Contents
What is the input impedance of a quarter wavelength monopole antenna?
As a result, the propagation characteristic of a quarter-wave antenna is similar to a dipole, above the ground plane. But there is no propagation under the ground plane (Figure 5.23). The impedance of the quarter-wave antenna is 36 Ohms, which is half the impedance of a dipole antenna.
What is the length of quarter-wave monopole?
At VHF band ranging from 30 MHz to 300 MHz, a quarter-wave monopole can be 2.5 m (approximately 8 ft) long.
What is the length of a common monopole antenna?
Therefore the length of the antenna is determined by the wavelength of the radio waves it is used with. The most common form is the quarter-wave monopole, in which the antenna is approximately one quarter of the wavelength of the radio waves.
What is the length of quarter wave monopole antenna for 2.4 Ghz?
about 23 mm
The quarter wavelength printed monopole antenna can be tuned simply by slight changes in length of antenna PCB trace. The length of the antenna trace which is presented in this paper for 2.4GHz is about 23 mm with 1.5 mm width using FR4 PCB.
How is monopole antenna length calculated?
Use the formula: Length (feet) = 234 / Frequency(MHz). For example, if you intend to operate on 27.5 Megahertz: (in the CB-Radio Citizens Band) 234 / 27.5 = 8.5 feet (rounded to nearest 0.1 foot). Your 27.5 MHz quarter wavelength wire monopole CB antenna needs to be 8.5 feet in length.
How reciprocity theorem is applicable for antenna?
The reciprocity theorem is fundamental to antenna theory. The ratio of transmitted power from the transmitting antenna to the received power by the receiving antenna will not change even when the modes of the antennas are interchanged. The whole system is considered isotropic and linear.
How can I calculate the 1 / 2-wave monopole monopole impedance?
To fully calculate the self impedance with this method requires a 40 step or so derivation which I will not execute here. But the interesting result is that for a 1/2 wave dipole (recall that this is the realized configuration of a 90 degree drop of the radials) the real part of the self impedance is:
What is the perfect angle for a quarter wave monopole?
A quarter wave monopole mounted against a perfect ground will have an impedance of around 36Ω but by bending the radials down at an angle of 45°, we increase this to around 50Ω whilst at the same time lowering the radiation angle more towards the horizon. (42° is the theoretical perfect angle for 50Ω feed, but who’s measuring!)
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).
When is the impedance of a ground plane antenna ignored?
Once a ground plane antenna is 0.5 wavelengths or so above ground, there is no significant effect from the ground on the impedance of the antenna so it can be ignored. A close approximation of the real part of the feedpoint impedance in ohms of a 1/4 wave ground plane antenna in free space is given by: