GB2612820A

GB2612820A - A radio frequency circuit with passive phase gain

Info

Publication number: GB2612820A
Application number: GB2116355.5A
Authority: GB
Inventors: Cash Ian
Original assignee: International Electric Co Ltd
Current assignee: International Electric Co Ltd
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2023-05-17
Also published as: GB202116355D0

Abstract

A radio frequency (RF) circuit 101 for use in a phased array comprises: an RF coupler 120 that receives a pair of anti-phase vector RF signals and resolves them into a pair of orthogonal vector RF signals corresponding to real and imaginary components of the received anti-phase vector RF signals; a phase multiplier circuit 100 comprising a pair of input ports 150a-b each receiving one of the resolved RF signals output from the RF coupler and at least one output port 111-112; in which the phase multiplier circuit generates a pattern of constructive and destructive interference between the two input RF signals, and the at least one output port is positioned relative to the pattern such that the phase of an RF signal output from the output port is a fixed multiple of the phase of the signal at a first one of the pair of input ports. The RF circuit may be used in a cascaded phase multiplying RF circuit (Figure 1). An RF element (400, Figure 5) for use as the phase multiplier circuit is also disclosed, which comprises a reflective boundary which may comprise a pair of intersecting elliptical arc boundaries (401, Figure 5).

Description

A RADIO FREQUENCY CIRCUIT WITH PASSIVE PHASE GAIN

This invention relates to radio frequency (RF) circuits for passive phase gain, i.e., phase amplification or multiplication. It also relates to a phased array and to an RF element for use in such circuits.

Both one-and two-dimensional phased arrays are well known. In a typical arrangement of a phased array, one phase-shifting device referred to in this document as a phase shifter is associated with each element (or between adjacent elements in the case of a serial configuration). The phase shifters can either be controlled independently or (more typically for uniformly spaced planar and linear arrays) varied such that the phase difference between each adjacent pair of elements is essentially the same for each dimensional axis. Thus, the RF wavefront emitted from the array can be steered in one or two dimensions (i.e., azimuth, elevation) with a simple relationship between steering angle and the common phase difference between adjacent elements in each axis. The requirement for multiple phase shifters and control circuitry adds to the bulk and complexity of the array.

US4408205A discloses an alternative passive array driving technique for one-dimensional arrays in which the multiple phase shifters could, in-principle, be replaced by a passive element known as a Rotman lens. A typical Rotman lens is shown in Figure 10 of the drawings. This essentially 2D structure can be implemented as a waveguide, printed circuit, or by other techniques.

Figure 10 depicts electromagnetic waves confined within a 2D plane (the Rotman lens), where the size of the lens is several multiples of the wavelength. For a dielectric medium with a dielectric constant K, this wavelength will be shorter than that seen in a vacuum (by 1h/K). Figure 10 shows RF power entering the lens at port 501, with beam dispersion effecting power splitting across the output ports 513 to 522. These output ports would then drive the elements of a phased array (dummy ports 505 to 508 and 509 to 512 connect to resistive loads).

If a further input port were to be placed between ports 502 and 503, then it is clear from inspection that output ports 513 to 522 are equidistant from this new port and thus zero phase difference (or nearly so) should be expected between any pair of output ports.

The phase difference between adjacent output ports, and the phase step resolution, is determined by the chosen input port, the lens geometry, and the number of output ports. A beam can be steered by switching RF power through to the appropriate input port to achieve the desired phase step and hence steering angle. However, it can be seen that such a lens cannot produce a continuous, smooth sweep of beam direction emitted from a connected phased array antenna. The number of active components is principally determined by the number of switched inputs to the lens but also includes controlled variable passive components.

It is an object of the invention to provide an RF circuit topology that is suitable for use in a one dimension or two-dimensional phased array that will greatly reduce the number of active components required, and at least one aspect to provide an array which is capable of emitting a smoothly swept beam of RF radiation at a fixed frequency with no steps in angle.

According to a first aspect the invention provides a radio frequency (RF) circuit suitable for use in a phased array comprising: an RF coupler which is adapted to receive a pair of anti-phase vector RF signals and to resolve them into a pair of orthogonal vector RF signals that each respectively correspond to the real and imaginary components of the received anti-phase vector RF signals, a phase multiplier circuit comprising a pair of input ports, each receiving a respective one of the pair of resolved RF signals output from the RF coupler, and at least one output port connected to the pair of input ports, in which the phase multiplier circuit is configured to generate a pattern of both constructive and destructive interference between the two RF signals at the input ports and in which the output port is positioned relative to that pattern such that the phase of an RF signal output from the at least one output port is a fixed multiple of the phase of the signal at a first one of the pair of input ports.

The phase multiplier circuit may have a fixed gain or multiplication factor for a defined frequency of RF signal which may be relatively constant over a narrow band of frequencies. The gain may be substantially constant over a range of phases of the input signals.

The multiplication factor may be an integer or non-integer value and may be less than one or greater than one. In at least one preferred arrangement the gain may be equal to 0.25. The value of the fixed gain can be set by appropriate sizing and positioning of the input and output ports and the interference pattern provided by the circuit.

