K-Band Focal Plane Array:Integrated Downconverter Module #1

Matt Morgan and Tod Boyd

National Radio Astronomy Observatory

8/7/2008

IDM1 is Complete

IDM2 is Not Complete – One Key Part Missing

I mistakenly ordered the wrong size feedthru header for this module. They havebeen re-ordered, and are expected to arrive in mid-September.

IDM1: Measured Gain

The bandpass is a little narrow. I will show later that it is not the filter.I probably just need to raise the lid slightly.

IDM1: Measured Gain

IF Response shows a lot of ripple. I believe this is related to cavity effects onthe PCB-side – which will not be present on IDM2.

IDM1: Measured Image Rejection

Image rejection at ±1.2-3 GHz offsets is better than 35 dB.

IDM1: Measured Image Rejection

Image rejection at ±5.9-7.7 GHz offsets is better than 32 dB.

IDM1: Measured Gain Compression

Output 1 dB compression point is about +7 dBm.

IDM1: Measured LO Power Requirements

IDM1: Measured Channel Isolation

There seems to be excessive crosstalk between channels (-20 dB), havinga strong IF dependance, but virtually no RF/LO dependance – this stronglysuggests that the crossover is occuring in the IF circuit inside the PCB cavity.

IDM1: Measured Return Loss

Poor return loss needs investigation.

IDM1: Measured Return Loss

Poor return loss needs investigation.

IDM1: Measured Return Loss

Poor return loss needs investigation.

Probe Measurements on Filters

Dynamic range of the measurement was limited at the high frequency end,but the passband looks perfect.

Probe Measurements on Filters

Perfect.

Compliance Matrix for Single Pixel Prototype

parameter symbol spec/predicted measurement comments

noise temperature Te 600 – 800 K not measured

gain G 30 dB 30 dB

gain ripple Gmax – Gmin 3 dB 8 dB presumed PCB cavity effect

output power Pout -25.5 0.5 dBm

-25.5 0.5 dBm

assuming predicted front-end gain

headroom HR +40 dB +33 dB probably ok

LO1 power required

PLO1 -3 5 dBm +1 8 dBm

LO2 power required

PLO2 +3 5 dBm +3 5 dBm

image rejection IR 25 dB 32 dB

channel isolation Iso 30 dB 20 dB presumed PCB cavity effect

return loss RF input

IF output

LO1 input

LO2 input

-17 dB

-19 dB

-12 dB

-10 dB

-11 dB

-11 dB

-6 dB

-12 dB

need to verify transition designs

mass M 250 g 316 g IDM2 will be much less, average should still meet spec

Future IDM1 Revisions

1. Modify ALH444 bias circuit for better gain repeatability.

2. Modify PCB cavity to include a metal barrier between IF circuits in bothchannels – this should improve channel isolation and IF gain flatness

3. Investigate cause of return loss problems – may require re-design ofthe transitions

4. Raise the lid above the filters to prevent de-tuning.

5. Clean up other minor PCB issues