GB2594935A

GB2594935A - Modular high frequency device

Info

Publication number: GB2594935A
Application number: GB2006724.5A
Authority: GB
Inventors: Powell Royston; Wade Barry
Original assignee: Blighter Surveillance Systems Ltd
Current assignee: Blighter Surveillance Systems Ltd
Priority date: 2020-05-06
Filing date: 2020-05-06
Publication date: 2021-11-17
Also published as: WO2021224628A1; GB202006724D0

Abstract

A modular high frequency device 1 comprises: a first module with a laminate structure including a support layer 20 and a high frequency signal path printed circuit board (PCB) layer 30; and a second module with a laminate structure including a support layer 120 and a high frequency signal path printed circuit board (PCB) layer 130, in which the first and second PCB layers are electromagnetically coupled by a waveguide 45. Also disclosed is a method of transmitting a steerable electromagnetic radiation beam, comprising providing a radio frequency (RF) signal carrying a waveform into a high frequency device, splitting the signal into a plurality of signal paths and processing each RF signal using at least a phase shifter. Converting the RF signal of each signal path into an electromagnetic wave and back again using first and second waveguide transitions at either end of a waveguide. The signals are propagated along convoluted transmission lines. Each of the signal paths couples the RF signal in series to a plurality of antenna elements arranged in a column, where the signal is converted to a steered electromagnetic beam which propagates in free space. The beam is steered in a first direction by phase modulation and steered in a second direction, perpendicular to the first direction, by frequency modulation.

Description

Modular High Frequency Device The invention relates to a modular high frequency device and to constituent modules of a modular high frequency device. The invention may relate to a device for transmitting or receiving centimetric or millimetric band electromagnetic radiation, such as an antenna for radar systems or mobile communications technologies. The invention may relate to phased array antennas.

Background

High frequency devices are devices that utilise high frequency electromagnetic radiation, typically classed as electromagnetic radiation having a frequency of greater than 3 MHz. Perhaps the widest range of applications are in the centimetric band between 300MHz and 30GHz. There is also much interest in developing high frequency devices that utilise extremely high frequency radiation having a frequency of greater than 30 GHz. Such devices are often said to operate in the millimetre band or with millimetre wave radiation, as the operational wavelength of electromagnetic radiation used in such devices is typically within the range from 10 mm to 1 mm. The demand for greater data rates has been one of the key drivers to operate communication networks at higher frequencies.

One example of a high frequency device is a phased array antenna used, for example, in radar imaging or in telecommunications. Phased array antennas utilise an array of radiating elements. The phase and amplitude of radiation emitted from the radiating elements can be adjusted in order to modify the radiated beam shape and steering angle.

Figure 1 is a diagram illustrating a transmit path from a phased array of antenna elements. The diagram shows, schematically, a high frequency signal from a RE feed passing through a RE power divider. Each separate divided signal then passes through an attenuator, a phase shifter, and a power amplifier before being propagated from a radiating element, which may be described as an antenna element. While Figure 1 shows a transmit path, a reciprocal scheme can be applied to receive electromagnetic signals, using low noise amplifiers rather than power amplifiers.

For radar and telecommunications applications additional switches are often incorporated to enable the same radiating elements to be used for both transmit and receive. A circuit containing phase shifters, attenuators, amplifiers and switches is often referred to as a Transmit/Receive (T/R) Module.

A traditional phased array antenna implementation may employ an array of discrete antenna elements, which are connected to a number of T/R modules. The T/R modules connect to the back face (i.e. the non-radiating face) of the antenna.

Some phased arrays enable scanning in azimuth only. Some phased arrays enable scanning in elevation only. Many systems, however, utilise an electronic module, for example a beamforming module or a T/R module, connected directly to each antenna element of an array in order to provide both azimuth and elevation scanning. Such implementation is often costly, as each antenna element requires its own electronic module. The need to accommodate a large number of electronic modules within a small space requires complex mechanical design. Furthermore, each electronic module produces a large amount of heat, which in turn requires complex thermal design to prevent the device from overheating.

An array of antenna elements may conveniently be printed upon a circuit board. For example, an array of antenna elements may be printed onto a multilayer mixed dielectric circuit board. Such a circuit board has electronic circuits, for example T/R module circuits, incorporated directly upon the back face of the board. However, it is increasingly difficult to obtain good radio frequency (RF) performance at high frequencies (particularly as the frequency increases above 6 GHz) due to the vertical RE transitions that are required to connect the various circuits to the radiating elements. There are also thermal issues to resolve.

Summary of Invention

The invention may provide a high frequency device as defined in any of the appended independent claims, to which reference should now be made. Preferred or advantageous features of the invention are set out in various dependent sub-claims.

In one aspect the invention may provide a modular high frequency device comprising a first module and a second module.

The first module has a laminate structure, including a first module support layer and at least one further layer arranged vertically with respect to the first module support layer. The at least one further layer includes a first module circuit board defining a high frequency signal path. The first module circuit board may comprise a plurality of dielectric layers stacked alternatively with a plurality of conductive layers. The at least one further layer may be a first module PCB layer.

The second module has a laminate structure including a second module support layer, and at least one dielectric layer arranged vertically with respect to the second support layer, the at least one dielectric layer supporting a high frequency electronic structure. The at least one dielectric layer may be a second module PCB layer.

The first module and the second module are electromagnetically coupled by a waveguide. The first module and the second module are electromagnetically coupled, through the first module support layer and the second module support layer, by the waveguide. In preferred embodiments, a high frequency signal path defined in a first module PCB layer of the first module is coupled, by means of a waveguide extending through the first module support layer and the second module support layer, to a high frequency signal path defined in a second module PCB layer of the second module.

A high frequency device according to some embodiments of the invention may be a radar device. A high frequency device according to some embodiments of the invention may be a telecommunications device. A high frequency device according to embodiments of the invention may be described as an antenna device.

The first module and the second module are preferably substantially two-dimensional (2D) in structure, and may be described as a first 2D module and a second 2D module. As used herein, the term two dimensional (2D) when used in respect of a structure, such as a module or a layer, indicates that the structure has length dimension and a width dimension that are greater than a thickness dimension, preferably substantially greater than a thickness dimension.

Particularly preferably, one or both of the first module and the second module may be planar in structure, and may be described as a first planar module and a second planar module. As used herein, the term "planar" when used in respect of a structure, such as a module or a layer, indicates that the structure substantially extends in a 2D plane, and that the structure has a length dimension and a width dimension that are greater than a thickness dimension, preferably substantially greater than a thickness dimension.

In any aspect above, either or both of the first module and the second module may be vertically arranged or vertically stacked 2D modules or planar modules. Vertically arranged or vertically stacked, when used in relation to planar modules, describes modules or layers disposed in parallel planes, one above the other. Preferably, the second module is disposed vertically above the first module. Preferably, an upper surface of the first module abuts a lower surface of the second module. Preferably, the second module is removably-couplable to the first module.

High frequency devices are constructed using specialised printed circuit boards (PCBs) to carry high frequency signals. High frequency PCB typically use specialist low-loss, controlled dielectric constant, dielectric material laminates in their construction. These dielectric materials are used for mounting RF integrated circuits (ICs) and the routing of high frequency transmission lines. Such dielectric material laminates may be termed microwave laminates. One example of a dielectric material that may be classed as a microwave laminate is R04350, produced by Rogers' Corporation. There are numerous types of materials that are tailored to different RF, manufacturing, and cost requirements. These specialist materials may be laminated with established standard PCB dielectric material layers (an example of a conventional PCB dielectric material is FR4) to produce high-frequency multilayer PCBs.

The propagation of RF signals in high frequency PCBs is often restricted to microwave laminates that are applied to outer layers (typically the top surface) of the PCB. The use of buried RF layers is possible, and enables shielding of the signal, but is typically more difficult to implement as the frequency increases. One problem restricting the implementation of buried RF layers is the routing of a RF signal between layers. Layers in a PCB can be described as vertically arranged, or vertically stacked, and routing of a RF signal between layers requires a vertical RF transition. The design of a vertical RF transition, which requires controlled impedance, becomes significantly more challenging with increasing frequency of signal, increasing vertical height of the transition, increasing number of layers, and increasing number of different material types forming the layers. These issues place practical limits on the frequency range and vertical height that can be achieved by the transition. The operating frequency range is also dependent upon the precision of the manufacturing technology.

Recent trends in communication systems are to provide higher data rates and bandwidth in conjunction with operation at much higher frequencies (e.g. 4G <2.6GHz and high band 5G at -28GHz). This means that the currently available vertical RF interconnects and PCB manufacturing tolerances may not be suitable for manufacture of future high frequency devices.

