Patent Description:
At millimetre/submillimetre frequencies, planar transmission lines have low voltage ratings, and tend to suffer from large parasitic power losses due to conductor "skin" and dielectric effects. In waveguides, the electromagnetic waves are guided and therefore energy leakage can be largely eliminated, allowing high power signals and wide bandwidths. In these frequency ranges, instruments such as radiometers and radar tend to use conventional waveguide modules along with coaxial interconnections.

However, miniaturisation of such systems is important for example to allow the development of new applications for microwave radiometers and instruments. One field of application is in the deployment of Earth observation satellites such as CubeSats. These satellite platforms tend to impose strict limitations on size and mass of instruments, for example in up to about six discrete units of about 100x100x100 mm<NUM> in size.

It would be desirable to address problems and limitations of the related prior art.

<CIT> provides an interface between a millimetre-wave bare die and a printed circuit board. <CIT> discloses a technique for forming imbedded microwave structures in a microwave circuit package. <CIT> describes a circuit board including a substrate, a waveguide line, and a laminated waveguide. <CIT> describes a microwave antenna structure manufactured by making holes in a number of electrically-conductive plates.

Embodiments of the invention provide an improved architecture for radio frequency modules which allow for very compact designs along with high performance in terms of sensitivity, power, signal to noise ratio and other relevant considerations. Radio frequency functions are stacked within a series of parallel metal plates brought together to form a radio frequency circuit block, in which radio frequency interconnections between the different functions are provided in waveguide form within the circuit block. Flexible circuit board connections between the interior of the circuit block and exterior elements such as support circuit boards can be used, especially for lower frequency signals, and such support circuit boards can be vertically stacked with the metal plates of the circuit block to form a particular compact and high performance module.

Waveguides and other spaces within the circuit block, for example spaces to accept processing components, microstrip transition circuits and intermediate frequency units, can be accurately formed for example by CNC milling techniques.

Embodiments of the invention can be used to provide functionally independent standalone RF modules, or modules which can be combined together into a larger system. Using a compact and regular form of the modules can promote good use of space in stacking or providing groups of arrays of such modules, for example in phase array applications.

In particular, the invention provides a radio frequency module as set out in claim <NUM>, a phased array as set out in claim <NUM>, and a method of constructing a radio frequency module as set out in claim <NUM>.

Embodiments of the invention comprise: a radio frequency circuit block which comprises a stack of at least two, or at least three metal plates, and a plurality of radio frequency waveguides defined by channels in the metal plates so as to carry radio frequency signals within the circuit block; and one or more radio frequency processing components arranged within the circuit block to interact with the signals carried by the waveguides.

The metal plates may typically be planar, parallel and in face to face contact with each other so as to form a continuous unit within which the waveguides extend to carry the radio frequency signals. At least three, and optionally all, of the metal plates may define a portion or a surface of at least one of the radio frequency waveguides.

The processing components may be active components such as integrated circuits, passive components such as diodes or functional waveguide or strip line arrangements, or a mixture of passive and active components.

The radio frequency module may then further comprise one or more support circuit boards, each support circuit board being in electrical communication with at least one of the processing components. At least one, and optionally all of the support circuit boards may be stacked in series with the metal plates.

Each adjacent pair of metal plates in the stack may define a mutual plate boundary, and a different one of the radio frequency processing components may then be located at each of at least two, at least three, or optionally all of the mutual plate boundaries.

The radio frequency modulefurther comprises one or more flexible circuit boards, or flexible printed circuit boards coupled to the radio frequency circuit block, extending from the outside to the inside of the radio frequency circuit block. These flexible printed circuit boards may be used for various purposes, but typically each may provide electrical connection between one or more of the radio frequency components (most typically active ones of the radio frequency components) to elements outside of the circuit block. Such a flexible printed circuit board may for example provide electrical communication between one or more of the support circuit boards and one or more of the processing components.

One, more than one, or all of the flexible printed circuit boards may in particular be arranged or installed as part of the radio frequency module with a significant curvature of the main plane of the PCB, for example with a radius of curvature which is less than <NUM>, or less than <NUM>.

In some aspects, the invention provides an above radio frequency module in which the radio frequency circuit block comprises a stack of at least three of the metal plates and a plurality of the radio frequency waveguides defined by channels in the metal plates so as to carry radio frequency signals within the circuit block. The metal plates may typically be planar, parallel and in face to face contact with each other so as to form a continuous unit within which the waveguides extend to carry the radio frequency signals.

One or more of the radio frequency processing components may then be disposed within the circuit block to interact with the signals carried by the waveguides. These processing components may be active such as integrated circuits, passive such as diodes or waveguide structures, or a mixture of the two.

One or more support circuit boards may then be provided, each in electrical communication with at least one of the processing components. In particular, the support circuit boards may be stacked in series with the metal plates, for example each support circuit board being parallel to the metal plates.

The radio frequency modules discussed may for example be arranged to handle radio frequency signals which have frequencies in the range <NUM> to <NUM>, and in particular the waveguides within the circuit block may be adapted or constructed for this range.

The modules discussed may further comprise one or more of the flexible printed circuit boards, or Flex PCBs, for example wherein each support circuit board is in electrical communication with at least one of the processing components via a said flexible printed circuit board extending from the relevant support circuit board into the circuit block. Conveniently, one or more of the processing components may be mounted on a said flexible printed circuit board within the circuit block, or may be closely coupled to or adjacent to such a flexible printed circuit board.

