In the previous chapter, we have studied V-antenna. Its operating frequency is limited. This can be modified by using another antenna, which is a non-resonant antenna or a travelling wave antenna. A travelling wave antenna produces no standing wave, as discussed previously.
The frequency range of operation of an inverted vee antenna (or V-antenna) is around 3 to 30 MHz. This antenna works in high frequency range.
A travelling wave antenna, used in high-frequency band is an inverted V-antenna. This inverted V-antenna is easily installed on a non-conducting mast.
Take a look at the following image. It shows an inverted V-antenna mounted on a roof top.
The maximum radiation for an inverted V-antenna is at its center. It is similar to a halfwave dipole antenna. The antenna is placed in the shape of an inverted V, with its two transmission lines or legs bent towards the ground making 120° or 90° angle between them. The center of the antenna should not be higher than λ/4.
The angle made by one of the legs with the axis of the antenna, is known as the tilt angle and is denoted by θ.
The radiation pattern of inverted V-antenna is uni-directional pattern, as no standing waves are formed here. It can be clearly understood by the radiation pattern shown below.
The figure illustrates the radiation pattern of an inverted V-antenna. Primary radiated field is shown along with the fields when the tilt angles are 120˚ and 90˚ in the figure given above. The gain and directivity are improved by having an array of antennas.
The following are the advantages of inverted V-antenna −
Occupies less horizontal place
No standing waves are formed
The following are the disadvantages of inverted V-antenna −
It has considerable undesired minor lobes
Minor lobes create horizontally polarized waves
The following are the applications of inverted V-antenna −
Used in tuned circuit applications
Used in radio communications
Used in commercial applications
After the V-antenna and inverted V-antenna, another important long wire antenna is the Rhombic antenna. It is a combination of two V-antennas. This is discussed in the next chapter.