The design of a vertical RE feed is a particular problem for planar phased array antennas that are intended to operate at high frequencies. Such antennas typically require laminates formed with different dielectric layers having different dielectric properties. Low dielectric constant materials (for example, materials having a relative permittivity (Er) of 2-3) are favoured for the radiating elements, which could comprise patches, dipoles or similar, to enhance radiation efficiency, yet conventional FR4 material having Er of about 4 is suitable for routing the multilayer high density interconnects associated with the control electronics. Planar antenna arrays that are designed using a new generation of beamformer ICs mounted upon the rear face of the PCB usually require an internal vertical RF feed to the antenna which is upon the opposite face of the PCB and, therefore, extends through multiple layers of the PCB.

In aspects of the present invention, a high frequency device is formed from two modular components. One of those modular components, the first module, defines a high frequency signal path and preferably comprises high frequency ICs forming high frequency control electronics. The other modular component, the second module, defines one or more functional high frequency elements, for example an antenna element or an array of antenna elements for transmitting or receiving electromagnetic waves. The vertical transition of the high frequency signal of the first module to the functional high frequency element of the second module is made by a waveguide.

As used herein, the term waveguide refers to a hollow or dielectric filled conductive conduit used to carry high frequency electromagnetic waves. A waveguide may be in the form of a conductive tube or pipe with a dielectric core. A preferred dielectric core material is air, but other dielectric core materials, such as PTFE, may be used. In the context of the present disclosure, the term waveguide does not refer to a co-axial cable nor to an optic fibre.

The use of a waveguide as a vertical RF transition may significantly improve performance compared to a traditional co-axial RF transition, particularly at higher frequencies. The use of a waveguide may enable improved impedance matching of a vertical transition through multiple circuit board layers.

Preferably, the second module is coupled to the first module such that a lower surface of the second module support layer faces an upper surface of the first module support layer. Thus, the first module PCB layer and the second module PCB layer are separated by the first module support layer and the second module support layer. Such coupling may be described as back-to-back coupling.

Preferably, the first module and the second module are substantially planar modules and the waveguide extends perpendicularly relative to the first module and the second module.

Dimensions of the waveguide can be selected to optimise performance at the desired frequency of operation of the high frequency device. Preferably, the frequency of an electromagnetic signal transmitted by the waveguide is between 3GHz and 300 GHz. As examples, standard rectangular waveguide WR42, covering the band 18 to 26.5 GHz has dimensions 10.668 mm by 4.318mm, and standard rectangular waveguide WR5, covering the band 140 to 220 GHz has dimensions 1.2954mm by 0.6477mm.

The first module preferably comprises one or more active electronic components for processing a high frequency signal travelling along the high frequency signal path. For example, a first module PCB layer may locate one or more active electronic components selected from the list consisting of a power amplifier, a low noise amplifier, a phase shifter, a switch, an attenuator, a beamformer, a PCB to waveguide transition, and other associated electronic circuits.

The high frequency electronic structure of the second module may be a passive electronic component. For example, a second module PCB layer may locate one or more passive electronic components selected from the list consisting of an antenna element, a stripline, a PCB-to-waveguide transition, and a RF-to-antenna element transition. The second module may be electronically passive in that it does not comprise any active electronic components.

The first module support layer is preferably an electrical and thermally conductive material, preferably a metallic material, particularly preferably aluminium or copper. The first module support layer preferably has a thickness of between 1 mm and 10 mm, preferably between 2 mm and 7 mm, for example about 3 mm, or about 4 mm, or about 5 mm, or about 6 mm. Advantageously, the first module support layer may act as a thermal plane in thermal communication with one or more electronic components comprised in the first module. Thus, heat generated from electronic components in the first module may be efficiently dissipated by the first module support layer. Electronic components such as power amplifiers and beamformers in particular generate a large amount of heat during operation.

The second module support layer is preferably an electrical and thermally conductive material, preferably a metallic material, particularly preferably aluminium or copper. The second support layer may act as a thermal plane in thermal communication with one or more electronic components comprised in the second module. When coupled to the first module, the second module support layer may be in intimate contact with the first module support layer and may also function as a thermal plane for electronic components on the first module. Preferably, the second module support layer has a thickness of between 1 mm and 10 mm, preferably between 2 mm and 7 mm, for example about 3 mm, or about 4 mm, or about 5 mm, or about 6 mm.

The first module and the second module may be mounted apart from each other, that is with the first module support layer and the second module support layer not in intimate contact but separated by a gap. The vertical transition of the high frequency signal of the first module to the functional high frequency element of the second module may then be made by a waveguide extending across the gap.

Preferably, a first module waveguide aperture is defined through a thickness of the first module support layer and a second module waveguide aperture is defined through a thickness of the second module support layer, the first module and the second module being couplable such that the first module waveguide aperture aligns with the second module waveguide aperture. Preferably, the waveguide extends through the first module waveguide aperture and the second module waveguide aperture. Advantageously, the first module support layer and the second module support layer may be formed from electrically conductive material and walls of the waveguide may be defined by inner surfaces of the first module waveguide aperture and the second module waveguide aperture. The first module waveguide aperture and the second module waveguide aperture may be rectangular shaped apertures and the waveguide may be a rectangular cross-section waveguide.

Preferably, the waveguide comprises a conductive tube or conduit surrounding a dielectric core, dielectric material within the core preferably selected from a list comprising, but not limited to, air and PTFE.

Preferably the first module is removably -couplable to the second module. That is, preferably the second module and the first module can be coupled together to form the high frequency device and de-coupled into separate modules. The first module may be coupled to the second module by means of a mechanical fastening acting between the first support layer and the second support layer, for example clamping, a screw fitting, or a nut and bolt fitting.

The at least one dielectric layer of the second module is preferably part of a circuit board, for example a second module PCB. The second module PCB may be a high frequency printed circuit board comprising layers of dielectric materials separated by conductive layers. At least one dielectric layer of the second module PCB layer may have a dielectric constant (Er) of lower than 3, for example lower than 2.5, or between 1.75 and 2.5. At least one dielectric layer of the second module PCB layer may have a dielectric constant (Er) of greater than 4, for example greater than 5, or between Sand 7. The second module PCB layer may comprise at least one dielectric layer having a dielectric constant (Er) of lower than 3 and at least one dielectric layer having a dielectric constant (Er) of greater than 4. At least one dielectric material of the second module PCB may be a dielectric material selected from the list consisting of PTFE, RO 4350B, R0588OLZ, and R04360G2. Many other suitable dielectric materials will be apparent to the skilled person.

In preferred embodiments, the high frequency electronic structure supported by the at least one dielectric layer of the second module, for example by the second module PCB layer, is an antenna element, the modular high frequency device being a modular antenna device.

Preferably, the second module comprises a second module PCB layer formed from a plurality of dielectric layers vertically spaced by at least one ground plane, the second module PCB layer being supported by the second module support layer. The antenna element is located on the surface of one of the plurality of dielectric layers to transmit or receive high frequency electromagnetic waves.

The second module may comprise the following elements; the second module support layer, a second module waveguide aperture being defined through the second module support layer, and a second module PCB layer comprising a first dielectric layer arranged vertically above the second module support layer, a waveguide transition element aligning with the waveguide aperture, preferably in which the waveguide transition element is a transducer supported by the first dielectric layer, a second dielectric layer arranged vertically above the first dielectric layer, and the antenna element, preferably supported by the second dielectric layer, for example in which the antenna element is printed on an upper or a lower surface of the second dielectric element.

The second module may further comprise; a first ground plane arranged vertically below the second dielectric layer, preferably in which the first ground plane comprises an aperture aligned with the antenna element.

Preferably, the second module comprises a plurality of antenna elements located in the same plane, for example an array of antenna elements.

The second module advantageously may comprise a horizontally extending transmission line, which may be termed a stripline, for electromagnetically coupling a plurality of antenna elements with the waveguide. The transmission line may, for example, be sandwiched between third and fourth layers of dielectric material and may be arranged vertically above the second support layer and vertically below the antenna elements.

Advantageously, the transmission line may follow a convoluted or serpentine path to increase the length of transmission line between successive antenna elements. By increasing the length of transmission line between successive antenna elements, a delay is introduced to the signal propagation from each of the successive elements. This allows an antenna to be steered by modulating the frequency of the signal slightly with respect to a nominal perfect frequency for a particular antenna array. The transmission line may be located within, or between layers of, dielectric material having high relative dielectric constant (values), for example materials having values of Er of greater than 4.

A modular high frequency device comprises a first module and a second module as described herein. A modular high frequency device may comprise a plurality of waveguides, each of the plurality of waveguides extending through the first module support layer and the second module support layer. Each of the plurality of waveguides may facilitate electromagnetic coupling between a high frequency signal travelling in the first module and at least one high frequency electronic structure, for example a transmission line and/or an antenna element, located in the second module.

The device may be configured to transmit or receive electromagnetic waves within a range of electromagnetic waves having a wavelength (A) of between about 0.5 mm and about 100 mm, preferably within a range of between about 1 mm and 50 mm.

The second module may comprise an array of antenna elements, the array comprising a plurality of columns of antenna elements, each column of antenna elements comprising two or more individual antenna elements. Each of the plurality of columns of antenna elements may be associated with at least one waveguide extending between the first module and the second module.

