Computed envelope linearity of several fm broadcast antenna arrays j dane jubera
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COMPUTED ENVELOPE LINEARITY OF SEVERAL FM BROADCAST ANTENNA ARRAYS J. Dane Jubera PowerPoint PPT Presentation


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COMPUTED ENVELOPE LINEARITY OF SEVERAL FM BROADCAST ANTENNA ARRAYS J. Dane Jubera. 2008 NAB Engineering Conference. Complex Envelope Linearity: Ideal is flat amplitude and flat delay response (vs frequency). Report maximum deviation from ideal.

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COMPUTED ENVELOPE LINEARITY OF SEVERAL FM BROADCAST ANTENNA ARRAYS J. Dane Jubera

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Computed envelope linearity of several fm broadcast antenna arrays j dane jubera

COMPUTED ENVELOPE LINEARITY OF SEVERAL FM BROADCAST ANTENNA ARRAYSJ. Dane Jubera

2008 NAB Engineering Conference


Computed envelope linearity of several fm broadcast antenna arrays j dane jubera

  • Complex Envelope Linearity: Ideal is flat amplitude and flat delay response (vs frequency). Report maximum deviation from ideal.

  • Computed Results – No measured data, with apologies.

  • Antenna System Analysis

    MININECTM for Antenna Z and Radiation Characteristics

    all balanced-mode mutual impedances are considered

    MathcadTM for offline data reduction and network analysis

2008 NAB Engineering Conference


Computed envelope linearity of several fm broadcast antenna arrays j dane jubera

General System Configuration

2008 NAB Engineering Conference


Antennas and transmitters to be considered

“Antennas” and “Transmitters” to be Considered

  • FM Panel Array, 4 bay, 3 faces, Omni, CP

  • FM Panel Array, as above, with lateral offset & turnstile phasing

  • Single λ/2 dipole, LP

  • Resistive Load, non-radiating

  • Norton Equivalent Current Source, Zs= 50 Ω

  • Norton Equivalent Current Source, Zs= 500 Ω

  • Norton Equivalent Current Source, Zs= ∞ Ω

  • Linear System Analysis

2008 NAB Engineering Conference


Ibiquity digital corporation hd radio tm specification for gain and delay flatness

iBiquity Digital Corporation HD RadioTM Specification for Gain and Delay Flatness

“The total gain of the transmission signal path as verified at the antenna output shall be flat to within ± 0.5 dB for all frequencies between (Fc – 200 kHz) to (Fc +200 kHz), where Fc is the RF channel frequency.”

“The differential group delay variation of the entire transmission signal path (excluding the RF channel) as measured at the RF channel frequency (Fc ) shall be within 600 ns peak to peak from (Fc – 200 kHz) to (Fc +200 kHz).”

[1] Doc. No. SY_SSS_1026s, Rev D, February 18, 2005,

“HD Radio FM Transmission System Specifications”

2008 NAB Engineering Conference


Top view of panel system

Top View of Panel System

Feed Region

Reflector Panel

Dipole

2008 NAB Engineering Conference


Isometric view of panel system

Isometric View of Panel System

2008 NAB Engineering Conference


Top view of offset panel system

Top View of Offset Panel System

2008 NAB Engineering Conference


Flow chart for mininec tm computations

Specify source locations.

Specify source currents – one “on”, others “off”.

Generate geometry of radiating structure.

Save configuration file.

Specify frequencies and far field directions.

Duplicate configuration file for each source current location. Modify source currents.

Execute analysis for each configuration file.

Flow Chart for MININECTM Computations

2008 NAB Engineering Conference


Flow chart for off line computations

Collect all port voltage data and construct antenna port Y matrix at each frequency.

Use network analysis to determine antenna feed currents when connected by model feed system.

Compute CP mode fields. Compute delay.

Collect all far field solutions. Scale by computed feed currents and superpose.

Display results.

