RF Power Amplifier for the Non-standard Frequency Band and Its Practical Implementation

This paper presents the design, development, and practical implementation of a Radio Frequency (RF) Power Amplifier (PA) optimized for a nonstandard frequency band of 720–760 MHz, intended for specialized broadcasting and communication applications. The amplifier was based on a Class AB topology, employing a laterally diffused metal–oxide semiconductor (LDMOS) transistor due to its high efficiency and linearity at sub-gigahertz frequencies. Simulation results obtained using ADS (Advanced Design System) predicted a small-signal gain of 18.7 dB, output power of 48.5 dBm (≈70 W) at a 1 dB compression point and a peak drain efficiency of 72.3%. The prototype was fabricated on a FR-4 substrate (εr = 4.4, thickness = 1.6 mm) with microstrip matching networks to achieve broadband performance across the target band. Experimental measurements demonstrated close agreement with simulations, yielding a measured gain of 18.1 dB, output power of 47.9 dBm, and a power-added efficiency (PAE) of 70.6% at 740 MHz. The amplifier maintained stable operation with a VSWR tolerance of up to 3:1 and harmonic suppression better than −42 dBc, meeting ITU spectral mask requirements. The successful realization of this RF power amplifier highlights its suitability for nonstandard frequency allocation scenarios, including emergency communications, experimental broadcasting, and defense-related RF systems