US Patent 10348340 Apparatus and methods for front-end systems with reactive loopback

Apparatus and methods for front-end systems with reactive loopback are provided. In certain configurations, a front-end system includes an antenna port, a transmit port operable to receive a transmit signal, a receive port, an antenna switch, a back switch, a transmit port DC blocking capacitor coupled between a first end of the antenna switch and the transmit port, an antenna port DC blocking capacitor coupled between a second end of the antenna switch and the antenna port, a receive port DC blocking capacitor coupled between a first end of the back switch and the receive port, and a reactive loopback impedance coupled between a second end of the back switch and the first end of the antenna switch. The reactive loopback impedance provides a portion of the transmit signal to the receive port when the back switch is activated.