| 摘要 |
PURPOSE:To obtain an antenna switching circuit at low cost with high spurious wave rejecting performance by providing an element preventing mixture of a transmission frequency and its harmonics to an operating section activating a switch means switching the transmission state and reception state. CONSTITUTION:A switching diode D5 goes to a low impedance state by applying a bias voltage to the D5 from a terminal 23 at transmission, a transmission signal inputted from a transmission side terminal 1 is subject to rejection of harmonics by an LPF9 and the result if led to an antenna terminal 7. The operating section activating the D5 is provided with microstrip lines 37, 39. The length of the strip lines 37, 39 is selected as 1/4 of the operating transmission/reception frequency band wavelength. Thus, the lines 37, 39 are of high impedance at the operating frequency and low impedance to even hamonics in the operating frequency, then the lines act like short-circuit circuits, which eliminate a spurious wave. Since no DC bias is fed to the terminal 23 at reception, the D5 is of high impedance and a reception signal inputted from the terminal 7 passes through a BPF27 and is inputted to a reception terminal 25. |
