# Questions tagged [smith-chart]

A graphical chart, named after the electrical engineer Phillip H. Smith, designed to help solve problems with transmission lines and impedance matching. Consider using this tag along with the "transmission-line", "impedance", "impedance-matching", "characteristic-impedance", and/or "rf" tags, as appropriate.

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### Why is the gain of the amplifier not considered in the frequency calculations? (Sedra and Smith 6th edition, Example 1.5)

In example 1.5 in Sedra & Smith 6th edition, the author's answer for item b) is 1 Mrad/s. To get this answer, the author considers the amplifier as a passive LP network and uses the time constant ...
1 vote
125 views

### Intuitive explanation of shorted stub behaviour

Can someone please give me an intuitive explanation of shorted stub behaviour? NOTE: This is not a duplicate of Intuitive explanation of open stub behaviour which has been narrowed to focus on open ...
117 views

### RF - Chip Antenna Matching

I've gotten a little bit into the weeds with RF and am attempting to tune a chip antenna for GNSS. I had test PCBs made according to the chip antennas integration guide/datasheet and have attempted ...
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### NanoVNA software not showing impedance

I am trying to use a NanoVNA to see the impedance on a Smith chart. But in the software I don't see any impedance value. Does anyone know how to get it to show up? I've tried the software on both ...
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### NanoVNA: Smith chart units

I am trying to understand the units NanoVNA uses for its smith chart. After calibration, for an "open", I see this: The units are: $1000m-j71.4m$ , where I suppose 'm' stands for mili, ...
1 vote
47 views

### Matching network for two-port with internally matched inputs/outputs

Background I had a lab in school where we were given an LNA with inputs/outputs matched to 50Ω, that will be connected to a 50Ω system: The task was to design the input and output matching networks: ...
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### Impedance matching on VNA does not match calculation (with detail steps included)

I have a PCB with a pi-matching network, and I want to calculate the component values for the matching network. I use LiteVNA and a WE-MCA Multilayer Chip Antenna for this project. Here is the basic ...
259 views

### Smith Chart is giving me an answer I didn't expect - Am I using it right?

I'm trying to track down a VSWR issue with a RF power amplifier (25 W, 150 MHz). The radio we're using to drive it has a VSWR alarm, which triggers during transmit. Older manufacture runs of the PA ...
605 views

### Is my VNA broken or miscalibrated, or are these weird results normal?

My company got a new vector network analyzer recently and I'm using it to try to learn more about microwave circuits, especially the resonant cavities that we use in our measurement systems. I've seen ...
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1 vote
214 views

### Why are stability circles circles on a Smith chart?

I am new to basic concepts in amplifier stability, so the question might seem obvious, sorry if it is the case. The amplifier stability translates into the equations for the reflection coefficients ...
617 views

### Calibrating a VNA

I am using the Siglent SSA3032A-R spectrum analyser which has a Vector Network Analyser (VNA). Before measuring the impedance of an antenna under test so that I can match this antenna, I have to ...
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1 vote
912 views

### How to interpret S parameters on a Smith chart

I am trying to understand S parameters on RF transistors. I chose the BFP840ESDH6327XTSA1 as my RF transistor, to operate it at 10 mA, 12GHz. The design should be optimal for simultaneously matching ...
2k views

### Tuning an antenna using a NanoVNA, Smith chart and impedance readings

I am new to antenna design and teaching myself how to optimize antennas using a VNA. I have created a monopole antenna on a PCB (i.e. a single length of track.) The antenna can be fed via a PI network ...
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240 views

### Transmission line and input impedance - Smith chart

According to "Smith Chart Supplement - Corrected Jan 2012" when f.e. calculating input impedance (from load impedance) it is necessary to use WLTG (wave lengths towards generator). WLTG ...
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### WiFi (2,4G) Antenna Isolation. Why 3 capcitors version does not work

I need to isolate the antenna from the WiFi transmitter. There are some solutions on the market but none suitable for my application. So I have started some experiments. 2x PCBs creating DIY ...
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1 vote
146 views