The phase multiplier circuit may have a second output port positioned relative to the interference pattern such that the phase of an RF signal output from the second output port is a second fixed multiple of the phase of the RF signal at one of the pair of input ports.

The second output port may be positioned relative to the interference pattern such that the phase of an RF signal output from the second output port is a second fixed multiple of the phase of the signal at a second one of the pair of input ports. This may be the same multiple as the first output port.

The phase multiplier circuit therefore will provide, in one arrangement, a pair of anti-phase RF signals whose phase difference is a multiple of the phase difference between the two RF signals at the input ports.

The phase multiplier circuit may have a third output port, and may have a fourth output port. It may have five or more output ports.

In a most preferred arrangement, there are third and fourth output ports, each located relative to the pattern of interference such that the phase of an RF signal output from the third and the fourth output ports is a different fixed multiple of the phase of one of the RF signals at one of the inputs ports.

The third and fourth output ports may have the same multiplication factor as each other, which is a different multiple to that of the first and second output ports.

The RF circuit may be entirely passive, and at least the phase multiplier circuit of the RF circuit may be entirely passive, wherein it comprises no active electronically or mechanically controlled components and requires no control signals to generate a required multiplication or gain. The entire RF circuit may comprise conductive circuit traces for example. The phase multiplier circuit may be implemented without any switches, only fixed components being used.

In one advantageous arrangement, the two RF signals output from the RF coupler may have equal but opposite phases. E.g., +45° for one and -45° for the other relative to an arbitrary zero phase RF signal.

The RF circuit may include, prior to the RF coupler, a splitter that receives a single RF signal and splits this into two anti-phase outputs. These may have equal magnitude. The RF coupler functions to resolve these two RF signals into their real and imaginary components.

The RF coupler may comprise a rat-race coupler. The RF coupler may include two input ports that receive a pair of out of phase RF signals and provide, at the output ports, the real and imaginary RF signals which respectively comprise a vector sum of the two received RF signals and a vector difference of the two received RF signals, the two resolved output RF signals being fed to the phase multiplier circuit.

In particular, for an RF signal with wavelength A, the rat-race coupler typically comprises four ports; two input ports and two output ports arranged alternately around a ring, with three path length separations of A/4 and one path length separation of 3A/4, closing the loop. With appropriate impedance matching, one output is the vector sum of the two in-phase inputs (A/4 -A/4 = 0), the other being the vector difference (3A/4 -A/4 = A/2, i.e., anti-phase). For two equal-magnitude RF signals at the input ports having differential phase, the outputs may also be considered as the resolved orthogonal (real / imaginary) magnitudes corresponding to the half-angle difference between the RF signals at the input ports. A rat-race coupler is reciprocal, i.e., inputs and outputs may be interchanged and the function reversed.

The phase multiplier circuit may comprise a reflective boundary, the input ports directing two RF signals towards the boundary and the reflected RF signals from the boundary generating the pattern of interference.

The boundary may define a pair of concave intersecting elliptical arc boundaries, from which the RF signals are reflected to generate the pattern of constructive and destructive interference.

The two intersecting elliptical arc boundaries may each have two foci, with one input port being located at one of the foci and one or more of the output ports located closer to the other foci than to the input port. The relative shape and configuration of the input and output ports of the phase multiplier circuit, the arc boundaries and the foci determine the relationship between the phases of the RF signals at the input ports and the RF signals output at the or at each of the output ports.

One focus of the first elliptical arc boundary may be substantially or exactly coincident with one foci of the other elliptical arc boundary. The input ports may be located at the two foci which are not coincident.

The phase multiplier circuit may include at least one additional output port which receives a part of the RF signal originating from the RF signals received at the input ports of the phase multiplier circuit and feeds that RF signal back to the input ports of the RF circuit where it propagates again through the RF circuit. This allows for the power loss that may otherwise be present in this design to be reduced. Such a loss may otherwise occur if some of the RF signal, from the RF signals received at the input ports, is not directed to the (non-additional) output ports. This RF signal may instead be incident on the additional output port.

In an alternative arrangement, the phase multiplier circuit may be configured such that RF signals received at the input ports are refracted so as to generate the interference pattern.

The phase multiplier circuit may have a refractive design and include a dielectric medium and one or more refractive lenses arranged to generate the interference pattern from the two RF signals received at the input ports. The use of a reflector, as in a mirrored arrangement, rather than a refractive lens has a potential benefit in that reflections caused by RF signals entering and leaving the dielectric medium in a refractive design may generate unwanted effects which are not a concern with a mirrored arrangement. However, the applicant appreciates that use of reflective design may lead to minimisation of the area of implementation and it is within the scope of an aspect of the invention to use lenses and not to include any reflective boundary.

The RF circuit may include a delay line which applies an additional 90° phase shift to one of the real and imaginary components to provide two resolved RF signals that have a 180° phase difference between their vector components.

Two RF circuits, each having the features recited above with two input ports and at least one pair of output ports, may be arranged in a cascade to form a cascaded phase multiplying RF circuit.

