High Efficientcy 1.5 kW LDMOS HF Broadband Radio Transmitter

The design of HF radio transmitters with a power more than 300W requires the use of summing devices that combine the powers of individual amplifiers. The use of combiners leads to the complication of the transmitter and increase its dimensions and weight, which is very critical for onboard equipment. Attempts to develop a broadband amplifier with a power 1500 … 1800 W on a modern LDMOS transistor revealed certain difficulties associated with the parasitic parameters of a powerful amplifier. To achieve high output power of a transistor amplifier, it is necessary to reduce the load resistance of the output circuit of the final stage. In this case, the negative influence of the parasitic parameters of the output oscillatory circuit increases. The dissipation inductance of the transformer-short circuit and the mounting inductance in a class AB linear amplifier cause an increased voltage level of the even harmonics of the oscillatory voltage at the transistor drains, which reduces the attainable power of the amplifier while maintaining its safe mode of operation. The energy stored in parasitic inductances in switching amplifiers can lead to the destruction of transistors by self-induction voltage. In this article, we propose a mode of operation of transistors in a switching mode, which ensures high energy efficiency and full use of transistors in terms of power. The proposed mode can be successfully applied as part of an amplifier implemented using the Envelope Elimination and Restoration method (EER, also known as the Kahn technique). This method are most preferred for use in onboard devices where the supply power is limited.