Preferably, each of the at least one waveguides provides electromagnetic signal to between two and eight discrete antenna elements within one of the plurality of columns of antenna elements, for example between three and six antenna elements, or four or five antenna elements.

Each one of the plurality of columns of antenna elements may be associated with between two and ten waveguides, each of the between two and ten waveguides providing electromagnetic signal to between two and ten discrete antenna elements within the column of antenna elements.

The first module may comprise one or more electronic components for processing the high frequency signal selected from the list of components consisting of an amplifier, a phase shifter, and a beamformer.

Although preferred embodiments of a high frequency device comprise a first module and a corresponding second module, other embodiments may comprise a plurality of second modules removably-coupled to a first module.

Embodiments of the invention may provide a modular high frequency device as described above in which the second module comprises a plurality of columns of antenna elements, each column of antenna elements fed in series by a meandering stripline within the second module, and the first module comprises a phase shifter associated with each column of antenna elements, the modular high frequency device being a steerable phased array antenna device.

In preferred embodiments of a modular high frequency device the second module may comprise the following layers; a first conductive layer, or antenna layer, having an array of discrete antenna elements arranged in columns, a first dielectric layer arranged vertically beneath the antenna layer, the first dielectric layer preferably having a dielectric constant of less than about 3, a second conductive layer arranged vertically beneath the first dielectric layer, a second dielectric layer arranged vertically beneath the first conductive layer, the second dielectric layer preferably having a dielectric constant of greater than about 4, a third conductive layer, or transmission line layer, located vertically beneath the second dielectric layer, the transmission line layer comprising a plurality of convoluted, horizontally extending transmission lines, at least one transmission line for each column of the array of antenna elements, a third dielectric layer arranged vertically beneath the transmission line layer, the third dielectric layer preferably having a dielectric constant of greater than about 4, a fourth conductive layer arranged vertically beneath the third dielectric layer, a fourth dielectric layer arranged vertically beneath the fourth conductive layer, the fourth dielectric layer preferably having a dielectric constant of greater less than about 3, and the second module support layer arranged vertically beneath the fourth dielectric layer, the second module support layer defining a plurality of second module waveguide apertures, one of the plurality of second module waveguide apertures being located vertically beneath each of the plurality of convoluted horizontally extending transmission lines.

In preferred embodiments the first module may comprise the following layers; the first module support layer, which when the first module is coupled to the second module is arranged vertically beneath the second module support layer, the first module support layer defining a plurality of first module waveguide apertures corresponding to, and aligned with, the plurality of second module waveguide apertures, and the first module PCB layer arranged vertically beneath the first module support layer, the first module PCB layer comprising a plurality of dielectric layers spaced by conductive layers and locating a plurality of electronic components selected from the list consisting of a power amplifier, a low noise amplifier, a phase shifter, and a beamformer.

Advantageously, the modular high frequency device may be a beam-steerable phased array antenna device, for example a steerable phased array antenna device for use in radar or telecommunications.

Each of the plurality of convoluted, horizontally extending transmission lines preferably feeds a high frequency signal to a plurality of antenna elements within a column of the array of discrete antenna elements, for example to between 2 and 10 of the antenna elements. Each column may comprise more than 10 antenna elements.

The high frequency signal passing through the convoluted, horizontally extending transmission lines is preferably coupled to the array of discrete antenna elements by aperture coupling. Thus, an aperture is preferably defined through the second conductive layer vertically beneath each of the plurality of discrete antenna elements to enable coupling of energy in the transmission line with each antenna element.

Each first module waveguide aperture is preferably associated with a PCB-to-waveguide transition structure defined in the first module PCB layer to allow energy to pass between the high frequency signal path defined in the first module PCB layer and a waveguide. Each second module waveguide aperture is preferably associated with a PCB-to-waveguide transition structure defined in the second module PCB layer to allow energy to pass between a waveguide and the transmission line.

Advantageously, the high frequency device may comprise an array of discrete antenna elements arranged in columns, the array of discrete antenna elements configured to transmit a beam of electromagnetic energy. The beam of electromagnetic energy can preferably be steered in a first direction, for example in azimuth, by modulating the phase of signal fed to adjacent columns of discrete antenna elements, and the beam of electromagnetic energy can preferably be steered in a second direction perpendicular to the first direction, for example in elevation, by modulating the frequency of the signal supplied to the columns of discrete antenna elements Advantageously, a modular high frequency device according to any aspect described herein may be used as a tile in an antenna array system. For example, a steerable phased array antenna system may comprise a plurality of antenna tiles arranged on a surface, each of the antenna tiles being a high frequency device as described or defined herein.

Preferably, each antenna tile comprises an array of between 4 and 256 discrete antenna elements, for example between 32 and 144 discrete antenna elements. Clearly, an antenna tile may comprise more than 256 antenna elements, particularly if the antenna elements are small and/or the dimensions of the antenna tile are large.

Preferably, a steerable phased array antenna system comprises an array of between 4 and 256 antenna tiles, preferably arranged on a planar surface. Clearly, there is a potential to form an array with a significantly greater number of antenna tiles.

Each antenna tile of the steerable phased array antenna system preferably comprises a RF input to receive a high frequency signal from a waveform generator. The waveform generator may be part of the steerable phased array system. It is particularly preferable that each antenna tile is configured with features as described above to allow a beam transmitted from the steerable phased array antenna system to be steered in one direction by means of phase modulation of a signal to adjacent columns of antenna elements, and also steered in a perpendicular direction by means of modulating the frequency of the input signal.

In one aspect the invention may provide an antenna device comprising a first circuit board and a second circuit board arranged in a vertically stacked configuration. The first circuit board defines a high frequency signal path and comprises at least one electronic device for processing a high frequency signal. The first circuit board further comprises a thermal-plane for cooling the at least one electronic device. The second circuit board comprises an antenna element. The high frequency signal path and the antenna element are electromagnetically coupled via a waveguide extending perpendicularly between the first circuit board and the second circuit board through the thermal plane of the first circuit board.

The high frequency device of the invention may be an antenna device. A plurality of antenna devices may be used as tiles to form a larger phased array antenna system.

A steerable phased array antenna system may comprise a plurality of antenna devices, each antenna device comprising; a first module having a first module support layer and a first module PCB layer; a second module having a first module support layer and a second module PCB layer; the first module and the second module being electromagnetically coupled by means of a waveguide.

Preferably, each second module comprises an array formed of a plurality of columns of antenna elements, discrete antenna elements within each column being coupled in series to a RF signal. Preferably, a meandering stripline is used to couple discrete antenna elements within a column.

Each first module may be any first module as described above or as defined herein.

Each second module may be any second module as described above or as defined herein. Each antenna tile may be a high frequency device as described above or as defined herein.

The steerable phased array antenna system may comprise at least four discrete antenna devices mounted on a surface. For example, the steerable phased array antenna system may comprise at least nine discrete antenna devices, or at least 20 discrete antenna devices, or at least 40 discrete antenna devices. The antenna tiles are preferably configured to transmit and/or receive electromagnetic radiation having a frequency of between 6GHz and 300GHz, for example between about 9 GHz and 30GHz, or between about 30GHz and about 200GHz.

The steerable phased array antenna system may further comprise a waveform generator for generating a RF signal to be coupled to each of the antenna tiles.

The steerable phased array antenna system may be a radar system.

The steerable phased array antenna system may be a telecommunications antenna device.

The invention may, therefore provide an antenna tile for a steerable phased array antenna system.

In one aspect, the invention may provide a method of transmitting an electromagnetic signal into free space comprising the steps of; inputting a RF signal carrying a waveform into a high frequency device; processing the RF signal with one or more electronic components of the high frequency device; converting the RF signal to an electromagnetic wave at a first waveguide transition within the high frequency device; propagating the electromagnetic wave through a waveguide within the high frequency device; converting the electromagnetic wave to a RF signal at a second waveguide transition within the high frequency device; coupling the RF signal to an antenna element of the high frequency device; and converting the RF signal to an electromagnetic wave that is propagated into free space.

The method of transmitting an electromagnetic signal into free space may be used with a modular high frequency device according to any aspect described or defined herein.

For example, a method of transmitting a steerable beam of electromagnetic radiation into free space may comprise the steps of; inputting a RF signal carrying a waveform into a high frequency device; splitting the signal into a plurality of signal paths processing the RF signal in each of the plurality of signal paths with one or more electronic components of the high frequency device including at least a phase shifter; for each of the plurality of signal paths, converting the RF signal to an electromagnetic wave at a first waveguide transition within the high frequency device; for each of the plurality of signal paths, propagating the electromagnetic wave through a waveguide within the high frequency device; for each of the plurality of signal paths, converting the electromagnetic wave to a RF signal at a second waveguide transition within the high frequency device; for each of the plurality of signal paths, propagating the RF signal along a convoluted transmission line; for each of the plurality of signal paths, coupling the RF signal in series to a plurality of antenna elements arranged in a column on the high frequency device; and for each of the plurality of signal paths, converting the RF signal to an electromagnetic wave that is propagated into free space.

