Antenna (electrical)
An antenna is a transducer that converts between guided electromagnetic waves in a transmission line and freely propagating electromagnetic waves in space, enabling wireless transmission and reception of signals. Key performance parameters include gain, radiation pattern, bandwidth, polarisation, and impedance; these are governed by the antenna's geometry, size relative to the operating wavelength, and surrounding environment. Antennas are central to radio broadcasting, mobile communications, radar, satellite links, and wireless sensor networks.
Key Formula
G = eta * D = eta * (4*pi*Ae) / lambda^2
LaTeX: G = \eta \cdot D = \eta \cdot \frac{4\pi A_e}{\lambda^2}
| Symbol | Meaning | Unit |
|---|---|---|
| G | Antenna gain | dimensionless (or dBi) |
| η | Radiation efficiency | dimensionless |
| D | Directivity | dimensionless |
| A_e | Effective aperture area | m² |
| λ | Free-space wavelength | m |
Worked Example
Problem
A parabolic dish antenna operates at 10 GHz with a physical aperture area A = 0.5 m² and aperture efficiency η_ap = 0.6. Calculate the effective aperture A_e and the antenna gain G.
Solution
Step 1: Compute free-space wavelength. λ = c/f = 3×10⁸ / 10×10⁹ = 0.03 m. Step 2: Effective aperture A_e = η_ap × A = 0.6 × 0.5 = 0.3 m². Step 3: Assuming radiation efficiency η = 1 (lossless): G = (4π × A_e) / λ² = (4π × 0.3) / (0.03)² = (3.7699) / (9×10⁻⁴) ≈ 4189 In dBi: G_dBi = 10 log₁₀(4189) ≈ 36.2 dBi.
Answer
A_e = 0.3 m²; G ≈ 4189 (36.2 dBi)
Common Antenna Types and Their Characteristics
| Antenna Type | Gain (dBi) | Bandwidth | Polarisation | Typical Use |
|---|---|---|---|---|
| Half-wave dipole | 2.15 | Narrow | Linear | Reference, broadcast |
| Yagi-Uda | 6–20 | Narrow | Linear | TV reception, amateur radio |
| Patch (microstrip) | 5–9 | Narrow | Linear/Circular | Mobile phones, GPS |
| Parabolic dish | 20–60 | Wide | Any | Satellite, radar |
| Horn antenna | 10–25 | Wide | Linear | Microwave, calibration |
Interactive Tools
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Related Terms
Transmission Line (electrical)
An electrical transmission line is a distributed-parameter structure—such as a coaxial cable, twisted pair, or microstrip—designed to guide electromagnetic energy from a source to a load with minimal radiation and reflection losses. At high frequencies, the physical length of the line becomes comparable to the signal wavelength, making lumped-circuit analysis invalid; instead, the line is modelled using the telegrapher's equations that treat resistance, inductance, capacitance, and conductance as distributed per-unit-length quantities. Impedance matching between the line and its terminations is critical to prevent standing waves and power loss.
Electrical Modulation
Electrical modulation is the process of varying one or more properties of a high-frequency carrier signal—such as amplitude, frequency, or phase—in proportion to a lower-frequency information signal. It is fundamental to all modern communication systems because modulated carriers can travel long distances with minimal energy loss and can be multiplexed to share a single channel. Applications include AM/FM radio, cellular networks, Wi-Fi, and satellite communications.
Digital Signal Processing
Digital Signal Processing (DSP) is the mathematical manipulation of discrete-time, discrete-amplitude representations of signals—obtained by sampling and quantising an analogue source—to extract information, filter noise, compress data, or transform the signal into a desired form. Core operations include convolution, Fourier analysis via the FFT, FIR/IIR filtering, and modulation; these are implemented in real time on dedicated DSP chips or general-purpose microprocessors. DSP underpins audio processing, medical imaging, telecommunications, radar, sonar, and machine learning inference at the edge.
From Latin "antenna" (yardarm of a sailing ship, originally "antemna"), referring to the long poles projecting from a ship's mast. The word was adopted by Italian radio pioneer Guglielmo Marconi around 1895 to describe the aerial rods in his wireless telegraphy apparatus.