Antenna gain is a critical parameter that describes how well a radar antenna concentrates radiated power in a specific direction. To fully understand antenna gain, one must first be familiar with three related concepts: antenna radiation pattern, directivity, and efficiency.
1. Antenna Radiation Pattern
The radiation pattern of an antenna represents how the radiated electric field or power varies spatially. In engineering applications, it’s typically visualized as a power pattern, showing the relative strength of radiation as a function of angle.
This pattern is inherently three-dimensional, depending on both elevation angle (θ) and azimuth angle (φ).
For practical analysis, two-dimensional projections are often used: typically in the E-plane and H-plane.
A key parameter of radiation patterns is the beamwidth, especially the 3 dB beamwidth (also called half-power beamwidth). This defines the angular width within which the radiated power is at least half (-3 dB) of its maximum. The main lobe (or main beam) contains most of the energy, while smaller side lobes (sidelobes) indicate undesired radiation directions.
2. Antenna Directivity
Directivity (D) quantifies how concentrated the antenna’s radiation is in one direction compared to an ideal isotropic radiator that radiates equally in all directions.
Mathematically, it’s the ratio of the power density in the main lobe to that of the isotropic radiator, under equal total power:
Where:
Sr: Power density from the actual antenna in the peak direction
S0: Power density from the isotropic source in the same direction
High directivity implies the antenna emits energy more tightly in a preferred direction. In radar applications, this helps enhance signal detection and range.
3. Antenna Efficiency
Antenna efficiency (η) measures how effectively input electrical power is converted into radiated electromagnetic power:
Where:
Pr: Radiated power
Pin: Input power
Rr: Radiation resistance
Rloss: Loss resistance (due to conductor and dielectric losses)
To improve efficiency, designers use materials with low resistive losses—like copper, silver, and Teflon insulators.
4. Antenna Gain (G)
Gain combines both directivity and efficiency into a single metric:
It reflects the antenna’s ability to direct input power into a specific direction efficiently. From the receiver’s perspective, gain also describes how well the antenna can capture incoming energy.
📌 Gain in Decibels (dB)
In practice, antenna gain is often expressed in decibels:
This allows engineers to easily compare gains of different antennas on a logarithmic scale.
Why High Gain Matters in Radar
High-gain antennas have:
Narrower beamwidths, allowing precise directional targeting
Higher power concentration, which improves detection range and sensitivity
Reduced interference, due to minimized sidelobes
In radar level measurement systems, using antennas with high gain and narrow beams helps improve accuracy, anti-interference ability, and detection distance. Therefore, gain is a vital design consideration in radar-based instrumentation.