A plurality of mounting rods may be provided, each mounting rod passing through a series of aligned apertures in all of the metal plates, and one or more of the mounting rods may then also pass through a corresponding mounting aperture in each of the support circuit boards which are stacked in series with the metal plates. The mounting rods may be at least partly threaded so as to accept nuts to secure the metal plates together and to fix the support circuit boards in place.

Each metal plate may have the same form factor as the other metal plates, and optionally wherein some or all of the support circuit boards have the same form factor as the metal plates. Typically, the form factor may be a square or rectangular form factor but other shapes may be used.

Each metal plate of the stack, and optionally also each of some or all of the support circuit boards, may be of substantially the same shape and size, at least in plan view. For example, each metal plate in the stack may be of sufficiently similar shape and size to overlap with all the other metal plates in plan view by at least <NUM>% surface area. Some or all of the support circuit boards may conform to the same criteria, although it may be convenient for one or more of the circuit boards to have smaller form factor, for example a half of the metal plate form factor.

The invention enables very compact and miniaturised RF modules to be formed, for example in which the top or major surface of each metal plate has a surface area of not more than <NUM><NUM>. Similarly, the stack of parallel metal plates and if present, parallel support circuit boards, may be required to be no more than <NUM> in height or depth.

One or more of the processing components may be coupled to one or more of the waveguides using one or more microstrip circuits located within the circuit block, for example microstrip circuits formed on quartz and disposed in channels within the circuit block which connect with the waveguides.

The one or more processing components may include or comprise one or more passive electrical or electronic components, such as a discrete diode, a combination of discrete diodes, a resistor or resistor network, an inductor, a capacitor, or combinations of passive components which may be mounted on a microstrip circuit or on a portion of a flexible PCB within the circuit block.

The one or more processing components may include or comprise one or more waveguide or strip line structures, typically passive such structures, for combining, dividing, or mixing the radiofrequency signals, for example a transmission line or waveguide directional coupler; a transmission line or waveguide hybrid coupler; a transmission line or waveguide power divider; and a transmission line or waveguide power combiner.

The one or more processing components may include or comprise one or more active electrical or electronic components, such as a transistor, an amplifier integrated circuit, a mixer integrated circuit, a filter integrated circuit, or a MEMS device. Again, such components may be mounted on a microstrip circuit or on a portion of a flexible PCB within the circuit block.

The processing components may for example implement, within the circuit block, one or more of: an amplifier, a mixer, a frequency multiplier, and a phase shifter.

The radio frequency module may be one or more of a receiver module, a heterodyne receiver module, a transmitter module, and a transceiver module, and a phased array may be provided comprising a plurality of said radio frequency modules.

Method embodiments corresponding to the above apparatus are also provided, for example a method of constructing a radio frequency module comprising stacking a plurality of metal plates to form a radio frequency circuit block which comprises a plurality of radio frequency waveguides defined by channels in the metal plates so as to carry radio frequency signals within the circuit block, while disposing one or more radio frequency processing components within the circuit block to interact with the signals carried by the waveguides. The method may then further comprise mounting one or more support circuit boards so as to be stacked in series with the metal plates, each support circuit board being in electrical communication with at least one of the processing components within the circuit block. Typically, the plates of the circuit block may be stacked in contact with each other.

Electrical communication between the inside and the outside of the circuit block, for example between one or more of the support circuit boards and one or more of the processing components, is then provided using one or more flexible printed circuit boards extending to or into the circuit block, and the method further comprises mounting one or more of the processing components on one or more of said flexible printed circuit boards within the circuit block.

Although embodiments of the invention may be depicted and/or described in certain orientations, for example using the terms top and bottom, these orientations are not to be taken as limiting, since the described radio frequency modules can be oriented in any desirable manner, for example depending on the application, platform and other factors.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings of which:.

Referring to <FIG> there is illustrated a radio frequency (RF) module <NUM> implemented in a compact or miniaturised form. The particular module illustrated is configured to operate as a heterodyne receiver or radiometer, but similar compact modules may be designed and configured to implement other functions such as those discussed below. Such modules may be installed and used in a variety of situations, for example being carried by an orbiting satellite, an aircraft, a high altitude balloon, a radar installation, a ship or land vehicle, or by any of a variety of other moving or static platforms. Such modules may be arranged to receive and process (for example to measure) the radio waves, to generate radio waves for transmission or other processing, or both to receive and transmit. Such modules may for example receive radio waves directly from an antenna or another such module, and/or direct radio waves to an antenna for transmission, or to another such module.

The module <NUM> of <FIG> comprises a radio frequency circuit block <NUM> which comprises a stack of at least two, or at least three, parallel metal plates <NUM> (in <FIG> five such plates are shown), and may also comprise one or more support circuit boards <NUM> (in <FIG> there are two such support circuit boards). The support circuit boards <NUM> as shown in <FIG> are mounted so as to be parallel to and stacked in series with the metal plates <NUM>, although other mounting locations and positions are possible as discussed below, for example see the arrangement of <FIG>. Typically the support circuit boards if stacked in series with the metal plates will be spaced from each other and from the circuit block <NUM> as shown in <FIG>, rather than being stacked in contact or in very close proximity.

The metal plates in <FIG> are labelled A - E for ease of discussion later in this document. Each adjacent pair of metal plates in the stack may be considered to define a mutual plate boundary, so that in the arrangement of <FIG> there are four such boundaries.

Within the circuit block <NUM> a plurality of radio frequency waveguides (visible in <FIG> only as an entrance port <NUM> through the top metal plate) are defined by channels in the metal plates, so as to carry radio frequency electromagnetic waveguide signals within the circuit block <NUM>. In some embodiments (and most notably where there are three or more metal plates), at least three, and optionally all of the metal plates define at least a portion or surface of at least one of the radio frequency waveguides.

