  This report presents a down-conversion method involving digital sideband
separation for the Yuan Tseh Lee Array to double the processing bandwidth. The
receiver consists of a MMIC HEMT LNA frontend operating at a wavelength of 3
mm, and sub-harmonic mixers that output signals at intermediate frequencies of
2 - 18 GHz. The sideband separation scheme involves an analog 90 degree hybrid
followed by two mixers that provide down conversion of the IF signal to a pair
of in phase (I) and quadrature (Q) signals in baseband. The I and Q baseband
signals are digitized using 5 Giga sample per second analog to digital
converters. A second hybrid is digitally implemented using field programmable
gate arrays to produce two sidebands, each with a bandwidth of 1.6 GHz. The 2 x
1.6 GHz band can be tuned to cover any 3.2 GHz window within the aforementioned
IF range of the array. Sideband rejection ratios (SRRs) above 20 dB can be
obtained across the 3.2 GHz bandwidth by equalizing the power and delay between
the I and Q baseband signals. Furthermore, SRRs above 30 dB can be achieved
when calibration is applied.
