Patent Application
20150288042
The present invention relates to phase shift circuitry, and in particular, to passive phase shift circuitry providing a substantially constant phase shift over a wide frequency band.
Many of today's electronic devices use wireless signal technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless signal technologies must adhere to various wireless signal technology standard specifications.
When designing such wireless devices, engineers take extra care to ensure that such devices will meet or exceed each of their included wireless signal technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless signal technology standard-based specifications.
When testing radio frequency (RF) devices and systems in general, and wireless RF devices and systems in particular, there is often a need for shifting the phase of a signal being transmitted or received via a particular signal path. For example, when testing devices using one or more wireless signal paths, such as within a shielded enclosure or another form of controlled signal path environment, one or more antenna elements (e.g., an antenna array) may be used along with phase shifting elements to allow for shifting of signal phases within the one or more signal paths between the signal source and each antenna element so as to mitigate multipath signal interference effects. (Such test enclosures and wireless signal testing techniques are disclosed in U.S. Patent Publications 2014/0266929 and 2014/0266930, the contents of which are incorporated herein by reference.)
A variety of RF signal path structures exist that can produce variable amounts of phase shift. For example, simply having two transmission lines of different lengths will cause the signals conveyed by such lines to experience mutually distinct phase shifts, thereby causing a phase shift of one signal relative to the other. However, simply using a selected length of transmission line will introduce a phase shift that varies as a linear function of signal frequency. Accordingly, a desired amount of phase shift can only be achieved over a very narrow bandwidth.
One technique that has been developed to increase the bandwidth available over a passive transmission line is known as the Schiffman phase shifter design, which uses a transmission line and a coupled section to provide a wider bandwidth over which a desired phase shift can be imparted. However, achieving that wider bandwidth requires tight signal coupling between transmission line elements, which can make implementation difficult.
Another technique that has been developed, often referred to as a compact ultra wideband phase shifter, can achieve a wide phase shift bandwidth (e.g., 3-11 GHz). However, the phase difference is limited to 30 degrees or less.
Accordingly, it would desirable to have a technique for providing selectable amounts of significant phase shift, e.g., 90 degrees or more, over a wide frequency band.
In accordance with the presently claimed invention, circuitry fur shifting a phase of a radio frequency (RF) signal. Mutually dissimilar and electrically coupled portions of an electromagnetic transmission line pattern on one side of a substrate interact with another electromagnetic transmission line pattern on the opposing substrate side to convey a RF signal with a phase shift that is determined by the RF signal frequency and respective dimensions of the electromagnetic transmission line patterns and is substantially constant over a wide bandwidth. With multiple implementations of such opposing electromagnetic transmission line patterns having different pattern dimensions and coupled between RF signal switches, multiple phase shifts can be selectively provided.
In accordance with one embodiment of the presently claimed invention, circuitry for shifting a phase of a radio frequency (RF) signal includes: a substrate formed of an electrical insulator and having mutually opposed first and second sides; a first electrically conductive layer disposed on the first side and including a first electromagnetic transmission line pattern with mutually dissimilar and electrically coupled first and second pattern portions electrically coupled between first and second signal terminals; and a second electrically conductive layer disposed on the second side and including a second electromagnetic transmission line pattern for electromagnetic communication with the second pattern portion.
In accordance with exemplary embodiments, the first pattern portion includes a microstrip structure, and the second pattern portion and second electromagnetic transmission line pattern together include a patch-slot structure.
The following detailed description is of example embodiments of the presently claimed invention with references to the accompanying drawings. Such description is intended to be illustrative and not limiting with respect to the scope of the present invention. Such embodiments are described in sufficient detail to enable one of ordinary skill in the art to practice the subject invention, and it will be understood that other embodiments may be practiced with some variations without departing from the spirit or scope of the subject invention.
Throughout the present disclosure, absent a clear indication to the contrary from the context, it will be understood that individual circuit elements as described may be singular or plural in number. For example, the terms “circuit” and “circuitry” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together (e.g., as one or more integrated circuit chips) to provide the described function. Additionally, the term “signal” may refer to one or more currents, one or more voltages, or a data signal. Within the drawings, like or related elements will have like or related alpha, numeric or alphanumeric designators. Further, while the present invention has been discussed in the context of implementations using discrete electronic circuitry (preferably in the form of one or more integrated circuit chips), the functions of any part of such circuitry may alternatively be implemented using one or more appropriately programmed processors, depending upon the signal frequencies or data rates to be processed. Moreover, to the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry.
Wireless devices, such as cellphones, smartphones, tablets, etc., make use of standards-based technologies, such as IEEE 802.11ab/g/n/ac, 3GPP LTE, and Bluetooth. The standards that underlie these technologies are designed to provide reliable wireless connectivity and/or communications. The standards prescribe physical and higher-level specifications generally designed to be energy-efficient and to minimize interference among devices using the same or other technologies that are adjacent to or share the wireless spectrum.
Tests prescribed by these standards are meant to ensure that such devices are designed to conform to the standard-prescribed specifications, and that manufactured devices continue to conform to those prescribed specifications. Most devices are transceivers, containing at least one or more receivers and transmitters. Thus, the tests are intended to confirm whether the receivers and transmitters both conform. Tests of the receiver or receivers (RX tests) of a device under test (DUT) typically involve a test system (tester) sending test packets to the receiver(s) and some way of determining how the DUT receiver(s) respond to those test packets. Transmitters of a DUT are tested by having them send packets to the test system, which then evaluates the physical characteristics of the signals sent by the DUT.
In general, testing of wireless devices is preceded by the connecting of those devices to their respective test subsystem or system using conductive signal connectors. However, in some instances (e.g., as discussed in the patent applications identified above), the interfaces between the devices and the test equipment include wireless signal paths over which the signals are conveyed electromagnetically. Confined to relatively small electromagnetically shielded enclosures, the test signal interface includes arrays of antenna elements within the enclosure thru which the wireless signals are received or transmitted, with the individual antenna signals adjusted in phase. Such a testing environment using arrays of antenna elements requires a mechanism for shifting signal phases in the respective signal paths between the signal sources and transmitter antenna array elements, or between the receiver antenna array elements and the signal receiving subsystem. Given the operating requirements of the devices, these phase shifters must operate over wide frequency ranges with minimal insertion losses. Further, they must be capable of matching the voltage standing wave ratio (VSWR) of the signal paths to which they are connected to minimize return losses.
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Similarly, referring to the adjoining circuit structure 20b, a signal entering the input port 32b and existing output port 34b will experience a phase shift as well. If the various circuit structure dimensions 23a, 25a, 27a, 29a, 31a are the same, the phase shift will be the same. However, if the dimensions of the second structure 20b differ from those of the first structure 20a, there will be a phase difference between the two signals existing the output ports 34a, 34b.
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Differences in phase shift between the first circuit structure 20 and second circuit structure 40 can be compensated using techniques well known in the art, such as including lumped circuit elements, such as lumped capacitances and/or inductances in the form of a network 41 such as a T-network (two shunt circuit reactances of a first type separated by a serial reactance of a second type) or a π-network (a shunt reactance of a first type connected between two serial reactances of a second type).
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Various other modifications and alternations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and the spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments, It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