Also within the circuit block <NUM> are one or more radio frequency processing components (not visible in <FIG>) which are arranged to interact with the waveguide signals in various ways. For example, such processing components may measure, amplify, split, mix, combine, frequency shift, otherwise transform, and/or generate such waveguide signals (note therefore that when we refer to processing components interacting with waveguide signals, this may include generation of such waveguide signals). Each such processing component may be coupled directly to the waveguide signals in the waveguides, or using coupling arrangements such as one or more microstrip transition circuits or other arrangements. In some embodiments (and most notably where there are three or more metal plates) at least one such processing component may be located at each of two or more, or at each of three or more, or at all of, the mutual boundaries between the metal plates. This condition does not necessarily require such a processing component to extend across the major plane of the boundary, because such a processing component could for example be located between the two metal plates while being contained wholly within an aperture in the boundary surface of one of the metal plates.

The waveguide signals may typically be electromagnetic signals within a frequency range from about <NUM> - <NUM>. Below about <NUM> the required sizes of the waveguides are increasingly large, and planar technologies are likely to be more suitable. Above about <NUM> the alignments required between the waveguide boundaries in adjacent metal plates become critical, with very slight misalignments increasing insertion loss significantly.

In the arrangement of <FIG>, each such support circuit board <NUM> is in electrical communication with one or more of the processing components within the circuit block <NUM>. The support circuit boards <NUM> may send support signals to the processing components, and/or receive support signals from the processing components. Such support signals may for example provide a bias signal for an amplifier component, a local oscillator signal for a mixer component, a control signal for a switch component, a measurement of a waveguide signal from a measuring component, and so forth.

In the arrangement of <FIG>, each support circuit board <NUM> is in electrical communication with one or more of the processing components within the circuit block via, or using, a connector, which may in particular be a flexible printed circuit board <NUM> (flexible PCB) as illustrated in <FIG>. Each such connector or flexible PCB may extend from a support circuit board (or from another entity) to, and more preferably into (as shown in <FIG>), the circuit block <NUM>. For example, each such flexible PCB <NUM> may extend at least from an edge of one of the support circuit boards at least to an edge of one of the parallel metal plates <NUM>, and typically further to the inside of the circuit block. By extending one or more of the flexible PCBs into the inside of the circuit block <NUM>, a processing component can be mounted directly onto such a flexible PCB to thereby improve integration and simplify construction, or mounted adjacent to the flexible PCB. The flexible PCB can then conveniently carry circuitry for driving and/or communicating with the processing component, in addition to that provided by the related and connected support circuit board.

Note that in some embodiments, flexible PCBs may extend from the inside to the outside of the circuit block for purposes other than for connecting to support circuit boards, noting that in some embodiments there may be no support circuit boards comprised in the module <NUM>. For example, one or more flexible PCBs may be used to provide a signal or data or power connection to or from elements outside of the radio frequency module, for example by comprising a coaxial connector for communicating a radio frequency signal, or other connection types.

The flexible PCBs enable connections between the inside of the circuit block and elements outside the circuit block to be made in a more compact but flexible manner. To this end, one, more than one, or all the flexible PCBs may be arranged or installed such that at least part of the flexible PCT has a radius of curvature of less than <NUM>, or less than <NUM>, where that radius of curvature is directed perpendicular to the main plane of the flexible PCB.

The metal plates <NUM> may be at least partly held together to form the circuit block <NUM> using a plurality of mounting rods <NUM>, such as threaded rods, as seen in <FIG>. Each mounting rod passes through some or all of the plates, for example through a series of corresponding aligned apertures <NUM> in the metal plates <NUM>, and threaded nuts or other fastenings may then be applied to the mounting rods <NUM> to secure the metal plates <NUM> together. Dowel metal pins may also be used to ensure fine alignment of waveguide portions defined by aligned apertures in adjacent metal plates, as described in more detail below in respect of <FIG> and <FIG>.

In order to mount the support circuit boards <NUM> parallel to and/or stacked in series with the metal plates <NUM> if required, each support circuit board <NUM> may also comprise a plurality of mounting apertures <NUM>, each such mounting aperture <NUM> corresponding to one of the mounting rods <NUM>. By providing mounting rods <NUM> of sufficient length, the support circuit boards <NUM> can then be secured in stacked series with the metal plates <NUM> by means of the mounting rods <NUM> also passing through these mounting apertures in the support circuit boards. Threaded nuts or other fastenings can then be applied to the mounting rods to secure each support circuit board in place.

In the arrangement of <FIG>, each metal plate <NUM> of the circuit block <NUM> is approximately square in plan view (of the major or largest face), although other shapes may be used if required, for example rectangular or hexagonal. For some applications, the ability to locate multiple such modules <NUM> in a closely spaced rectangular, hexagonal or other grid form may be advantageous. Typically, each support circuit board may be of approximately the same shape and size as the metal plates, or may be of a smaller size if appropriate.

The dimensions of the major or largest face each metal plate (i.e. in plan view from above) in the arrangement of <FIG> are approximately <NUM> x <NUM>, but more generally the surface area of each major surface of each metal plate may be limited for example no more than <NUM><NUM> or no more than <NUM><NUM>. Similarly, the widest dimension of each metal plate may be limited for example to no more than <NUM> or no more than <NUM>. Each metal plate may typically be around <NUM> to <NUM> thick, and may be made of a variety of different metals such as copper, brass or aluminium. The metal plates may be electroplated with gold to prevent oxidation.

