The RAEGE triband S/X/Ka feed and receiver developmentF. Tercero, J.A. López-Pérez, O. Pérez, J.A. López-Fdez

Observatorio de Yebes. Instituto Geográfico Nacional. SPAIN

ABSTRACT

The Yebes Observatory is developing a tri-band cryogenic receiver for the first light observations of the RAEGE antennas. The receiver envisaged for these antennas will operate in the S (2.2–2.7 GHz), X (7.5–9 GHz) and Ka (28–33 GHz) bands simultaneously in order to be backwards compatible with non-VLBI2010 stations.

BLOCK DIAGRAM

At a first stage, the signals from the feed probes are properly combined in cryogenic hybrid couplers to get both circular polarizations. Two directional couplers allow the injection of NoiseCal and PhaseCal signals in front of the LNAs. In Ka-band, a septum polarizer/coupler is designed to split both circular polarizations and it allows the injection of calibration signals generated in the Noise Module. After this stage, six cryogenic LNAs amplify their corresponding signals inside the cryostat. The estimated receiver noise temperature is lower than 15 Kelvin for all the frequency bands. Finally, three dual channel down-converter modules, one for each band, perform signal amplification, filtering and down-conversion to the standard IF VLBI band from 500 MHz to 1000 MHz. The receiver will be monitored and controlled through a low-speed I2C bus to avoid RFI signals.

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-50.00

-40.00

-30.00

-20.00

-10.00

-0.00

10.00

20.00

Y1

Tri-band feed f=2.45GHz

Curve Info

dB(DirLHCP)Setup1 : LastAdaptiveFreq='2.45GHz' Phi='45deg'

dB(DirRHCP)Setup1 : LastAdaptiveFreq='2.45GHz' Phi='45deg'

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-50.00

-40.00

-30.00

-20.00

-10.00

-0.00

10.00

20.00

Y1

Tri-band feed f=8.25GHz

Curve Info

dB(DirLHCP)Setup1 : LastAdaptiveFreq='8.25GHz' Phi='45deg'

dB(DirRHCP)Setup1 : LastAdaptiveFreq='8.25GHz' Phi='45deg'

TRI-BAND FEED

The receiver feeder has been designed to illuminate the ring focus antenna. It is made of a coaxial waveguide, for the S and X bands, and a circular waveguide for the Ka band. The three horns have independent outputs. In the case of the coaxial horns, 4 field probes must be combined with 180ºand 90º hybrid circuits to get dual-circular polarization. In the Ka band case, the dual-circular polarization is obtained with a septum polarizer. The feed, hybrids and polarizer will operate at cryogenic temperature inside of the cryostat with the LNAs.The feeder is 25 cm high and 20 cm in diameter. It weights 3 Kg.

FEED FAR FIELD RADIATION PATTERNS

The HFSS simulations in circular polarisation in S/X/Ka bands show an adequate subreflector illumination. The optimum illumination is -16dB at 65º.

13.2m RAEGE ANTENNA FAR FIELD RADIATION

PATTERNS

The feeder radiation patterns are used as source in Physical Optics simulations with GRASP software.

13.2m RAEGE ANTENNA APERTURE EFFICIENCY

The efficiency includes the contribution of spillover, illumination, blockage and phase

90º HYBRID.

Cryogenic Low Noise Amplifier

LNAs designs in S and X bands are prototypes from classical models developed bay Yebes. The design of Ka band LNA (graphs below) will be a MMIC device developed in collaboration with the IAF (FraunhoferInstitute for Applied Solid State Physics)

20 22 24 26 28 30 32 34 36 38 400

10

20

30

40

50

60

70

80

90

Tn goal

T(K

)F(GHz)

Tn (K) C11 C18

0

5

10

15

20

25

30

R732b (100 nm) - Tamb=16K

G (dB) C11 C18

G(d

B)

SEPTUM POLARIZER

Septum in a 8.4mm circular waveguide. It includes the couplers to inject the noise and phase cal. In the figure, the K band model with a 0.5mm septum gives 0.5dB of axial ratio

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-50.00

-40.00

-30.00

-20.00

-10.00

-0.00

10.00

20.00

Y1

Tri-band feed f=30.50GHz

Curve Info

dB(DirL3X)Setup1 : LastAdaptiveFreq='30.5GHz' Phi='45deg'

dB(DirL3Y)Setup1 : LastAdaptiveFreq='30.5GHz' Phi='45deg'