Non-Matching Impedance: Effects & Distortions

In summary, having a non-matching impedance between the transmission line and the antenna for a RF transmitter circuit can lead to inefficiency and additional effects such as distortion and instability. The amount of distortion caused by the non-matching impedance can vary and there are bibliographies available that explain this in detail. Reflection of energy from an unmatched load can also damage the output transistor and cause oscillation in the circuit. In higher power circuits, the amount of reflection is monitored and used to prevent damage.
  • #1
Ionito
14
0
Besides the obvious inefficiency (waste of energy) of a non-matching impedance between the transmission line and the antenna for a RF transmitter circuit, what are the additional effects?

Is it safe to say the reflected portion of the signal returning to the source will also cause distortion in the signal? If this is the case, what is the bibliography which I can use that explain in details the amount of distortion caused by the non-matching impedance?

Thanks.
 
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  • #2
The energy reflected from an unmatched load returns to the output transistor and heats it up. If the amount of energy is sufficient such as from an open or short on the output it can destroy the output transistor. In higher power circuits the amount of reflection is detected and used to lower the output power in order not to damage the circuit.

Apart from that, even a small amount of refection can change the output impedance and move it into an unstable region and cause the output stage to oscillate. I once designed an exciter with a good 50 ohm output match that was unconditionally stable in band, yet when attached to a power amp with a 50 ohm input impedance it oscillated. Why, because outside of band the power amp input appeared open and the small amount of out of band energy escaping from the exciter was reflected and caused it to oscillate.
 
  • #3


I can confirm that a non-matching impedance between a transmission line and an antenna can have several additional effects besides inefficiency. These effects include increased signal loss, reduced signal bandwidth, and potential damage to the transmitter components.

One of the main effects of non-matching impedance is signal loss. This occurs because when the impedance of the transmission line and the antenna do not match, a portion of the transmitted signal is reflected back towards the source instead of being radiated into the environment. This reflected signal results in a decrease in the overall signal strength and can lead to a weaker and less reliable communication link.

Another effect is a reduction in signal bandwidth. When the impedance is mismatched, the signal can become distorted and distorted signals have a wider bandwidth than the original signal. This means that more frequency channels are required to transmit the same information, leading to a decrease in efficiency and potentially causing interference with other signals.

In addition, a non-matching impedance can cause damage to the transmitter components. When a portion of the signal is reflected back towards the source, it can cause standing waves and high voltages at the point of reflection. This can damage the transmitter and potentially lead to costly repairs or replacements.

To answer your question about the amount of distortion caused by non-matching impedance, there are several resources available in the literature. One possible source is the "Handbook of RF and Microwave Power Amplifiers" by John L. B. Walker, which discusses the effects of impedance mismatch on signal distortion in detail. Another source is the "RF Circuit Design" by Chris Bowick, which also covers the topic of impedance mismatch and its effects on signal distortion. Additionally, there are several research papers and articles available online that discuss the effects of non-matching impedance on signal distortion in specific applications.
 

1. What is impedance in the context of electronics?

Impedance refers to the measure of opposition to the flow of electrical current in a circuit. It is measured in ohms and can include resistance, capacitance, and inductance.

2. How does non-matching impedance affect electronic circuits?

Non-matching impedance can cause reflections and distortions in electronic circuits. This can result in signal loss, noise, and other unwanted effects that can degrade the performance of the circuit.

3. What types of circuits are most affected by non-matching impedance?

Circuits that involve high-frequency signals, such as radio or telecommunications circuits, are most affected by non-matching impedance. This is because these circuits are more sensitive to reflections and distortions.

4. How can non-matching impedance be minimized?

To minimize non-matching impedance, it is important to match the impedance of the source and load components in a circuit. This can be achieved by using components with similar impedance values or by using impedance matching techniques, such as using transformers or baluns.

5. What are some common symptoms of non-matching impedance in a circuit?

Some common symptoms of non-matching impedance include signal loss, attenuation, ringing, distortion, and noise. These can manifest as poor signal quality, reduced range or bandwidth, and reduced overall performance of the circuit.

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