Importance Of Antenna Characteristics To Radar Performance

The UK Met Office has been operating the national weather radar network for nearly 30 years. It is a relatively dense network of 15 radars which have seen continuous in-house development to its infrastructure and data processing systems. Currently the hardware and signal processing systems are being renewed to an in-house design to add dual-polarisation capability. The project has been under way for a number of years and upgrades have now been completed on eight radars and all are now in operational use. As a result, the Met Office now has post-upgrade performance data. While many parts are being replaced, several key components are being reused where possible. Due to their high quality design (as well as for environmental and cost reasons), the existing dishes are upgraded with a new dual polarisation feed horn and then tested to confirm they are within specification. Range test measurements are carried out for each antenna to optimise the position of the feed-horn and to provide full characterisation of the cross polar isolation, side lobe levels, antenna gain, beam-squint, and beam-width several different cuts. The new radars operate in two transmission modes allowing production of either ZDR, ρHV, and ΦDP, or LDR. The quality of the overall system is evaluated following each installation in a number of ways, including the monitoring of peak ρHV and LDR in rain.

This paper will present the results of both antenna range testing and radar performance. The quality of all data is high with peak ρHV of 0.9955 to 0.9985 and LDR of -31.1 to -38.5 dB across the eight radars. Notable conclusions include: comparison of range and operational data shows correlation between them which serves to underline the importance of the antenna to radar performance; the decision to test dishes prior to use has been vindicated as several dishes were considered not suitable for reuse, so maintaining a high quality across the network; the expectation that the existing dishes were of good quality has been confirmed as only two dishes have been not been suitable for reuse so far.