The depth of the stack of parallel metal plates and support circuit boards as illustrated in <FIG> is approximately <NUM>, but may for example be limited to no more than <NUM>. Consequently, the volume of the module, as defined by the perimeter of the upper most metal plate and extending down around the plates and support circuit boards to the perimeter of the lowest support circuit board may limited to no more than <NUM><NUM> or no more than <NUM><NUM>.

More generally, the approximate shape and size in plan view of each metal plate and support circuit board may be referred to as a particular form factor. With this in mind, the module <NUM> may be constructed such that all of the metal plates <NUM>, and optionally some or all of the support circuit boards are of the same form factor. To use a different definition, each metal plate of the stack, and optionally also each of some or all of the support circuit boards, may be required to overlap with all the others by at least <NUM>% of the surface area of its major surface (i.e. in plan view). In some cases, one or more of the support circuit boards may have a different form factor, for example corresponding to about half or about one quarter of a metal plate of the stack.

<FIG> illustrates schematically a heterodyne receiver RF circuit that may be implemented in modules such as that illustrated in <FIG>. A radio frequency input is received for example via an antenna <NUM>. The signal from the antenna <NUM> is passed to a low noise amplifier (LNA) <NUM> which is supported by an LNA bias <NUM> which provides the one or more required amplifier bias signals <NUM> for the low noise amplifier <NUM>. The amplified RF signal from the low noise amplifier <NUM> is passed to a mixer <NUM> which mixes the amplified signal with a local oscillator signal <NUM> received from a local oscillator chain <NUM>. The mixer then outputs the resulting intermediate frequency (IF) signal to an IF backend <NUM> which amplifies, conditions and otherwise processes the IF signal electronically, and outputs the IF signal as IF output <NUM> for further use, for example to a spectrometer, data store, or for transmission to other equipment or locations.

In implementing the receiver of <FIG> in the context of <FIG>, the function of the top metal plate A seen in <FIG> is to couple antenna <NUM> into the circuit block <NUM>. For example, a horn antenna for collecting the RF input may be mounted directly to plate A, and direct the RF input into the entrance port <NUM> of plate A seen in <FIG>. An antenna spaced from the module and coupled using a suitable waveguide, may be used instead if required, or another type of RF input such as an RF input from another similarly constructed RF module, or another component or system.

Metal plates B and C of <FIG> are then used to implement the low noise amplifier <NUM> shown in <FIG>. The aim of the low noise amplifier function is to amplify the RF input received through metal plate A with minimal noise additions. Plates B and C adapted for this function are shown separately in plan view in <FIG>. Plate B is seen from the underside and plate C from the top side relative to the perspective view of <FIG>. When the faces of plates B and C as shown are brought together, channels in the plates define an LNA input waveguide <NUM> and an LNA output waveguide <NUM> for the low noise amplifier <NUM>. The LNA input waveguide <NUM> includes an LNA input aperture <NUM> which passes though the plate B and couples with the entrance port <NUM> of plate A to receive the RF input from the antenna <NUM> or other input source.

The LNA input waveguide <NUM> carries the RF input as an electromagnetic waveguide signal to an LNA microstrip transition circuit <NUM> fabricated on a quartz substrate which is located between plates B and C and which couples into both the LNA input and LNA output waveguides. The LNA microstrip transition circuit <NUM> is mounted onto the end of, and in electrical communication with, an LNA flexible PCB <NUM> which passes into the circuit block through an aperture <NUM> defined between plates B and C.

A processing component in the form of a low noise amplifier integrated circuit <NUM> (for example a Fraunhofer MMIC chip such as the ALN001MB165TESS, or the ALN072MB-W-TH), typically implemented as a monolithic microwave integrated circuit MMIC, is mounted on the LNA flexible PCB <NUM>, and within the circuit block <NUM> between plates B and C. This integrated circuit receives the RF input from the LNA input waveguide <NUM> via the LNA microstrip transition circuit <NUM>. The amplified output from the integrated circuit <NUM> is then delivered by the LNA flexible PCB <NUM> back to the LNA microstrip transition circuit <NUM> for injection into the LNA output waveguide <NUM>.

As also illustrated in <FIG>, an external end portion <NUM> of the LNA flexible PCB <NUM> connects to an LNA support circuit board <NUM> mounted in series with the stack of metal plates <NUM>. The LNA support circuit board <NUM> implements the LNA bias <NUM> of <FIG> in generating the DC bias signals required to operate the integrated circuit <NUM>. These DC bias signals are communicated to the integrated circuit <NUM> via the LNA flexible PCB <NUM>.

The amplified signal passes as a waveguide signal along the LNA output waveguide <NUM> to LNA output aperture <NUM> in plate C, through which it passes to enter metal plate D as illustrated in <FIG>.

Metal plates D and E of <FIG> may be used to implement the mixer <NUM> shown in <FIG>. The aim of the mixer is to mix the amplified RF signal with a local oscillator signal to generate an intermediate frequency signal more suitable for further processing and analysis. Plates D and E are shown separately in plan view in <FIG>. Plate D is seen from the underside and plate E from the topside relative to the perspective view of <FIG>.

When the faces of plates D and E as shown are brought together, channels in the plates define a mixer input waveguide <NUM> for the mixer function <NUM>. The mixer input waveguide <NUM> includes a mixer input aperture <NUM> which passes though the plate D and couples with the LNA output aperture <NUM> of plate C seen in <FIG>, to receive the amplified RF signal from the low noise amplifier function <NUM>.