### Relationship between Smith chart and frequency response graph?

What is the relationship, if any, between a Smith Chart and a frequency response (magnitude and phase) graph? If there is any relationship, what additional constraints or information (topology, port ...
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1 vote
129 views

### Double Stub Matching Impedance

I'm trying to understand the double stub matching impedance using Smith Chart. Here is the diagram for the double stub impedance: The impedance on the right has to appear purely resistive. So ...
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### which antennas is better for 433 Mhz 30dbi LoRa module [closed]

I am searching a antenna for LoRa module. my first priority is distance. which is more long range, it is better for me. There are 3, 433Mhz 3dBi antennas. Can you help me which is best and why? if you ...
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359 views

### RF Matching Problem

I am having some fundamental issues trying to create an impedance matching network for an 868MHz antenna, I have a PI network between the antenna's connector and the antenna feed point I have measured ...
1 vote
397 views

### Meaning of S11 performing a clockwise arc circle about the smith chart origin?

I've tested a device with my VNA. It displays S11 in a Smith chart as a plot x(w) + iy(w) (w the frequency). Curiously, as w increases from 50KHz to 600MHz, the plot is an almost perfect 1/3 circle ...
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1 vote
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### Smith chart tutorial question

I am looking at a Smith Chart tutorial on the antenna-theory.com website. Unfortunately, I'm confused by one of the examples given...I don't get the same answer, so it's safe to say I'm doing ...
1 vote
1k views

### RLC equivalent model and Impedance Smith Chart

I have done some impedance measurements on an unknown 1 port device. I have measured its impedance at different frequencies (from 10 MHz to 600 MHz) and I have seen it on the normalized (on 50 Ohm) ...
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### How is a transmission line with a different characterisitc impedance shown on the smith chart?

A transmission line can be shown on the smith chart as a clockwise rotation, each 180 degrees corresponding to a quarter wavelength. But this is when the characteristic impedance (Z0) of the ...
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### Where would a pure inductive or capacitive load be placed on a Smith chart, assuming the TL impedance is real?

I'm a new HAM operator, and just started learning about the amazing tool that is Smith charts; and it got me wondering what the edge case of a pure inductive or capacitive load would be? Since the ...
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### Smith Chart for Dummies

I am not just an electrical engineering noobie, I'm an electrical engineering dummy. (No, you can't use me for testing your newly designed electric chair.) What I need is a simple, direct answer, to ...
143 views

### Can a Unilateral Amplifier be Unstable?

When designing microwave amplifiers, stability is an important factor to consider. Stability is usually measured with the K factor. In a unilateral network, S_12 = 0, and this makes the K factor ...
• 302
1 vote
3k views

### How to interpret s parameters including S21 on Smith chart on VNA display

I'm trying to become re-acquainted with S parameters, VNA, and transmission lines for some projects at work. I'm using Agilent, Advanced Design Simulator, to practice on the computer and to get the ...
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1 vote
634 views

### Smith chart of λ/4 Transmission Line

I came across the following slide on power combiner circuit and I have questions about it. Why traverse across the upper half circle ? Why "ZT-line is the geometric mean of Zout and Zin." ?
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### Interpreting scattering parameters on a Smith chart.

I'm trying to become reacquainted with microwave circuits and how to analyze them, especially with a VNA. Just to get some practice I'm using Keysite ADS simulator. To get the feel of it I used the ...
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1 vote
310 views

### S-Parameters, Smith Chart, and Reflection Coefficients

Please help guide my ignorance on this topic. From what I understand, S-parameters are reflection coefficients generalized to N-port systems (via an S matrix), but for a 1-port system, these converge ...
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### Why real part of load change as we look through transmission line?

