Yagi-Uda antenna

Yagi-Uda antenna

Yagi-Uda antenna is the most regularly utilized kind of antenna for TV reception, many other domestic and commercial applications. It is an electromagnetic device that collects radio waves.The Yagi-Uda antenna derived its name from its two Japanese inventors Hidetsugu Yagi and Shintaro Uda.

It is mostly known for simple utilization and better execution. Itis highly appreciated for its high gain typically greater than 10 db and directivity. The gain and directivity of the Yagi antenna enables the receiving capacity by improving better degrees of noise ratio to be accomplished, and by reducing interference levels by just getting signals from a provided direction. The frequency of this antenna extends around 30 MHz to 3GHz which is of the VHF and UHF band range and covers about 40 to 60 Km.

Fig: 1 Yagi-Uda antenna

Construction of Yagi-Uda Antenna:

A Yagi-Uda antenna was seen over pretty much every house during the past decades. The parasitic components and the dipole together form a Yagi-Uda antenna. The Yagi antenna design has a dipole as the principle transmitting driven element to which power is applied from a feeder.

The ‘parasitic' components draw power from the driven element and re-radiate it. The stage is in such a way, that it influences the properties of the entire Yagi antenna on the whole, making power be focussed one specific direction and expelling out other directions.

The amplitude and phase of the current that is induced in the parasitic components is decided on their length and the spacing among them and the dipole or driven component. In this event if a component is longer than the resonant length, it gets inductive and shorter, it gets capacitive.

Fig: 2 Components of Yagi-Uda Antenna

There are three kinds of component in a Yagi antenna:

   1. Driven element:

 It is the Yagi antenna component to which power is applied and is a half wave dipole.

   2. Reflector:

 The reflector component is made to be about 5% longer than the driven element and it will have one reflector. It is behind the driven component.

Further reflectors behind the first make no difference to the reception apparatus performance. The reflecting plate gives a slight improvement in execution.

   3.  Director:

These are made to be shorter than the driven element. There might be none, one or more directors in the Yagi reception apparatus. These are put before the driven element, toward the maximum sensitivity. Normally every director will include around 1 dB of gain in the forward direction.

Designing:

For designing this antenna for the given frequency, the following design specifications are should be followed.

Fig: 3 Designing specifications 

Radiation Pattern:

The directional pattern of the Yagi-Uda antenna is highly directive and the radiation patterns are:

Fig: 4 Radiation pattern

The minor lobes are suppressed and the directivity of the major lobe is increased by the addition of directors to the antenna.

The antenna exhibits a directional pattern consisting of a main forward lobe and a number of spurious side lobes. The main one of these is the reverse lobe caused by radiation in the director of the reflector. The antenna can be optimised to either reduce or produce the maximum level of forward gain.

Advantages:

The Yagi antenna offers numerous advantages over different sorts of antenna in numerous applications.

• High gain is achieved.
• High directivity is achieved.
• Ease of handling and maintenance.
• Less amount of power is wasted.
• Broader coverage of frequencies.

Disadvantages:

The negative factors that needed to be taken care while constructions of Yagi antenna are:

•  Long for high gain
•  Prone to noise.
• Prone to atmospheric effects.