The mixer input waveguide <NUM> carries the amplified RF signal to a mixer microstrip circuit <NUM> fabricated on a quartz substrate. A processing component in the form of a Schottky diode <NUM> or pair of such diodes (typically in an antiparallel configuration) is mounted by soldering onto the mixer microstrip circuit <NUM>, and any required diode matching circuits are also included as part of the circuit <NUM>.

A local oscillator flexible PCB <NUM> passes into the circuit block <NUM> through an aperture <NUM> defined between plates D and E. An external end portion <NUM> of the local oscillator flex PCB <NUM> connects to a local oscillator support circuit board <NUM> mounted in series with the stack of metal plates <NUM>, which implements the local oscillator chain <NUM> of <FIG> in providing the local oscillator signal <NUM> required for mixing with the amplified RF signal. In particular, the local oscillator flexible PCB <NUM> carries the local oscillator signal to the mixer microstrip circuit <NUM> for mixing with the amplified RF signal at the Schottky diode or diodes <NUM>. The local oscillator support circuit board <NUM> may typically comprise a suitable frequency synthesiser integrated circuit and associated circuitry for generating the local oscillator signal.

An IF output flexible PCB <NUM> passes into the circuit block <NUM> through an aperture <NUM> defined between plates D and E, and couples to the mixer microstrip circuit <NUM> so as to receive the intermediate frequency (IF) signal from the Schottky diode. The IF output flexible PCB <NUM> may then either deliver the IF signal to a further support circuit board <NUM> (not shown in <FIG>) mounted in series with the rest of the stack of circuit boards and metal plates, or to another circuit board or an output connector of some kind.

As mentioned above, one or more dowel pins may be used to assist in accurate alignment of adjacent metal plates of the stack so as to ensure exact or optimal positional matching between adjacent portions of a waveguide defined by channels in adjacent plates, for example to exactly align the plate B and plate C portions of LNA input waveguide <NUM>, or the interface between the plate C LNA output aperture <NUM> and plate D mixer input aperture <NUM>. Such dowel pins may typically be made of metal, and each such dowel pin may extend into two, more than two, or all of the metal plates. Two or more of these dowel pins may extend between and therefore serve to align any or all of the adjacent pairs of metal plates, although just one dowel pin may be sufficient between two plates in some circumstances.

To this end, <FIG> and <FIG> show two dowel pin apertures <NUM> in each of metal plates C, D, E and F, with these apertures aligning between the metal plates when brought together to form the circuit block, so as to accept dowel pins as discussed above. Similar dowel pin apertures may be provided also in plate A aligned with those shown.

<FIG> shows more schematically, and in a cross sectional form, an RF module <NUM> such as that of <FIG> adapted to implement a heterodyne receiver RF circuit such as that of <FIG>, using the arrangements of <FIG> and <FIG>. In this figure, a pyramidal horn antenna <NUM> is shown as coupled directly to the first metal plate A, to deliver the RF input through entrance port <NUM> in plate A, through the LNA input aperture <NUM> in plate B, and along the LAN input waveguide <NUM> defined by channels in one or both of plates B and C.

The RF input is then coupled using the LNA microstrip transition circuit (not shown) or other arrangement to the LNA processing component provided by the low noise amplifier integrated circuit <NUM> which is mounted on or adjacent to the LNA flexible PCB <NUM>. The LNA processing component is supplied with suitable LNA bias signals <NUM> communicated from the LNA support circuit board <NUM> via the LNA flexible PCB <NUM>.

The amplified RF signal output of the LNA processing component <NUM> is then passed via the LNA microstrip transition circuit or other arrangement to the LNA output waveguide <NUM>, and through the LNA output aperture <NUM> in plate C to the mixer input aperture <NUM> in plate D.

The amplified output passes along the mixer input waveguide <NUM> formed by channels in one or both of plates D and E to be coupled using the mixer microstrip circuit (not shown) to the mixer processing component mounted on the microstrip circuit which is provided by the one or more Schottky diodes <NUM>. The mixer processing component is supplied with a suitable local oscillator signal <NUM> communicated from the mixer support circuit board <NUM> via the local oscillator flex PCB <NUM>.

Whereas in <FIG> the output of the mixer processing component is coupled for output to a further flexible PCB, and in particular the IF output flexible PCB <NUM>, in the arrangement of <FIG> the output is instead coupled more directly to an IF backend circuit <NUM> located within the circuit block itself, for example within a cavity defined by the metal plates as shown in <FIG>. An IF backend output <NUM> may then be provided, for example, by a coaxial connection. Such an IF backend circuit <NUM> may be provided for example in the form of an LTCC (low-temperature cofired ceramic) unit.

<FIG> illustrates schematically how a more complex heterodyne receiver may be implemented in an RF module similar to that of <FIG>. In particular, <FIG> illustrates a multi-band receiver in which a waveguide diplexer is used prior to low noise amplification to split the received RF signal input into two bands, which can be further processed in the IF backend to generate quadrature inputs for a digital spectrometer. Suitable implementation of the receiver of <FIG> using a series of stacked plates as shown in <FIG> is illustrated by a broken line box corresponding to each such stacked plate, and labelled A - I which together form a circuit block <NUM>.

The arrangement of <FIG> can be used for example in atmospheric monitoring by a satellite platform, in which radiation at oxygen and water vapour band frequencies of <NUM> and <NUM> are measured.