The electromagnetic waves propagated from each antenna element of each column interact with each other to form the electromagnetic beam. The electromagnetic beam is steerable in a first direction by modulating the phase of the RF signal in each of the plurality of signal paths. The electromagnetic beam is steerable in a second direction perpendicular to the first direction, by modulating the frequency of the RF signal input into the high frequency device.

Aspects of the invention may provide a first module for use in a modular high frequency device as described and defined herein. For example, the first module may have a laminate structure including a first module support layer, and at least one further layer arranged vertically with respect to the first module support layer, the at least one further layer including a circuit board defining a high frequency signal path, in which one or more waveguide aperture is defined through the first module support layer. The first module may comprise a first module support layer and a first module PCB layer.

Aspects of the invention may provide a second module for use in a modular high frequency device as described and defined herein. The second module may have a laminate structure including a second module support layer, and at least one dielectric layer arranged vertically with respect to the second module support layer, the at least one dielectric layer supporting a high frequency electronic structure, and at least one waveguide aperture being defined through the second module support layer. The second module may comprise a second module support layer and a second module PCB layer.

In some aspects of the invention, a high frequency device may comprise a first module and a second module. The first module and the second module are preferably two-dimensional (2-D) in structure. The first module and the second module may be planar in structure. The first module and the second module are vertically coupled. The first module and the second module are electromagnetically connected by a waveguide.

The first module may comprise a first circuit board, which may be termed a first module circuit board. The first module circuit board preferably comprises a dielectric layer, which may be termed a first module dielectric layer.

The second module may comprise a dielectric layer, which may be termed a second module dielectric layer. The second module dielectric layer may be a part of a second circuit board, which may be termed a second module circuit board.

The second module dielectric layer supports or defines a high frequency electronic structure. For example, the second module dielectric layer may support or define a radiating element for radiating electromagnetic radiation. The radiating element may be described as an antenna element. The first module circuit board may support or define a high frequency electronic structure. For example, the first module circuit board may support or define a high frequency signal path and/or electronic components for processing a high frequency signal.

In one aspect the invention may provide a high frequency device comprising a first circuit board defining a high frequency signal path, and a second circuit board defining a high frequency signal path. The first circuit board and the second circuit board are vertically stacked. The first circuit board and the second circuit board are electromagnetically connected by means of a waveguide extending perpendicularly between the first circuit board and the second circuit board.

In its various aspects the invention may provide a number of advantages over known high frequency devices, and in particular over known antenna devices, high frequency planar arrays, and phased array antennas. The advantages may include; Second modules forming antennas with different performance characteristics (for example, gain, beam width, sidelobe and scanning) can be substituted upon the same first module with associated electronics, such as beamformers, according to different system design requirements.

Electronic components on the first module, such as beamformers, can be tested independently of antenna elements on the second module. For example, the ability to measure the amplitude and phase at beamformer RF ports on a first module before the first module is paired with a second module comprising antenna elements is a major advantage. This enables known good beamformers to be paired with antennas prior to near field antenna testing that is time consuming and requires specialist facilities.

Because the second module can be de-coupled from the first module, electronic components, such as beamformers, can be tested, reworked or repaired independent of the antenna elements. A major advantage is provided by the ability to connect directly with the RF ports of a beamformer when the first module is not connected with the second module, rather than having to characterise beam patterns to resolve faults The second module has fewer layers than a conventional multilayer planar array so may provide have higher manufacturing yields. The second module is typically be a passive structure and so is easier to manufacture.

Second modules comprising antenna elements can be selected based upon performance characteristics. Antennas elements can also be tested independent of electronics such as beamformers.

Modular high frequency devices as described allow antenna design and materials to be optimised for antenna performance, rather than being selected to enable co-manufacture with the beamformer and control electronics (and vice versa).

A vertical waveguide RE transition may provide better performance than a vertical coaxial RE transition particularly with increasing RE frequency.

The first module support layer and the second module support layer define waveguide apertures, but also provides a good thermal path for dissipating heat generated by the beamformer and control electronics.

The first module support layer and the second module support layer may provide convenient mountings for the antenna, as well as strength, rigidity and flatness.

The modular design means that operational maintenance and replacement of faulty parts is easier, particularly when an antenna system is formed using a plurality of high frequency devices as antenna tiles.

In embodiments, the structure allows the formation of a fully steerable phased array antenna without the need to include costly electronics such as a beamformed with each antenna element.

Specific Embodiments of the Invention Specific embodiments of the invention will now be described with reference to Figures, in which: Figure 1 is a schematic diagram illustrating a transmit path from a phased array of antenna elements (prior art); Figure 2 illustrates a schematic cross-sectional view of a conventional PCB configuration (not according to the present invention); Figure 3 is a schematic upper plan view of a first module of a high frequency device according to an embodiment of the invention; Figure 4 is a schematic cross-sectional view of the first module of Figure 3, schematically illustrating the vertical arrangement of layers of the first module; Figure 5 is a schematic lower plan view of the first module of Figure 3; Figure 6 is a schematic upper plan view of a second module of a high frequency device according to the invention; Figure 7 is a schematic cross-sectional view of the second module of Figure 6, schematically illustrating the vertical arrangement of layers of the second module; Figure 8 is a schematic lower plan view of the second module of Figure 6; Figure 9 is a schematic cross-sectional view of the second module of Figures 6 to 8 being coupled with the first module of Figures 3 to 5; Figure 10 is a schematic cross-sectional view of the second module of Figures 6 to 8 when coupled to the first module of Figures 3 to 5; Figure 11 is a flowchart illustrating steps in the transmission of an electromagnetic wave from a modular high frequency device according to an embodiment of the invention; Figure 12 is a flowchart illustrating steps in the reception of an electromagnetic wave from a modular high frequency device according to an embodiment of the invention; Figure 13 is a schematic upper plan view of a first module of a phased array antenna according to an embodiment of the invention; Figure 14 is a schematic cross-sectional view of the first module of Figure 13, schematically illustrating the vertical arrangement of layers of the first module; Figure 15 is a schematic lower plan view of the first module of Figure 13; Figure 16 is a schematic upper plan view of a second module of a phased array antenna according to an embodiment of the invention; Figure 17 is a schematic cross-sectional view of the second module of Figure 16, schematically illustrating the vertical arrangement of layers of the second module; Figure 18 is a lower plan view of the second module of Figure 16; Figure 19 is a schematic cross-sectional view of the first module of Figures 13 to 15 when coupled to the second module of Figures 16 to 18; Figure 20 is a schematic cross-sectional view of the second module of Figure 16, schematically illustrating waveguide extension vias extending from the waveguide aperture; Figure 21 is a schematic plan view showing a preferred waveguide transition structure in the second module of Figure 20; Figure 22 is a schematic plan view showing an alternative waveguide transition for a high frequency device according to an embodiment of the invention; Figure 23 is a schematic plan view showing an alternative waveguide transition for a high frequency device according to an embodiment of the invention; Figure 24 is a schematic plan view showing an alternative waveguide transition for a high frequency device according to an embodiment of the invention; Figure 25 is a schematic plan view of a second module of a high frequency device according to an embodiment of the invention illustrating aperture coupling between a meandering transmission line and a column of antenna elements; Figure 26 is a schematic plan view illustrating the position of insulating via posts surrounding the meandering transmission line of Figure 25; and Figure 27 is a schematic plan view of a planar array antenna system according to an embodiment of the invention, the planar array antenna system comprising a plurality of tiles, each tile being a high frequency device according to an embodiment of the invention.

Figure 2 illustrates a cross-sectional view of a conventional PCB configuration (not according to the present invention) that might be used to implement a prior art planar antenna design. On a lower side of the conventional PCB, various electronic components are located. These components may include, for example, a field programmable gate array (FPGA) and a beamformer integrated circuit. The electronic components may also include a power amplifier (PA) and/or a low-noise amplifier (LNA). An upper surface of the conventional PCB locates antenna elements for radiating electromagnetic waves into free space. Between the antenna elements and the electronic components, the PCB comprises a number of layers of dielectric material separated by ground layers. A vertical radio frequency (RF) transition conveys the RF signal vertically through the PCB to a stripline. The stripline conveys the RF signal horizontally through the board and further vertical RF transitions feed the RF signal to the antenna elements. Vertical transitions may be made by vias extending vertically through layers of the PCB. This type of configuration, or stack-up as it may be termed, can be problematic for use at high frequencies.

In order to function efficiently in a high frequency device, different dielectric layers of the PCB need to be manufactured from materials having different dielectric properties. The reason for this is that dielectric properties required for the layers supporting the antenna elements may be different to those for the layers supporting the stripline, or for mounting the various electronic components. Different dielectric materials may not be compatible with a common manufacturing process. For example, PCB bowing / warping, or cracked vias may result from different thermal expansion coefficients of different layers of dielectric materials. Hence, the choice of materials used in such a conventional PCB tends to be a compromise, and not the selection of the best dielectric materials for each application.

