inverse-square law, as well as systems with point sources, such as radio antennas. Radially asymmetric systems may also be modeled with polar coordinates. For example, a microphone's pickup pattern illustrates its proportional response to an incoming sound from a given direction, and these patterns can be represented as polar curves. The curve for a standard cardioid microphone, the most common unidirectional microphone, can be represented as at its target design frequency. The pattern shifts toward omnidirectionality at lower frequencies. See also Curvilinear coordinates List of canonical coordinate transformations Log-polar coordinates Polar decomposition Unit circle References General references External links Coordinate Converter — converts between polar, Cartesian and spherical coordinates Polar Coordinate System Dynamic Demo Two-dimensional coordinate systems Orthogonal coordinate systems