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.

MR-DC?

What is MR-DC?

MR-DC (Multi-RAT Dual Connectivity) is similar to Intra LTE (E-UTRA) Dual Connectivity in which UEs with multiple TRX configured to utilize resources provided by two different node (eNB/gNB) which are connected via non-ideal backhaul. One node provides E-UTRA access and the other NR access.

Out of two nodes one node acts as a Master Node (MN) and the other as Secondary Node (SN). At least one node (MN) have access to or connected to Core network.

What is an Ideal Backhaul and non Ideal Backhaul?

Ideal Backhaul : Very High Throughput and Very Low Latency backhaul such as dedicated Point-to-Point connection using optical fiber.

An Ideal Backhaul is defined as Latency less than 2.5µs and throughput up to 10Gbps. Usually between eNB and RRH (Remote Radio Head)

Backhaul Technology	Latency (One way)	Throughput	Priority (1 is the highest)
Fiber Access 4 (NOTE 1)	less than 2.5 us (NOTE2)	Up to 10Gbps	1

Non-Ideal Backhaul: This is the typical backhaul widely used in the market for example xDSL, Microwave link, relaying ..etc

In simple, any backhaul which does not satisfy above requirements (Latency and Throughput) are considered as Non-Ideal Backhaul.

Backhaul Technology	Latency (One way)	Throughput	Priority (1 is the highest)
Fiber Access 1	10-30ms	10M-10Gbps	1
Fiber Access 2	5-10ms	100-1000Mbps	2
Fiber Access 3	2-5ms	50M-10Gbps	1
DSL Access	15-60ms	10-100 Mbps	1
Cable	25-35ms	10-100 Mbps	2
Wireless Backhaul	5-35ms	10Mbps – 100Mbps typical, maybe up to Gbps range	1

Based on the core network access, MR-DC can be as below.

(i) MR-DC with EPC and
(ii) MR-DC with 5GC (work still ongoing)

Let's see how option (i) is implemented.

Below picture is self explanatory.

EN-DC, E-UTRA-NR Dual Connectivity where an UE is connected to one eNB which acts as a Master Node (MN) and one en-gNB acting as Secondary Node (SN).

eNB is connected to EPC via S1-U interface where as it is optional for the en-gNB to connect to EPC. eNB and en-gNBs talk to each other over X2 interface.

MR-DC with 5GC :

It is basically to which node the UE is connected to and the Core Network type that the MN is connected to. In this case the Core Network type is 5GC. UE can be connected to either gNB node or ng-eNB.

(a). E-UTRA-NR DC and

(b). NR-E-UTRA DC

Ref :
1. 3GPP 37.304
2. 3GPP 36.932