This invention relates to a multilayer printed wiring board radiating device. In particular, this invention relates to phased array antennae based on such technology.

Nowadays, the multitude of functionalities of active phased array radar antennae are difficult to be realised within a given small volume and a limited weight budget, while maintaining a high performance and high reliability at an acceptable cost, in particular at high operating frequencies (> 10 GHz). These antennae must become even more compact due to emerging requirements for e.g. planar and conformal systems.

Active phased array antennae are typically characterised by a large bill of materials. A large number of separate, individually manufactured radiators (e.g. waveguides or vivaldi-type radiators) must be assembled of individual parts, requiring tight assembly tolerances and many complex interconnections. Therefore, production and assembly costs are high, and further miniaturization is limited.

Traditionally, various manufacturing and assembly technologies are used: for example for radiators, feed circuits and interconnections.

The patent application EP 1 071 161 relates to such an antenna. The radiator design consists of a stack of discs or patches comprising a lower active radiator on a so called dielectric puck, fed by a pair of a so called probes (basically a number of via connections and a parasitic radiator separated from the active radiator by dielectric material. Thus, this antenna is not optimised and has the above mentioned drawbacks as the known of the art technologies.

Moreover, in this antenna, the dielectric pucks comprising the lower active radiators must each be disposed in a surrounding recess formed in an upper dielectric layer of a different material. This is a rather complicated design requiring highly toleranced assembly steps. A contemporary X-Band antenna array for radar application may be an assembly of thousands of individually manufactured sub assemblies, each consisting of, for example, a radiator and a number of impedance matching components, a connector assembly, etc. Every part must be manufactured and assembled, hence requiring significant effort and accuracy. Obviously, the involved costs are significant. For example, a radar system of this type could contain significantly more than 3000 transmitting/receiving module channels per antenna array.

This invention solves the above-mentioned drawbacks using a printed wiring board radiating device more optimised at least in use of available volume by allowing at least some radiators not to be aligned with their respective input/output connectors. The obtained system design is thus less complex and requires less tight assembly tolerances.

An object of this invention is a multilayer printed wiring board radiating device comprising - A feed layer comprising the feed circuitry; and - A radiator layer coupled to the first face of the feed layer, the radiator layer comprising an array of tab radiator elements (e.g. microstrip patch radiator elements), - Input/output connectors for connecting transmitter/receiver modules to their respective radiator elements, and - An offset layer for correcting the positional shift due to a non-alignment of the radiator with its respective input/output connector, the offset layer being coupled directly or indirectly to the second face of the feed layer.

A further object of this invention is a phased array antenna comprising the above described multilayer printed wiring board radiating device and at least one transmitter / receiver module connected to the input/output connector linked to the radiator element to be activated.

Further features and advantages of the invention will be apparent from the following description of examples of embodiments of the invention with reference to the drawing, which shows details essential to the invention, and from the claims. The individual details may be realised in an embodiment of the invention either severally or jointly in any combination.

- Figure 1 , an impression of part of a printed wiring board radiating device according to the invention, - Figure 2, a cross section through a printed wiring board radiating device according to the invention, - Figure 3, an example of an offset layer according to the invention, - Figures 4a and 4b, an implementation of a printed wiring board radiating device according to the invention with T/R modules, Figure 4a is zooming in on a part of Figure 4b showing the link between the T/R modules and the radiators, - Figure 5, an example of calibration layer according to the invention.

Figure 1 shows an impression of a layered structure of an Antenna PWB (printed wiring board). Only part of the total laminated structure is shown, not to scale.

The printed wiring board comprises dielectric laminates in several striplines 11-14 linked with adhesive 19. Each radiator could be surrounded by metallized trenches 18, on the sides of which a metallization has been deposited, to create mentioned "box" structure. Alternatively, the "trenches" could be replaced by a pattern of closely spaced metallized holes (blind via's).

Figure 2 shows a cross section through a typical antenna PWB.

