Glossary#
Technical terms used in phased array antenna analysis.
- Amplitude Taper#
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.
- Aperture#
The physical area of an antenna that captures or radiates electromagnetic energy. For arrays, this is typically the area encompassing all elements.
- Aperture Efficiency#
The ratio of the effective aperture area to the physical aperture area. Reduced by amplitude tapering and other non-uniform illumination.
- Array Factor#
The radiation pattern of an array of isotropic elements. The total pattern equals the element pattern multiplied by the array factor (pattern multiplication principle).
- Azimuth#
The angle in the horizontal plane, measured from a reference direction (typically the x-axis). Also called the phi angle.
- Beam Squint#
The phenomenon where a phase-steered beam points at different angles for different frequencies. Caused by frequency-dependent phase shifts.
- Beam Steering#
The process of electronically pointing the main beam by adjusting element phase shifts, without physically moving the antenna.
- Beamwidth#
The angular width of the main beam, typically measured at the half-power (-3 dB) points. Also called Half-Power Beamwidth (HPBW).
- Broadside#
The direction perpendicular to the array face (θ = 0°). An array with uniform phase radiates broadside.
- Chebyshev Taper#
An amplitude taper that produces equi-ripple sidelobes, providing the narrowest beamwidth for a given sidelobe level.
- Conformal Array#
An array mounted on a curved surface where elements have different orientations. Requires accounting for element normal directions in pattern calculations.
- Direction Cosines#
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).
- Directivity#
The ratio of radiation intensity in a given direction to the average intensity over all directions. Expressed in dBi (decibels relative to isotropic).
- E-Plane#
The plane containing the electric field vector and the direction of maximum radiation.
- Element Pattern#
The radiation pattern of a single antenna element. Combined with the array factor via pattern multiplication to get the total pattern.
- Element Spacing#
The distance between adjacent array elements, typically expressed in wavelengths. Spacing > λ/2 can cause grating lobes.
- Elevation#
The angle measured from the zenith (z-axis) or from the horizon, depending on convention. Also called the theta angle.
- Graceful Degradation#
The ability of an array to maintain acceptable performance when some elements fail. Large arrays degrade gradually rather than catastrophically.
- 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.
- H-Plane#
The plane containing the magnetic field vector and the direction of maximum radiation. Perpendicular to the E-plane.
- Half-Power Beamwidth (HPBW)#
The angular width between the -3 dB points of the main beam. A key performance metric for antenna resolution.
- Hybrid Steering#
A beamforming architecture using TTD at the subarray level and phase shifters within subarrays. Balances cost and wideband performance.
- LCMV#
Linearly Constrained Minimum Variance - an adaptive beamforming algorithm that minimizes output power while satisfying linear constraints on the response in specified directions.
- Main Beam#
The lobe containing the direction of maximum radiation. Also called the main lobe.
- Monopulse#
A tracking technique using sum and difference patterns to determine target angle. Provides angle information from a single pulse.
- Mutual Coupling#
Electromagnetic interaction between array elements that affects element patterns and input impedance. Can cause beam pointing errors if not compensated.
- Null#
A direction where the radiation pattern has zero (or very low) response. Can be intentionally placed to reject interference.
- Null Steering#
The process of placing pattern nulls in specific directions, typically to reject interference sources while maintaining the main beam.
- Pattern Multiplication#
The principle that an array’s total pattern equals the product of the element pattern and the array factor.
- Phase Quantization#
The discretization of phase shifter settings to a finite number of levels. Causes beam pointing errors and increased sidelobes.
- Phase Shifter#
A device that adjusts the phase of the signal to/from each element, enabling beam steering.
- Planar Array#
A 2D array of elements arranged in a flat plane, typically rectangular or triangular grid.
- Scan Blindness#
A phenomenon where the array reflection coefficient approaches unity at specific scan angles, causing severe gain loss. Related to surface wave excitation.
- Scan Loss#
The reduction in gain when steering away from broadside, primarily due to the element pattern and projected aperture reduction.
- Sidelobe#
Any lobe other than the main beam. Sidelobe Level (SLL) is typically specified as dB below the main beam peak.
- Sparse Array#
An array with some elements removed (thinned) to reduce cost while maintaining aperture size. Results in higher sidelobes.
- Steering Vector#
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.
- Subarray#
A group of elements that share a common phase shifter. Reduces hardware cost but limits scan range due to quantization lobes.
- Taylor Taper#
An amplitude distribution designed to produce a specified number of nearly-equal sidelobes. Provides good tradeoff between beamwidth and sidelobe control.
- True Time Delay (TTD)#
A beamforming technique using actual time delays instead of phase shifts. Provides frequency-independent beam pointing, eliminating beam squint.
- UV-Space#
A coordinate system using direction cosines u and v, where the visible region is defined by u² + v² ≤ 1.
- Visible Region#
The range of direction cosines (u, v) corresponding to real angles: u² + v² ≤ 1. Grating lobes outside this region are evanescent.
- Wavenumber#
The spatial frequency of electromagnetic waves: k = 2π/λ. Used to calculate phase shifts for steering.
- Weights#
The complex excitation coefficients applied to each element, determining amplitude and phase. Control beam direction, sidelobes, and nulls.