As we move from an imaginary load towards generator through a transmission line, we can see that real and imaginary part of that impedance changes. In fact, an ideal transmission line is comprised of ...
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### Self-resonance frequency of chip inductors

I am studying chip inductors and here's one of the frequency responses: There is more than one resonance frequency for a single inductor. When we say inductor resonance frequency, it usually means ...
974 views

### Find impedance matching in a quarter wave transformer

I would like to know if there is a way you can find the impedance that has to be set between the load $Z_L$ when it is complex and the characteristic impedance $Z_0$ to have impedance matching ...
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### Mark specific frequencies in smithchart

I have a smithchart created by MATLAB using the following code (the S22 is a 801x1 vector obtained from a file): n = 801; fStart = 45*10^6; fStop = 15*10^9; f = linspace(fStart,fStop,n); figure() ...
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1 vote
773 views

### How to get complex reflection coefficients?

If I terminate a line with an open circuit, I'll get reflections of any incoming signals with the same phase (a reflection coefficient of 1). If I terminate the line with a short circuit, I'll get ...
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### How do I convert S-parameters for impedance matching?

How do I derive the Z-parameters to calculate a matching network for a device? I'm not sure what terms to even search for as I get all sorts of information I am not familiar with. My task is to ...
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### Finding unknown load using a smith chart

I am asked to find the impedance of an unknown load. The precise formulation is provided below: The following two step procedure was used to measure the value of an unknown load $Z_{L}$. The ...
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1 vote
1k views

### Stub matching at smith chart

I'd like to clarify some concepts about microwaves that I still can't understand it at all. I'm reading Pozar's Microwave Engineering, more specifically stub adaptation in the Smith Chart. The circuit ...
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1 vote
956 views

### Impedance matching a capacitive source

I am trying to work out how to match a current source coupled with a capacitor to a 50 Ω load for maximum power transfer. Specifically, I have a 6 pF PIN photodiode which driven by a 2.5 GHz optical ...
465 views

### Smith chart plot from simulation is opposite from experiment?

I did a simulation of an antenna and replicated the antenna in an experiment however the simulation is coming out to be roughly the opposite. From the experiment I was expecting this plot to spiral ...
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### How to plot Smith chart

I need to plot Smith chart, having frequency, VSWR, reflection coefficient and phase. I'm aware there's smithchart command in matlab and as an argument I should use ...
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579 views

### What options do I have to measure directly impedance change (ohm) or deduce it indirectly from S-Parameters?

Basically I want to measure how impedance (Ohm) relative to Z0 (50 Ohm) waveguide is changing by varying a parameter. I currently measure the reflection coefficient S11 in a 1-port setup. Our VNA can ...
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### Drawing Smith Chart from Network Analyzer file

I have a file as a .dat format taking from network analyzer. I want to plot Smith chart graph. The file has 3 columns which are frequency, S11(linear value), S11 (ang value) respectively. How can draw ...
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2k views

### Smith Chart Conjugate Matching

In an example in Pozar's Microwave Engineering, a conjugate matching circuit for maximum gain is designed using Smith chart. In the shown Smith chart, the matching circuit for input is designed. We ...
544 views

### S11 all on the outside of the Smith Chart

How should someone conclude what's going on on a TX line that has a Smith Chart that goes around and around the outside? I've reworked a board and expected to see a curve pass close to (0,0), but what ...
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### Balun/matching network question

I am having problem to verify what an app note (AN068) explains to calculate Balun values. I would appreciate if someone could tell me what/where am I doing wrong? The summary of the RF part: Blue ...
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### Use of Smith charts

There are Smith charts with impedance and admittance coordinates and Smith charts with only impedance coordinates. I believe I learned how to use the first one. Is there any sense in studying how to ...
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I want to match RF power amp to aerial. There is no 50 ohm or 75 ohm transmission line inbetween. So, I consider my aim to be matching certain load-reflection coefficient (Γload) to a short circuit (...
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### What application do you use for plots?

What application do you use for creating plots? Years ago, I was using gnuplot and then matplotlib (which is just Python library). But none of those were perfect. For example, I was unable to create ...
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