Evaluating Microwave BJTs for Use as a 6 GHz Noise Source

Solid state noise sources are a tool to evaluate noise figures (n/f) of low noise amplifiers (LNA). With noise diodes becoming more difficult to acquire, sourcing alternative and readily available RF transistors operating as a reversed bias diode would be beneficial in the study of receivers. Several microwave bipolar junction transistors (RF BJT), from new old stock (NOS) and currently manufactured, were sourced and evaluated for a noise output goal of more than 25 dB. The noise source design frequency was initially in the lower C band spectrum of 3.4 to 6 GHz. Two different circuit configurations were used for the BJTs. Evaluation of the highest excess noise ratio (ENR) device was then extended and optimized to cover the range of 100 to 6000 MHz while operating from a 28 V source.