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Measurement of Energy Flux Density and Electromagnetic Field Strength, Method of Accuracy Increasing

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Measurement of Energy Flux Density and Electromagnetic Field Strength, Method of Accuracy Increasing

O. Kapral

The Basis of Measurement of Energy Flux Density and Electromagnetic Field Strength are Devices М3-90, М3-91, М3-92. Device М3-90 provides measuring of Power of Microwaves Energy in the Frequencies Range 0.02...17.85 GHz. Device М3-91 provides measuring in the Frequencies Range 17.44...25.86 GHz, and М3-92 in the Frequencies Range 25.86... 37.5 GHz. In the Devices is used Thermo-electric method of measuring. The Basis of measuring is Transformation of Power in Electro-motive Force. The measured parameters are found in limits 0.1......10 ·10 micro W.

Measurement of Energy Flux Density and Electromagnetic Field Strength is provides according to a formula:

W – Energy Flux Density, W/m;
P – Device reading, W;
S – Effective Area of measuring Antenna, m;
N– Radiation Efficiency. Radiation Efficiency depends on material of manufacture, sizes, transmissions of Electro-motive Force.

Z – Attenuation in Feeder. Attenuation in Feeder is determined as the product of Attenuation Factor Z(f) into Length ;
КСВ – Standing-wave Ration (SWR) in the Feeder. If the Feeder is absent Z = 0 and N = 1. SWR can be determined at the help of the Reflection Factor.

The effective area of Antenna is determined by a formula:

– Area of Antenna, м;
- Area Utilization Factor. Utilization Factor depends on the Type of Antennas. Utilization Factor for Horn Aerials (Antennas) is 0.49; 0.49. Utilization Factor for Parabolic Aerials (Antennas) is 0.55; 0.55.
D – Directive Antenna Gain. Directive Antenna Gain is determined by a formula:

– Wave-length. Wave-length is determined by a formula:

C – Speed of Electromagnetic Waves.

C = 2.998 · 10 m/sec

f – Frequency which measuring is produced at, Hz.

We make substitution of formulas (3) & (5) into a formula (4). We have:

, and:

Let substitute formula (6) in a formula (1), and we will have formula for determination of Energy Flux Density:

For devices М3-90, М3-91, М3-92 the Basic Error is ± 4...6 %.

The use of different Antennas (Aerials) does not influence on Accuracy of measuring (formulas (4) & (6)). Only the determinations of Amplification Factors have an effect on Accuracy of measuring. A formula (7) can be rewrite with allow for an Error:

– Truth Value of Energy Flux Density,
– Absolute Error.

A formula (8) can be written down as:

- Energy Flux Density Error.

When Standing-wave Ration (SWR) = 1.2, The Error is ± 3…5 %.
In the Range of Frequencies 0.03...300 MHz it is necessary to measure the Electromagnetic Field Strength. Communication between Electromagnetic Field Strength and Flux Density is determined by a formula:

E - Electromagnetic Field Strength,
– Characteristic Wave Impedance.

Wave Impedance is determined by a formula:

- Magnetic Permeability

– Dielectric Permittivity ( 376.8 Ohm).
We make substitution of formulas (6) & (11) into a formula (10), also taking into account Radiation Efficiency N, and get a formula for consideration Electromagnetic Field Strength:

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added 18.07.07 01:01:27 | looked over 14590 times