A multiband horn antenna <NUM> couples a received input RF signal into an aperture in the top plate A which in turn couples the input RF signal into plates B and C which implement a diplexer function, in which waveguides defined by plates B and C passively split the input RF signal into two streams. Each stream is separately directed through a corresponding entrance aperture in plate D into waveguides defined between plates D and E, where it is separately amplified using one of the two LNA amplifier integrated circuit processing components <NUM> located between plates D and E. These two processing components are both mounted within the circuit block <NUM> but on a suitable flexible PCB which connects the components to an LNA bias support circuit board <NUM> which may be stacked with the metal plates in the manner illustrated in <FIG>.

Each output of the LNA amplifier components <NUM> is then separately directed through a corresponding entrance aperture in plate F into waveguides defined between plates F and G, where it is mixed using one of the two double sideband (DSB) mixer processing components <NUM>. These DSB mixer processing components <NUM> may for example each be provided by one or more Schottky diodes each mounted on a suitable mixer microstrip circuit.

In the arrangement of <FIG>, the DSB mixer processing components <NUM> are not directly coupled to any flexible PCB. Instead, separate local oscillator signals are provided through waveguides from a passive splitter function <NUM> implemented using waveguides between two more metal plates of the stack H and I, and communicating the local oscillator signals to the DSB mixer components using waveguides passing from plate H to plate G. In turn, the passive splitter function is fed a local oscillator signal through a flexible PCB by a phase locked dielectric resonator oscillator PDRO support circuit board <NUM> which is stacked with the metal plates in the manner illustrated in <FIG>.

The outputs of the mixer components <NUM> are then each passed to IF backend <NUM> which may be implemented as a unit located in an aperture within the circuit block <NUM>, for example as a low temperature co-fired ceramic package. In particular, the IF backend <NUM> may use a second downconverter to generate image and quadrature outputs fed to a digital spectrometer included in the IF backend package <NUM>.

<FIG> illustrates schematically how an active transmitter may be implemented in an RF module similar to that of <FIG>. At millimetre and sub-millimetre wave frequencies, limited practical technologies are available for generating and detecting signals, leading to what is sometimes referred to as the terahertz gap. In <FIG> a cascade of multipliers is used to generate power at higher frequencies using a relatively lower frequency but high power source, using a stack of metal plates A - F and further support circuit boards configured in the manner illustrated in <FIG>.

To this end, an RF source circuit board <NUM>, which may be stacked with the metal plates A - F, generates a source frequency signal which is passed through a flexible PCB to a first metal plate G, to an injector processing component, such as a microstrip for coupling the source frequency signal into a waveguide of that plate. The waveguide in plate G then couples through to waveguides in plates F and E, between which a x2 processing component <NUM> comprising a Schottky diode mounted on a quartz circuit board. The x2 multiplier processing component receives the source frequency signal and outputs an RF signal or twice that frequency, which couples through waveguides of the plates E and F into waveguides of the plates C and D, and to a x3 multiplier processing component <NUM> mounted within the circuit block <NUM> on a quartz circuit board. The active transmitter may comprise various combinations of such x2 and x3 multipliers, typically up to about ten in number, which then constitute a multiplier chain.

The tripled frequency output of the x3 multiplier then outputs through waveguides of plates C and D into waveguides of plates A and B to be received by a power amplifier integrated circuit processing component <NUM> mounted within the circuit block on a flexible PCB coupling amplifier bias signals from an amplifier bias support circuit board <NUM>. The amplified output of the amplifier component <NUM> then couples into further waveguides of plates A and B and into an antenna <NUM> which may be mounted directly onto the plate A, or coupled with an output waveguide aperture of plate A via one or more further waveguide structures.

In the arrangement of <FIG>, as in other examples, one or more of the processing components may be coupled to the waveguides via suitable microstrip or other arrangements as appropriate.

Although <FIG> and <FIG> depict arrangements in which the support circuit boards <NUM> are stacked in series with the metal plates <NUM>, in some embodiments one, more than one, or all of the support circuit boards <NUM> comprised in the radio frequency module <NUM> may be located at other positions not stacked with and/or not in series with the metal plates <NUM>. These support circuit boards <NUM> may then be mounted directly to the metal plates for example using suitable brackets, or may be secured in other ways, for example to a sub frame of a satellite within which the radio frequency module <NUM> is installed. To this end, <FIG> depicts the radio frequency module <NUM> of <FIG> where one of the support circuit boards <NUM> is still stacked in series and parallel with the metal plates, in this instance using the mounting rods <NUM> as discussed above, and another one of the support circuit boards <NUM>' is located away from and out of the stack, in this case in an orientation which is perpendicular to the stack. In such arrangements, any support circuit board <NUM>' not stacked in series with the metal plates may still be electrically coupled into the circuit block using a flexible PCB <NUM> as shown in <FIG>, or in other ways.

Such arrangements where one or more of the support circuit boards <NUM> are not stacked in series with the metal plates can have advantages in terms of enabling improved cooling or thermal control of such support circuit boards.

Although <FIG>, <FIG> and <FIG> depict arrangements in which both support circuit boards and flexible PCBs are provided as part of the radio frequency module <NUM>, in some embodiments one or both of these component types are omitted. For example, <FIG> depicts one example of a radio frequency module <NUM> which does not include any support circuit boards (either stacked in series with the metal plates <NUM> or otherwise), and does not include any flexible PCB.

However, such arrangements may still benefit from various of the advantages described above for example by being implemented using at least three of the metal plates <NUM> to form the circuit block <NUM>, with one or more of the radio frequency processing components being disposed with the circuit block <NUM> to interact with the radio frequency signals carried by the waveguides. In particular, referring to the mutual plate boundary defined by any two adjacent ones of the metal plates, such an embodiment may in particular use a plurality of radio frequency processing components, with a different one of the processing components being located at each of at least two, and optionally at all, of the plate boundaries.