Further, passing a vertical RF via feed or transition through different dielectric materials poses design difficulties, due to impedance matching issues, and may degrade the RF performance of the feed.

Electronic components, such as beamformers, may have a large number of interconnects requiring a large number of conductor layers in the PCB. Each conductor layer is spaced by a dielectric layer. This increases the overall PCB thickness, which can significantly degrade vertical RF transition performance. Vertical RF feeds are difficult to design through multiple layers.

Thus, the structure of such a conventional PCB configuration may be complex and, consequently, may be difficult to manufacture. RF interconnects may, for example, require blind or buried via technology and sequential processing.

The electronic components comprise integrated circuits (ICs) which dissipate heat through their mounting bases. Beamformers and power amplifiers in particular produce a large amount of heat that needs to be dissipated. The lateral heat spreading of the PCB illustrated in Figure 1 is poor even if an array of thermal vias is used beneath each IC to extract heat to a buried ground plane. Thermal issues are, in particular, a major problem in many phased array antenna designs Every layer of the PCB increases its overall thickness and also increases the potential for a fault that will cause the PCB to fail operational testing. A unitary construction means that electronic components such as beamformer circuits need to be tested in conjunction with the antenna. Thus, problems with one or the other may reduce the manufacturing pass yields.

Figures 3 to 10 illustrate a simplified modular high frequency device according to an embodiment of the invention.

Figure 3 is an upper plan view of a first module of the device, Figure 4 is a cross-sectional view of the first module, schematically illustrating the vertical arrangement of layers of the first module, and Figure 5 is a lower plan view of the first module.

The first module 10 is a substantially planar module comprising a first module support layer 20 and a first module PCB layer 30. The first module has a length dimension and a width dimension that are each greater than a thickness dimension, and may be described as a tile. The first module support layer 20 is a sheet of metal, for example an aluminium plate or slab. The first module support layer is substantially rigid, so as to support the first module PCB layer, having a thickness of, for example, between 1 mm and 10 mm.

The first module PCB layer 30 has a conventional PCB structure, and comprises a plurality of vertically stacked dielectric layers separated by conductive layers (separate layers not shown). The dielectric layers of the first module PCB layer may be conventional PCB dielectric materials, for example FR4.

Various electronic components, for example a RF input 31, a power amplifier 32, and a beamformer 33, are mounted to a lower surface 35 the first module PCB layer 30. The first module PCB layer defines a RF signal path. A lower surface 25 of the first module support layer 20 is bonded to an upper surface 36 of the first module PCB layer. A first module waveguide aperture 40 is defined through a thickness of the first module support layer 20. The first module waveguide aperture 40 preferably extends perpendicularly to length and width dimensions of the first module support layer and is preferably a rectangular aperture.

Figure 6 is an upper plan view of a second module of the device, Figure 7 is a cross-sectional view of the second module, schematically illustrating the vertical arrangement of layers of the second module, and Figure 8 is a lower plan view of the second module.

The second module 100 is a substantially planar module comprising a second module support layer 120 and a second module PCB layer 130. The second module has a length dimension and a width dimension that are each greater than a thickness dimension, and may be described as a tile. In some embodiments, the length and width dimensions of the second module may be the same as the length and width dimensions of the first module.

The second module support layer is a sheet of metal, for example an aluminium plate or slab. The second module support layer is substantially rigid, so as to support the second module PCB layer, having a thickness of, for example, between 1 mm and 10 mm.

The second module PCB layer 130 comprises a plurality of vertically stacked dielectric layers separated by conductive layers (layers not illustrated). Different layers of dielectric material of the first module may be formed from dielectric materials having different relative permittivities, for example RO 588OLZ and RO 4360G2.

An antenna element 160 is supported on an upper surface 136 the second module PCB layer 130. The antenna element 160 is for propagating electromagnetic radiation into free space. It is noted that in some embodiments a further, protective, dielectric layer may be present vertically above the antenna element, as long as the electromagnetic radiation is capable of propagating through any such dielectric layer. Such a further dielectric layer may also be used to implement a stacked patch configuration to improve the radiative performance and particularly the operating bandwidth.

An upper surface 126 of the second module support layer 120 is bonded to a lower surface 135 of the second module PCB layer. A second module waveguide aperture 140 is defined through a thickness of the second module support layer 120. The second module waveguide aperture 140 preferably extends perpendicularly to length and width dimensions of the second module support layer and is preferably a rectangular aperture. The second module waveguide aperture has the same dimensions as the first module waveguide aperture.

The first module 10 and the second module 100 are coupled together in a vertical arrangement to form the high frequency device 1. As shown in Figures 9 and 10, the first module and the second module are brought together such that an upper surface of the first module support layer 20 abuts a lower surface of the second module support layer 120. The first module and the second module may be described as being coupled in a back-to-back arrangement. Coupling of the first module and the second module may be conveniently effected by mechanical fastening or clamping, such as bolts or screws, between the first module support layer and the second module support layer.

The first module waveguide aperture 40 and the second module waveguide aperture 140 are of the same dimensions, and are aligned on coupling the first and second modules to form a waveguide 45 as seen most clearly in Figure 10. The waveguide 45 is essentially a tube formed by conductive internal surfaces of the first module waveguide aperture and the second module waveguide aperture, with a dielectric (air) in the centre of the tube. The length of the waveguide is defined by the combined thickness of both the first module support layer 20 and the second module support layer 120. While air is a convenient dielectric in the waveguide, other dielectrics may be used. For example, in some embodiments the centre of the waveguide may be filled with a plug of a solid dielectric, such as PTFE, to modify the waveguide properties.

When the first module and the second module are coupled, the high frequency device can be used as an antenna device. To transmit high frequency electromagnetic radiation, a RF signal is fed into the first module and travels along the RF signal path defined in the first module PCB layer 30. The RF signal is modified by any integrated circuits located on the first module PCB layer, for example a power amplifier chip and a beamformer chip, and passes into a first PCB-to-waveguide transition structure located at a first end of the waveguide 41, adjacent the first module waveguide aperture 40. The RF signal is converted to an electromagnetic waveform signal, and vertical transition of the signal occurs via transmission through the waveguide 45. In other words, the first module and the second module are electromagnetically coupled via the waveguide 45.

A second PCB-to-waveguide transition structure is located at a second end of the waveguide 141, adjacent the second module waveguide aperture 140. The electromagnetic wave signal is converted back to RF and is transmitted through the second module PCB layer 130. The RF signal may be transmitted horizontally through the second module PCB layer, for example by means of a stripline. A stripline is beneficial if the module is to provide a series feed of the RF signal to more than one antenna element located on the second module. A further transition structure is present to couple the RF signal in the second module PCB layer with the antenna element, which converts the signal into electromagnetic radiation propagated from the antenna element.

The step by step transmission of an electromagnetic wave may be represented schematically in the flowchart illustrated in Figure 11.

Step Ti, a RF signal is input into the first module PCB layer.

Step T2, the RF signal is processed by electronics located on the first module PCB layer. Step T3, the RF signal is converted to an electromagnetic wave at a waveguide transition.

Step T4, the electromagnetic wave propagates between the first module and the second module via a waveguide.

Step TS, the electromagnetic wave is converted to a RE signal at a waveguide transition. Step T6, the RE signal propagates through the second module PCB layer. Step T7, the RE signal is coupled to the antenna element.

Step T8, the antenna element converts the RF signal to an electromagnetic wave that is propagated into free space.

The high frequency device may, alternatively or in addition to, be capable of receiving high frequency electromagnetic radiation. To act as a receiver, the steps of transmission may be reversed. For example, the step by step reception of an electromagnetic wave may be represented schematically in the flowchart illustrated in Figure 12.

Step R1, the antenna element receives an electromagnetic wave from free space and converts it to a RE signal.

Step R2, the RE signal is coupled to the second module PCB layer.

Step R3, the RE signal propagates through the second module PCB layer.

Step R4, the RE signal is converted to an electromagnetic wave at a waveguide transition.

Step RS, the electromagnetic wave propagates between the first module and the second module via a waveguide.

Step R6, the electromagnetic wave is converted to a RE signal at a waveguide transition. Step R7, the RE signal is processed by electronics located on the first module PCB layer. Step R8, the RE signal is output from the first module PCB layer.

The electronics of the first module PCB layer may include a switch allowing the high frequency device to operate as an antenna device in both transmit and receive. Alternatively, separate modules may be used for transmit and receive operations. In some embodiments, a single first module may be coupled, via waveguides, to a plurality of second modules.

Figures 13 to 18 illustrate a modular phased array antenna 1001 according to an embodiment of the invention comprising a first module 1010 and a second module 1100. The first module and the second module are both substantially planar modules in the form of tiles, and can be coupled together in a vertical relationship to form the phased array antenna. The essential elements of construction and operation of the modules, in particular the vertical waveguide transition, are as described above in relation to Figures 3 to 12.

