Wave transmission lines and networks – Plural channel systems – Having branched circuits
Patent
1999-02-22
2000-08-29
Gensler, Paul
Wave transmission lines and networks
Plural channel systems
Having branched circuits
333104, H01P 115, H01P 512
Patent
active
061114758
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns a multi-port switching circuit. The embodiments of one realization may operate at frequencies around 60 GHz; but with appropriate devices embodiments may operate at other frequencies including higher frequencies up to and even exceeding 100 GHz.
BACKGROUND ART
Switching networks have been developed which operate at frequencies up to and exceeding 40 GHz. The switching elements in such networks use a combination of shunt passive FET devices and quarter-wave transformers, or combinations of series and shunt passive FET devices. Passive FET devices, in one type of switch, require bias to be applied to the gate and not between the source and drain. Broadband switches using a combination of active and passive switching elements have also been demonstrated.
SUMMARY OF THE INVENTION
The invention provides a multi-port switching circuit, comprising at least three ports, interconnected by transmission lines. The transmission lines are arranged with a central ring and outwardly extending arms. The ports are positioned at the ends of respective arms. The term "ring" has been used in a loose descriptive sense and does not necessarily imply circularity.
A switching device, such as a FET or HEMT, is associated with each port. The switching device is arranged between a first and a second transmission line. Each switching device may be arranged to shunt the main signal path of the circuit with its main current path extending between the junction of the first and the second transmission line, and signal ground. The first transmission line extends between the port and the switching device to provide impedance matching, and the second transmission line also provides impedance matching and a connecting path to the ring. The first and second transmission lines are initially chosen to have lengths of a quarter wavelength at the centre of the band of operation of the switch. The dimensions of the matching lines and the lines which form the connections to the ring are then determined using a procedure to optimize the performance of the circuit.
The optimisation procedure involves the selection of two of the ports as the input and output ports of the switching network. The switching devices associated with these ports are modelled by ON state representations. The other port, or ports, are isolated, and their associated switching devices are modelled in the OFF state. Optimisation of the transmission lines lengths and widths then aims to provide desired performance levels such as low transmission loss, good isolation at all other ports, low return loss or high power handling.
Other parameters such as gate width and length and substrate thickness may also be optimised, but these parameters are usually predetermined by selection of a particular fabrication process for the switching circuit.
The optimisation procedure continues by varying the signal flow in the circuit. That is, in the first step, the signals flow from a first port to a second port, with the other ports isolated; in the second step, signals flow from the second port to a third port with the other ports isolated. This process continues until a set of optimised parameters is established for each signal path configuration. The range of optimised parameters are then examined and a single best set of parameters is used to complete the design. The optimisation process uses conventional techniques and is able to take into account the effects of all the bends and discontinuities in the switch.
The optimisation provides similar switching performance between any pair of ports, independent of the chosen input and output.
The switching devices may be arranged symmetrically around the ring to simplify the optimisation process. However, symmetry is not a requirement.
HEMTs (High Electron Mobility Transistors) may be used to provide operation at high microwave frequencies. The choice of switching device influences, amongst other things, the power-handling capability of the circuit. Any switching device may be chosen. Two terminal device
REFERENCES:
patent: 4129838 (1978-12-01), Wallington et al.
patent: 4151489 (1979-04-01), Berman et al.
patent: 4302734 (1981-11-01), Stockton et al.
patent: 5757249 (1998-05-01), Gabara et al.
Gensler Paul
The Commonwealth of Australia Commonwealth Scientific and Indust
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