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SEMI E114-0302 E © SEMI 2002 3 9 Test Procedure for Determ ining Electrical Length 9.1 Two test procedures ca n be used to dete rmine the electrical length of a cable assembly. One method measures it directly at the oper…

SEMI E114-0302

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 CVD — Chemical Vapor Deposition

5.1.2 PVD — Physical Vapor Deposition

5.1.3 VSWR — Voltage Standing Wave Ratio

5.2 Definitions of Terms

5.2.1 cable assembly — the section of cable

(transmission line), including the connectors, used to

connect various parts of the RF power delivery system.

5.2.2 device under test (DUT) — the cable assembly

intended to be tested.

5.2.3 electrical length — the length of the cable

assembly at the operating frequency expressed in terms

of degrees, where one wavelength at the nominal

operating frequency is equal to 360 degrees.

5.2.4 half wave resonant frequency — the frequency of

the cable assembly where the electrical length of the

assembly is equal to one half (0.5) of a wavelength.

For example, the half wave resonant frequency of a

cable assembly with an electrical length of 2 meters

would be 74.95 MHz ((c/2-meters)/2).

5.2.5 harmonic frequency — the harmonic frequencies

are defined as integer multiples of the fundamental

frequency. For example, the second harmonic of 13.56

MHz is 27.12 MHz.

5.2.6 quarter wavelength — the length equal to one

quarter of the wavelength at a given frequency, where

the wavelength is equal to the speed of light divided by

the frequency.

5.2.7 S-parameters — the scattering matrix used to

describe a network. The reflection coefficient is the

S11 parameter and the transmission coefficient is the

S21 parameter.

5.2.8 speed of light (c) — the speed of light in free-

space is assumed to be 2.9979 × 10

meters/second.

5.2.9 velocity of propagation (VP) — the velocity of

propagation, VP, is defined as the ratio of the speed of

an electrical signal down a length of cable divided by

the speed in free space. It is the reciprocal of the square

root of the relative dielectric constant of the dielectric

material between the inner and outer conductor of a

coaxial assembly. For example, the VP for cable type

RG-217 is nominally 0.66.

6 Test Apparatus

6.1 RF Vector Network Analyzer — The network

analyzer is used to measure the electrical length and can

also be used to determine the attenuation (power

losses). The network analyzer requires vector

capability so that both the magnitude and phase of the

reflection coefficient and transmission coefficient can

be measured as a function of frequency. The frequency

range shall include the operating frequency and the

quarter-wave resonant frequency of the RF cable

assembly.

6.2 Time Domain Reflectometer (TDR) — The TDR is

used to measure and verify the characteristic impedance

as a function of distance along the transmission line.

6.3 RF Adapters and Terminations — Various adapters

may be necessary to convert between different types of

coaxial connectors (e.g., type N to type HN adapters,

etc.). All adapters used shall have the same nominal

characteristic impedance as the cable assembly to be

tested (DUT), which is typically 50 ohms. For some

measurements, additional coaxial cable assemblies may

be necessary. These cable assemblies, which should

not be confused with the DUT cable assembly, shall be

of the same nominal characteristic impedance as the

DUT cable assembly. Standard terminations will also

be used, such as shorts, opens, and precision 50-ohm

loads.

7 Safety Precautions

7.1 Work should be conducted in accordance with local

safety requirements and test device manufacturer

recommended safety procedures. The tests described in

this document involve using low output power test

instrumentation (typically less than 10 milli-Watt).

7.2 The area immediately surrounding the Test Setup

should be keep free and clear of unnecessary equipment

and materials. Some of the cable assemblies to be

tested may be long and can be trip and lift/weight

hazards.

8 Test Setup for Electrical Length Test

8.1 The Test Setup for the electrical length test consists

of the Network Analyzer, the cable assembly to be

tested (DUT), the appropriate adapter (if any) to

connect the DUT to the network analyzer, and the

appropriate adapter (if any) to connect a coaxial short

circuit termination to the output of the DUT. A

schematic of the Test Setup is shown in Figure 1. Care

should be taken to ensure that the cable assemblies to

be tested do not exceed the vendor specified bending

radius, which is typically 5 times the outer diameter of

the cable.

8.2 Prior to making any measurements, the Network

Analyzer shall be turned on and allowed to warm up

before the testing is to take place. This time allows for

electronics to come to a stable operating condition for

the measurements.

