5 Ghz Vector Network Analyzer• HP 8753D: 50 Ohm 6 Ghz Vector Network Analyzer• HP 8753D: 75 Ohm 3 Ghz Vector Network Analyzer

Return Loss Insertion Loss VSWR Crosstalk RF Leakage

Vector Network Analyzer (S Parameter Measurements)

RF Leakage Test chamber

Passive Intermodulation Distortion Testing

• There are no “high tech” computer programs to predict IMD performance

• Devices must be built and tested• State of the art measurement test set using 20 watt (+43 dbm)

signals with a system noise floor of -130 to -135 dbm• Computer Automated-in house programming capabilities to

customize test measurements• Typical specifications of –116 to –120 dBm for 7-16 and Type N

connectors on helical and annular cables

PIM Testing – Cont’d

PIM Testing – Cont’d

Computer Control (HP VEE Interface)

How to Select an RF Connector Select a connector based on the information learned from

asking questions about the 10 RF parameters:1. Impedance Typical impedance of a system is 50 or 75 ohm. See Overview in catalog for impedance by series.2. Frequency Range Connector series range from 100 MHz to 26.5 GHz. See Overview in catalog for frequency range by series.3. Cable Type Connector series are designed to terminate to a limited number of cable types. Is it a new cable required by the customer? Is it a PC style? See the “Cable Selection Chart” in the catalog.4. Electrical/Mechanical requirements VSWR, Voltage Rating, Temperature Range, and other environmental requirements are all key specifications.5. Coupling Type Choose between Threaded, Bayonet, Snap-on, and Push-pull based on all of the above.

Use all of the information gathered to make a final decision

• Coupling style• Frequency range: 6 Ghz• Power Handling: 5 Watts Average• RF Leakage: -70 dB (Eliminates Push on or

Bayonet styles)• PIM requirements: -None

• Connector style• Impedance: 50 Ohms• Return Loss: -20 dB• Insertion Loss: -.1 dB• Mechanical Restrictions

• Available Real Estate: .5 “ long• Cable: RG-142

• Cost, other mechanical requirements, etc.

N, TNC, SMA, 7-16

SMA, TNC

Final Connector Choice