A novel image-rejection amplifier for wireless communications

The theory and design of a high-gain amplifier with image rejection capability is described, where the image rejection is accomplished by placing the transmission zeroes in the impedance match circuitry. The resulting amplifier provides high gain as well as high image rejection ratio. A 5.8 GHz image-rejection amplifier was designed and fabricated to verify the proposed technique. The measured results show 22 dB gain in the ISM band (5.725-5.850 GHz) and at least 43 dB image rejection at the image frequencies of 5.4 GHz and 6.15 GHz, which agree very well with the predicted theory.