Each of the RF circuits may be identical, with the phase multiplying circuit of each one having the same phase multiplication factor.

The cascaded phase multiplying RF circuit may comprise two RF circuits arranged in a cascade where an RF signal from one output port of one phase multiplying circuit forms an input RF signal fed to an input of the RF coupler on the other phase multiplying circuit.

Each RF circuit in a level of the cascade may have two or more output ports, with the output RF signals of at least two of the output ports being fed to a subsequent level in the cascade or in the case of the bottom level fed to an antenna.

The cascaded phase multiplying RF circuit may provide a linear or a tree like configuration of RF circuits or a combination of both linear and tree like configurations as required.

The cascaded phase multiplying RF circuit may comprise a plurality of RF circuits arranged in a cascade of at least two, or three or more levels, with each level comprising two or more RF circuits to give a tree configuration.

According to a second aspect, the invention provides a phased array comprising a cascaded phase multiplying RF circuit according to the first aspect, and a set of antennae, each antenna connected to a respective one of the output ports of the phase multiplying circuits of the RF circuits in a final level of the cascaded phase multiplying RF circuit.

The RF circuits and antennae of the phased array may be linearly arranged as one row of antennae, to form a linear phased array, or as a two-dimensional array in which the antennae are arranged in a grid to define rows and columns of antennae.

The phased array may include an active phase shifter which is in a path upstream of the splitter of the RF circuit which receives a single RF signal from an RF source and generates the pair of anti-phase RF signals, the active phase shifter setting the phase difference between the two anti-phase RF signals. For example, the active phase shifter may be configured to vary the phase difference between the generated anti-phase RF signals may be varied between 00 and 180°. This will in turn control a steering angle of the antennae as it will vary the phase difference between the RF signals output from adjacent output ports in the phased array.

The phased array may include a controller which controls the phase shift set by the active phase shifter. In this way, a continuous, smoothly steered output RF signal could be achieved at the cost of a single (high-resolution) active phase-shifter, where the required passive circuitry may be implemented as a copper pattern in the printed circuit. Cost is then determined principally by the area of PCB material required, not by the intricacy of the copper pattern produced.

The phased array may comprise only passive componentry to generate the required output RF signals for each antenna with the only active parts of the phased array being the active phase shifter(s) and any RF power amplifier(s) at the very input to the RF circuit.

In an alternate arrangement, a plurality of cascaded phase multiplying RF circuits may be connected in two layers where the second layer comprises double the number of cascaded phase multiplying RF circuits as the first layer. The first layer comprises two cascaded phase multiplying RF circuits which each receive RF signals at their input ports from a separate active phase shifter. Each of the active phase shifters receiving an input RF signal from an RF source and generating a pair of anti-phase RF signals. The second layer comprises four cascaded phase multiplying RF circuits where the RF signals output at the output ports of the first layer are connected to the input ports of the second layer. The two layers are connected such that each cascaded phase multiplying RF circuit in the second layer receives one RF signal from each cascaded phase multiplying RF circuit in the first layer. The output ports of the cascaded phase multiplying RF circuits in the second layer are each connected to antennae arranged in a 2D grid. In this way the RF circuit may be utilised in a two-dimensional phased array. It will be obvious to a person skilled in the art that this arrangement may be replicated to increase the size of the array.

The phased array may be operable to provide a range of beam directions or beam patterns from a single fixed frequency (or narrow band) RF source, with the output RF signals having a fixed RF frequency over the range of different beam patterns.

According to a third aspect the invention provides an RF element comprising: a pair of input ports, and at least one output port connected to the pair of input ports, in which the phase multiplier circuit is configured to generate a pattern of both constructive and destructive interference between the two input signals and in which the output port is positioned relative to that pattern such that the phase of an RF signal output from the output port is a fixed multiple of the phase of the signal at a first one of the two input ports.

By element we mean a component or functional building block that can be used within an RF circuit.

The RF element provides a multiplication of the of one of the two RF signals at the input port without the need for any active components. By performing this function over a range of input phase differences the circuit performs the function of a passive phase multiplier circuit.

The RF element may generate the pattern of interference through reflection of one or both input signals from a boundary. Preferably both signals are reflected from the boundary.

The reflective boundary may comprise a pair of intersecting elliptical arc boundaries from which the RF radiation is reflected, each area bounded by the pair of intersecting elliptical arc boundaries having two foci for reflected RF radiation.

Boundary refers to a region in which an RF signal is incident on an elliptical arc will see a sharp impedance change at the elliptical arc, which may be implemented as an open circuit, or short-circuit between the RF signal and ground layers (a series of electrical vias connecting the layers, spaced by a small fraction of the local wavelength, would be an effective short circuit).

This sudden impedance change will cause the ray to reflect off the elliptical arc boundary.

The pair of intersecting elliptical arc boundaries may be arranged so that one foci of each elliptical arc is coincident or close to one foci of the other elliptical arc, with the two remaining foci located either side of these coincident foci, and whereby the output port is located at or close to one of the two coincident foci and each of the input ports at or close to a respective one of the non-coincident foci.