To this end, the top part of <FIG> depicts in cross section a circuit block <NUM> comprising three of the already described parallel metal plates <NUM>, here labelled A, B and C. The middle part of <FIG> then depicts in plan view the mutual boundary between plates A and B, and the lower part depicts in plan view the mutual boundary between plates B and C.

As can be seen from the top cross section view, the top plate A provides two upward facing microwave ports which comprise an entrance port <NUM> and an exit port <NUM>, each of which could be coupled to a horn antenna, an external waveguide, or other arrangements for delivering microwaves to and collecting microwaves from the ports. A first waveguide <NUM> then couples from the entrance port <NUM> downwards to the boundary between plates A and B to couple into a power divider component <NUM> formed from a Y-shape waveguide structure located at the boundary between plates A and B.

The power divider component <NUM> serves to divide the microwave power received from the entrance port <NUM> and to direct it into two second waveguides <NUM>, <NUM> which carry the divided power down through plate B to the mutual boundary with plate C. Here, the divided power is delivered, for amplification, to two separate active amplifier components <NUM>, <NUM> which are located at the mutual boundary between plates B and C. The divided microwave power may be coupled from each second waveguide <NUM>, <NUM> into the respective active amplifier components <NUM>, <NUM> by use of strip lines <NUM> extending from the amplifier components into the second waveguides <NUM>, <NUM>.

The amplifier components <NUM>, <NUM> then output the amplified microwave power, for example through further strip lines <NUM>, into respective third waveguides <NUM>, <NUM>, which carry the amplified microwave power up through plate B to a power combiner <NUM> formed from a suitable Y-shaped waveguide structure located at the boundary between plates A and B. the power combiner <NUM> combines the microwave power from the third waveguides <NUM>, <NUM> for output into a fourth waveguide <NUM> which couples the combined power upwards through plate A to the exit port <NUM>.

If required, one or more flexible PCBs (not shown) can be used to couple the active amplifier components <NUM>, <NUM> to suitable circuitry located outside of the circuit block <NUM>, for example suitable power supply, bias, and/or control circuitry which may be located partly on the flexible PCB(s) if required, and/or on suitable support circuit boards (not shown). However, such electrical connections to the active amplifier components may be made in other ways, and some such circuitry for servicing the amplifier components may be provided for example using circuit boards located wholly within the circuit block <NUM>.

In <FIG>, the power divider <NUM> and power combiner <NUM> permit an input microwave signal to be amplified using two separate active amplifier components <NUM>, <NUM>, for example to enable higher amplification levels to be achieved using available components, to assist with thermal control and for other reasons. Note that instead of using just two active amplifier components, the input microwave power may be divided amongst a larger number of amplifiers by using multiple levels of dividers and combiners, or in other ways. Although simple three port waveguide combiners and dividers are shown in the figure, four port directional and/or hybrid couplers could be used.

Although some particular radio frequency processing components, in particular the power divider, amplifier components, and power combiner, are used in the arrangement of <FIG>, other arrangements of the radio frequency module <NUM> may use different combinations of components. When the location of a radio frequency component at a boundary between two plates is mentioned, it is not necessary for the component to be disposed across the major plane of the boundary between the plates, rather such a component could instead be located wholly within a suitable aperture of one of the plates, in particular where that aperture is open to the other plate forming the mutual boundary.

Although in <FIG> a particular combination of radio frequency components located at each of at least two boundaries of the metal plates of a stack are shown, various other radio frequency circuits may be constructed in a similar manner using three or more such metal plates, active and/or passive radio frequency components, and waveguide structures within and between the plates. The various aspects described in respect of the arrangements of <FIG>, <FIG> and <FIG> such as the stacking or other positioning of support circuit boards, the use of mounting rods, form factors, sizes and alignments of the metal plates and any support circuit boards, and so forth, also apply to the arrangement of <FIG>.

Although <FIG>, <FIG>, <FIG> and <FIG> depict arrangements in which three or more metal plates <NUM> are stacked to form the circuit block <NUM>, in some embodiments as few as two such metal plates <NUM> may be used, with a plurality of radio frequency waveguides being defined by channels in the two or more metal plates so as to carry radio frequency signals within the circuit block. One or more radio frequency processing components are then arranged within the circuit block to interact with the signals carried by the waveguides. In such arrangements, one or more flexible printed circuit boards may then be provided, wherein each such flexible printed circuit board is arranged to provide external electrical communication with at least one of the processing components, by said flexible printed circuit board extending from the circuit block, or more particularly from the inside of the circuit block, to outside of the circuit block.

<FIG> depicts a variation of the radio frequency module <NUM> discussed above in which only two metal plates <NUM> are used to form the radio frequency circuit block <NUM> containing a plurality of radio frequency waveguides (not shown in <FIG>) defined by channels in the metal plates, and one or more radio frequency processing components (not shown in <FIG>) arranged within the circuit block <NUM> to interact with the signals carried by the waveguides. Variations of this embodiment could comprise more than two such metal plates if required, for example three, four or more metal plates.

In this embodiment, one or more flexible PCBs extend from the inside to the outside of the circuit block, and may be used for various purposes. For example a first flexible PCB <NUM>' may carry power into, and/or carry data or control signals to or from, processing components located within the circuit block, and may connect to a support circuit board <NUM> external to the circuit block, or to some other element not comprised in the radio frequency module such as to further circuitry, data or power facilities, or another radio frequency module. Typically, each such flexible PCB extends from the inside to the outside of the circuit block at a boundary between a pair of adjacent ones of the metal plates, through an aperture or slot defined between the pair of metal plates as shown in <FIG>. Such apertures or slots may correspond to the apertures <NUM>,<NUM>,<NUM> already shown and described in respect of <FIG>, <FIG> and <FIG>.

