Antenna Fundamentals -1 (Radiation Pattern)

Antenna Fundamentals:

When I started looking into 3GPP and many other online material which is available on 5G, most of the documents talk about antenna fundamentals. I had to go back to my university days and recollect the fundamentals of Antenna and Wave Propagation. I am trying to collate all the information here.

Antenna, in simple a piece of wire/rod that is used to transmit/receive signals.

Here signal can be any thing, could be AM/FM/micro waves/mmWaves ..etc

Some of the Fundamental Parameters of Antenna :

1. Radiation Pattern

2. Radiation Power Density

3. Directivity

4. BeamWidth

5. Efficiency / Beam Efficiency

6. Gain

7. Bandwidth

8. Polarization

There are many other parameters but the above parameters are heard very often.

As per Webster's dictionary,An Antenna is defined as " A usually metallic device (either rod or a wire) for radiating or receiving radio waves. In simple An Antenna is the transitional structure between free space and a guiding device.

There are various types of antennas serving different purposes. 

(a). Wire Antenna

(b). Aperture Antenna

(c). Microstrip Antenna

(d). Array Antennas

(e). Reflector Antennas

(f). Lens Antennas

(1). Radiation Pattern :

An Antenna Radiation Pattern or Antenna Pattern is defined as "mathematical function or a graphical representation of the radiation properties of antenna as a function of space coordinates".

Usually the radiation pattern is determined in far field region and is represented as a function of the directional coordinates. 

Radiation properties mainly includes below features/properties.

(i). Power flex density

(ii). Radiation Intensity

(iii). Field Strength

(iv). Directivity

(v). Phase/Polarization

What is Near Field and Far Field?

In general there is no formal definition for Near Field or Far Field. But the most agreed definition is that Near Field is the one which is less than one wavelength (λ) from the antenna.

Like Near Field definition, there is no specific definition for Far Field. It's an assumption, few say 2λ and few insist on 3λ  or 10λ  from antenna.

The real radio waves are in far field. The waves propagates through space with a speed equal to speed of light. 

λ = 300/fMHz

for a mmWave with frequency 30GHz

λ = 300/30000 = 0.01 meters

λ = 300/900 = 0.33 meters

Frequency and wavelength are inversely related.

Wavelength: Wavelength is the distance between similar points on a two back to back waves. 

Usually  (1) used to refer for Wavelength.

Coming back to our Radiation Pattern, you might have heard the name "Lobe". This a popular word in AWP.  Various parts of the radiation pattern is referred as "Lobes" . There are different lobes such as Main Lobe, Major Lobe (*both same), Minor lobe, side lobe and back lobes.

A radiation lobe is a portion of the radiation pattern bounded by  regions of relatively weak radiation intensity. 

Below picture shows different lobes. 

Picture taken from Antenna Theory by Wiley. 

Different antenna types which we discussed above will have different radiation patterns. 

I will discuss about other topics in a separate post.