Phase and delay in corporate-fed arrays
The distribution of phase and delay in corporate-fed phased arrays is examined. RMS phase errors versus scan angle are shown for digital phasers. The phaser bits should all be located at each element. The delayer bits can be also, but delayer loss, dispersion, temperature sensitivity, and size mitigate against using so many delayers. Alternative topologies, where delay bits are distributed in the corporate feed, are examined.
Fitting time delay units in a large wideband corporate fed array
Phase shifters distort a wideband signal as well as cause beam squint in a large array. Time delay units are expensive, so they are used sparingly. This paper explains the performance tradeoffs associated with the selection, size, and distribution of time delay units in a large wideband phased array antenna. Design equations and examples are given.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%