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

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

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

2008 NAB Engineering Conference

- 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

General System Configuration flat delay response (vs frequency). Report maximum deviation from ideal.

2008 NAB Engineering Conference

“Antennas” and “Transmitters” to be Considered flat delay response (vs frequency). Report maximum deviation from ideal.

- 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 flat delay response (vs frequency). Report maximum deviation from ideal.TM 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 flat delay response (vs frequency). Report maximum deviation from ideal.

Feed Region

Reflector Panel

Dipole

2008 NAB Engineering Conference

Isometric View of Panel System flat delay response (vs frequency). Report maximum deviation from ideal.

2008 NAB Engineering Conference

Top View of Offset Panel System flat delay response (vs frequency). Report maximum deviation from ideal.

2008 NAB Engineering Conference

Specify source locations. flat delay response (vs frequency). Report maximum deviation from ideal.

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 Computations2008 NAB Engineering Conference

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 Computations2008 NAB Engineering Conference

Results, Configuration 1 matrix at each frequency.

Source Impedance: 50Ω

2008 NAB Engineering Conference

Antenna Input Impedance, matrix at each frequency.Γ Plane

2008 NAB Engineering Conference

Return Loss, Antenna Input matrix at each frequency.

≈ 18 dB over 3.5 MHz

2008 NAB Engineering Conference

Far Field Behavior, Single Channel matrix at each frequency.

Δ = 0.05 dB

Δ = 0.3 ns

2008 NAB Engineering Conference

Far Field Behavior vs Azimuth, 3 Channels matrix at each frequency.

Worst Case

Δ = 0.7 ns

Δ = 0.09 dB

2008 NAB Engineering Conference

Far Field Behavior vs Azimuth, Magnitude, Polar matrix at each frequency.

2008 NAB Engineering Conference

Results, Configuration 1 matrix at each frequency.

Source Impedance: 500Ω

2008 NAB Engineering Conference

Load Impedance Presented to Transmitter matrix at each frequency.

≈ 500 ft Transmission Line

Γ Plane

2008 NAB Engineering Conference

Far Field Behavior, Single Channel matrix at each frequency.

Δ = 1.87 dB

Δ = 251 ns

2008 NAB Engineering Conference

Far Field Behavior vs Azimuth, 3 Channels matrix at each frequency.

Worst Case

Δ = 251 ns

Δ = 1.87 dB

2008 NAB Engineering Conference

Results, Configuration 2 matrix at each frequency.

Source Impedance: 50Ω

2008 NAB Engineering Conference

Antenna Input Impedance, matrix at each frequency.ΓPlane

2008 NAB Engineering Conference

Return Loss, Antenna Input matrix at each frequency.

2008 NAB Engineering Conference

Far Field Behavior, Single Channel matrix at each frequency.

Δ = 0.2 dB

Δ = 2.2 ns

2008 NAB Engineering Conference

Far Field Behavior Vs Azimuth, 3 Channels matrix at each frequency.

Worst Case

Δ = 3.49 ns

Δ = 0.25 dB

2008 NAB Engineering Conference

Far Field Behavior vs Azimuth, Magnitude, Polar matrix at each frequency.

2008 NAB Engineering Conference

Results, Configuration 2 matrix at each frequency.

Source Impedance: 500Ω

≈ 500 ft Transmission Line

2008 NAB Engineering Conference

Load Impedance Presented to Transmitter matrix at each frequency.

≈ 500 ft Transmission Line

Γ Plane

2008 NAB Engineering Conference

Far Field Behavior, Single Channel matrix at each frequency.

Δ = 0.31 dB

Δ = 11.3 ns

2008 NAB Engineering Conference

Far Field Behavior vs Azimuth, 3 Channels matrix at each frequency.

Worst Case

Δ = 11.3 ns

Δ = 0.31 dB

2008 NAB Engineering Conference

Single Dipole, 98 MHz matrix at each frequency.± 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

50 0.04 dB 0.01 ns 16.3 dB

1.44 dB 81 ns 16.3 dB

0.54 dB 32 ns 26.4 dB

0.30 dB 19 ns 32.0 dB

2008 NAB Engineering Conference

Resistive Load, Non-Radiating matrix at each frequency.

- 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 matrix at each frequency.

- 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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