Tools

PROCOM's products make use of an extensive technical knowledge

How to describe how good an antenna is?

How good is an antenna?

How to describe how good an antenna is?

How good is an antenna?

Four "figures" describe how good an antenna is compared to the required performance:

 

- SWR = Standing wave ratio

- D = Directivity

- G = Gain

- BW = Bandwidth.

 

SWR

 

SWR

If the impedance of the antenna is different from the impedance of the cable, the antenna will reflect back some of the induced energy through the feeder cable to the transmitter, which naturally is undesirable.

 

Normally, the impedance of the cable is 50 Ω. If Ra indicates the impedance of the antenna, the standing wave ratio is defined as:

 

SWR = Ra/50 Ω (if Ra is more than 50 Ω)

SWR = 50/Ra Ω (if Ra is less than 50 Ω)

 

 

Examples

If Ra = 50 Ω is SWR = 1.0

If Ra = 100 Ω is SWR = 2.0

If Ra = 25 Ω is SWR = 2.0

 

Consequently, it is of importance that the SWR is as close to 1.0 as possible thus obtaining the highest power being transmitted from the cable to the antenna.

 

Directivity D

 

Directivity D

The directivity D is an indication of the capability of the antenna to conduct the radiated power "to a certain site".

 

Normally, omnidirectional or directional antennas are mentioned.

 

 

Omnidirectional

An omnidirectional antenna with high directivity has a radiation being similar to a pancake.

 

omnidirectional-e-plane medium omnidirectional-h-plane medium

Omnidirectional E-Plane

Omnidirectional H-Plane

 

 

omnidirectional medium

 

Omnidirectional

 

Directional

 

Directional

A directional antenna with high directivity has a radiation being similar to the cone of light from a projector.

 

directional-e-plane medium directional-h-plane medium

Directional E-Plane

Directional H-Plane

 

 

Gain G

The gain of an antenna is defined as G = η x D, where η indicates the efficiency of the antenna.

 

Consequently, in the gain value possible loss in the antenna is comprised.

 

The η-figure is always less than the directivity.For most antenna types the own loss is so low that G = D can be considered.

 

 

Bandwidth

The bandwidth of the antenna is the frequency range, in which it operates properly, i.e. both gain and SWR are within the more specified limits.

 

See what we are up to

Connect with us online, to get latest news

and see where the next exhibition is going to take place

Exhibition Calendar

We are Social

APN Logo Blue