Design of a broadband LNA with multifunction Circuitry based on composite right /left handed transmission lines for impedance matching and suppression of unwanted frequencies

This article presents a low-noise amplifier based on the use of a composite right-left handed transmission line consisting of a single microstrip line and a split ring resonator at the transistor input and output. This design ensures optimum matching over a wide frequency range while eliminating an unwanted frequency band. The circuit is designed to operate at a center frequency of 2.4 GHz while simultaneously eliminating the frequency band around 4.8 GHz, meeting key performance criteria including improved gain, better stability, and significant noise reduction. To achieve these objectives, the transistor used undergoes precise biasing via a DC power supply. In this process, a specifically selected capacitor is arranged in series with a λ/4 transformer. This transformer, in turn, is connected in series to a radial line section. The dimensions of the proposed amplifier are 70 × 34 mm2.For validation purposes, the proposed method was implemented through design, manufacture, and testing. The results obtained show that the proposed low noise amplifier achieves a high gain of 15.27 dB, an input reflection loss S11 of −16.26 dB, an output reflection loss S22 of −13.94 dB, and an inverse isolation S12 of −22.82 dB at 2.4 GHz, with a resonance peak at 4.8 GHz allowing the surrounding frequency band to be eliminated with an attenuation of 77 dB at 4.8 GHz. What's more, the noise figure is kept below 2 dB, with unconditional stability in the desired frequency band.