Fundamental Antenna Parameters

To grasp the concept of how an antenna interacts with signals and its efficiency in transmitting or receiving them, understanding these fundamentals is crucial.

Antenna Gain (dBi)

Antenna gain is a metric that assesses the antenna’s capacity to transmit or receive power in a direction when compared to an isotropic antenna, showcasing its effectiveness in focusing input power and effectively radiating it outwards.

Antenna gain in dBi (decibels relative to an isotropic radiator) is calculated using the following formula:

\[G_{dB_i}=10\times{log}_{10}{\left(\frac{P_{radiated}}{P_{input}}\right)}\]

\(P_{radiated}\) is the Power radiated by the antenna (in watts) and \(P_{input}\) is the Input power supplied to the antenna (in watts).

Directivity

Antenna directivity indicates how well an antenna can concentrate its signal in a direction, calculated by dividing the maximum radiated power in one direction by the average power radiated in all directions.

It can be also defined as the ratio of the radiation intensity (RI) of the antenna in a given direction and the RI of an isotropic radiator fed by the same amount of power:

\[D\left(\theta,\varphi\right)=\frac{U\left(\theta,\varphi\right)}{U_{av}}=4\pi\frac{U_{max}}{\mathrm{\Pi}}\]
and
\[D_{max}=D_0=4\pi\frac{U_{max}}{\mathrm{\Pi}}\]

Where \(U(\theta,\phi)\) represents the radiation intensity.

Bandwidth and Range of Operation

The bandwidth refers to the span of frequencies within which an antenna can function optimally. The effectiveness of an antenna tends to diminish as the frequency moves away, from its frequency in real-world scenarios.

Separate bandwidths may be introduced: impedance bandwidth, pattern bandwidth, etc.

The FBW of broadband antennas is expressed as the ratio of the maximum frequency \(f_{max}\) to the minimum frequencies \(f_{min}\), where the antenna performance is acceptable:

\[FBW=\frac{f_{max}}{f_{min}}\]

For narrowband antennas, the FBW is expressed as a percentage of the maximum and minimum frequency difference over the center frequency:

\[FBW=\ \frac{f_{max}-f_{min}}{f_0}\ .100\%\]

Polarization of Antenna Waves (Angle)

The antennas polarization refers to how the electric field’s positioned around it. It can either be linear, with the electric field moving in a single plane (either horizontally or vertically), or circular or elliptical, with the electric field rotating.
It is important to have receiving and transmitting antennas with matched polarization, or some of the power of the signal will be lost due to the polarization mismatch. This is known as the polarization loss factor (PLF), which can be described with the equation:

\[PLF={cos}^2{\emptyset}\]

Radiation Pattern and its Representation

An antenna’s radiation pattern serves as a depiction of how it emits radiation, illustrating the distribution of power in various directions from the antenna’s location.

VSWR and Impedance Matching (Typ.)

The Voltage Standing Wave Ratio (known as VSWR) quantifies the efficiency of power conversion into radiation by showing the level of impedance harmony between the antenna and the transmission line.

Any imperfection in the antenna design or antenna port/feed that results in an impedance mismatch leads to a degraded VSWR where some of the RF energy is reflected from the antenna port and the transmitter/receiver ports.

\[VSWR=\frac{\left|v_z\right|_{max}}{\left|v_z\right|_{min}}=\frac{1+\left|\mathrm{\Gamma}\right|}{1-\left|\mathrm{\Gamma}\right|}\]

Advanced Antenna Characteristics

You can adjust these settings to customize antenna selection according to your performance requirements.

Front-to-Back Ratio in Directional Antennas

The front-to-back ratio (referred to as the F/B ratio) measures the strength of the signal emitted in the intended direction (front) and compares it with the signal emitted in the opposite direction (back). This comparison is usually quantified in decibels (dB), providing insight into the extent of radiation that an antenna produces and aiding in assessing its performance relative to interference from behind—particularly critical in scenarios like point-to-point communication setups.

Half Power Beam Width (HPBW) and Antenna Coverage

The Half-Power Beam Width (HPBW) refers to the angle encompassing the half-power points of the lobe. Basically where the power is 3dB lower than the peak gain level at two distinct points. The HPBW serves as a measure of how broad the antenna beam offers insight, into its coverage area.

Antenna Efficiency and Total Performance

The efficiency of an antenna is determined by comparing the power emitted by the antenna with the power provided at its input point. Considers all losses leading up to the antenna’s opening. This encompasses losses from reflections caused by mismatches in transmission lines, as well as losses from conductors and dielectrics.

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Conclusion

In conclusion, grasping essential antenna characteristics such as gain, directionality and effectiveness aids in enhancing antenna efficiency for uses guaranteeing dependable communication and signal strength.

References:

[1]AgileAdmin. 2024. What Are the Fundamental Parameters of Antennas? https://www.seimw.com/blog/what-are-the-fundamental-parameters-of-antennas/

[2]Steven Petten. 2021. Basic Antenna Parameters. https://aemantennas.com/antenna-terms/

[3] Antenna-Experts. 2023. Different Types of Antennas & Characteristics of Antenna. https://antennaexperts.co/blog/different-types-of-antennas-characteristics-of-antenna

[4]2023. LECTURE 4: Fundamental Antenna Parameters. https://www.ece.mcmaster.ca/faculty/nikolova/antenna_dload/current_lectures/L04_Param.pdf

[5]A.H. Systems, inc. Practical Overview of Antenna Parameters. https://www.ahsystems.com/articles/Practical-overview-of-antenna-parameters.php