SEMI E114-0302

9 Test Procedure for Determining Electrical

Length

9.1 Two test procedures can be used to determine the

electrical length of a cable assembly. One method

measures it directly at the operating frequency and the

other measures the half-wave resonant frequency to

determine the electrical length. Each method has

advantages, depending on the length of the cable

assembly. Prior to choosing a method, the equivalent

free-space length of the DUT shall be estimated in units

of distance (i.e., meters). This length can be estimated

by dividing the physical length of the DUT by the

velocity of propagation for the particular type of cable.

For example, a DUT made from RG-217 cable with a

physical length of 20 meters and a velocity of

propagation of 0.66 would have an equivalent free-

space length of 30.303 meters (20/0.66 = 30.303). A

flow chart showing the steps for choosing which test

method to use is shown in Figure 2.

9.2 The equivalent free-space length of the DUT shall

be compared with the wavelength of the nominal

operating frequency. Test Method 1 (Section 9.3) shall

be used if the equivalent free-space length is less than a

quarter wavelength of the nominal operating frequency.

Test Method 2 shall be used if it is equal to or greater

than a quarter wavelength of the nominal operating

frequency. For example, if the estimated free-space

length is 3 meters and the nominal operating frequency

is 13.56 MHz (quarter wavelength = 0.25 × c/13.56 ×

= 5.527 meters), then Test Method 1 is

recommended. If the estimated free-space length is 25

meters, then Test Method 2 is recommended.

9.3 Test Method 1 for Determining Electrical Length

9.3.1 This test method measures the phase angle of the

reflection coefficient at the nominal operating

frequency of the DUT when the DUT is terminated by a

short circuit.

9.3.2 Calibrate the Network Analyzer at the desired

operating frequency (e.g., 13.56 MHz). If adapters are

to be used to connect the DUT to the Network Analyzer

and/or to the short circuit termination, then the

calibration shall be made with the adapters in place.

The Network Analyzer shall be calibrated for

measuring the reflection coefficient at test Port 1 (see

Figure 1) using the calibration kit provided with the

Network Analyzer. This measurement is equivalent to

measuring the S11 S-parameter. The calibration shall

be performed at fixed frequency (continuous-wave

operation) using the lowest bandwidth possible

(typically 10 Hz).

9.3.3 After calibration, the cable assembly to be tested

(DUT) shall be attached to Port 1 on the Network

Analyzer. The other end of the DUT shall be

terminated with a short circuit. After all connections

have been visually inspected to ensure proper contact

and the Network Analyzer measurement has stabilized,

the value of the reflection coefficient phase angle shall

be recorded.

9.3.4 If the indicated phase angle of the reflection

coefficient is positive, then the electrical length of the

DUT is equal to one half of the value of the difference

between 180 and the measured phase angle. For

example, if the measure reflection coefficient phase

angle is 120 degrees, then the electrical length is 30

degrees ((180-120)/2).

9.3.5 If the indicated phase angle of the reflection

coefficient is negative, then the electrical length of the

DUT is greater than a quarter wavelength. For this

case, the electrical length is equal to one half of the

absolute value of the measured value of the reflection

coefficient phase angle plus 90. For example, if the

measure reflection coefficient phase angle is -10

degrees, then the electrical length is 95 degrees (90 +

10/2).

9.4 Test Method 2 for Determining Electrical Length

9.4.1 This test method determines the electrical length

of the cable assembly DUT by measuring the half wave

resonant frequency when the DUT is terminated by a

short circuit. For this measurement, the frequency of

the network analyzer is swept. The frequency range of

the sweep is determined from the estimated free-space

length of the DUT.

9.4.2 Estimate the half wave resonant frequency of the

DUT. This frequency is equal to one half of the ratio of

the speed of light divided by the estimated free space

length determined in Section 9.2. For example, if the

estimated free space length of the DUT is 25 meters,

then the estimated half wave resonant frequency is

5.996 MHz (0.5 × c/25).

9.4.3 Calibrate the Network Analyzer. If adapters are

to be used to connect the DUT to the Network Analyzer

and/or to the short circuit termination, then the

calibration shall be made with the adapters in place.

The center frequency of the frequency sweep shall be at

the estimated half wave resonant frequency calculated

in Section 9.4.2, and the frequency span of the sweep

shall be no greater than 10% of the estimated

frequency. For example, if the estimated half wave

resonant frequency is 6.0 MHz, then the frequency span

shall be no greater than 0.6 MHz. The Network

Analyzer shall be calibrated for measuring the

reflection coefficient at test Port 1 (see Figure 1) using

the calibration kit provided with the Network Analyzer.