Most preferably, there are two output ports each located at equal but opposite distances from the coincident foci.

The RF element may include at least one additional output port which receives a part of the RF radiation applied to the input ports in the form of RF signals and feeds that RF radiation back to the input ports where it passes again through the volume. This allows for the power loss due to some of the RF radiation at the input ports not being passed to the primary output ports but being fed to the additional output port(s) rather than being reflected further around the volume or absorbed by the boundary.

The additional output port or port may be located between the input ports and the output ports.

The interference pattern may be generated within a volume which may be substantially two dimensional and may be defined by a conductive track, for example of copper, formed on a substrate. The intersecting elliptical arc boundaries may be defined by edges of the copper track.

The use of reflective boundaries having shapes which differ from pure elliptical in place of the intersecting elliptical arc boundaries may also be considered, which may benefit the linearity of the relationship between the phase of the RF signals at the input ports to the phase of the RF signals at the two output ports, or more-equally distribute the power across the two output ports. Additionally, this may result in there being more than two foci for each reflective section.

The RF element is mostly described here in-terms of a printed circuit implementation but could equally be implemented using waveguides or over free-space.

Whilst the RF element of the third aspect may be used in a phased array, the applicant has appreciated that the mirrored arrangement of the phase multiplier circuit may also be used in reverse, where a pair of RF signals fed into the primary output ports may generate a broad steerable lobe within the volume where the power in the lobe is split at the intersection of the elliptical arc boundaries with proportions of the lobe being output from the input ports according to the steering angle.

This arrangement may be useful in a range of applications such as a phase-controlled variable attenuator, a switch capable of RF switching between outputs ports without contacts or semiconducting switch elements, and an ultrafast digital logic operating in the RF domain, such-as an AND / NAND, etc. The applicant has appreciated that the RE element of the third aspect can require less material area than other means (due to the overlap of incident and reflected RE radiation) and provide a concentration of output power around the coincident foci from small input and output port apertures.

There will now be described by way of example several embodiments of the present invention with reference to and as illustrated in the accompanying drawings of which: Figure 1 is an overview of the RE component parts of an exemplary cascaded phase multiplying RE circuit according to an aspect of the invention; Figure 2 is a detailed view of one RE circuit of the cascaded phase multiplying RE circuit of Figure 1; Figure 3 is a detailed view of an alternative arrangement of an RE circuit for use in the cascaded phase multiplying RE circuit of Figure 1; Figure 4 is a simple overview of the key components of a linear phased array in accordance with a second aspect of the invention; Figure 5 is a representation in cross section of an RE element according to a third aspect of the invention in an RE circuit of the type shown in Figures 3 and 4; Figure 6 is an analysis of the magnitude and phase response of the RE element when two equal wavelength, equal magnitude and equal phase RE signals are applied at the input ports; Figure 7 is an analysis of the magnitude and phase response of the RE element when two equal wavelength, equal magnitude RE signals with a 180° phase difference are applied at the input ports; Figure 8 is an analysis of the magnitude and phase response of the RE element when the two RE signals applied at the input ports are resolved signals and +45° phase difference.

Figure 9 is an analysis of the magnitude and phase response of the RE element when the two RE signals applied at the input ports are resolved signals and -45° phase difference Figure 10 is an illustration of a Rotman lens; Figure 11 shows a rat-race coupler that can be used to resolve the two anti-phase RE signals applied to each RE circuit of the array of Figure 4; Figure 12 shows the power division with phase gain of the RE element of Figure S with no power feedback as shown for the RF circuit of Figure 2; Figure 13 shows the power division with phase gain of the RE element of Figure 5 with some power feedback as shown for the circuit block of Figure 3; and Figure 14 shows an implementation of RF circuits within a two-dimensional phased array Figure 1 shows an embodiment of a cascaded phase multiplying RF circuit 1 which incorporates at each level one or two RF circuits that are within the scope of one or more aspects of the invention.

The cascaded phase multiplying RF circuit 1 comprises four levels, although the reader will understand that it may include any whole positive integer N number of levels, depending on how much phase multiplication is needed. In the context of this invention the term phase multiplication refers to the number of different phases of RF signal are provided at the output ports compared to the two phases provided at the input. In the example of Figure 1, the two phases of the RF signals at the input ports form four different phases of RF signal at the output ports, where the phase difference between each adjacent pair of output ports is essentially equal to the phase difference between the RF signals at the input port pair. The amount of multiplication is not therefore dependent on the number of levels.

The first level of the cascaded phase multiplying RF circuit 1 comprises an RF circuit 101. Each subsequent level of the cascaded phase multiplying RF circuit of Figure 1 comprises two identical RF circuits with phase multiplying capabilities 102-102, 103-103 and 104-104. The input ports for the cascaded phase multiplying RF circuit 1 comprise the input ports of the RF circuit 101 in the first layer while the output ports of the cascaded phase multiplying RF circuit 1 comprise a pair of output ports 122a-122b and 122a1-122131from each RF circuit 104, 104' in the final layer (fourth in this example).

