The sidelobes of the REU (Reflector Evaluation Unit) are measured with the GEMAC facility facility at GSFC. This facility is operated by Ken Hersey and the chief technician is Steve Seufert.
The source is close to a plane wave in the sweet spot. The main issue is getting the full REU into the sweet spot. Also, any reflective surfaces in the chamber can reflect power back to the GEMAC source reflector (the white surface with ragged edges in the GEMAC facility picture) and then back onto the system. For a decent map, all big non-reflector surfaces must be covered with microwave absorber. To get the reflector into the sweet spot while measuring angles where the sidelobes were expected to be substantial, a large L-bracket was used to hold the REU. This was done for only the K-band measurements.
In the GEMAC, co- or crosspolar beams are measured. In other words, the polarization angle is 45 degrees with respect to an azimuth scan. Thus the scans are not in the E or H planes. To compute the Galactic contribution, the unpolarized response is needed (to first order). This is obtained from adding the co and cross polar responses in quadruture.
This map may be compared directly to the YRS prediction at the same frequency. The forward gain is about 45 dBi and has been suppressed.
After this map was made, it found that the VSWR was horrible. This probably led to the wide beam in ???. The problem was due to an improperly machined groove in the throat section. The sidelobe data are still believed to be OK.
The YRS code predicts yrs_unpol_22_sc.ps at 22.1 GHz with a feed located in the same spot. Note the similarity! The real beam has more scattered radiation above the main beam. This is most likely due to the top of the FPA structure. The sidelobe in the measured beam is a bit larger than the prediction, and the main beam is not as compact. ( This is not the final prediction-LP found a bug in the code that will lead to small corrections.)
Gary Hinshaw put together all the available maps for the K feed, regardless of polarization. He obtains full reu test (PS)
Data files K1B+cs_22.2.dat and K1B+xs_22.2.dat from the archive were used in the analysis. These data were taken Jan 22, 1999. They were converted to maps in spacecraft coordinates to produce two HEALPIX resolution 5 maps, K1B+cs_22.2.hp5 and K1B+xs_22.2.hp5 . These were then combined to produce K1B+cxs_22.2.hp5 and are shown in K1B+cxs_22.2.ps. The K feed was mounted on the opposite side of the REU as for the K1A case, thus the predominant sidelobe comes out on the opposite side.
Data files Q2a+cs_39.8.dat and Q2a+xs_39.8.dat were converted to maps in spacecraft coordinates with the IDL procedure reu_to_sc_map.pro to produce two HEALPIX resolution 5 maps, Q2a+cs_39.8.hp5 and Q2a+xs_39.8.hp5 . These may be read with read_hp5map.pro . These two maps were combined using combine_2_maps.pro to produce the result Q2a+cxs_39.8.ps .
Data files Q2b+cs_39.8.dat and Q2b+xs_39.8.dat were converted to maps in spacecraft coordinates with the IDL procedure reu_to_sc_map.pro to produce two HEALPIX resolution 5 maps, Q2b+cs_39.8.hp5 and Q2b+xs_39.8.hp5 . These may be read with read_hp5map.pro . These two maps were combined using combine_2_maps.pro to produce the result Q2b+cxs_39.8.ps .
Data files V2b+cs_60.2.dat and V2b+xs_60.2.dat from the archive
were used in the analysis. They were converted to maps in spacecraft
coordinates to produce two HEALPIX resolution 5 maps,
V2b+cs_60.2.hp5 and
V2b+xs_60.2.hp5 . These two maps were
combined to produce the result V2b+cxs_60.2.hp5
as shown in V2b+cxs_60.2.ps .
Note that, similar to the above, the noise level is a bit high
(-20 dBi) and that there is some scatter about the main beam.
Because this feed was mapped on the opposite side as V2a, the lobe
over the primary is on the opposite side.
Data files W1a+cs_90.dat and W1a+xs_90.dat from the archive were converted to HEALPIX res 5 maps as above. The maps are W1a+cs_90.hp5 and W1a+xs_90.hp5 These two maps were combined to produce the result W1a+cxs_90.hp5 and W1a+cxs_90.ps .
Data files W1B+cs_90.0.dat and W1B+xs_90.0.dat from the archive were converted to HEALPIX res 5 maps as above. The maps are W1B+cs_90.0.hp5 and W1B+xs_90.0.hp5 These two maps were combined to produce the result W1B+cxs_90.0.hp5 and W1B+cxs_90.0.ps .
Data files W3a+cs_90.0.dat and W3a+xs_90.0.dat from the archive were converted to HEALPIX res 5 maps as above. The maps are W3a+cs_90.0.hp5 and W3a+xs_90.0.hp5 These two maps were combined to produce the result W3a+cxs_90.0.hp5 and W3a+cxs_90.0.ps .
Data files W3b+cs_90.dat and W3b+xs_90.dat from the archive were converted to HEALPIX res 5 maps as above. The maps are W3b+cs_90.hp5 and W3b+xs_90.hp5 These two maps were combined to produce the result W3b+cxs_90.hp5 and W3b+cxs_90.ps .
In a number of these files there is a very small lobe at positive angles.