RS103 Test Field Calculator

What amplifier an RS103 radiated-susceptibility test needs: the forward power for a stated field at a stated distance, the power once cable loss and mismatch are paid for, the average against the peak for the standard’s own pulse modulation, and the power density the field represents — because a test field of this size is an RF hazard.

Last updated 24 Sep 2026

Amplifier power for an RS103 test field

Field, distance, gain, losses -> amplifier power

Platform, from MIL-STD-461G Table XITable XI is TABULATED in the standard, not graphed, so these are read values rather than traced ones. The table also carries two notes worth knowing: equipment external to a submarine’s pressure hull but within the superstructure uses the ships (metallic) below deck column, and equipment in an aircraft carrier’s hangar deck uses the ships (non-metallic) below deck column.

ServiceTable XI gives a separate row for each service in each frequency band, and they differ: Air Force aircraft internal is 20 V/m below 1 GHz where Army and Navy are 200, and ground is 50 V/m for the Army and 10 for the Navy and Air Force below 1 GHz. Several columns have no Air Force entry at all.

Required field strength (V/m)Used when you have chosen to type the level yourself — a tailored level, a programme specification, or a level from another standard. With a platform selected this box shows Table XI’s value for your service and frequency band and is locked.

Distance from the transmit antenna to the EUT (m)MIL-STD-461G paragraph 5.21.3.3c(1) places transmit antennas 1 metre or more from the test setup boundary, so 1 m is the usual planning figure. Power goes as the square of distance, so backing off to 2 m costs four times the power — which is the single biggest lever on the amplifier bill.

Transmit antenna gain (dBi)At the frequency concerned, from the antenna’s own data. A biconical is around 0 to 3 dBi, a log periodic 5 to 8, a double ridge horn 6 to 15 rising across its band. Gain varies enormously with frequency and the worst point in the band is what sizes the amplifier. Use the figures from your part’s datasheet; typical values vary widely between manufacturers.

Cable and connector loss to the antenna (dB)Measured, at the frequency concerned, for the actual run through the chamber wall panel. This is paid for in POWER: 3 dB of cable loss doubles the amplifier you have to buy, and at a few gigahertz a long run of ordinary coax is easily that.

VSWR looking into the antennaTransmit antennas are rarely well matched across their whole band, and the reflected power never reaches the EUT. A VSWR of 2 costs half a decibel; a VSWR of 3 costs 1.25 dB. It also matters for the amplifier’s own survival — check what reverse power it tolerates.

Modulation duty cycle (%)RS103 paragraph 5.21.3.4c(1)(a) requires 1 kHz pulse modulation at 50 per cent duty, with at least 40 dB of modulation depth. THE FIELD LEVEL IS THE PEAK, so the amplifier has to make the peak power; the duty cycle only sets the average and therefore the thermal load. An amplifier rated in CW terms may or may not make the peak — check which.

FrequencyUsed to pick the Table XI band, to work out the wavelength for the far-field check, and for nothing else — the power calculation itself is frequency independent once the gain is known.

Frequency unit

Largest dimension of the transmit antenna (m)Used only for the far-field check. A 137 cm biconical is 1.37 m tip to tip; a 69 × 94.5 cm horn has a 1.17 m diagonal. At RS103’s 1 metre distance most antennas put the EUT inside their own near field, which is why the standard establishes the field with a calibrated probe rather than by calculation.

The RS103 test, drawn as a layout. A signal generator drives an amplifier, the amplifier drives a transmit antenna through a cable whose loss is paid in power, and the antenna illuminates the EUT at a distance of 1 metre or more from the test setup boundary. The field is NOT calculated in the test: an electric field sensor beside the EUT reads it, and the level is raised until the sensor shows the limit. The power figures here are for choosing an amplifier. The amplifier turns amber as the power density approaches 10 W/m² and red past it, because a test field of this size is an RF hazard.

