UWB Antennas & Measurements

Gabriela QuinteroMICS UWB Network Meeting

11/12/2007

Outline

UWB Antenna AnalysisFrequency DomainTime Domain

Measurement TechniquesPeak and Average Power MeasurementsSpectrum Analyzer Settings

Fourier SeriesFourier Transform

UWB Measurements

Outline

UWB Antenna AnalysisFrequency DomainTime Domain

Measurement TechniquesPeak and Average Power MeasurementsSpectrum Analyzer Settings

Fourier SeriesFourier Transform

UWB Measurements

UWB Antennas

Impulse radioUWB pulse (3.1 – 10.6 GHz)MICS pulse (4 – 4.5 GHz)

Time and frequency domain AnalysisStill with basic antenna architectures

Monopole

Vivaldi

Time and Frequency Domain

Two different softwares used to characterize the antennasAnsoft HFSS – FD

Frequency Sweep at all frequenciesParameters in FD (S11, Gain, E-field, etc.)

CST Microwave Studio – TDSelect the pulse BW

Parameters in FD (S11, Gain, etc.)E-field in TD

Frequency DomainTransfer Function - S21

Relates the output voltage with the input voltage

Can be derived from the Friis’ Transmission Equation

And obtain

( ) ( ) ( )j rc

r tV H V eω

ω ω ω−

=

( )( )2

2 2P ˆ ˆ1 1 ( , ) ( , )4

rcdt cdr t r t t t r r r t

t

e e D DP R

λ 2rθ φ θ φ ρ

π⎛ ⎞= − Γ − Γ ⎜ ⎟⎝ ⎠

ρ⋅

( )211

( ) 1 ( , , )( ) 4

rcdt t t t

t

V e S EV R

ω λ ω θ φω π

⎛ ⎞= − ⎜ ⎟⎝ ⎠

Tx Rx

Frequency Domain

HFSS Simulation

S11 E-field

Transfer FunctionMatlab

Pulse PSD

Rx Pulse PSDIFFT

Rx Pulse TD

Tx Rx

Monopole System

0 2 4 6 8 10 12 14 16 18 20-35

-30

-25

-20

-15

-10

-5

0Return Loss

Frequency [GHz]

Mag

nitu

de [d

B]

SimulatedMeasured

0 5 10 15 200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Normalized Magnitude

Frequency [GHz]

SimulatedMeasured

0 5 10 15 20-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

Frequency [GHz]

Phase [radians]

S11

HFSSNWA

TF – S21

Rx + Tx Pulse PSD Rx + Tx Pulse0 2 4 6 8 10 12

-120

-100

-80

-60

-40

-20

0

20

Frequency [GHz]

Gau

ssia

n Pu

lse

[dB]

Power Spectral Density

0 2 4 6 8 10 12-120

-100

-80

-60

-40

-20

0

20

MIC

S Pu

lse,

[dB]

Frequency [GHz]

InputSimulatedMeasured

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-1

-0.5

0

0.5

1

Time [ns]

Gau

ssia

n Pu

lse

Input Vs. Output pulse (normalized)

-1 0 1 2 3 4-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

MIC

S Pu

lse

Time [ns]

InputSimulatedMeasured

Tx Rx

0 5 10 15 200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Normalized Magnitude

Frequency [GHz]

SimulatedMeasured

0 5 10 15 20-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

Frequency [GHz]

Phase [radians]

0 2 4 6 8 10 12 14 16 18 20-35

-30

-25

-20

-15

-10

-5

0Return Loss

Frequency [GHz]

Mag

nitu

de [d

B]

SimulatedMeasured

Vivaldi SystemS11

HFSSNWA

TF – S21

Rx + Tx Pulse0 2 4 6 8 10 12-120

-100

-80

-60

-40

-20

0

20

Frequency [GHz]

Gau

ssia

n Pu

lse,

[dB]

Power Spectral Density

InputSimulatedMeasured

0 2 4 6 8 10 12-120

-100

-80

-60

-40

-20

0

20

MIC

S Pu

lse,

[dB]

Frequency [GHz]

Rx + Tx Pulse PSD 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-1

-0.5

0

0.5

1

Time [ns]

Gau

ssia

n Pu

lse

Input Vs. Output pulse (normalized)

InputSimulatedMeasured

-1 0 1 2 3 4-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

MIC

S Pu

lse

Time [ns]

Tx Rx

CST: Monopole Antenna

4.25 GHz 6.85 GHz

H-plane

E-plane

CST: Vivaldi Antenna

4.25 GHz 6.85 GHz

H-plane

E-plane

0 0.5 1 1.5 2 2.5 3 3.5 4-1

-0.5

0

0.5

1UWB Pulse

0 2 4 6 8 10 12 14 16-1

-0.5

0

0.5

1MICS Pulse

Input PulseE-field at 80°

Time Domain

0 0.5 1 1.5 2 2.5 3 3.5-1

-0.5

0

0.5

1UWB Pulse

0 2 4 6 8 10 12 14 16-1

-0.5

0

0.5

1MICS Pulse

Input PulseE-field at 80°

Monopole Vivaldi

Time Domain

Fidelity FactorMeasures the faithfulness with which a device reproduces the time shape of the input signal.

