Mismatch Accumulation Effects of Cascaded Switches for Multi-Bit Delay Path Selection of Phased Array Beam Steering

Abstract

Phased array radars require beam boresights that are capable of fast switching between different azimuths and elevations, typically in two dimensions simultaneously. Narrowband radar can use phase shifter components to achieve phase change, which translates to time delay for very narrow band signals. A radar having an appreciable bandwidth, such as a chirped radar, requires selection of variable true signal time delay with different time delays spatially distributed over the face of the radar in order to enable the spatial combining of the transmitted or received signal required to achieve beam steering. These electrically adjustable true time delay devices, or Time Delay Units (TDUs), are constructed from cascades of radio frequency (RF) signal switches typically configured into groups of two switches, referred to as bits. Each bit can then, by operation of its electrical switches, select one signal propagation path or a second propagation path, where the second path is a predetermined electrical length longer than the first path. In construction of this cascaded switch arrangement, mismatch errors can occur at each interface between switch elements and between a switch element and a delay line, due to the non-ideal nature of electrical semiconductors used for enabling the electrical switching function. In order to effectively bound the cumulative effect of these mismatch errors when taken over the entire cascaded switching structure, an understanding of the composition of each error is necessary. Also useful is a method for bounding the cumulative effects of the cascaded network. Components of an error vector are examined using the phasor domain. Choice of statistical methods to bound the cascaded network are also discussed.