Figure 13 is an upper plan view of a first module 1010 of the phased array antenna 1001, Figure 14 is a cross-sectional view of the first module 1010, schematically illustrating the vertical arrangement of layers of the first module, and Figure 15 is a lower plan view of the first module 1010.

The first module 1010 is a substantially two-dimensional planar module having a width of 100 mm a length of 200 mm, and a thickness of 10 mm (excluding electronic components). The first module comprises a first module support layer 1020 stacked vertically above a first module PCB layer 1030.

The first module support layer 1020 is an aluminium plate or slab having a thickness of 5 mm. The first module PCB layer 1030 comprises a plurality of vertically stacked layers of FR4 separated by conductive layers.

Electronics mounted on the first module PCB layer 1030 include a RF input/output 1031, a switch, a low noise amplifier, a power amplifier 1032, and four beamformers 1033. The first module PCB layer defines a RF signal path from the RF input/output that splits into four, with a beamformer in each of the four split signal paths.

Four first module waveguide apertures 1040 are defined through the thickness of the first module support layer 1020. Each first module waveguide aperture 1040 is preferably a rectangular aperture having a long dimension of about 10.66 mm and a short dimension of about 4.32 mm. The size of the waveguide aperture is selected to carry electromagnetic waves having a frequency in the range 18 to 26.5 GHz. It is noted that the dimensions of the waveguide apertures will be selected depending on the frequency of the RF signal being used for the particular radar antenna.

Figure 16 is an upper plan view of a second module 1100 of the phased array antenna, Figure 17 is a cross-sectional view of the second module, schematically illustrating the vertical arrangement of layers of the second module, and Figure 18 is a lower plan view of the second module. Figure 19 illustrates the first module and the second module when coupled.

The second module support layer 1120 is an aluminium plate or slab having a thickness of 5 mm. Four second module waveguide apertures 1140 are defined through the thickness of the first module support layer 1020. Each second module waveguide aperture 1140 has the same dimensions as a corresponding first waveguide aperture 1040 with which it will align when the first module and the second module are coupled.

The second module PCB layer 1030 comprises the following vertically stacked layers: Conductive layer 1(3000); this is the vertically uppermost layer of the second module PCB layer and comprises an array of 16 rectangular copper patches having a thickness of 35 micrometres. These conductive patches form 16 antenna elements 1160. Each antenna patch 1160 has a length and a width, and the dimensions of the antenna elements can be varied to optimise desired transmission properties for specific applications. For example, it may be desired that the length of the antenna element is close or equal to half the wavelength of the electromagnetic radiation propagating through the supporting dielectric layer 3010 (dielectric layer 1). Width of the antenna element may be varied to control impedance and influence the radiation pattern emitted by the antenna element.

Dielectric layer 1 (3010); this dielectric layer supports the antenna elements and is formed from a 508 micrometre thick sheet of Rogers Corporation's RD 5880LZ. This material has a relative permittivity, or dielectric constant -Er, of about 2.

If the dielectric layer supporting an antenna element has a low permittivity, the radiation efficiency of the antenna element is improved. Thus, low permittivity dielectric materials are preferred for dielectric layers supporting the antenna elements in embodiments of this invention, for example dielectric materials having Ervalues of less than 3, for example between 2 and 3.

Bandwidth of an antenna element refers to the range of frequencies within which the antenna element can operate. A high bandwidth may be desirable in radar and communication applications. Bandwidth of the antenna device may be improved by increasing the thickness of the dielectric layer supporting the antenna elements. Thus, referring to the present specific embodiment, bandwidth may be improved by increasing the thickness of dielectric layer 1. Dielectric layer 1 may compromise multiple layers of dielectric material, stacked to increase the overall thickness of the layer. Dielectric layer 1 may, therefore, be formed from two vertically stacked layers of 508 micrometre thick sheet RO 5880LZ, giving a total thickness of dielectric layer 1 of 1016 micrometres.

Conductive layer 2(3020); this is a 17 micrometre thick copper ground plane with an aperture 3021 located vertically below each antenna element 1160 to couple the RF signal flowing in the second module PCB layer with the antenna elements. The apertures are shaped as rectangular slots, each slot positioned beneath the centre of an antenna element. The apertures need not be slot shaped and may be in other shapes to optimise bandwidth or coupling, for example the apertures may be H-shaped, or bow tie shaped.

Dielectric layer 2 (3030); this dielectric layer forms the upper portion of a stripline feed and is formed from a 508 micrometre thick sheet of Rogers Corporation's RO 4360G2. This material has Er of about 6.3.

Dielectric layer 2 is the uppermost dielectric layer constraining the stripline 3040. Radiation from the stripline is not desired, and it is desirable to contain the electromagnetic fields from the stripline as much as possible. High permittivity of dielectric layers surrounding the stripline reduces the wavelength of a propagating RF wave. Thus, high permittivity dielectric materials are preferred for dielectric layers supporting the striplines in embodiments of this invention, for example dielectric materials having srvalues of greater than 4, for example between Sand 12.

Conductive layer 3(3040); this is a convoluted stripline feed, which may also be termed a meander line. The stripline 3040 is a 17 micrometre thick track of copper.

To facilitate beam steering in both azimuth and elevation, it is advantageous to introduce a phase shift in the radiation emitted by successive antenna elements. This can be achieved by increasing the length of stripline between antenna elements. The individual antenna elements 1160 on dielectric layer 1 are spaced by approximately half a wavelength (X/2). To enable phase shifts to be introduce, the stripline meanders in a convoluted or serpentine path. Furthermore, the use of high permittivity dielectric layers above and below the stripline effectively reduces the wavelength of the propagating RF wave. Thus, it is possible to introduce stripline lengths of between 5A. to 6A between successive antenna elements that are themselves only spaced by A/2.

Dielectric layer 3(3050); this dielectric layer forms the lower portion of the stripline feed and is formed from a 508 micrometre thick sheet of RO 4360G2.

Conductive layer 4(3060); this is a 17 micrometre thick copper ground plane forming a lower ground plane for the stripline. In the illustrated embodiment, conductive layer 4 also comprises a 17 micrometre copper patch 3061 located vertically above the second module waveguide aperture. This patch forms part of the waveguide to PCB transition in the second module.

Dielectric layer 4(3070); this dielectric layer is the vertically lowest dielectric layer in the second module and is formed from a 508 micrometre thick sheet of RO 5880LZ.

Conductive layer 5(3080); this is a 35 micrometre thick copper ground plane and forms a lower ground plane for the second module PCB layer. A lower surface of conductive layer 5 is bonded to the second module support layer 1120.

The waveguide-to-PCB transition (and vice versa) may be implemented in various ways dependent upon the stack-ups of each PCB and the layers used to propagate the RF signals.

One of the simplest/common waveguide transitions is to have a probe protruding into a waveguide that is spaced approximately quarter of a wavelength (A/4) from a waveguide short. A modified form of this transition can be used to interface with a PG. The PCB is sandwiched between the waveguide approximately A/4 from the waveguide back short with the track that defines the RE signal path forming a probe. Whilst good RF performance is possible with this configuration it is unsuitable for many applications due to the presence of a waveguide back short that protrudes from the PCB surface. Alternative configurations are possible that may enable a more compact waveguide to PG transition without the protruding back short.

A preferred PCB-to-waveguide transition, as illustrated in a second module according to the embodiment of figures 16 to 18, is explained in more detail with reference to figures 20 and 21. As stated above, the waveguide 1045 is, in part, formed by an aperture 1140 in the thick metal of the second module support layer 1120. The aperture 1140 forms an upper portion of the waveguide 1045 when the second module 1100 is coupled to the first module 1010. At the waveguide to PCB dielectric interface, waveguide extension vias 1148 are used to extend the waveguide walls into the second module PCB layer. These waveguide extension vias 1148 extend between conductive layer and conductive layer 2. A matching patch element 3061 is present within the waveguide aperture on conductive layer 4 and this matching patch 3061 is proximity coupled to the stripline 3040 that protrudes to overlap with the waveguide on conductive layer 3. The waveguide is terminated (shorted) by the ground plane 3020 on conductive layer 2, which may be referred to as a back short.

Simulation for a frequency of 16GHz shows this transition can achieve approximately 0.5dB insertion loss together with a good RE match.

While this PCB-to-waveguide transition structure has been illustrated with respect to the second module, it is noted that the same structure, with the order of layers inverted, would serve as a PCBto-waveguide transition in the first module.

Figure 22 illustrates an alternative possible structure for a PCB-to-waveguide transition. In this transition structure, the matching patch 3061' is on conductive layer 4, and the stripline 3040' is on conductive layer 3. However, the back short 3046' is also on conductive layer 3, insulated by a gap 3047' from the stripline 3040'.

Figure 23 illustrates another alternative possible structure for a PCB-to-waveguide transition. In this transition structure, the matching patch 3061" is on conductive layer 4 or conductive layer 5, the stripline 3040" is on conductive layer 3, and the back short 3020" is on conductive layer 2. A vertically extending via 3049" is used to connect the matching patch 3061" with the stripline 3040".