Figure 2 shows a first design of an RF circuit that can be used. The RF circuit has two input ports 113a-113b and 2 pairs of output ports 1113-111b and 112a-112b. Each RF circuit comprises an RF coupler 120 and a phase multiplier circuit 100. The two input ports 150a-150b to the phase multiplier circuit 100 are connected to output ports of a rat-race or similar RF coupler. Many different RF coupler types are known in the fields of RF, microwave and millimetre-wave engineering such-as the "magic -rn waveguide component.

A suitable rat-race coupler 900 is shown in Figure 11. For an RF signal with wavelength X, the rat-race coupler 900 comprises four ports 901 to 904; two input ports and two output ports arranged alternately around a ring, with three path length separations of X/4 (905) and one path length separation of 3X/4, (906) closing the loop. With appropriate impedance matching, one output is the vector sum of the two in-phase inputs (A/4 -X/4 = 0), the other being the vector difference (3X/4 -A./4 = X/2, i.e., anti-phase).

The RF coupler 120 can convert a pair of equal magnitude differential-phase vectors, with up-to a ±90° swing, into a pair of resolved orthogonal vectors with magnitude which can vary from zero to that equivalent to the combined input power of the differential-phase pair (ignoring losses). It is these resolved vectors (with inputs limited to a smaller maximum swing, for example ±45° swing) which are fed to the input ports 1001 and 1004, but with an additional fixed phase shift of 900 (which may be implemented through passive circuitry) to bring their phase difference to 180.

Figure 3 shows an alternative design of RF circuit 104 in which power is recycled back from two additional output ports 121a-121b of the phase multiplier circuit 100 to the input ports of the RF circuit 123a-123b to reduce potential power losses through the phase multiplier circuit 100.

Figure 4 shows the cascaded phase multiplying RF circuit 1 of Figure 1 incorporated into a linear phased array 800. The two input ports of the RF coupler of the top level of the cascaded phase multiplying RF circuit receive respective RF signals from an active phase shifter 802 which in turn receives an RF signal from an RF source 801. The linear phased array 800 also includes a set of antennae 814, 813, 812, 811, each antenna connected to a respective one of the output ports 122a, 122b, 122b, 122a of a RF circuits 104, 104'of the cascaded phase multiplying RF circuit 1. The function of the active phase shifter 802 is to generate a pair of anti-phase RF signals from the RF signal output from the RF source 801. The active phase shifter 802 is controlled by a controller which can vary the phase difference between the two RF signals. In this example they can be varied from 0° (no phase difference) to an extreme of ±45° for each phase giving a maximum total phase difference of -90° to +90°. The active phase shifter 802 can sweep smoothly across the range allowing any phase difference in the range to be selected.

In one arrangement each RF circuit may include an RF element 400 (mirrored arrangement of a phase multiplier circuit). Figure 5 shows the basic form of such a passive RF element 400. This comprises a conductive area 403 which may be implemented as a printed circuit, typically comprising a copper signal layer on one side of a low-loss, high-frequency dielectric substrate, with the other side as an uninterrupted copper plane area (the ground return reference for the signal layer).

The copper signal layer comprises a conductive area that is bounded along one side by two intersecting elliptical arc boundaries 401 and has on an opposing side several ports 420, 421, 422, 423, 424. These ports would be impedance-matched to the surrounding parts of the RF circuit (typically 50 ohms) by appropriate choice of trace geometry according to the dielectric constant and thickness of the dielectric medium.

Each elliptical arc bounded area has two foci, 411 and 412, plus 413 and 414 for the second area. Foci 412 and 413 may be coincident, or nearly so, causing the elliptical arcs to intersect. As shown, a ray traced from focus 411 will see a sharp impedance change at the elliptical arc boundary, which may be implemented as an open circuit, or short-circuit between the signal and ground layers (a series of electrical vias connecting the layers, spaced by a small fraction of the local wavelength, would be an effective short circuit). This sudden impedance change will cause the ray to reflect off the first elliptical arc boundary and arrive at focus 412. similarly, a ray traced from focus 414 will reflect off the second elliptical arc boundary and arrive at focus 413. By the principle of reciprocity, rays emanating from foci 412 and 413 would arrive at foci 411 and 414. L1

Figure 6 shows the phase and magnitude response because of Huygens wavelet analysis 1000 of the case where two equal wavelength, equal magnitude, equal phase RF signals enter at input ports 1001) and 1004). RF signals are then output at the output ports 1002, 1003, 1005 and 1006. The trace 1011 schematically shows the intersecting elliptical arc boundaries 401.

Trace 1012 represents the power intensity (per unit length) across a sample line bounded by the two elliptical arc regions and passing through all foci. The horizontal axis representing the phase angle. It can be seen that power is concentrated at foci 412 and 413, with additional smaller lobes either side.

Trace 1010 represents the phase (in degrees) of the wavefront arriving at this same sample line. It can be seen that the phase across the central main (primary) lobe remains fairly flat; wavelengths and geometry have been arbitrarily chosen to set this central phase as 0°. It may be noted that, for this case, that the phases associated with the two secondary lobes are approximately 180° different to the central primary lobe (+180° is the same as -180°).

