K-Band Focal Plane Array Project Integrated Downconverter Modules Matt Morgan National Radio Astronomy Observatory 2/27/2008

Two Downconverters Two downconverters are needed to implement multiplexing scheme described earlier. The second downconverter simply omits one mixing stage.

IF Frequency Plan The LO and IF frequencies were chosen to minimize the risk from LO spurs, to allow adequate image filtering, and to ease the design of the IF multiplexer.

Multi-chip MMIC modules All downconverter functions are integrated for compactness and low-cost production.

Multi-chip MMIC modules All downconverter functions are integrated for compactness and low-cost production. IDM #1IDM #2

Module Layout Chip-level components are mounted in a tightly drawn shallow cavity which is designed to be cutoff at the active operating frequencies to ensure adequate isolation. RF1RF2 waveguide transition coaxial transition DC feedthrus custom filters commercial MMICs LO1 LO2

Use of Commercially Available MMICs All active chips are commercially available for less than $50 each.

Custom Components: WR-42 to Microstrip Transition

Custom Components: Coax to Microstrip Transition

Custom Components: GHz Band-Pass Filter

Extended RF Bandpass RF Band was extended to capture especially interesting spectral lines. However, this represents a tradeoff with image-rejection.

Custom Components: GHz Low-Pass Filter

Custom Components: LO Dual-Band Splitter

Predicted Performance parametersymbolvalueconditions noise temperatureTeTe 600 – 800 K gainG30 dB gain rippleG max – G min 3 dBattenuators fixed attenuator control range G adj  8 dB  14 dB IDM1, after freq. variation is taken out IDM2, after freq. variation is taken out output powerP out  0.5 dBm T sys = 95 K, attenuators mid-range headroomHR+40 dBT sys = 95 K LO1 power requiredP LO1 -3  5 dBm LO2 power requiredP LO2 +3  5 dBm IDM1 only image rejectionIR25 dB return lossRF input IF output LO1 input LO2 input -17 dB -19 dB -12 dB -10 dBIDM1 only massM250 g

Mounting Adapter for Easy Access Although the downconverters have standard UG595/U WR-42 flanges for testing, an adapter plate is used to permit easy access to mounting holes from the bottom of the cryostat when fully assembled.