Antenna Knowledge Graph

Antennas are a rather broad topic, and it’s difficult to cover every aspect of them in a single article, but I’ll try to provide a general overview of various aspects of antennas, primarily as they relate to cellular applications. 

What is an antenna?

How is antenna performance characterized?

Radiation Models

Antenna Gain

Total Radiated Power (TRP)

Total Isotropic Sensitivity (TIS)

Effective Isotropic Radiated Power/Equivalent Isotropic Radiated Power (EIRP)

S11 

What is an antenna? As is well known, an antenna is a device that converts electrical energy (electrical signals) into electromagnetic waves and transmits them into space.

How is antenna performance characterized?

There are two main criteria for evaluating antenna performance, as follows:

(a) It should convert electrical energy into electromagnetic energy while minimizing losses as much as possible;

(b) It should radiate in the desired direction.

Several metrics can be used to characterize antenna performance, as follows:

Radiation pattern;

Total radiated power;

Total isotropic sensitivity

Radiation Model

The first step in understanding or evaluating antenna performance is to examine the antenna’s radiation pattern. In most cases, electrical energy flows along predetermined paths—typically copper wires or copper traces on printed circuit boards—but once that energy is converted into electromagnetic waves, it propagates in virtually all directions. Depending on how we design the antenna, electromagnetic waves propagate in different directions through the air. The antenna transmits strong energy in certain directions, minimal energy in others, and moderate energy in still others; this pattern of energy transmission is called the “radiation pattern.” (For more practical examples of radiation patterns, see http://rcexplorer.se/educational/gain/gain.html.) The following are just a few examples of possible radiation patterns. In fact, you can conceive of an almost infinite variety of different patterns. The goal of antenna design is to ensure that, during the conversion from electrical energy to electromagnetic energy, the antenna transmits energy exactly as intended, without any energy loss.

In reality, the signal propagates in three-dimensional directions, as illustrated in Figure (b). However, depicting energy propagation patterns in three-dimensional space is not always straightforward, and quantitatively estimating these patterns can sometimes be particularly challenging. Therefore, in many cases, we slice the 3D pattern along a specific two-dimensional plane, as shown in Figures (c) and (d).

Antenna  Gain (G)

I believe “antenna gain” is a misleading term because

(a) When we hear the term “gain,” we usually assume that “this device amplifies the signal, causing it to produce more energy.” But this is not the case with antennas. Most antennas are “passive devices” that do not amplify anything.

(b) When we consider gain, the higher the gain, the higher the total energy emitted by the device. However, this may not be the case with antennas. Higher antenna gain may mean “more energy transmitted in a specific direction,” but it does not necessarily mean “more total energy emitted by the device.” Antenna gain is defined as the ratio of the power radiated in a given direction to the power at a reference point. It is typically expressed in dB, dBi, or dBD. This serves as an indicator of “how efficiently the antenna transmits energy in a specified direction.” The basic concept can be explained as follows:

Given the variability in antenna structure and material, a single matching configuration may not necessarily yield the best performance across all antenna samples. To address this issue, the industry has introduced the concept of a dynamically tunable matching circuit. The basic idea is as follows: Suppose we build a matching circuit using variable inductors and variable capacitors. These variable components should not be the kind you can purchase from a local electronics supply store and set manually by turning a knob. Instead, they should all be electronically controlled so that the circuit operates without human intervention. The challenge now is to find (or develop) variable inductors and capacitors. These variable devices should operate with minimal energy (voltage and current) consumption. Variable capacitors are much easier to find than variable inductors.