Milestone 9.5: Evaluation of T/R switch prototypes completed

Task 9.3 of the EISCAT_3D Preparatory Phase is concerned with verification and evaluation of the transmitter/receiver switch design.

This T/R-switch was realised on microstripline technology, which simplifies the integration in a modular system with a combined Transmit/Receive module.

T/R switch prototype

As designed, the prototype T/R switch meets the power handling and switching time design targets. It also approaches the isolation and loss targets to within acceptable tolerances, considering the
intended application:

  • At 350 W incident power, only -20 dBm leaks through to the receiver; this is about 10 dB less than the level that low noise HEMTs can withstand indefinitely without degradation.
  • With a sky temperature exceeding 200 K and a receiver noise temperature of > 35 K, an extra 15 K noise temperature added by the T/R switch (36 K instead of 21 K) translates to a S/N loss of less than 6 %.

However, when the tests were started in the beginning of January, PIN-diode D1 in two different prototype T/R switches failed, even though the thermal load on these was estimated to be far below the specified maximum. The manufacturer admitted that the bonding strips connecting the diode chips to the external microstrip tabs were underrated and probably fusing under the RF current load. The factory promised to ship some improved engineering samples of the
diode, with larger bonding strips, for further tests.

The completed evaluation of the T/R switch prototypes is Milestone 9.5 of the project. This Milestone was reached in February 2013.