Microwave switch (MS) comprising an antenna branch (AB), a receive branch (RB), and a transmit branch (TB). According to one embodiment, the switch comprises a protection circuit (CPL, DTC, CTRL), which upon a high power signal (Dtc_h) being present on the antenna branch effectuates a biasing of semiconductors on both the receive branch (RB) and the transmit branch (TB). According to one embodiment PIN diodes are provided for controlling switching between the transmit and the receiv branch as well as enabling a protective mode, the control being accomplished by selectively biasing respective diodes.

An inventory management system which includes a transponder, an interrogation transceiver and control devices utilized therewith. The control devices operate to minimize the power consumption of the transponder while permitting selected, coded operation of the inventory management system. The interrogation transceiver provides linkage to the transponder by means of a modulated radio frequency (RF) carrier during system operation. A transmit/receive switch is also included in the invention to prevent harmful coupling between the transponder receiver and the transponder transmitter. This could occur during data exchanges between the transponder and the interrogation receiver.

A high performance single-pole-double-throw (SPDT) Transmitter/Receiver (T/R) FET switch utilizes a plurality of multi-gate FETs in series to realize low insertion loss, low harmonic distortion and high power handling capabilities. The SPDT switch consists of an antenna port, a transmitter branch coupled to a transmitter port through a plurality of multi-gate FETs in series and a receiver branch coupled to a receiver port through a plurality of multi-gate FETs in series. When a high power signal passes from the transmitter port to the antenna port through the transmitter branch, the receiver branch is required to be shut off electrically to prevent the high power signal from leaking to receiver port. This leakage can degrade the isolation of the switch and cause harmonic distortion. Furthermore, the transmitter branch is required to provide a resistance as small as possible to reduce the power loss when it passes through the transmitter branch to the antenna port. In the receiver branch, two of the gate metals in the multi-gate FETs are fabricated with gate sizes several times larger than the others. Furthermore, a heavily doped cap layer is utilized between the gate fingers in a multi-gate FET to reduce the channel resistance of FET, thereby lowering the insertion loss.

A SPDT switch includes an antenna port. A transmitter section is coupled to a transmitter port. The transmitter section includes a plurality of transistors that are coupled in series relative to each other. A receiver section is coupled to a receiver port. The receiver section includes a plurality of transistors that are coupled in series relative to each other, so that when the transmitter section transmits high power to the antenna port, the receive section is effectively off to provide isolation to the receive port. The receiver port is coupled to the receiver section using at least one external capacitor. The at least one external capacitor is used to improve the power handling capability and harmonic performance of the switch.

An apparatus and method are provided for continuously and automatically protecting an electrical device (22) from a potential threat of damaging voltage levels. The apparatus includes a detector (24) for the threat and a protection switching circuit (30) for grounding the electrical device and the detector upon detection. Grounding occurs for a predetermined time interval, after which the detector is again automatically re-activated. Embodiments of detectors include detectors which detect the degree of electrical changes in a surrounding field and detectors comprising a tuned radio receiver. One embodiment includes a device utilization monitor (222) and a detector disable circuit (224) for disabling the detector, and thereby precluding grounding, while a device such as a radio frequency transmitter is being utilized.