This measurement is equivalent to measuring the S11

S-parameter. The calibration shall be performed using

the lowest bandwidth possible (typically 10 Hz).

SEMI E114-0302

9.4.4 After calibration, the cable assembly to be tested

(DUT) shall be attached to Port 1 on the Network

Analyzer. The other end of the DUT shall be

terminated with a short circuit. After all connections

have been visually inspected to ensure proper contact

and the Network Analyzer measurement has stabilized,

the value of the reflection coefficient phase angle can

be examined.

9.4.5 The indicated frequency where the reflection

coefficient phase angle is ± 180 degrees shall be

recorded. The electrical length of the DUT at the

desired nominal operating frequency (for example,

13.56 MHz) is equal to 180 degrees multiplied by the

ratio of the nominal operating frequency divided by the

measured frequency where the phase angle of the DUT

is equal to ± 180 degrees. For example, if the measured

frequency where the reflection coefficient is ± 180

degrees is 6.1 MHz, then the electrical length of the

DUT at 13.56 MHz is 400.13 degrees (180 × 13.56 /

6.1).

10 Test Setup for Power Dissipation (Loss)

Test

10.1 The Test Setup for the power dissipation (loss)

test consists of the Network Analyzer, the cable

assembly to be tested (DUT), an additional short test

cable (for transmission calibration), the appropriate

adapter (if any) to connect the DUT input to the

network analyzer, and the appropriate adapter (if any)

to connect the DUT output to the network analyzer. A

schematic of the Test Setup is shown in Figure 3.

11 Test Procedure for Determining Power

Dissipation

11.1 The test procedure for determining power

dissipation in cable assemblies will also use a Network

Analyzer. In this case, both Ports of the Network

Analyzer will be used. The transmission coefficient

will be measured (also called the S21 S-parameter).

11.2 Calibrate the Network Analyzer at the desired

operating frequency (for example, 13.56 MHz). If

adapters are to be used to connect the DUT to the

Network Analyzer and/or to the short circuit

termination, then the calibration shall be made with the

adapters in place, along with the additional section of

test cable needed for the calibration. The Network

Analyzer shall be calibrated for measuring the

transmission coefficient, S21 (see Figure 3). The

calibration shall be performed at fixed frequency

(continuous-wave operation) using the lowest

bandwidth possible (typically 10 Hz).

11.3 Connect the cable assembly DUT between the two

test Ports on the Network Analyzer (including the

additional test cable used for calibration). After

visually inspecting the connections to ensure proper

contact and the Network Analyzer measurement has

stabilized, the value of the transmission coefficient

(S21) shall be recorded.

11.4 The recorded number shall be expressed in terms

of dB (decibels) and percentage of power transferred in

the DUT. The conversion between dB and percentage

is expressed as:

)10/dBin loss(

10100% ×=TransferPower

For example, if the transmission coefficient is measured

to be –0.4 dB, then the power transfer percentage would

be 91.2%. In other words, 8.8% of the power is lost in

the DUT.

12 Test Setup for Characteristic Impedance

Variation Measurement

12.1 The Test Setup for the Characteristic Impedance

variation measurement consists of a Time Domain

Reflectometer (TDR), the cable assembly to be tested

(DUT), the appropriate adapter (if any) to connect the

DUT input to the TDR, and a standard 50-ohm load

termination (see Figure 4).

12.2 Prior to making any measurements, the TDR shall

be turned on and allowed to warm up. This time allows

for electronics to come to a stable operating condition

for the measurements.

13 Test Procedure for Determining

Characteristic Impedance

13.1 Connect a standard 50-ohm load termination to

the input of the TDR and measure the impedance. This

measurement determines the normalization factor for

the measured impedances. All reported measurements

shall be scaled by this factor by multiplying subsequent

measurements by the ratio of 50 divided by the

impedance value measured with the 50-ohm standard

load.

13.2 Prior to measuring the DUT, the nominal velocity

of propagation of the cable shall be entered into the

TDR. For example, the velocity of propagation is 0.66

for cable type RG-217.

13.3 Connect one end of the DUT to the TDR and

terminate the other end of the DUT with a short circuit.

Measure the characteristic impedance as a function of

distance along the DUT by moving the measurement

distance indicator of the TDR. Record the minimum

and maximum impedance measured over the length of

the cable assembly. The measurement shall be made

throughout the length of the DUT, including the

connectors, up to the short circuit termination.