5.533WExample

MIL-STD-461G RS103 for a Navy SPACE application at 100 MHz — 20 V/m from Table XI — with the antenna 1 metre away, 6 dBi of gain, 2 dB of cable loss and a VSWR of 1.5

Power for a field, in the far field

S = P G / 4πr² S = E² / η₀ so P_forward = 4πr²E² / (η₀G)
equivalently E = √(30 P G) / r, with 30 = η₀/4π = 29.979
mismatch loss = −10 log₁₀(1 − |Γ|²), Γ = (VSWR − 1)/(VSWR + 1)
P_amplifier = P_forward × 10^{(cable loss + mismatch loss)/10} P_average = duty × P_amplifier

G: the transmit antenna’s gain at that frequency, as a ratio. It varies across the band, and the lowest gain in the band is what sizes the amplifier
r: the distance from the antenna to the EUT. Power goes as its SQUARE, so distance is the most expensive variable on the page
Γ: the reflection coefficient at the antenna. Reflected power never reaches the EUT and it goes back into the amplifier, which may or may not tolerate it
duty: RS103 uses 1 kHz pulse modulation at 50 per cent. The field LIMIT is the peak, so the amplifier must make the peak power; the duty only sets the average and the thermal load

Worked example

MIL-STD-461G RS103 for a Navy SPACE application at 100 MHz — 20 V/m from Table XI — with the antenna 1 metre away, 6 dBi of gain, 2 dB of cable loss and a VSWR of 1.5
Table XI gives space 20 V/m in every band and for every service, so the required field is 20 V/m — which is 1.062 W/m² of power density, or 106.2 mmW/cm²
The forward power that makes that field at 1 metre from a 6 dBi antenna is 4πr²E²/(η₀G) = 3.352 W
A VSWR of 1.5 means a reflection coefficient of 0.2, so 4 per cent of the power comes back — 0.177 dB
Adding the 2 dB of cable loss, the amplifier has to produce 3.352 W × 10^(2.177/10) = 5.533 W of PEAK power
At 50 per cent duty the average is 2.767 W, which is what sets the thermal load — but the amplifier must still make the peak without compressing, or the field will be lower than the setting suggests
For scale: the same test at 200 V/m instead of 20 would need a hundred times the power, 553.3 W, and moving the antenna to 2 metres would quadruple whatever you started with
The honesty. At 100 MHz a 1.37 m biconical has a Rayleigh distance of 1.252 m, so at 1 metre the EUT is inside the antenna's near field and this far-field arithmetic is a PLANNING ESTIMATE. MIL-STD-461G does not calculate the field: it raises the level until a calibrated electric field sensor at the EUT position reads the limit. Buy the amplifier with margin and let the probe set the level

MIL-STD-461G Table XI, RS103 limit levels in volts per metre

Read from Table XI on printed page 145 of MIL-STD-461G. A = Army, N = Navy, AF = Air Force; a dash means the table has no entry for that combination. Two notes travel with the table: equipment external to a submarine’s pressure hull but inside the superstructure uses the ships (metallic) below deck column, and equipment in an aircraft carrier’s hangar deck uses the ships (non-metallic) below deck column — which is why that column is 50 V/m from 2 to 30 MHz, a band in which measurements on nine carriers found levels up to 42 V/m. Unlike the RE102 limits these are tabulated rather than graphed, so they are read values and not traced ones.
Platform	Service	2–30 MHz	30 MHz–1 GHz	1–18 GHz	18–40 GHz
Aircraft, external or safety critical	A	200	200	200	200
Aircraft, external or safety critical	N	200	200	200	200
Aircraft, external or safety critical	AF	200	200	200	200
Aircraft, internal	A	200	200	200	200
Aircraft, internal	N	200	200	200	60
Aircraft, internal	AF	20	20	60	60
All ships above deck and exposed below deck, and submarines external	A	200	200	200	200
All ships above deck and exposed below deck, and submarines external	N	200	200	200	200
All ships above deck and exposed below deck, and submarines external	AF	—	—	—	—
Ships, metallic, below decks	A	10	10	10	10
Ships, metallic, below decks	N	10	10	10	10
Ships, metallic, below decks	AF	—	—	—	—
Ships, non-metallic, below deck	A	50	10	10	10
Ships, non-metallic, below deck	N	50	10	10	10
Ships, non-metallic, below deck	AF	—	—	—	—
Submarines, internal	A	5	10	10	10
Submarines, internal	N	5	10	10	10
Submarines, internal	AF	—	—	—	—
Ground	A	50	50	50	50
Ground	N	10	10	50	50
Ground	AF	10	10	50	50
Space	A	20	20	20	20
Space	N	20	20	20	20
Space	AF	20	20	20	20