Flow Chart For Off-line Computations

2008 NAB Engineering Conference


Results configuration 1

Results, Configuration 1

Source Impedance: 50Ω

2008 NAB Engineering Conference


Antenna input impedance plane

Antenna Input Impedance, Γ Plane

2008 NAB Engineering Conference


Return loss antenna input

Return Loss, Antenna Input

≈ 18 dB over 3.5 MHz

2008 NAB Engineering Conference


Far field behavior single channel

Far Field Behavior, Single Channel

Δ = 0.05 dB

Δ = 0.3 ns

2008 NAB Engineering Conference


Far field behavior vs azimuth 3 channels

Far Field Behavior vs Azimuth, 3 Channels

Worst Case

Δ = 0.7 ns

Δ = 0.09 dB

2008 NAB Engineering Conference


Far field behavior vs azimuth magnitude polar

Far Field Behavior vs Azimuth, Magnitude, Polar

2008 NAB Engineering Conference


Results configuration 11

Results, Configuration 1

Source Impedance: 500Ω

2008 NAB Engineering Conference


Load impedance presented to transmitter

Load Impedance Presented to Transmitter

≈ 500 ft Transmission Line

Γ Plane

2008 NAB Engineering Conference


Far field behavior single channel1

Far Field Behavior, Single Channel

Δ = 1.87 dB

Δ = 251 ns

2008 NAB Engineering Conference


Far field behavior vs azimuth 3 channels1

Far Field Behavior vs Azimuth, 3 Channels

Worst Case

Δ = 251 ns

Δ = 1.87 dB

2008 NAB Engineering Conference


Results configuration 2

Results, Configuration 2

Source Impedance: 50Ω

2008 NAB Engineering Conference


Antenna input impedance plane1

Antenna Input Impedance, ΓPlane

2008 NAB Engineering Conference


Return loss antenna input1

Return Loss, Antenna Input

2008 NAB Engineering Conference


Far field behavior single channel2

Far Field Behavior, Single Channel

Δ = 0.2 dB

Δ = 2.2 ns

2008 NAB Engineering Conference


Far field behavior vs azimuth 3 channels2

Far Field Behavior Vs Azimuth, 3 Channels

Worst Case

Δ = 3.49 ns

Δ = 0.25 dB

2008 NAB Engineering Conference


Far field behavior vs azimuth magnitude polar1

Far Field Behavior vs Azimuth, Magnitude, Polar

2008 NAB Engineering Conference


Results configuration 21

Results, Configuration 2

Source Impedance: 500Ω

≈ 500 ft Transmission Line

2008 NAB Engineering Conference


Load impedance presented to transmitter1

Load Impedance Presented to Transmitter

≈ 500 ft Transmission Line

Γ Plane

2008 NAB Engineering Conference


Far field behavior single channel3

Far Field Behavior, Single Channel

Δ = 0.31 dB

Δ = 11.3 ns

2008 NAB Engineering Conference


Far field behavior vs azimuth 3 channels3

Far Field Behavior vs Azimuth, 3 Channels

Worst Case

Δ = 11.3 ns

Δ = 0.31 dB

2008 NAB Engineering Conference


Single dipole 98 mhz 200 khz

Single Dipole, 98 MHz ± 200 kHz

  • Table above shows performance of a single λ/2 dipole antenna fitted with a low Q matching circuit with which to adjust impedance.

  • Assumed transmission line length is 201 feet. Not as much gain and delay variation as seen with 500 feet of transmission line.

Source ZΔ GainΔ DelayAntenna Return Loss

500.04 dB0.01 ns16.3 dB

1.44 dB81 ns16.3 dB

0.54 dB32 ns26.4 dB

0.30 dB19 ns32.0 dB

2008 NAB Engineering Conference


Resistive load non radiating

Resistive Load, Non-Radiating

  • Resistive Load (RL + j 0)

  • Long Transmission Line, Lossless

  • Current Source (Zs = )

  • Evaluate voltage on load resistor vs frequency

  • ρ=|Γ|, Γ = (RL-Z0)/(RL+Z0)

  • For sufficiently long transmission line (≈ 600’ @ FM)

    Δt = 4ρ(L/v)/(1- ρ2)

    ΔG = 20 log(VSWR) = 20 log [(1+ρ)/(1-ρ)]

    (L/v is 1-way transit time in transmission line)

  • Example 1: For ρ=0.2, L/v = 720 ns ( ≈ 700 ft) =>

    Δt = 600 ns & ΔG = 3.5 dB

    Example 2: For ρ=0.126 (18 dB RL), L/v = 508 ns ( ≈ 500 ft) =>

    Δt = 260 ns & ΔG = 2.2 dB

2008 NAB Engineering Conference


Summary of results

Summary of Results

  • Contribution to envelope non-linearity is primarily via the antenna input mismatch, length of transmission line, and transmitter source mismatch.

  • Systems using transmitters which are source matched to the transmission line show very good performance in all cases studied here relative to HD Radio specification of 1 dB gain variation and 600 ns delay variation.

  • Systems using transmitters with high VSWR relative to line impedance require low antenna VSWR to achieve similar envelope linearity performance.

2008 NAB Engineering Conference


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