This glossary provides definitions for technical terms used in phased array antenna design and analysis.
A weighting applied to element excitations to control sidelobe levels. Common tapers include Taylor, Chebyshev, and Hamming windows. Tapering reduces sidelobes at the cost of increased beamwidth and reduced aperture efficiency.
The physical area of an antenna that captures or radiates electromagnetic energy. For arrays, this is typically the area encompassing all elements.
The ratio of the effective aperture area to the physical aperture area. Reduced by amplitude tapering and other non-uniform illumination.
The radiation pattern of an array of isotropic elements. The total pattern equals the element pattern multiplied by the array factor (pattern multiplication principle).
The angle in the horizontal plane, measured from a reference direction (typically the x-axis). Also called the phi angle.
The process of electronically pointing the main beam by adjusting element phase shifts, without physically moving the antenna.
The angular width of the main beam, typically measured at the half-power (-3 dB) points. Also called Half-Power Beamwidth (HPBW).
The direction perpendicular to the array face (θ = 0°). An array with uniform phase radiates broadside.
An amplitude taper that produces equi-ripple sidelobes, providing the narrowest beamwidth for a given sidelobe level.
An array mounted on a curved surface where elements have different orientations. Requires accounting for element normal directions in pattern calculations.
A simplified model for element directivity where gain decreases as cos(θ) from broadside.
The projections of a unit vector onto coordinate axes. For antenna patterns: u = sin(θ)cos(φ), v = sin(θ)sin(φ), w = cos(θ).
The ratio of radiation intensity in a given direction to the average intensity over all directions. Expressed in dBi (decibels relative to isotropic).
The plane containing the electric field vector and the direction of maximum radiation. For a vertical dipole, this is typically the elevation plane.
The radiation pattern of a single antenna element. Combined with the array factor via pattern multiplication to get the total pattern.
The distance between adjacent array elements, typically expressed in wavelengths. Spacing > λ/2 can cause grating lobes.
The angle measured from the zenith (z-axis) or from the horizon, depending on convention. Also called the theta angle.
The direction along the array axis (θ = 90°). Requires close element spacing (< λ/4) to avoid grating lobes.
Unwanted secondary main beams that appear when element spacing exceeds λ/2. Located at angles where the path difference between elements equals a multiple of wavelengths.
The ability of an array to maintain acceptable performance when some elements fail. Large arrays degrade gradually rather than catastrophically.
The plane containing the magnetic field vector and the direction of maximum radiation. Perpendicular to the E-plane.
The angular width between the -3 dB points of the main beam. A key performance metric for antenna resolution.
An amplitude taper that provides good sidelobe suppression with moderate beamwidth increase. Defined as 0.54 - 0.46·cos(2πn/N).
A theoretical antenna that radiates equally in all directions. Used as a reference for gain measurements (dBi).
An adaptive beamforming algorithm that minimizes output power while satisfying linear constraints on the response in specified directions.
The lobe containing the direction of maximum radiation. Also called the main lobe.
A tracking technique using sum and difference patterns to determine target angle. Provides angle information from a single pulse.
Electromagnetic interaction between array elements that affects element patterns and input impedance. Can cause beam pointing errors if not compensated.
A direction where the radiation pattern has zero (or very low) response. Can be intentionally placed to reject interference.
The process of placing pattern nulls in specific directions, typically to reject interference sources while maintaining the main beam.
The principle that an array's total pattern equals the product of the element pattern and the array factor.
The discretization of phase shifter settings to a finite number of levels. Causes beam pointing errors and increased sidelobes.
A device that adjusts the phase of the signal to/from each element, enabling beam steering.
A 2D array of elements arranged in a flat plane, typically rectangular or triangular grid.
The spatial distribution of radiated power as a function of angle. Can be expressed in terms of field strength or power density.
A phenomenon where the array reflection coefficient approaches unity at specific scan angles, causing severe gain loss. Related to surface wave excitation.
The reduction in gain when steering away from broadside, primarily due to the element pattern and projected aperture reduction. Approximately cos(θ) for planar arrays.
Any lobe other than the main beam. Sidelobe Level (SLL) is typically specified as dB below the main beam peak.
An array with some elements removed (thinned) to reduce cost while maintaining aperture size. Results in higher sidelobes.
The complex weights that produce a beam in a specified direction. For direction (θ₀, φ₀): w = exp(-jk·r·û) where û is the unit vector toward the beam direction.
A group of elements that share a common phase shifter. Reduces hardware cost but limits scan range due to quantization lobes.
An amplitude distribution designed to produce a specified number of nearly-equal sidelobes. Provides good tradeoff between beamwidth and sidelobe control.
The polar angle measured from the z-axis (zenith). θ = 0° is broadside for a planar array in the xy-plane.
An array with randomly or systematically removed elements to reduce cost. See Sparse Array.
A 1D array with equally-spaced elements and uniform amplitude weighting.
A coordinate system using direction cosines u and v, where the visible region is defined by u² + v² ≤ 1.
The range of direction cosines (u, v) corresponding to real angles: u² + v² ≤ 1. Grating lobes outside this region are evanescent.
The spatial frequency of electromagnetic waves: k = 2π/λ. Used to calculate phase shifts for steering.
The complex excitation coefficients applied to each element, determining amplitude and phase. Control beam direction, sidelobes, and nulls.
k = 2π/λ = 2πf/c
u = sin(θ)cos(φ)
v = sin(θ)sin(φ)
w = cos(θ)
AF(θ) = Σ wₙ exp(jknd·sin(θ))
wₙ = exp(-jkxₙu₀ - jkyₙv₀)
d > λ/(1 + sin(θₘₐₓ))
HPBW ≈ 0.886λ/L (radians)
where L is the aperture length.
D = 4πA/λ² = 4π(Lₓ·Lᵧ)/λ²
- Balanis, C.A. (2016). Antenna Theory: Analysis and Design, 4th Edition. Wiley.
- Mailloux, R.J. (2017). Phased Array Antenna Handbook, 3rd Edition. Artech House.
- Hansen, R.C. (2009). Phased Array Antennas, 2nd Edition. Wiley.
- Skolnik, M.I. (2008). Radar Handbook, 3rd Edition. McGraw-Hill.