It is recognised that Huygens wavelet analysis is not fully correct for the general case of electromagnetic waves confined in two dimensions. However, for the limited case of a single common frequency for all inputs (i.e., narrowband signals), applied over an extended time frame (relative to the period), the results will be essentially indistinguishable from a deeper analysis undertaken using Maxwell's equations and/or Quantum Electrodynamics (QED).

Figure 7 shows a similar Huygens wavelet analysis 1100 for the case when there is a 180° phase difference between the RF signals at the input ports 1001 and 1004. Trace 1110 similarly represents the phase (in degrees) of the wavefront arriving at this same sample line. Now it can be seen that most of the power intensity (per unit length) 1012 lies in two symmetric lobes either side of the foci 412 and 413, where can be found one of the minima due to destructive interference. With equal magnitude at input ports 1001 and 1004, the phase response is again fairly flat across both lobes, but with 180° offset between them. The geometry has been arbitrarily chosen such-that the rightmost lobe is at approximately zero-phase.

Figure 8 also shows a similar Huygens wavelet analysis 1200 to that of Figure 6, the RF signals at input ports 1001 and 1004 are driven with phase equivalent to +45°, where the RF signal input at port 1001 has zero magnitude and 1004 is maximal. Here 1210 and 1212 represent the phase difference and power intensity (per unit length) for this case respectively.

Figure 9 shows Huygens wavelet analysis of the opposite case (1300) with -45° phase RF signals at the input ports, where 1310 and 1312 represent the phase difference and power intensity for this case respectively. By observing a point on the phase difference traces (1110, 1210, 1310) to the right-of and near-to the vertical axis for Figures 7-9, it can be seen there is approximately a twofold gain in the phase of the RF signals. The same is also true to the left of the vertical axis, in anti-phase to the right (the additional fixed offset is unimportant), and at points crossing the horizontal axis towards the outer minima of the two main lobes in Figure 7.

In-order to extract useful power, the output port apertures must be greater than an infinitesimal point. In this example, the aperture of the output port 1003 shown to the right of the vertical axis in Figure 6 and 7 corresponds to an approximate ±67.5° swing, with appreciable output power, when integrated across the aperture. Similarly, a second output port 1006 aperture is chosen here to have a mean phase swing of ±22.5°, and with similar magnitude, but in anti-phase to the first.

It is important to note that these choices result in the maximum phase difference between output ports 1003 and 1006 is ±90°, so, relative to a midpoint offset phase of ±22.5°, each of these output ports 1003 and 1006 could be considered as having a swing of 45°. This equal magnitude, phase swing and anti-phase relationship is thus the same as the resolved RE signals at the input ports to the RF element, allowing multiple such RF elements to be cascaded.

Considering again Figure 7, and the second primary lobe of the phase (1110) to the left of the vertical axis, it should be evident from Figures 7-9 that the apertures of the output ports 1002 and 1005 could produce a similar second pair of output RF signals with ±67.5° and ±22.5° swing, in anti-phase to the first pair. This performs the dual action of dividing the combined power of the two input RF signals (approximately) equally between four output RF signals (with some inevitable loss) and achieving phase gain of ±22.5° for each of the two pairs of output RF signals.

In the RF circuit 104 shown in Figure 3, the output ports of the second primary lobe of the phase of the wavefront may be arranged symmetrically about its central peak, generating two equal magnitude RF signals with ±45° swing, i.e., in-phase with the two inputs to the RF element. By using a rat-race (or other) RF coupler 120 with approximate 70:30 power split (for example), this would allow the power of the second primary lobe to be recycled back to the input ports. Similarly, power from additional minor lobes could be recycled, though with diminishing returns; i.e., this would require an ever-greater size and complexity of passive circuitry in comparison to the relatively small amount of power recouped. This second configuration (with recouped power from one-or-more lobes) performs the action of asymmetric phase gain of ±22.5° for the RF signals of one pair of output ports from one pair of input ports.

These two configurations 200 and 204 are shown in Figures 12 and 13, with maximum instantaneous phase swings of the RF signals of the output ports 211a, 211b, 212a and 212b - 67.5°, +22.5°, -22.5° and +67.5° respectively.

Figures 1 to 14 are intended to convey general arrangements, with no regard given to physical scale, propagation delay matching or additional componentry required for implementation Using the cascaded phase multiplying RF circuit shown in Figure 1, it is possible to achieve indefinite power division and gain multiplication; the phase difference between one pair of RF signals at the input ports (maximum ±90°) is duplicated across one or more adjacent pairs of output ports (three pairs, in this instance).

Some of the embodiments described use a mirrored arrangement of the phase multiplier circuit (an RF element) as part of each RF circuit. The applicant has appreciated that other means may be used for generating suitable diffraction patterns that allow the RF signals at the input ports to be coupled to the output ports.

