# What is S11 and S21?

## What is S11 and S21?

The physical meaning of S11 is the input reflection coefficient with the output of the network terminated by a matched load (a2 = 0). S21 is the forward transmission (from port 1 to port 2), S12 the reverse transmission (from port 2 to port 1) and S22 the output reflection coefficient.

## What is S21 measurement?

An important performance measure of a 2-port network is S21. An S-parameter indicates the amount of power leaving one port of the network, given power entering another (or the same) port of the network. In the case of S21, the suffix “21” denotes the power leaving port 2, with power delivered to port 1.

**What are Y and Z-parameters?**

Y or admittance parameters tie voltage to current, in a way similar to Z-parameters. The difference is that here the input variables are voltages and output ones are currents.

### How do you calculate impedance parameters?

Z-parameters are also known as “open-circuit impedance parameters”, as they are calculated under open-circuit conditions. That is to say that Ix=0, where x=1, 2 refers to the input and output currents flowing through the ports of a two port network.

### What is S11 formula?

S11 = b1/a1 for a2= 0 or Zl=Zo. This is an input reflection coefficient. S11 is equal to the ratio of a reflected wave and an incident wave with Zl=Zo. Thus, S11 can be plotted on a Smith chart and the input impedance of the two-port device can be found immediately.

**What is S11 in VNA?**

S11 represents how much power is reflected from the antenna, and hence is known as the reflection coefficient (sometimes written as gamma: or return loss. The remainder of the power was “accepted by” or deliverd to the antenna. This accepted power is either radiated or absorbed as losses within the antenna.

#### What is RF S11?

S11 represents how much power is reflected from the antenna, and hence is known as the reflection coefficient (sometimes written as gamma: or return loss. If S11=0 dB, then all the power is reflected from the antenna and nothing is radiated.

#### What are S-parameters in RF?

S-parameter file represents full combination of the reflection and transmission parameters in a multiport network with frequency component. It gives an idea of how the DUT behaves with a signal in both forward and reverse direction. Let’s consider a two port network.

**Why do we use Z-parameters?**

The Z-parameters are also known as the open circuit parameters because they are measured or calculated by applying current to one port and determining the resulting voltages at all the ports while the undriven ports are terminated into open circuits.

## What are two port parameters?

Following are the types of two port network parameters.

- Z parameters.
- Y parameters.
- T parameters.
- T’ parameters.
- h-parameters.
- g-parameters.

## What are open-circuit impedance parameters?

Z-parameters are also known as open-circuit impedance parameters as they are calculated under open circuit conditions. i.e., Ix=0, where x=1,2 refer to input and output currents flowing through the ports (of a two-port network in this case) respectively.

**What are S parameters in RF?**

### What does high input impedance mean?

In electronics, high impedance means that a point in a circuit (a node) allows a relatively small amount of current through, per unit of applied voltage at that point. High impedance inputs are preferred on measuring instruments such as voltmeters or oscilloscopes .

### How do you measure output impedance?

To find the output impedance the output voltage is measured first with no load resistor, then with a fixed load (purely resistive). First, the load resistor RL is removed and output voltage (V) measured and recorded. Then RL is placed back in circuit and the output voltage under load (V L).

**Why is high input impedance good?**

To Prevent Loading. Another reason op amps need high input impedance is because the loading effect. If op amps had very low input impedance, it would draw significant amounts of current into it. Thus, it would be a large load on the circuit.

#### Why input impedance of op amp is high?

Op amps have high input impedance and low output impedance because of the concept of a voltage divider , which is how voltage is divided in a circuit depending on the amount of impedance present in given parts of a circuit. Op amps are voltage gain devices.