f(t) = Input signal at antenna terminalsr(t) = Radiated E-field in time domainThe signals are normalized to have unit energy

and2/1

2)(

)()(ˆ

⎥⎦⎤

⎢⎣⎡

=

∫∞

∞−dttr

trtr1/ 2

2

( )ˆ ( )( )

f tf tf t dt

∞

−∞

=⎡ ⎤⎢ ⎥⎣ ⎦∫

Time Domain

The fidelity parameter, F, is determined by the peak of the cross-correlation function of the signals

ˆ ˆmax ( ) ( )F f t r t dtτ

τ∞

−∞= +∫

Time Domain

CST Simulation

E-field (t,θ, )

Input signal

Fidelity Factor

φ

Time Domain

0°

30°

60°

90°

120°

150°

±180°

-150°

-120°

-90°

-60°

-30°

0.70.8

0.91

Vivaldi Fidelity Factor

UWB PulseMICS Pulse

0°

30°

60°

90°

120°

150°

±180°

-150°

-120°

-90°

-60°

-30°

0.70.8

0.91

Monopole Fidelity Factor

UWB PulseMICS Pulse

Outline

UWB Antenna AnalysisFrequency DomainTime Domain

Measurement TechniquesPeak and Average Power MeasurementsSpectrum Analyzer Settings

Fourier SeriesFourier Transform

UWB Measurements

MEASUREMENTS

Average PowerPeak Power

TPP

TPPE

effavg

avgeff

τ

τ

=

==

0

0

MEASUREMENTS

Spectrum Analyzer

RBW VBW

Scan Time

Spectrum Analyzer

Line Spectrum Pulse Spectrum

A pulse repetition rate equal to the resolution bandwidth is the demarcation line between a true Fourier-series spectrum, where each line is a response representing the energy contained in that harmonic, and a “pulse” or Fourier-transform response. Agilent Spectrum Analyzers Series.

Application note 150-2pp. 32

1B> or B>PRFT

Line Spectrum

Line Spectrum

All individual frequency components are resolved.Line spacing is 1kHZ = PRFSpacing of sidelobe minima is 10kHz = The amplitude of each line will not change when RBW is changed, as long as RBW<0.3PRF

1

effτ

Line Spectrum

Pulse DesensitizationOnly valid for Fourier line spectrum.

( )10 10

10

[ ] 20log 20log

[ ] 10log ( )

τα τ

τ

⎛ ⎞= = ×⎜ ⎟

⎝ ⎠

= ×

effL eff

avgeff

peak

dB PRFT

PdB PRF

P

Pulse Spectrum

It’s a combination of time and frequency display.

The lines that form the envelope are pulse lines in time domain.

Each line is displayed when a pulse occurs.

Frequency domain display of the spectrum envelope.

The amplitude of the envelope increase linearly as RBW increases. (As long as RBW < 0.2/ τeff).

Pulse Spectrum

-30dBm CW carrier modulated by a pulse train with a PRF of 100Hz, τeff = 100µs and RBW = 1kHz = 0.1/ τeff

Pulse Spectrum

In Figure 23, we lost the linear relationship between bandwidth and display amplitude RBW > 0.2/ τeff . The resolution of the sidelobes is lost to a great extent.In Figure 24 RBW = 1/ τeff, we get a display with an amplitude practically equal to the peak amplitude of the pulsed signal.

Pulse Spectrum

Pulse desensitization correction factor

RBWB

K

RBWKdB

imp

effp

=

××= )(log20][ 10 τα

K = 1.617 for Agilnet ESA Series 856x or 859x

Average Power

FCC DefinitionThe average limit is 500 uV/m, as measured at 3 meters with a 1 MHz resolution bandwidth (RBW). Equivalent to an EIRP of -41.25 dBm/MHz

0 2 4 6 8 10 12-80

-75

-70

-65

-60

-55

-50

-45

-40FCC Indoor Spectral Mask

EIR

P [d

Bm

/MH

z]

Frequency [GHz]

Average Measurements

If 10 kHz > VBW >10 HzVideo averaging should be used in conjunction with peak hold.

If NO dithering or PPMLine spectrum setting (VBW ≥ RBW)RBW < 0.3 PRFAverage level = highest line in the emission line spectrum

Average Measurements

If dithering or PPMTrue pulse spectrum settingsA pulse desensitization correction factor would be added to the measurement to obtain a peak level.The average is calculated using the duty cycle factor in dB

( )10[ ] 10logavgeff

peak

PdB PRF

Pτ= ×

Peak Measurements

pp. 174

Peak Measurements

Peak level when measured over a bandwidth of 50 MHz

50MHz → widest victim receiver that is likely to be encountered.

Peak measurements based on a 50 MHz (resolution) bandwidth may not be feasible. The widest available RBW that can be employed for peak measurements is 3 MHz.

Peak Measurements

Peak Measurements

Peak emission level of 0 dBm/50 MHz = 58mV/m at 3 meters is adopted.Equivalent to:

A peak EIRP of -24.44 dBm/3 MHzPeak field strength of 3.46 mV/m at 3 meters with a 3 MHz RBW.

Rules of Thumb

Line Spectrum Pulse Spectrum

RBW<0.3PRF

Pavg No dithering or PPM

Pavg Dithering or PPM

Peak Interference Power

PRF[Hz]10]time[s/Div scan

RBWPRF

≥

<<effτ1.05.1

QUESTIONS?