Figure 10 shows how a Rotman lens could be utilised: a pair of RF signals could be transformed into its orthogonal components (as previously described), then further power-divided into 4 + 4 proportions, with 180° phase difference between the two sets of 4. The first set of 4 could then be applied to ports 513 to 516, with the second to ports 519 to 522. It would then be expected that an interference pattern similar to Figure 7 would be seen, with symmetric primary lobes across the output ports 502 and 503 apertures. Note that the "Rotman lens" is not technically a lens in the normal sense -it does not rely on refraction across a boundary of two dissimilar media to achieve ray convergence or divergence -instead (for the case just described) it is the reciprocal of simple wave dispersion from a finite aperture, created by arranging multiple finite apertures around a virtual circular wavefront.

A third alternative could utilise an actual lens, for example a polymer dielectric placed within a waveguide, or a change in the characteristic impedance of a printed circuit pattern, such as by changing the dielectric constant within a lens-shaped region, or by utilising a multi-layer printed circuit and changing the distance between signal and ground layers in a lens-shaped region.

The applicant also appreciates that alternatives of the phase multiplier circuit may not require the presence of an RF coupler and as such this may be omitted from the RF circuit.

Figures 5 to 9 as well as Figures 12 and 13 show a symmetrical arrangement with all foci arranged on a common line, which need not be the case; the distance between foci may differ on the left and right sides (with differing semi-major and semi-minor axes), and the angle between the lines connecting foci 411 and 412 and foci 413 and 414 may be other than 180°. Also, the input ports are shown to emit RF signals perpendicular to these lines. The applicant has however appreciated that there may be some benefit in angling the source wavefronts such that they initially propagate away from the central foci, for example by reducing the amount of unwanted reflected power returned from these ports.

Figure 14 shows an embodiment of implementation of RF circuits within a two-dimensional phased array. A plurality of cascaded phase multiplying RF circuits la,lb are connected in two layers. The first layer comprises two cascaded phase multiplying RF circuits la which each receive RF signals at their input ports from a separate active phase shifter (not shown). Each of the active phase shifters receiving an input RF signal from an RF source and generating a pair of anti-phase RF signals. The second layer comprises four cascaded phase multiplying RF circuits lb. The RF signals output at the output ports of the first layer are connected to the input ports of the second layer. The two layers are connected such that each cascaded phase multiplying RF circuit lb in the second layer receives one RF signal from each cascaded phase multiplying RF circuit la in the first layer. The output ports of the cascaded phase multiplying RF circuits in the second layer are each connected to antennae 815 arranged in a 2D grid.

Taking X and Y to be orthogonal axes, the points at which the RF signals are input to the first layer of the cascaded phase multiplying RF circuits la of the phased array 300 lie along a common X-Y plane, having phase difference 8x along an axis X (passing through two inputs to the same cascaded phase multiplying RF circuit la) and phase difference by along an axis Y (orthogonal to X). The RF signals are output at the 2D array of antennae that lie along a common plane XIY where X' and Y' are orthogonal axes that may be parallel to X and Y axes respectively. The phase difference between RF signals at adjacent pairs of antennae 815 may also be 6x along an axis X' and by along an axis Y' such that the two phase differences 8x and by may be multiplied across a larger 2D array.

The applicant has appreciated that either or both of the X' and Y' axes may or may not be parallel to the axes X and Y respectively. A such the XIV' plane may or may not be parallel to the X-Y plane.

