VHF (100-450 MHz) 250W Power Amplifier

Two octave wideband amplifier (covering both the civil and military airbands between 100 and 450 MHz), equipped with two MOSFET devices, which is capable of generating 250 W of output power are given on this design procedures and measurement results report. One of the two octave wideband amplifier has to use the device s with the output capacitance reduced to the utmost minimum in order to achieve a good broadband capability. It was possible to obtain a respectable power gain of more than 10 dB throughout the whole band while applying PHILIPS’ BLF548 MOSFETs. The BLF548 is a balanced N-channel enhancement mode vertical D-MOS transistor in a SOT262 package. This device is especially designed for use in wideband amplifiers up to 500 MHz. 150 W nominal output power at a supply voltage of 28 Volts can be delivered by the transistor. The attainable bandwidth will exceed 300 MHz due to the low output capacitance.

Notes
1. American Technical Ceramics type 100B or capacitor of same quality.
2. American Technical Ceramics type 175B or capacitor of same quality.
3. The striplines are on a double copper-clad PCB with P.T.F.E. fibre-glass dielectric (er = 2.2); thickness 1/32 inch.
4. T2 and T3 are equipped with a Toroidal core, grade 4C6 (cat.no. 4322 020 97171).

[Source: NXP Application Note]