K-band SATCOM ground terminal LNA with dual mode performance

Objectives

The primary product is a low noise amplifier (LNA) for K band SATCOM (18-26 GHz) ground terminals which will have two operating modes: normal and turbo. In turbo mode the noise figure is significantly reduced compared to normal mode by cryo-cooling the LNA circuit. By switching to the turbo mode the User can counter-act the effects of severe weather degradation on his communications link, which is a particular problem for K Band SATCOM.

The secondary product is standard uncooled LNA for K band SATCOM ground terminals. This product will be developed using the same MMIC circuit as for the primary product and so will benefit from a shared design and chip fabrication effort. The uncooled LNA will be competitive with existing K Band LNA products by offering state-of-the-art noise temperature performance.

Challenges

Given that the cryo/thermal design is already established and proven, the major technical risks in the proposed development of a K band LNA (both cooled and uncooled cases) are in the design of the RF circuit and its interfaces. Callisto has elected to work with the OMMIC foundry for the MMIC design using working relationships and experiences developed over the course of the past few years. The OMMIC Metamorphic HEMT process has been proven to offer very good noise performance for LNA designs in millimeter wave bands.

Benefits

The following table is a list of specification parameters for the dual mode LNA:

Parameter Value
Frequency Range 18 – 21.6 GHz
Overall gain > 55dB
Noise Figure Normal Mode 1.3 dB
Noise Figure Turbo Mode 0.4 dB
Input VSWR 1.7:1
Output VSWR 1.7:1
Output Power handling 1dB CP +5dBm
Environment temperature -40°C to + 60°C
Cool down time < 2hrs
Size (max) 280 mm x 220 mm x 160 mm
Mass < 3Kg
Mounting Any orientation. Both vertical and horizontal polarisations
Power Supply +24VDC
MTBF with nominal duty cycle >50000 hrs
Input RF Connection Waveguide
Output RF Connection Coax
Automatic Control of Operational Mode Normal/Turbo

The following table is a list of specification parameters for the uncooled LNA:

Parameter Value
Frequency Range 18 – 21.6 GHz
Overall gain > 25dB
Noise Figure Normal Mode <1.3 dB
Input VSWR 1.7:1
Output VSWR 1.7:1
Output Power handling 1dB CP +5dBm
Environment temperature -40°C to + 60°C
Input RF Connection Waveguide
Output RF Connection Coax

 

Features

The figure below is a block diagram of a typical small satellite ground terminal showing the Dual Mode LNA in the reception chain. The Dual Mode LNA subsystem is shown inside the dotted frame.


click for larger image

The signal coming from a satellite is received by the antenna, amplified by the LNA, down-converted to IF frequency and Data are extracted by the Modem. The Modem monitors the BER / EbNo and can generate an alarm if too much noise is received (due to weather conditions for example). This alarm is remotely accessible via serial or Ethernet auxiliary interfaces. This alarm is treated by the processor which activates or not the turbo mode of the LNA to compensate fading.

Plan

The starting point of this activity will take advantage of an existing project for a Miniature X Band cryo LNA which was done at Callisto. The thermal/mechanical design of the K band prototype was taken over from the small modifications and adaptations (for example due to different waveguide size). However, the RF design for the K band amplifier circuit was started from scratch.

Objectives were to design and develop a prototype dual mode LNA and to validate the performance by laboratory test and by field trials.

The key activities of the development phase were as follows:

  • RF circuit design and development using MMIC technology.
  • RF interface and support circuit design.
  • Thermal/mechanical housing (Dewar) design adaptation from existing X-Band design.
  • Prototype build and assembly.
  • Test bench development including preparation of operating, logging and processing software.
  • Laboratory testing.

Current status

The project is now completed. A fully functional prototype of the dual mode K Band LNA has been built and tested in the laboratory and validated by means of operational tests on a small ground terminal receiver. Some problems have been discovered with the prototype MMIC design which has resulted in a few non-conformances. However, design modifications have been implemented to improve the MMIC performance which will be proved by a 2nd chip fabrication run in Q3 2011. Manufacture and delivery of first production units is programmed for 2012.

Callisto would like to thank the ESTEC TIA-TTG team for their cooperation and support during the project. We would also like to say thank you to CNES DCT/RF/AR for their loan of ground terminal equipment under the CESAR program.

Contacts

Status date

Friday, August 5, 2011 - 12:13