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Free Online Equiangular Spiral Antenna Calculator   
This free online equiangular spiral antenna calculator uses a wire grid method of moments formulation to model a single or multiple arm spiral. The electric current is computed and used to construct the far zone radiation power pattern. The input impedance and directivity are also computed.
Directivity This metric is used to describe the ability of the antenna to radiate or receive enery in the direction of maximum intensity. This description is measured against a isotropic source which radiates or receives energy equally in all directions.
Far Zone The far zone region of an antenna is defined at a radial distance away from the antenna such that certain approximations become valid. If D is defined as the diameter (in wavelengths) of the smallest sphere enclosing the antenna, then the far zone begins at a radial distance of 2D2 away from the antenna.
Input Impedance The antenna input impedance is a function of the frequency and is determined by the physical configuration. Maximum power transfer between the antenna and the associated electrical network transmission line is dependent on a conjugate match between the input impedance and the line impedance.
Power Pattern The antenna power pattern describes the angular distribution of power. For a transmitting antenna, the pattern represents the directional flow of power radiated by the antenna. The pattern on transmit also shows the ability of the antenna to concentrate power within a particular angular region. For a receiving antenna, the pattern represents the ability of the antenna to capture enery from a particular direction.
[1] W. C. Gibson, "The Method of Moments in Electromagnetics," Chapman & Hall/CRC, 2008.
[2] B. D. Popovic and B. M. Kolundzija, "Analysis of Metallic Antennas and Scatterers," IEE, 1994.
[3] R. F. Harrington, "Field Computation by Moment Methods," Krieger, 1982.
[4] M. R. Hestenes, "Conjugate Direction Methods in Optimization," Springer-Verlag, 1980.
[5] T. J. Peters, "A Fast Algorithm for Plotting and Contour Filling Radiation Patterns in Three Dimensions," IEEE Transactions on Antennas and Propagation, April 1992.


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