A New UHF High Dynamic Range Receiver for the Arecibo Observatory

Open Access
Author:
Mills, Amanda Christine
Graduate Program:
Electrical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 03, 2013
Committee Members:
  • Julio Urbina, Thesis Advisor
Keywords:
  • low noise amplifier
  • cryogenic noise temperature measurement
  • coupled resonator filter
Abstract:
The Arecibo Observatory’s radio telescope studies the upper regions of the atmosphere using its 430 MHz receiver system. The current receiver has limited dynamic range and can saturate when detecting high power signals. The receiver is also plagued with a lengthy recovery time when overpowered by leakage from the nearby radar transmitter pulse. In this paper, a new design of a low noise amplifier (LNA) is presented, which will extend the receiver’s sensitivity and exhibit a faster recovery time from interference caused by the radar’s transmitter pulse. In addition, a compact high temperature superconducting (HTS) bandpass filter is introduced to the receiver chain to replace the receiver’s current cavity resonator filter. This newly designed planar filter improves the rejection of undesired signals detected by the 430 MHz receiver chain. Prototypes of both the low noise amplifier and bandpass filter have been designed, fabricated, and tested with successful results. Arranged in a balanced configuration, the LNA employs Gallium Arsenide (GaAs) high electron mobility transistor (HEMT) packaged-integrated circuits selected for their low noise characteristics. The amplifier prototypes were tested at room temperature and in a cryogenic environment. Final verification of the amplifier design involved precision cryogenic noise temperature measurement techniques commonly used in the field of radio astronomy instrumentation. Such methods eliminate many errors present in the standard cryogenic measurements. In addition, the bandpass filter design utilizes distributed microstrip elements to be fabricated from an Yttrium Barium Copper Oxide (YBCO) thin film superconductor on a Magnesium Oxide (MgO) substrate. The new filter prototype uses interdigital and hairpin resonators to improve spurious suppression and size reduction. This thesis will present a full description of the design process, validation, measurements, and results of each prototype’s performance. From analysis of the measurement results, the optimal amplifier and filter are selected as the new receiver components.