---
title: "V antenna construction and working"
subject: "Propagation and Antenna"
chapter: 3
key: "semester_6/propagation_and_antenna:v-antenna"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/v-antenna
site: BCT Engineering
---

# V antenna construction and working

Propagation and Antenna · Chapter 3: Antenna Classification

- Asked in: 2080 Asoj, 6 marks; 2077 Chaitra, 6 marks; 2076 Baisakh, 4 marks; 2070 Magh, 7 marks (asked 4 times)
- Video: [V Antenna (Basics, Structure, Designing, Working, Radiation, Applications, Pros & Cons) Explained](https://www.youtube.com/watch?v=FhirfLrqTGE) — Engineering Funda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/v-antenna
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-3

## Question

Explain the construction, working principle and characteristics of V-antenna with necessary diagrams (structure and radiation pattern).

## Short answer

A V-antenna has two long wires meeting at an apex, fed there by a balanced line. Each leg radiates a conical lobe at angle θm, and choosing the apex angle as 2θm makes the lobes add along the bisector. The resonant type is bidirectional; the terminated type is unidirectional with gain 10–15 dBi.

## Answer

A **V-antenna** is a travelling/standing-wave wire antenna made of two long straight wires (legs) arranged in the shape of a "V", fed at the apex by a balanced line. It is a simple directive HF antenna for point-to-point links.

#### Construction

```text
 Structure (top view)           Non-resonant type
                                    R/2
         leg 1 (l = several λ) ____/\/\_
        /                         |
 feeder<  apex angle 2θₘ  ===> beam  (bisector)
        \                         |
         leg 2 ________________/\/\_
                                    R/2
```

- Two straight wires of length l (2λ to 8λ), horizontal, on poles above ground.
- Apex angle = **2θₘ**, where θₘ is the angle of the main lobe of one long wire: cosθₘ ≈ 1 − 0.371λ/l.
- Fed at the apex by a 600 Ω open-wire balanced line, 180° out of phase.
- Far ends left open (resonant V) or terminated with resistors (non-resonant V).

#### Working principle

1. Each long wire radiates a conical main lobe at angle θₘ to the wire.
2. Since the legs are fed in antiphase and are mirror images, choosing the apex angle equal to 2θₘ makes one main lobe of each leg lie along the **bisector**; there they add in phase.
3. Lobes in other directions are out of phase and partly cancel, giving a directive beam.
4. In the **resonant (unterminated)** V, the wave reflects from the open ends, forming standing waves; radiation goes both ways along the bisector (bidirectional).
5. In the **non-resonant (terminated)** V, matched resistors absorb the forward wave, so only a travelling wave exists and the beam is unidirectional.

#### Radiation pattern

```text
 Resonant V (bidirectional)   Terminated V (unidirectional)
    <===  ◁V▷  ===>              ◁V  ====>
   back lobe = front lobe        weak back lobe
```

#### Characteristics

| Property | Value |
|---|---|
| Frequency | HF (3–30 MHz) |
| Gain | ≈ 2× a single long wire of same length; ~ 10–15 dBi for long legs |
| Polarization | Horizontal (in plane of V) |
| Bandwidth | Wide, especially terminated type |
| Input impedance | ~ 500–800 Ω |

**Advantages**: simple, cheap, needs only 3 poles, wide band. **Disadvantages**: large area, side lobes, fixed beam, power loss in terminating resistors. **Applications**: HF point-to-point communication, amateur radio.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The apex angle of a V-antenna is chosen as
   A. 2 theta_m, where theta_m is the main-lobe angle of one long wire
   B. 90° always
   C. theta_m / 2
   D. 180°
   Answer: A. This puts one main lobe of each leg along the bisector. (Key point: Apex angle)

2. The two legs of the V are fed
   A. in phase
   B. in antiphase (180° out of phase) at the apex
   C. with 90° difference at the far ends
   D. through a coaxial cable only at the ends
   Answer: B. Antiphase feed of mirror-image legs makes the lobes add in phase along the bisector. (Key point: Feeding)

3. What happens in the terminated (non-resonant) V compared with the resonant one?
   A. Standing waves form and the beam is bidirectional
   B. Radiation stops
   C. Only a travelling wave exists and the beam is unidirectional
   D. Gain falls to zero
   Answer: C. Terminating resistors absorb the forward wave; the open-ended V reflects it and radiates both ways. (Key point: Resonant versus terminated)

4. A disadvantage of the V-antenna listed is
   A. very narrow bandwidth
   B. needs ionosphere-free operation
   C. vertical polarization only
   D. large area, side lobes, fixed beam, and power loss in terminating resistors
   Answer: D. Despite simplicity and wide bandwidth, it needs space and wastes power in terminations. (Key point: Drawback)

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