Glossary ======== Technical terms used in phased array antenna analysis. .. glossary:: :sorted: 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 Steering The process of electronically pointing the main beam by adjusting element phase shifts, without physically moving the antenna. Beam Squint The phenomenon where a phase-steered beam points at different angles for different frequencies. Caused by frequency-dependent phase shifts. 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. 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. Graceful Degradation The ability of an array to maintain acceptable performance when some elements fail. Large arrays degrade gradually rather than catastrophically. 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.