LDMOS Transistors in Power Microwave Applications

More than ten years ago LDMOS transistors were introduced as a replacement of bipolar transistors for RF power applications [1,2].

Nowadays LDMOS technology is the leading RF power technology for base station applications, in particular for GSM-EDGE applications at 1 and 2 GHz, WCDMA applications at 2.2 GHz and more recently for WiMax applications around 2.7 GHz and 3.8 GHz.

One of the last niche application areas in which bipolar devices were used was the 3-4 GHz microwave area, such as S-band radar. Main reason for this was that earlier generations of LDMOS showed a similar performance at 3 GHz compared to bipolar, which did not justify redesign of complex radar systems.

The main driver for LDMOS is a high volume application, which enables continuous improvement of the LDMOS technology [3,4], and this has resulted in the latest generation LDMOS, which outperforms bipolar at S-band frequencies with some additional advantages such as ruggedness and better thermal behaviour. In this article an overview is given of the LDMOS improvements at 3-4 GHz and the LDMOS performance for microwave products is presented.