Bent Dipoles headerBent Dipole Animation

Discussion about Laterally bent V-Dipoles.

Navigation Menu

Center-fed Bent-Dipoles
 Horizontal Lateral
Vertical
OCF
EFHW
Slow-Wave
Other Topics

Home 		For long-wire dipole antennas, space may be a problem in a yard or attic.  Bending into a V-shape is one of the most used possibilities to get on the air with good results.

Compared to the V-antenna or inverted-V, the effects on antenna characteristics of a laterally bent dipole are simpler because the distance to the ground is constant.

Lateral VWhat Happens If...
A Dipole is Bent Sideways
into a "V"?

In the following study, the standard antenna computer model is configured to define any angle as small as 30° between the arms of a dipole bent sideways. The model then optimizes the length of wire that gives the lowest SWR and reactance (R-in) when bent to that angle. Angle data is taken in 30° steps. 

4NEC2 Antenna Model: Here

Figure 1 below sumarizes Gain, SWR and Length data the results from computer modeling.

Lateral Equal-Arm V-dipole study
Figure 1
A graphic indication of the V-bend is shown in red.


Note that along the top of the graph, there is representation in red of the V-angle of the dipole as looking down from above. 

The first observation is that as a dipole is bent into a V-form, the Gain dBi  goes down (blue line).  Curiously, as the V-angle becomes less than 60°, the gain rises... unfortunately so does the SWR.
This also happens when the V-arms are oriented vertically.

As the V-angle gets smaller, the impedance goes down from the normal 68.9 ohms and passes through 50 ohms to give a match with coaxial cable.  Looking at the SWR curve (red line) this 50 ohm point occurs with the V-angle around 120°.

The length of wire (green line) needed to maintain resonance increases as the amount of bend increases. A practical bend maximum would be at around 80°-90° V-angle and 2% longer.  Antenna performance falls significantly at angles narrower than this.

Does the V shape increase signal?

No.

The far field radiation is always basically the same as a dipole no matter the angle of the V.
Contrary to popular myth about V-beams, antenna modeling shows that no discernable front-to-back ratio develops at any degree of lateral V-bend in half-wave or full-wave dipoles.  Increased signal only applies for 3-halfwave Gull-wing antennas, multi-wavelength V-beams or full rhombic Diamonds.

Figure 4 below shows the the far field radiation pattern and 3D view of a half-wave lateral V-dipole optimized for coaxial cable feed.

3D Lateral V-dipole composite
Figure 4
Far field radiation; Polar graph and 3D flyover view
  • Lateral V-Angle: 125.1°
  • Impedance: 51.3 ohms, j=0.26, SWR: 1.03
  • Gain: 6.87 dBi, Side Null: -0.4 dBi
  • Maximum Radiation Angle: 60°, -3dB Beamwidth: 30°
  • Length increase: 1.07%
Clearly the radiation is symetrical front-to-back... no increase in signal relative to the V-form. Gain is 0.45 dBi less than a straight dopole. The only other performance difference is that the normal side null of -2.7 dBi for signal rejection is essentially gone.

Dick Reid, KK4OBI at QSL.net