Figure 24 illustrates another alternative possible structure for a PCB-to-waveguide transition. In this transition structure, the matching patch 3081" is on conductive layers, the stripline 3040" is on conductive layer 3, and the back short 3020" is on conductive layer 2. Conductive layer 4 is a ground plane 3060-with a slotted aperture 3065-allowing coupling between the matching patch 3081" and the stripline 3040".

Coupling between the RE energy in the stripline and the antenna elements may be achieved by a number of known methods. For example, vias, in particular blind vias, may be used as direct couplings, or as probes to concentrate the electric field and allow a proximity coupling. Via feeds become more difficult to implement as the frequency of the signal increases, however, due to the tolerances of the manufacturing processes required versus the decreasing wavelength.

In the embodiment illustrated in Figures 16 to 18, coupling is achieved by means of aperture coupling. As illustrated in Figure 25 and 26, apertures 3021 are defined through conductive layer 2 between the stripline 3040 and each antenna element 1160. Aperture coupling is an indirect method of feeding an antenna element. RF energy in the stripline is coupled to an antenna element via an aperture 3021 in a ground plane 3020 positioned between the stripline 3040 and the antenna element 1160.

The modular phased array antenna 1001 of figures 13 to 18 comprises an array of antenna elements 1160 for transmitting a beam of electromagnetic radiation. The array utilises phase shifters to vary the phase of signal provided to separate columns of the array, and thereby enable scanning in azimuth. Each column includes antenna elements connected by a series feed to enable frequency scanning in elevation. Using frequency scanning enables fewer active elements to be used compared with a fully populated array that uses a phase shifter for each element. This can significantly reduce the cost of the array.

The beam steering effect with frequency is optimised by increasing the electrical length of the series feed used to connect the radiating elements. This is achieved using a buried transmission line commonly referred to as a "stripline". This comprises a conductor that is routed between a lower and an upper ground plane. The physical length of the stripline can be increased using a serpentine section between each radiating element. The radiating elements are typically spaced X/2 apart in both azimuth and elevation so the area available for this serpentine line section is very restricted.

Other constraints may also apply. For example, the width of the stripline conductor must enable the desired characteristic impedance to be met and the spacing between the folds must prevent excessive RF coupling. In practice there is a limit upon the number of folds and hence the physical line length that may be achieved between each radiating element.

To further increase the "electrical length" of the stripline preferred embodiments of the present invention use a high relative dielectric constant microwave laminate material to fill the space between the lower and upper ground planes. This reduces the wavelength of the propagating RF wave. Using these techniques electrical line lengths of 5Xto 6X are possible between each radiating element. This provides a much greater beam steering rate with frequency compared with the more common surface fed approach for the radiating elements.

In the embodiment illustrated, the meandering stripline 3040 forms conductive layer 3. Dielectric layer 2 and conductive layer 2 are located vertically above the stripline and dielectric layer 3 and conductive layer 4 are located vertically below the stripline. Dielectric layer 2 forms an upper stripline dielectric and dielectric layer 3 forms a lower stripline dielectric. Conductive layer 2 forms an upper stripline ground layer and conductive layer 4 forms a lower stripline ground layer. A via fence is formed around the stripline by vias 3049 extending between conductive layer 2 and conductive layer 4 in order to prevent the formation of a parallel plate mode between conductive layers 2 and 4 and to isolate the stripline.

Advantageously, a single stripline acts as a feed to a plurality of antenna elements. In the embodiment illustrated in Figures 16 to 18, each stripline feeds four antenna elements, but it is clear that this number may be increased or decreased.

Advantageously, a plurality of modular phased array antennas 1001 can be combined to form a larger phased array antenna 2001. Thus, each modular phased array antenna 1001 of the specific embodiment described above may be an individual tile of a larger phased array antenna. Figure 27 is a schematic illustration of such an antenna. The phased array antenna 2001 comprises nine tiles, each tile formed from a modular phased array antenna 1001 as described above. Scanning in azimuth is achieved by use of phase shifters that can alter the phase of each column. Scanning is elevation is achieved by frequency shifting allowed by the phase shift between individual antenna elements connected in series via a meandering stripline. The total number of electronic components used in the overall phased array antenna is significantly reduced by the use of the modular construction and vertical waveguide coupling as described herein. Heat from the electrical components is more efficiently removed due to the metallic support layers within each tile.

