# How do you find the input impedance of a dipole antenna?

## How do you find the input impedance of a dipole antenna?

Before examining the fields radiated by a dipole antenna, consider the input impedance of a dipole as a function of its length, plotted in Figure 2 below. Note that the input impedance is specified as Z=R + jX, where R is the resistance and X is the reactance.

## How do you measure input impedance on an amp?

For the input, the voltage is measured across the input terminals and the current measured by inserting the meter in series with the signal generator. Use a fixed frequency say 1kHz and set the generator level to around 20 mV RMS. For example, if you read 20mV RMS and 10uA for current, then the impedance is 2k.

How do you measure dipole impedance?

The dipole feed impedance is determined by the ratio of the voltage and the current at the feed point – it is simply calculated using Ohm’s Law. Although a dipole can be fed at any point, it is normal for the feed point to be at the middle of the dipole. This is the current maximum and voltage minimum point.

What is the input impedance of a dipole antenna?

Design of Dipole Antenna Real Input impedance is < 68Ω.

### What is the impedance of a dipole?

The values of the real and imaginary input impedance are well known for a dipole antenna. The impedance varies vs. frequency (wavelength compared to the antenna physical length). The half wavelength resonant frequency real part of the impedance should be 73 ohms, and the imaginary part should be 42.5 ohms.

### What is the feed point impedance of a dipole?

Feeding a dipole antenna. Ideally, a half-wave dipole should be fed using a balanced transmission line matching its typical 65–70 Ω input impedance.

What is the input impedance dipole antenna?

The dipole antenna is one of the simplest structures in electromagnetic compatibility problems. The values of the real and imaginary input impedance are well known for a dipole antenna. The half wavelength resonant frequency real part of the impedance should be 73 ohms, and the imaginary part should be 42.5 ohms.

How is the impedance of a dipole determined?

Dipoles are anti-resonant at lengths slightly longer or shorter (which?) than an even number of half-wavelengths As frequency increases, a dipole’s impedance converges to a finite value or diverges to infinity (which?) If a linear wire antenna is resonant, then its feedpoint impedance is real everywhere along its length

#### How is the impedance of an ohm meter measured?

Connecting an Ohm meter across the input or output of an amplifier only indicates the DC resistance. It is quite possible however to measure input and output impedance at any frequency using a signal generator, an oscilloscope (or AC voltmeter) and a decade resistance box or a variable resistor. Fig 7.3.1 Measuring Input Impedance

#### How are impedances set in a voltage amplifier?

Two criteria are mostly used in order to set the impedances : the transferred power or the efficiency. Generally, a high efficiency is preferred for voltage amplifiers. It can be achieved by setting the input impedance of the stage n+1 much higher than the output impedance of the stage n.

How is an oscilloscope used to measure impedance?

The set up for measuring input impedance is illustrated in Fig. 7.3.1. A variable resistor or a decade resistance box is connected between the signal generator and the amplifier input and its resistance is set to zero Ohms. An oscilloscope or AC voltmeter is connected across the amplifier load (e.g. loudspeaker).