ForHosting KIT · Engineering & construction

SWR from reflection coefficient calculator

A reflection coefficient of 0.2 means an SWR of 1.5 and about 14 dB of return loss. Enter the reflection magnitude or your forward and reflected power readings to get SWR, return loss and the share of power delivered. Free in your browser.

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Worked example

If you enter

Gamma: 0.2

You get

Calculation mode: reflection_coefficient
Gamma mag: 0.2
Reflection coefficient: 0.2
Power reflection coefficient: 0.04

Standing wave ratio and return loss are the everyday figures of merit for how well a radio-frequency load, antenna, cable, or filter is matched to its system impedance. When a traveling wave hits a mismatch, part of the power reflects; the magnitude of that reflection coefficient |Γ| sets both the voltage standing wave ratio along the line and the return loss seen by the source. The closed forms are simple and universal: VSWR equals one plus |Γ| over one minus |Γ|, and return loss in decibels equals minus twenty times the base-ten log of |Γ|. Bench meters often report forward and reflected power instead of |Γ| directly; the magnitude then follows as the square root of reflected over forward power, after which the same two formulas apply. This SWR from reflection coefficient calculator accepts either a reflection magnitude in [0, 1) or a positive forward power with a non-negative reflected power not exceeding it, evaluates those identities with deterministic floating-point arithmetic, and returns VSWR, return loss, power reflection fraction, transmitted fraction, and mismatch loss so lab notebooks, homework keys, and production scripts share one ground truth. Zero reflection is a perfect match (SWR one, infinite return loss); total reflection is rejected because VSWR diverges.

How VSWR and return loss follow from the reflection coefficient

On a transmission line the incident and reflected phasors add to form a standing wave. The envelope maxima and minima define the voltage standing wave ratio, which for a single-frequency steady state collapses to the algebraic identity VSWR equals (1 + |Γ|) divided by (1 − |Γ|), where |Γ| is the magnitude of the load reflection coefficient. When |Γ| is zero the load absorbs everything, the standing-wave envelope is flat, and VSWR is exactly one.

As |Γ| approaches one the numerator and denominator force VSWR toward infinity, which is the total-reflection limit of an open, short, or pure reactive termination. Return loss is the complementary decibel view of the same magnitude: RL_dB equals minus twenty times log ten of |Γ|, so a smaller reflection yields a larger positive return-loss number and a quieter match on the spectrum analyzer. Power reflection coefficient is simply |Γ| squared, which is also the fraction of incident power that bounces back when phases average out.

The complementary transmitted (delivered) fraction is one minus |Γ| squared; converting that fraction to decibels gives the mismatch loss that appears in link budgets as −10·log10(1−|Γ|²). This calculator implements those identities only. It does not solve for complex ZL from a Smith chart, convert S11 phase, apply connector de-embedding, or fold in free-space path loss.

Keeping the landing focused on |Γ| to VSWR and return loss matches the search intent of technicians who already have a reflection reading or a pair of wattmeter numbers and need the standard scalar figures without a multi-formula RF suite.

What you can do with it

Antenna and feedline match checks

Convert a measured |Γ| or wattmeter forward/reflected pair into VSWR and return loss before transmitting at full power.

Cable and filter acceptance tests

Turn dual-directional power readings into RL_dB and SWR for pass/fail against the connector or filter datasheet.

Lab drills and CI answer keys

Script the same VSWR=(1+|Γ|)/(1-|Γ|) product used in the browser so automated graders share one ground truth.

FAQ

What formulas does this SWR calculator use?

VSWR = (1+|Γ|)/(1-|Γ|) and return loss RL_dB = −20·log10(|Γ|). In power mode, |Γ| = √(P_reflected/P_forward) first, then the same two formulas apply.

Can I send both gamma and forward/reflected power?

No. Provide either gamma (reflection coefficient magnitude) or the power pair, not both.

What does it cost?

The browser tool is free and runs locally.

How do I get SWR from forward and reflected power readings?

Enter both powers in the same unit. The reflection magnitude is the square root of reflected over forward power, so 100 W forward and 4 W reflected give 0.2 and an SWR of 1.5.

