RF Matching Network Calculator

Calculator Inputs

Center Frequency (MHz)

Source Resistance Rs (Ω)

Load Resistance RL (Ω)

Source Power (W)

Displayed Topology

Sweep Span (±%)

Sweep Points

Use real positive resistances. The tool compares ideal low-pass and high-pass L-section matches and graphs return loss across the chosen sweep.

Example Data Table

Case	Frequency	Rs	RL	Topology	Series Element	Shunt Element	Loaded Q
Example A	100 MHz	50 Ω	100 Ω	Low-pass	79.5775 nH inductor	15.9155 pF capacitor	1.0000
Example B	100 MHz	50 Ω	100 Ω	High-pass	31.8310 pF capacitor	159.1549 nH inductor	1.0000
Example C	144 MHz	75 Ω	25 Ω	Low-pass	39.0762 nH inductor	20.8407 pF capacitor	1.4142

Formula Used

Let R_H be the higher resistance and R_L be the lower resistance.

Minimum loaded Q: Q = √(R_H / R_L − 1)
Series reactance magnitude: |X_S| = Q × R_L
Shunt reactance magnitude: |X_P| = R_H / Q
Inductor conversion: L = X / (2πf)
Capacitor conversion: C = 1 / (2πfX)
Approximate bandwidth: BW ≈ f₀ / Q
Reflection coefficient: Γ = (Z_in − R_S) / (Z_in + R_S)
Return loss: RL = −20 log₁₀ |Γ|
VSWR: (1 + |Γ|) / (1 − |Γ|)

Low-pass matches use an inductor in series and a capacitor in shunt. High-pass matches use a capacitor in series and an inductor in shunt, with element placement changing when the source resistance exceeds the load resistance.

How to Use This Calculator

Enter the design frequency in MHz.
Enter the source resistance and load resistance in ohms.
Set the available source power for quick voltage and current estimates.
Choose the displayed topology, or keep the automatic view.
Adjust sweep span and points to control graph resolution.
Press the calculate button to show the result above the form.
Review the compared topologies, bandwidth estimate, and return loss sweep.
Export the current result to CSV or PDF when needed.

Frequently Asked Questions

1. What kind of impedances does this calculator support?

It is built for real positive source and load resistances. It does not directly solve complex terminal impedances, transmission-line sections, or multi-element broadband matching networks.

2. Why are there low-pass and high-pass solutions?

An L-network can usually be realized with two different element types. One form behaves as a low-pass section, and the other behaves as a high-pass section, while both can create the same center-frequency resistance transformation.

3. What does loaded Q mean here?

Loaded Q is the minimum network quality factor required for the L-match. Higher Q means narrower useful bandwidth and steeper reactance behavior around the design frequency.

4. Is the bandwidth exact?

No. The shown bandwidth is a practical estimate based on f0 divided by Q. Real circuits with parasitics, finite component Q, and complex loads will shift the true response.

5. Why can return loss become very high at center frequency?

With ideal components and purely resistive terminals, the designed network transforms the load exactly at the chosen frequency. That drives reflection toward zero and makes return loss very large.

6. When should I prefer the low-pass option?

Low-pass matching is often chosen when harmonic attenuation is helpful and a series inductor fits the implementation. Final selection still depends on layout, parasitics, and available parts.

7. When should I prefer the high-pass option?

High-pass matching can be useful when DC blocking is needed in the series path or when inductive shunt placement is easier. It may also behave better with some stray capacitances.

8. Can I use the values directly in hardware?

Use them as a solid starting point. Real components, pad capacitance, package inductance, trace length, and measured load variation should still be checked with simulation and bench tuning.