Conception et intégration en technologie LTCC d'un amplificateur faible bruit à structure balancée dans la bande C

Abstract

The performance of modern electronic systems for space and military applications are faced to high expectations, including higher integration densities and smaller form factors. This challenge has generated a strong need for miniaturization and higher levels of integration. Furthermore, broader-band performances are often sought due to the increased data rates, or in the case of tactical communications systems, due to the nature of the application. Achieving these goals simultaneously is a challenging task that requires well suited circuit fabrication technologies. Low temperature co-fired ceramic (LTCC) technology provides the ability to embed passive components within the body of the substrate which reduces significantly the size of a circuit. Among other things, LTCC technology is particularly useful for microwave and millimeter RF module designs due to the low losses at these frequencies. This promotes energy efficiency for power circuits and involves higher quality factors in different types of passive structures. However, one must ensure that RF performance of a given component is maintained while burying inside the substrate and adding the necessary transitions between various layers. This project covers the design and integration of a broadband balanced low noise amplifier (LNA) in LTCC technology for tactical applications. The main goal is to identify and validate experimentally the means to reduce the size of the LNA design that is centered at 4.7 GHz with a minimum of 600 MHz bandwidth. The balanced LNA structure consists essentially of two 90° hybrid couplers and two low-noise RF transistors. The LNA prototype is among the first complex circuits fabricated using LTCC technology at ETS’s LACIME laboratory. Preliminary results confirm the importance of developing a second iteration. In addition, this research presents a 3D integrated hybrid coupler 90° design hidden in the body of the substrate. The coupler, created initially for easy integration within balanced LNA structure, stays suitable for other RF applications. Particular care is placed on the design and optimization of transitions from the buried strip line coupler to coplanar probing pads at the surfaces. Measured results of the fabricated coupler are in good agreement with simulations and show good performance over a wide frequency band from 3.2 to 5.1 GHz; the return loss is better than 15 dB, the direct and coupled ports insertion losses are around 3±0.5 dB and the phase balance is 90° 1.5. These results are achieved with a small size (3.3mm × 6.8mm × 2.15mm) of the fabricated coupler. The operating temperature of the coupler is -55 to +85ºC.

Date	20 Apr 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Gagnon (Supervisor) & Ammar B. Kouki (Co-supervisor)