What happens with a perfect match or total reflection?

Zero reflection is a perfect match: an SWR of exactly 1 and infinite return loss. A magnitude of 1 or more, or reflected power above forward power, is rejected because the SWR would be infinite.

Related tools

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/elec/swr-from-reflection

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/elec/swr-from-reflection \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"gamma":0.2,"reflection_coefficient":1}'

const res = await fetch("https://api.kit.forhosting.com/elec/swr-from-reflection", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "gamma": 0.2,
    "reflection_coefficient": 1
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/elec/swr-from-reflection",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "gamma": 0.2,
    "reflection_coefficient": 1
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/swr-from-reflection", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"gamma":0.2,"reflection_coefficient":1}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"gamma":0.2,"reflection_coefficient":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/swr-from-reflection", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "gamma": 0.2,
  "reflection_coefficient": 1
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "elec.swr_from_reflection",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Technical notes

What you send and what you get back

Choose exactly one input mode. Numeric values and numeric strings are accepted so form widgets and spreadsheet paste stay convenient. Classic checks include |Γ| equals zero point two for VSWR one point five and about fourteen decibels of return loss, and one hundred watts forward with four watts reflected for the same |Γ|. Reflection mode sends a finite magnitude under gamma, also accepted as reflection_coefficient, rho, gamma_mag, Gamma, or abs_gamma, with the domain zero inclusive through one exclusive so that VSWR stays finite. Power mode sends p_forward (aliases forward_power, pf, P_forward, P_f, p_f) strictly greater than zero and p_reflected (aliases reflected_power, pr, P_reflected, P_r, p_r) greater than or equal to zero and not greater than forward power; the engine forms |Γ| as the square root of reflected over forward, then reuses the same VSWR and return-loss formulas. Providing both modes at once, missing the power pair half, negative magnitudes, |Γ| at or above one, or reflected power exceeding forward power fails with invalid_input and a clear message; those validation failures do not consume prepaid balance. On success the response includes mode, cleaned gamma and its aliases gamma_mag and reflection_coefficient, power_reflection_coefficient and reflected_power_fraction as |Γ| squared, transmitted_power_fraction as one minus that square, swr and vswr as the same ratio, mismatch_loss_db, method swr_from_reflection, the formula string, and a short expression. When |Γ| is positive, return_loss_db is the finite −20·log10 value and return_loss_infinite is false; when |Γ| is zero, return loss is infinite in the continuous model so the JSON omits a finite dB field and sets return_loss_infinite true. Power mode also echoes cleaned p_forward and p_reflected. Pricing for successful API calls is the published base of $0.002 per item.

Where SWR and return-loss calculations show up in real work

Amateur radio and commercial RF shops tune antennas until the SWR at the feedpoint falls under a band-plan limit such as one point five to one or two to one; converting a network-analyzer |S11| magnitude into that VSWR is the daily check before keying a transmitter. Cable and connector vendors quote return loss in decibels on datasheets; acceptance tests measure reflected power on a dual-directional wattmeter, form |Γ|, and confirm RL meets the catalog figure. Filter and amplifier manufacturers record input match as both SWR and return loss so system integrators can add mismatch loss into cascade budgets without re-deriving the reflection math. Classroom labs assign the identity VSWR equals (1+|Γ|)/(1−|Γ|) so students stop confusing voltage ratios with power ratios and stop using twenty-log where ten-log belongs for power. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance. The browser tool is free for interactive use; scripted API traffic uses prepaid KIT balance at the published rate without hidden per-field surcharges.

Technical questions

What if |Γ| is 1 or reflected power equals forward power?

That is total reflection and infinite VSWR. The calculator rejects |Γ| ≥ 1 and P_r = P_f with invalid_input so results stay finite and JSON-safe.

Is VSWR the same as SWR?

In this scalar power and magnitude context, yes: the response fields swr and vswr are the same voltage standing wave ratio (1+|Γ|)/(1-|Γ|).

Read the full KIT documentation →

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