What each field level costs, at 1 metre from a 6 dBi antenna

Power goes as the SQUARE of the field, so the jump from 20 V/m to 200 V/m is a factor of a hundred and the jump from 50 to 200 is a factor of sixteen. The five levels above are all of the values Table XI actually uses. Note that these are peak powers: at RS103’s 50 per cent duty the average is half, but an amplifier that compresses on the peaks produces a field lower than the setting says, and a low field is the direction that hides a susceptibility.
Field	Power density	Forward power	With 2 dB cable and VSWR 1.5
5 V/m	66.36 mW/m²	209.5 mW	345.8 mW
10 V/m	265.4 mW/m²	837.9 mW	1.383 W
20 V/m	1.062 W/m²	3.352 W	5.533 W
50 V/m	6.636 W/m²	20.95 W	34.58 W
60 V/m	9.556 W/m²	30.16 W	49.8 W
200 V/m	106.2 W/m²	335.2 W	553.3 W

Where the RS103 requirement applies, from paragraph 5.21.1

Paragraph 5.21.2 adds the polarisation rule: up to 30 MHz the requirement is met for vertically polarised fields, above 30 MHz for BOTH horizontal and vertical, and circularly polarised fields are explicitly not acceptable. That doubles the test time above 30 MHz and it doubles nothing about the amplifier — the same power, twice.
Band	Who	Note
2 MHz to 30 MHz	Army and Navy; optional for all others	Optional means required only if the procurement specification says so
30 MHz to 18 GHz	All	The core of the requirement
18 GHz to 40 GHz	Optional for all	Again, only if the contract calls for it
Any band	Army and Air Force	No requirement at the tuned frequency of antenna-connected receivers
Any band	Receivers with permanently attached antennas	Reduced performance is allowed in band, provided performance recovers afterwards

What amplifier do I need, and what does that field mean?

RS103 illuminates the equipment under test at a stated field strength and looks for anything that misbehaves. The levels are in MIL-STD-461G’s Table XI — tabulated, not graphed, so they can simply be read — and they range from 5 V/m for equipment inside a submarine’s pressure hull to 200 V/m for aircraft external or safety-critical equipment. Space is 20 V/m in every band and for every service, which is one of the few places in this standard where a satellite programme gets an unambiguous number.

The arithmetic is simple and the consequences are not. Power density is PG/4πr², field is √(η₀S), and turning that round gives the forward power. Then cable loss and mismatch are paid on top, in power rather than in decibels of margin — three decibels of cable loss doubles the amplifier you have to buy. And power goes as the SQUARE of distance, so moving the antenna from 1 metre to 2 metres quadruples the bill. Distance and cable loss are the two variables worth arguing about before anything is ordered.

The level is a peak. RS103 requires 1 kHz pulse modulation at 50 per cent duty with at least 40 dB of depth, and the limit applies to the peak field. So the amplifier has to make the peak power this page prints; the duty cycle halves the average and therefore the thermal load, and that is all it does. An amplifier specified in CW terms may or may not produce the peak cleanly, and one that compresses produces a field lower than the setting says — which is the direction that lets a susceptibility through. There is a matching trap on the measurement side: a broadband diode field probe under pulse modulation does not read the peak, and the standard’s data presentation clause asks for exactly the correction factors that fix it.

This is a planning estimate, not a prediction. At RS103’s 1 metre distance most transmit antennas put the EUT inside their own near field — a 137 cm biconical at 100 MHz has a Rayleigh distance of about 1.3 metres — so the far-field relation used here does not describe the field that will actually exist. MIL-STD-461G knows this and does not calculate the field at all: the procedure is to raise the level until an electric field sensor positioned at the EUT reads the limit. Use this page to choose an amplifier with margin; let the probe set the level.