Claims

Claims 1. A modular high frequency device comprising, a first module having a laminate structure including a first module support layer, and a first module PCB layer arranged vertically with respect to the first module support layer, the first module PCB layer defining a high frequency signal path, and a second module having a laminate structure including a second module support layer, and a second module PCB layer arranged vertically with respect to the second module support layer, the second module PCB layer supporting a high frequency electronic structure, in which, the first module PCB layer and the second module PCB layer are electromagnetically coupled by a waveguide.
2. A modular high frequency device according to claim 1 in which, the second module is coupled to the first module such that a lower surface of the second module support layer faces an upper surface of the first module support layer, the waveguide extending through both the first module support layer and the second module support layer.
3. A modular high frequency device according to claim 1 or 2, in which, the first module and the second module are planar modules and, when the first module and the second module are coupled, the waveguide extends perpendicularly relative to length and width directions of both the first module and the second module.
4. A modular high frequency device according to any preceding claim, in which, the frequency of an electromagnetic signal transmitted by the waveguide is between 3 GHz and 300 GHz.
S. A modular high frequency device according to any preceding claim, in which, the first module comprises one or more active electronic components for processing a high frequency signal travelling along the high frequency signal path.
6. A modular high frequency device according to any preceding claim, in which, the high frequency electronic structure of the second module is a passive electronic component.
7. A modular high frequency device according to any preceding claim, in which, the first module support layer and/or the second module support layer is a thermally conductive material, preferably a metallic material, particularly preferably aluminium or copper, and preferably in which the first module support layer has a thickness of between 1 mm and 10 mm.
8. A modular high frequency device according to any preceding claim, in which, the first module support layer is a thermal plane in thermal communication with one or more electronic components comprised in the first module.
9. A modular high frequency device according to any preceding claim, in which, a first module waveguide aperture is defined through a thickness of the first module support layer and a second module waveguide aperture is defined through a thickness of the second module support layer, the first module and the second module being coupleable such that the first module waveguide aperture aligns with the second module waveguide aperture.
10. A modular high frequency device according to claim 9, in which, the waveguide extends through, and/or is formed by, the first module waveguide aperture and the second module waveguide aperture.
11. A modular high frequency device according to claim 10, in which, the first module support layer and the second module support layer are formed from electrically conductive material and walls of the waveguide are defined by inner surfaces of the first module waveguide aperture and the second module waveguide aperture.
12. A modular high frequency device according to any preceding claim, in which, the waveguide is a rectangular cross-section waveguide.
13. A modular high frequency device according to any preceding claim, in which, the waveguide comprises a dielectric core material selected from the list consisting of air, PTFE, or other low dielectric constant material.
14. A modular high frequency device according to any preceding claim, in which, the first module is removably -coupleable to the second module.
15. A modular high frequency device according to any preceding claim, in which, the first module is coupleable to the second module by means of a mechanical fastening acting between the first module support layer and the second module support layer.
16. A modular high frequency device according to any preceding claim, in which, the second module PCB layer comprises at least one dielectric layer formed from a material having a dielectric constant of lower than 3 and/or at least one dielectric layer formed from a dielectric material having a dielectric constant greater than 4.
17. A modular high frequency device according to any preceding claim, in which, the high frequency electronic structure of the second module PCB layer is an antenna element, the modular high frequency device being a modular antenna device.
18. A modular high frequency device according to claim 17 in which the second module PCB layer comprises a plurality of dielectric layers vertically spaced by at least one conductive layer, in which the antenna element is located on a surface of one of the plurality of dielectric layers to transmit or receive high frequency electromagnetic waves.
19. A modular high frequency device according to claim 17 or 18 in which, the second module comprises the following elements; the second support layer, a waveguide aperture defined through the second support layer, a first dielectric layer arranged vertically above the second support layer, a waveguide transition element aligned with the waveguide aperture, preferably in which the waveguide transition element is a transducer supported by the first dielectric layer, a second dielectric layer arranged vertically above the first dielectric layer, and the antenna element, preferably supported by the second dielectric layer, for example in which the antenna element is printed on an upper or a lower surface of the second dielectric element.
20. A modular high frequency device according to claim 19, further comprising; a first ground plane arranged vertically below the second dielectric layer, preferably in which the first ground plane comprises an aperture aligned with the antenna element.
21. A modular high frequency device according to any of claims 17 to 20 in which the second module comprises a plurality of antenna elements located in the same plane, for example an array of antenna elements.
22. A modular high frequency device according to any of claims 17 to 21 in which, the second module comprises a horizontally extending transmission line for electromagnetic coupling a plurality of antenna elements with the waveguide, the horizontally extending transmission line being arranged vertically below the antenna elements.
23. A modular high frequency device according to claim 22, in which, the horizontally extending transmission line is sandwiched between third and fourth layers of dielectric material, the third and fourth layers of dielectric material being arranged vertically above the second module support layer and vertically below the antenna elements.
24. A modular high frequency device according to claim 22 or 23, in which, the horizontally extending transmission line follows a convoluted path to increase the length of transmission line between successive antenna elements.
25. A modular high frequency device according any of claims 22 to 24, in which, the horizontally extending transmission line is located within, or between layers of, dielectric material having a dielectric constant of greater than 4, for example between S and 7.
26. A modular high frequency device according any preceding claim, comprising a plurality of waveguides, each of the plurality of waveguides extending through the first module support layer and the second module support layer.
27. A modular high frequency device according to claim 26 in which each of the plurality of waveguides facilitates electromagnetic coupling between a high frequency signal travelling in the first module and at least one high frequency electronic structure, for example a transmission line and/or an antenna element, located in the second module.
28. A modular high frequency device according to any preceding claim, in which, the device is configured to transmit or receive electromagnetic waves within a range of electromagnetic waves having a wavelength (A) of between about 0.5 mm and about 100 mm, for example between about 1 mm and about 50 mm.
29. A modular high frequency device according to any preceding claim, in which, the second module comprises an array of antenna elements, the array comprising a plurality of columns of antenna elements, each column of antenna elements comprising two or more individual antenna elements.
30. A modular high frequency device according to claim 29 in which each of the plurality of columns of antenna elements is electromagnetically coupled to the first module PCB layer by at least one waveguide extending between the first module and the second module.
31. A modular high frequency device according to claim 30 in which each at least one waveguide provides electromagnetic signal to between 2 and 8 discrete antenna elements within one of the plurality of columns of antenna elements.
32. A modular high frequency device according to claim 31, in which each one of the plurality of columns of antenna elements of the second module is electromagnetically coupled to the first module PCB layer by between two and ten waveguides, each of the between two and ten waveguides providing electromagnetic signal to between two and ten discrete antenna elements within the column of antenna elements.
33. A modular high frequency device according to any preceding claim in which the first module comprises one or more electronic component for processing the high frequency signal selected from the list of components consisting of a power amplifier, a low noise amplifier, a phase shifter, and a beamformer.
34. A modular high frequency device according to any preceding claim, comprising, a plurality of second modules removably-coupled to a single first planar module.
35. A modular high frequency device according to any preceding claim in which the second module comprises the following layers; a first conductive layer, or antenna layer, having an array of discrete antenna elements arranged in columns, a first dielectric layer arranged vertically beneath the antenna layer, the first dielectric layer preferably having a dielectric constant of less than about 3, a second conductive layer arranged vertically beneath the first dielectric layer, a second dielectric layer arranged vertically beneath the first conductive layer, the second dielectric layer preferably having a dielectric constant of greater than about 4, a third conductive layer, or transmission line layer, located vertically beneath the second dielectric layer, the transmission line layer comprising a plurality of convoluted, horizontally extending transmission lines, at least one transmission line for each column of the array of antenna elements, a third dielectric layer arranged vertically beneath the transmission line layer, the third dielectric layer preferably having a dielectric constant of greater than about 4, a fourth conductive layer arranged vertically beneath the third dielectric layer, a fourth dielectric layer arranged vertically beneath the fourth conductive layer, the fourth dielectric layer preferably having a dielectric constant of greater less than about 3, and the second module support layer arranged vertically beneath the fourth dielectric layer, the second module support layer defining a plurality of second module waveguide apertures, one of the plurality of second module waveguide apertures being located vertically beneath each of the plurality of convoluted horizontally extending transmission lines, and in which the first module comprises the following layers; the first module support layer, which when the first module is coupled to the second module is arranged vertically beneath the second module support layer, the first module support layer defining a plurality of first module waveguide apertures corresponding to, and aligned with, the plurality of second module waveguide apertures, and the first module PCB layer arranged vertically beneath the first module support layer, the first module PCB layer comprising a plurality of dielectric layers spaced by conductive layers and locating a plurality of electronic components selected from the list consisting of a power amplifier, a low noise amplifier, a phase shifter, and a beamformer, the modular high frequency device being a beam-steerable phased array antenna device.
36. A modular high frequency device according to claim 35 in which each of the plurality of convoluted, horizontally extending transmission lines feeds a high frequency signal to a plurality of antenna elements within a column of the array of discrete antenna elements, for example to between 2 and 10 of the antenna elements.
37. A modular high frequency device according to claim 36 in which the high frequency signal passing through the convoluted, horizontally extending transmission lines is coupled to the array of discrete antenna elements by aperture coupling, an aperture being defined through the second conductive layer vertically beneath each of the plurality of discrete antenna elements.
38. A modular high frequency device according to any of claims 35 to 37 in which each first module waveguide aperture is associated with a PCB-to-waveguide transition structure defined in the first module PCB layer to allow energy to pass between the high frequency signal path defined in the first module PCB layer and a waveguide, and each second module waveguide aperture is associated with a PCB-to-waveguide transition structure defined in the second module PCB layer to allow energy to pass between a waveguide and a convoluted, horizontally extending transmission line.
39. A modular high frequency device according to any preceding claim comprising an array of discrete antenna elements arranged in columns, the array of discrete antenna elements configured to transmit a beam of electromagnetic energy, in which the beam of electromagnetic energy can be steered in a first direction, for example in azimuth, by modulating the phase of signal fed to adjacent columns of discrete antenna elements, and the beam of electromagnetic energy can be steered in a second direction perpendicular to the first direction, for example in elevation, by modulating the frequency of the signal supplied to the columns of discrete antenna elements
40. A first module for use in a modular high frequency device according to any preceding claim, the first module being a planar module having a laminate structure including a support layer, and a PCB layer arranged vertically with respect to the support layer, the PCB layer including a circuit board defining a high frequency signal path, in which one or more waveguide aperture is defined through the support layer.
41. A first module according to claim 40, in which, the first module is a first module as described as forming part of a modular high frequency device in any of claims 1 to 39.
42. A second module for use in a modular high frequency device according to any of claims 1 to 39, the second module being a planar module having a laminate structure including a support layer, and a PCB layer arranged vertically with respect to the support layer, the PCB layer supporting a high frequency electronic structure, at least one waveguide aperture being defined through the support layer.
43. A second module according to claim 42, in which, the second module is a second module as described as forming part of a modular high frequency device in any of claims 1 to 39.
44. A steerable phased array antenna system comprising a plurality of antenna tiles arranged on a surface, each of the antenna tiles being a high frequency device as defined in any one of claims 1 to 39.
45. A steerable phased array antenna system according to claim 44 in which each antenna tile comprises an array of between 4 and 256 discrete antenna elements, for example between 32 and 144 discrete antenna elements.
46. A steerable phased array antenna system according to claim 44 or 45 comprising an array of between 4 and 256 antenna tiles.
47. A steerable phased array antenna system according to any of claims 44 to 46 in which each antenna tile comprises a RF input to receive a high frequency signal from a waveform generator.
48. A method of transmitting an electromagnetic signal into free space comprising the steps of; inputting a RF signal carrying a waveform into a high frequency device; processing the RF signal with one or more electronic components of the high frequency device; converting the RF signal to an electromagnetic wave at a first waveguide transition within the high frequency device; propagating the electromagnetic wave through a waveguide within the high frequency device; converting the electromagnetic wave to a RF signal at a second waveguide transition within the high frequency device; coupling the RF signal to an antenna element of the high frequency device; and converting the RF signal to an electromagnetic wave that is propagated into free space.
49. A method of transmitting a steerable beam of electromagnetic radiation into free space comprising the steps of; inputting a RF signal carrying a waveform into a high frequency device; splitting the signal into a plurality of signal paths processing the RF signal in each of the plurality of signal paths with one or more electronic components of the high frequency device including at least a phase shifter; for each of the plurality of signal paths, converting the RF signal to an electromagnetic wave at a first waveguide transition within the high frequency device; for each of the plurality of signal paths, propagating the electromagnetic wave through a waveguide within the high frequency device; for each of the plurality of signal paths, converting the electromagnetic wave to a RF signal at a second waveguide transition within the high frequency device; for each of the plurality of signal paths, propagating the RF signal along a convoluted transmission line; for each of the plurality of signal paths, coupling the RF signal in series to a plurality of antenna elements arranged in a column on the high frequency device; and for each of the plurality of signal paths, converting the RE signal to an electromagnetic wave that is propagated into free space, in which the electromagnetic waves propagated from each antenna element of each column interact with each other to form the electromagnetic beam, in which the electromagnetic beam is steerable in a first direction by modulating the phase of the RF signal in each of the plurality of signal paths, and in which the electromagnetic beam is steerable in a second direction perpendicular to the first direction, by modulating the frequency of the RF signal input into the high frequency device.