Claims

CLAIMS1. A radio frequency (RF) circuit suitable for use in a phased array comprising: an RF coupler which is adapted to receive a pair of anti-phase vector RF signals and to resolve them into a pair of orthogonal vector RF signals that each respectively correspond to the real and imaginary components of the received anti-phase vector RF signals, a phase multiplier circuit comprising a pair of input ports, each receiving a respective one of the pair of resolved RF signals output from the RF coupler, and at least one output port connected to the pair of input ports, in which the phase multiplier circuit is configured to generate a pattern of both constructive and destructive interference between the two RF signals input at the input ports and in which the at least one output port is positioned relative to the pattern such that the phase of an RF signal output from the at least one output port is a fixed multiple of the phase of the signal at a first one of the pair of input ports.
2. An RF circuit according to claim 1 additionally comprising a splitter that receives a single RF signal and splits this into two anti-phase RF signal outputs whereby the splitter is positioned upstream of the RF coupler optionally wherein the two anti-phase RF signals output by the splitter have equal magnitude.
3. An RF circuit according to claim 1 or claim 2 wherein the phase multiplier circuit has either a fixed gain or fixed multiplication factor for a defined frequency of RF signal optionally whereby the gain is substantially constant over a range of phases of the RF signals at the input ports.
4. An RF circuit according to any preceding claim wherein the phase multiplier circuit additionally comprises a second output port positioned relative to the pattern such that the phase of an RF signal output from the second output port is a second fixed multiplication factor of the phase of the RF signal at one of the pair of input ports, such that the phase multiplier circuit outputs a pair of anti-phase RF signals whose phase difference is a multiple of the phase difference between the two RF signals at the input ports, optionally whereby the second fixed multiplication factor is equal to the first fixed multiplication factor.
5. An RF circuit according to any preceding claim wherein the phase multiplier circuit additionally comprises a third output port, and optionally a fourth output port and optionally comprises five or more output ports.
6. An RF circuit according to claim 4 wherein the phase multiplier circuit comprises the third and the fourth output port whereby each of the third and fourth output ports are located relative to the pattern such that the phase of an RF signal output from the third and the fourth output ports is a different fixed multiplication factor of the phase of one of the RF signals at one of the inputs ports.
7. An RF circuit according to claims or claim 6 wherein the multiplication factors of the third and fourth output ports are equal, optionally whereby the multiplication factors of the third and fourth output ports are different to the multiplication factor of the first and/or second output ports.
8. An RF circuit according to any preceding claim wherein the phase multiplier circuit comprises no active electronically or mechanically controlled components and requires no control signals to generate a required multiplication or gain and is thereby entirely passive optionally wherein the RF circuit is entirely passive.
9. An RF circuit according to any preceding claim wherein the RF coupler comprises two input ports that receive a pair of out of phase RF signals and output the real and imaginary RF signals which respectively comprise a vector sum of the two received RF signals and a vector difference of the two received RF signals, the two resolved RF signals output by the RF coupler being fed to the phase multiplier circuit.
10. An RF circuit according to any preceding claim wherein the RF coupler comprises a rat-race coupler.
11. An RF circuit according to any preceding claim wherein the phase multiplier circuit additionally comprises at least one additional output port which receives a part of the RF signal originating from the RF signals received at the input ports of the phase multiplier circuit and feeds that RF signal to the input of the RF circuit where it propagates again through the RF circuit, such that power loss that may be reduced.
12. An RF circuit according to any preceding claim additionally comprising a delay line which applies an additional phase shift to one of the real and imaginary components, optionally whereby the additional phase shift is 900 such that the delay line provides two resolved RF signals that have a 180° phase difference between their vector components.
13. An RF circuit according to any preceding claim wherein the phase multiplier circuit has a refractive design and comprises a dielectric medium and one or more refractive lenses arranged to generate the pattern from the two RF signals received at the input ports.
14. A cascaded phase multiplying RF circuit comprising a plurality of RF circuits according to any preceding claim arranged in a cascade of at least two, or three or more levels, to provide a linear or a tree like configuration of RF circuits or a combination of both linear and tree like configurations such that the RF signal from one output port of one phase multiplying circuit in a layer forms an input RF signal fed to the input of the RF circuit on the next layer.
15. A phased array comprising a cascaded phase multiplying RF circuit according to claim 14, and a set of antennae, each antenna connected to a respective one of the output ports of the phase multiplying circuits of the RF circuits in a final level of the cascaded phase multiplying RF circuit.
16. A phased array according to claim 15 wherein the set of antennae are either linearly arranged as one row of antennae, to form a linear phased array, or arranged as a two-dimensional array in which the set of antennae are arranged in a grid to define rows and columns of antennae.
17. A phased array according to claim 15 or claim 16 when dependent on claim 2 additionally comprising an active phase shifter which is in a path upstream of the splitter, of the RF circuit in the first layer of the cascaded phase multiplying RF circuit, which receives a single RE signal from an RF source and generates the pair of anti-phase RE signals, the active phase shifter setting the phase difference between the two anti-phase RF signals which at least partially determines a steering angle of the set of antennae.
18. A phased array according to any of claims 15 to 17 comprising a plurality of cascaded phase multiplying RF circuits connected in two layers whereby: the first layer of the phased array comprises two cascaded phase multiplying RF circuits which each receive RF signals from a separate active phase shifter, each of the active phase shifters receiving an input RF signal from an RF source and generating a pair of anti-phase RF signals; the second layer of the phased array comprises four cascaded phase multiplying RF circuits where the RF signals output at the output ports of the first layer of the phased array are connected to the inputs of the second layer of the phased array; the two layers of the phased array are connected such that each cascaded phase multiplying RF circuit in the second layer of the phased array receives one RF signal from each cascaded phase multiplying RF circuit in the first layer of the phased array; and the output ports of the cascaded phase multiplying RF circuits in the second layer of the phased array are each connected to antennae arranged in a 2D grid such that the phased array may be utilised as a two-dimensional phased array.
19. An RF element for use as the phase multiplier circuit of any preceding claim comprising a reflective boundary whereby: the reflective boundary may comprise a pair of intersecting elliptical arc boundaries from which RF signals are reflected; each area bounded by the pair of intersecting elliptical arc boundaries comprises two foci for reflected RF signals; and the pattern is produced through reflection of one or both input signals from a boundary.
20. An RF element according to claim 19 wherein the pair of intersecting elliptical arc boundaries are arranged so that one focus of each intersecting elliptical arc boundary is substantially coincident to one foci of the other intersecting elliptical arc boundary, with the two remaining foci located either side of the substantially coincident foci, and whereby the output port is located at or close to one of the two substantially coincident foci and each of the input ports is located at or close to a respective one of the non-coincident foci.