The antenna of a transceiver couples through a low pass filter to the input port of a high pass filter network. The high pass network is designed to reflect a very high impedance to its input port when its output port is at ground potential. The transmitter portion of the transceiver couples to the input port of the network with the receiver coupling to the network output port. A semiconductor diode couples from the output port to ground potential. In the receive mode the combination low pass and high pass filters couple received signals in the desired frequency band to the input of the receiver. Upon activation to the transmit mode the diode is forward biased whereby the network output port is taken to ground potential. In this mode the filter network effectively isolates the receiver from the transmitter.
A broadband PIN diode transmit/receive switch. The switch is used for electrically coupling a single antenna alternately to a transmitter and to a receiver. A first PIN diode for switching is connected between the antenna and an output port of a second order network, an input port of the second order network being connected to an output of the transmitter. A tuned tank circuit has an input port connected to the antenna and has an output port connected to an input of the receiver. A second PIN diode for switching is connected from the output port of the tuned tank circuit to an RF ground. A DC source controls the PIN diodes. When both diodes are forward biased the transmitter is connected to the antenna and is provided a good impedance match over a substantial bandwidth, otherwise the receiver is connected to the antenna.
A transmitting circuit is connected to an antenna via a first diode. The antenna is connected to a receiving circuit with the circuit including a strip line and a second diode. Two diodes are turned ON by applying a positive voltage to a first control terminal. In this state, a signal from the transmitting circuit is transmitted from the antenna. The transmission signal is not transferred to the receiving circuit side due to a series resonance circuit with the inductance of the second diode and a capacitor. When the high-frequency switch is used for reception, a positive voltage is applied to a second control terminal. The voltage is divided by a resistors respectively connected to the diodes in parallel, and applied to the diodes as a backward voltage. And hence, the diodes are surely maintained in the OFF state. The isolation between the transmitting circuit and the antenna is improved by a parallel resonance circuit with the capacitance of the first diode and a inductor.
An antenna switching apparatus for selectively connecting an antenna to either a transmitter for transmitting a transmitting signal having a transmitting frequency, or a receiver for receiving a receiving signal having a receiving frequency, which is different from the transmitting frequency, includes an antenna terminal electrically connected to the antenna; a transmitting terminal electrically connected to the transmitter, and a receiving terminal electrically connected to the receiver. A receiving filter for passing a receiving signal therethrough is electrically connected between the antenna terminal and the receiving terminal. An impedance adjusting element is electrically connected to an input end of the receiving filter, and has an element value such that an impedance when seen from the antenna terminal looking toward the receiving filter becomes substantially infinity at the transmitting frequency. Further, a switching device is electrically connected between the antenna terminal and the transmitting terminal, wherein it is turned on or off in response to a control signal.
A transmit-receive switching circuit is provided for switching a transmitter and a receiver to common antenna via a common signal path. A circulator is employed in the common signal path. The flow of transmitter RF energy and received RF energy is controlled through the circulator by a selectively actuable impedance element coupled to the circulator.
A changeover switch switches connection between an antenna and a transmitter amplifier and connection between the antenna and a receiver low noise amplifier, from one to the other. A first wire having characteristic impedance of 50 .OMEGA. connects the antenna and the changeover switch. A receiver matching circuit matches input impedance of the receiver low noise amplifier with the output impedance of the transmitter amplifier. An antenna side matching circuit matches the input impedance of the receiver low noise amplifier, which is matched with the output impedance of the transmitter amplifier by the receiver matching circuit, and the output impedance of the transmitter amplifier with the characteristic impedance of the first wire. The transmitter amplifier is connected with the changeover switch via a first coupling capacitance, and the receiver matching circuit is connected with the changeover switch via a second coupling capacitance.