And it is a hazard. A 200 V/m field is about 10.6 mW/cm². The ICNIRP 2020 guidelines’ reference level for occupational exposure in the 30 to 400 MHz band is 139 V/m, so 200 V/m exceeds even that, and the general-public level is lower still. The standard requires the test area to be assessed for RF hazards before anything is switched on. That means interlocks, a written procedure, and nobody in the chamber — none of which a calculator provides. This page is not an RF safety calculator and does not replace one. Your programme’s RF safety officer, your local exposure regulations and your own risk assessment decide what may be switched on and who may be in the room.

What this page does not cover. The reverberation-chamber method in paragraph 5.21.4 works completely differently: the field is established from a measured calibration factor with the tuner rotating, and the chamber’s lowest usable frequency comes from a mode-count criterion on its own dimensions. For the other direction — emissions rather than immunity — the RE102 margin page is the sibling of this one, and the field and power density converter handles the unit work. Once a susceptibility is found, the aperture page and the transfer impedance page are where the fix usually lives, because the same openings and the same shield terminations govern both directions.

Frequently asked questions

What field level does a satellite have to be tested to?

MIL-STD-461G Table XI gives space 20 V/m, in every frequency band and for all three services. That is one of the few places in the standard where a space programme gets an unambiguous number — RE102’s limits, by contrast, point at a figure whose curves are all labelled in aircraft terms. As always the contract may tailor it.

Is the power on this page peak or average?

Peak. RS103 modulates with a 1 kHz pulse at 50 per cent duty and the field limit is the peak value, so the amplifier must produce the peak power without compressing. The average, which is what sets the thermal load, is the duty cycle times that — both are printed. An amplifier rated in CW terms is not necessarily rated for this.

Why does the page say the calculation is only an estimate?

Because at RS103’s 1 metre distance the EUT is usually inside the transmit antenna’s near field, where the far-field relation P = 4πr²E²/η₀G does not describe the field. The standard does not calculate the field either: it raises the level until a calibrated electric field sensor at the EUT position reads the limit. The right use of this page is choosing an amplifier with margin.

How much does cable loss really cost?

It is paid in power, not in margin. Three decibels doubles the amplifier, six quadruples it, ten is a factor of ten. At a few gigahertz a long run of ordinary coax through a chamber wall panel is easily 3 to 6 dB, so a better cable or an amplifier sited closer to the panel is often cheaper than the extra watts.

Why does VSWR matter if the field is set by a probe anyway?

Two reasons. The reflected power never reaches the EUT, so you need more forward power to make the level — a VSWR of 2 costs half a decibel and a VSWR of 3 costs 1.25 dB. And the reflected power goes back into the amplifier, which has a reverse-power rating that transmit antennas at the edges of their bands can exceed.

Do I need to test both polarisations?

Above 30 MHz, yes — paragraph 5.21.2 requires the requirement to be met for both horizontally and vertically polarised fields, and circularly polarised fields are explicitly not acceptable. Up to 30 MHz vertical alone is required. That doubles the test time above 30 MHz and changes the amplifier not at all.

Related calculators

References

MIL-STD-461G, paragraph 5.21 RS103, radiated susceptibility, electric field. Paragraph 5.21.1 gives the applicability and the optional bands; 5.21.2 gives the limit and the polarisation rule and points at Table XI; 5.21.3.3c places the transmit antenna 1 metre or more from the test setup boundary and 5.21.3.3d places the field sensors; 5.21.3.4b requires the test area to be assessed for RF hazards; 5.21.3.4c(1)(a) specifies 1 kHz pulse modulation at 50 per cent duty with 40 dB of depth. The limit levels in the table above are read from TABLE XI, printed page 145 — tabulated in the standard rather than graphed.
MIL-STD-461G, paragraph 5.21.4 RS103 alternative test procedures — reverberation chamber (mode-tuned). A different method with a different calibration, which this page does not cover.
ITU-R Recommendation P.525, Calculation of free-space attenuation, which gives the field from a radiator as e = √(30 p)/d. The 30 is η₀/4π = 29.979; the rounding is worth 0.0030 dB, which is why this page uses η₀ rather than 30.
ICNIRP, Guidelines for Limiting Exposure to Electromagnetic Fields (100 kHz to 300 GHz). Health Physics 118(5): 483–524, 2020. Cited for the 30 to 400 MHz reference levels — 139 V/m occupational and 62 V/m general public — quoted here only to put an RS103 test field in context. This page is not an exposure assessment.