The MAP Satellite Feed Horns

We present the design, manufacturing methods, and characterization of 20microwave feed horns currently in use on the Microwave Anisotropy Probe (MAP)satellite. The nature of the cosmic microwave background (CMB) anisotropyrequires a detailed understanding of the properties of every optical componentof a microwave telescope. In particular, the properties of the feeds must beknown so that the forward gain and sidelobe response of the telescope can bemodeled and so that potential systematic effects may be computed. MAP requireslow emissivity, azimuthally symmetric, low-sidelobe feeds in five microwavebands (K, Ka, Q, V, and W) that fit within a constrained geometry. The beampattern of each feed is modeled and compared with measurements; the agreementis generally excellent to the -60 dB level (80 degrees from the beam peak).This agreement verifies the beam-predicting software and the manufacturingprocess. The feeds also affect the properties and modeling of the microwavereceivers. To this end, we show that the reflection from the feeds is less than-25 dB over most of each band and that their emissivity is acceptable. Thefeeds meet their multiple requirements.