A second flexible PCB <NUM>" may carry an RF signal into and/or out of the circuit block, to or from RF components located with the circuit block, and to that end may comprise one or more coaxial or other RF connectors <NUM> for making such RF connections.

In some variations of this embodiment, one or more of the flexible PCBs may connect from one inside portion of the circuit block to another inside portion of the circuit block, by extending through an aperture or slot between a first pair of adjacent ones of the metal plates, and also extending through an aperture or slot between a second pair of adjacent ones of the metal plates. The first and second pairs are typically different pairs of the metal plates so that the flexible PCB then connects between different levels or different metal plate boundaries of the circuit block.

The radio frequency module <NUM> of <FIG> may also comprise one or more radio frequency entrance ports <NUM> and/or exit ports <NUM> for example as depicted in earlier figures, may include one or more support circuit boards, and include various other features of the described radio frequency modules discussed above.

In some embodiments, a radio frequency module <NUM> according to this disclosure may combine both transmitter and receiver functions within a single circuit block and associated support circuit boards. In other embodiments, transmitter and receiver functions may be located adjacent or near to each other using separate such stacks and support circuit boards for each.

Because of the compact nature and geometry of the described radio frequency modules <NUM>, a plurality of such modules may be located adjacent to each other in a grid, for example in a rectilinear or hexagonal grid, and in particular to implement a phased array, which can be used to steer a beam of such an array by suitable control of the separate modules. Such a phased array may implement a phased array transmitter being formed of an array of transmitter modules, a phased array receiver being formed of an array of receiver modules, or a phased array transceiver being formed either of an array of transceiver modules, or an array comprising both transmitter and receiver modules.

<FIG> illustrates schematically how such a phase array might be structured. In <FIG> there are five radio frequency modules forming a one dimensional linear array, but any number of such modules may be used in such a one dimension, or in a two dimensional array. Each radio frequency module <NUM> comprises a radio frequency circuit block <NUM> which comprises a stack of at least three parallel metal plates and a plurality of radio frequency waveguides defined by channels in the metal plates so as to carry radio frequency signals within the circuit block, as already described above. One or more radio frequency processing components are then arranged within the circuit block to interact with the signals carried by the waveguides, and one or more support circuit boards <NUM> are disposed parallel to and stacked in series with the metal plates, each support circuit board being in electrical communication with at least one of the processing components.

Each radio frequency module <NUM> may include or be associated with a separate antenna unit <NUM>, such as a horn antenna, optionally mounted to the module itself.

In <FIG>, each radio frequency module <NUM> is coupled to a separate steering element <NUM> which controls a phase timing of radio frequency signals either transmitted from the associated radio frequency module, or controls a phase timing (for example by using a suitable phase delay) of radio frequency signals received then output by the associated radio frequency module. However, these steering elements could be implemented using support circuit boards of the radio frequency modules themselves, or elsewhere for example within the illustrated control unit <NUM>. The control unit <NUM> may be responsible for controlling the steering elements <NUM> to implement the required mean steering, as well as controlling timing of radio frequency transmissions and/or suitably combining received radio frequency signals.

Although the detailed embodiments as described demonstrate some particular RF systems which may be implemented using the described architectures, the illustrated principles are advantageous in their flexibility and usefulness to implement a wide variety of functions in a radio frequency module as generally described, such as:.

Noting the above particular RF systems, these may be used for a wide range of applications including both active and passive meteorological sensing (for example of water vapour, temperature and so forth), radar applications such as in military, aviation, ground vehicle, shipping, altimeter and other areas, and telecommunications of various types. In some applications where beam focus and/or steering are required, the described RF modules may be combined into phased arrays.

The RF modules may be used for example on an orbiting satellite, an aircraft, a high altitude balloon, a radar installation, a ship or land vehicle, or by any of a variety of other moving or static platforms.

Similarly, although the detailed embodiments as described implement various functional subsystems which operate together in a single RF module <NUM> to implement a particular application, the potential range of such functional subsystems is very wide, including for example:.

Although various particular radio frequency processing components for locating within the circuit block <NUM> to provide different functionalities and interactions with RF signals in the waveguides have been described in the detailed embodiments, a wide range of other different processing components may be used to fulfil a wide range of different functions. For example, processing components may be any of:.

In the detailed embodiments, the use of various modes and means of interconnectivity between different functional and physical parts of the described RF modules have been mentioned, but both these and a wide range of interconnection schemes and methods may be used for radio frequency, intermediate frequency, control and other signals within the modules, including:.

Claim 1:
A radio frequency module (<NUM>) comprising:
A radio frequency circuit block (<NUM>) which comprises a stack of at least two metal plates (<NUM>) and a plurality of radio frequency waveguides (<NUM>, <NUM>) defined by channels in the metal plates so as to carry radio frequency signals within the circuit block;
one or more radio frequency processing components (<NUM>) arranged within the radio frequency circuit block to interact with the signals carried by the waveguides,
characterised in that:
the radio frequency module (<NUM>) further comprises one or more flexible printed circuit boards (<NUM>, <NUM>) extending between the outside and the inside of the radio frequency circuit block,
wherein each of one or more of the radio frequency processing components is mounted on a said flexible printed circuit board within the circuit block.