A receiver system is being built which will cover the widest instantaneous bandwidth ever achieved by an astronomical heterodyne receiver. Theentire 75-111 GHz band will be covered with a backend spectrometer having 30 MHz resolution. The receiver is intended for astronomical use insearching for the highly redshifted spectral lines from galaxies of unknown redshift. The receiver will use InP MMIC based low noise amplifiersoperated at 20 K, and will operate with dual polarization feeds. The two receivers used with each feed are combined using a full band ortho-modetransition. Two such feeds are used in conjunction with a beam switch to maintain one dual polarized beam on the source at all times. The backendspectrometer will use an analog autocorrelator built using very low cost microwave and analog/digital components.

Redshift Search Receiver

Completely unique receiver of novel design. 74-110.5 GHz covered instantaneously with a

receiver/spectrometer having 30 MHz resolution. Preamps use InP MMIC’s operated at 20 K. Two dual polarization feeds, 4 receivers. High speed electrical beam switch for very flat

baselines. Backend spectrometer is analog autocorrelator

with 6.5 GHz bandwidth per section, 6 sections per receiver, 146 GHz total bandwidth!

Front end design

•Front end like SEQUOIA, except that both signal polarizations combined with ortho-mode transition.

•Entire signal band down-converted at once to two 18.5 GHz wide IF bands.

•Four receivers with 8 outputs in total.

112.5 GHz LO

95 GHz LO

Beamswitch

HEMT amplifiers require a fast (~1 KHz) beam switch.

Switch changes polarization 0 90 ,

wire grid passes reflects beam.

Beams separated in azimuth with spacing of 3 HPBW.

Receiver has two dual polarized beams with a beamswitch. One beam always on source.

In Out

Faraday Rotation Switch•Beamswitch developed for this work improves enormously on any previous device.

•Dual polarized beam is rotated by 45 using a switched magnetic field in a ferrite.

•Added noise <10K, switching time <10 sec.

Analog autocorrelator vs digital

•Analog correlation requires no high speed signal sampler-digitizer.

•Analog requires no signal quantization:

•Very wide dynamic range.

•No noise degradation.

•Analog bandwidth is much larger -- 8.0 GHz.

•High accuracy analog autocorrelation is practical with low cost, ~$10/lag.

Analog Autocorrelator Basics

Delay lines Nyquist sampled (/4) for 8 GHz bandwidth with weak coupling using a resistive tap.

Many taps are practical, we use 64 on each line.

Tap signals are detected with silicon diodes which act as multipliers.

•Correlator board presently in test, everything works.

•Delay lines with 256 taps, detectors, AC amplifiers, A/D converters, FPGA for digital signal processing all on one board. 31 MHz resolution.