The printed wiring board radiating device 1 integrates radiators 143, phase matched offset circuits 11 , feed circuits 13 including their respective microwave interconnections embedded into one multilayer printed wiring board 1 , and eventually calibration networks 12. The functional design uses a two layer dielectric loaded stripline structure containing the feed circuit within the stripline feed layer 13, and an offset circuit within the stripline offset layer 11. The offset circuit, for example a phase matched offset circuit, is used to overcome a planar offset between the position of the radiator 143 and its respective feed connector 111 at the back side of the assembly. This feed connector 111 could be an RF Coaxial Input/Output.

This could be complemented by a stripline layer 12 containing a testpulse distribution network for antenna calibration, using couplers for each channel as shown by figure 5.

The circuit of the stripline feed layer 13 is slot coupled 141 (non galvanic) to an array of arbitrarily shaped microstrip patch radiators 143. This transfer could occur inside a dielectric cavity to reduce RF coupling inside the structure. The radiator 143 is surrounded by a conducting "box" 142, 18 to eliminate surface wave coupling phenomena. The radiator 143 itself could consist of a arbitrarily shaped patch metallization 142, which is surrounded by machined trenches 18, on the sides of which a metallization has been deposited, to create mentioned "box" structure. Essentially, this box is a plated structure again realised using state of the art PCB technology.

Alternately the radiators 143 could have different 3D shape using the same PCB technology. For example, the radiator 143 could consist of one or multiple stacked patches, with or without the metallized box structure, e.g. by surrounding the patches with plated trenches 18. The stripline feed layer 13 may also be galvanically connected to the (bottom) patch using a metallized hole (via). The box structure can also acts as a dielectric loaded waveguide radiator while the patch metallization 142 could be adapted to an iris type aperture.

The multiple continuous metallic ground layers 18 and 20 present within the laminate 1 generate a very high EMI shielding effectiveness. Optional is a further integration with a radome- 16 and Frequency Selective Screen 161 (FSS), the latter for reducing RCS (Radar cross- section) of the antenna.

Thus, the baseline multilayer printed wiring board radiating device can comprise a total of 10 individual dielectric layers, with the option to add specific layers, for example in case integrated filtering is required. The multitude of machined trenches (or via's) tends to undermine the mechanical stability of the laminate; to overcome this problem an auxiliary dielectric layer 15 is attached to make sure that structural integrity is maintained throughout the manufacturing process. This auxiliary layer is later used as a spacer for radome 16/FSS structure 161.

An optional feature could be a built-in RF filter using, for example, a photonic bandgap structure inside one of the existing stripline layers or an additional dedicated layer (not shown).

Multilayer printed wiring board technology is an enabling technology used, consisting of organic, controlled dielectric laminates A to J and patterned metallizations 18, with which all features required can be manufactured in a batch process. Thus, the number of individual parts and assembly steps usually associated with Phased array antennae can be greatly reduced. At the same time, this enables a more flexible, compact and highly integrated design that is also less susceptible to assembly tolerances. Furthermore it facilitates good structural integrity, scalability, integrated calibration, high bandwidth, good scan performance, excellent EMI shielding and low RCS.

Because the outside of the array of radiators 142 is merely a planar structure, hence the array can be regarded as a flat plate, the multilayer printed wiring board radiating device has a low RCS.

Moreover, a RF-Via Z axis layer-to-layer interconnect could be implemented through the offset layer 11 and, if needed, the calibration layer 12 to the feed layer 13 in order to bypass layer 11 and 12. Generally, multilayer printed circuit board technology is based on a laminated structure consisting of selectively plated dielectric layers, together forming a concurrent circuit thanks to post machining and post plating. The combination of basic technologies involved, i.e. photochemical etching, laminating, machining and galvanic technologies will enable a clever designer to create more unconventional RF-structures like radiating elements and 3D transitions embedded into and functionally interfacing with the existing RF circuitry, all in one product. This can be done by considering these 3D RF structures as a stack of 2D substructures, which can merge into one concurrent structure after applying a clever sequence of process steps. Each printed circuit board can contain hundreds or even thousands of identical RF structures. Moreover, it enables further integration of additional functionality.

Due to the mechanical simplicity offered by the technology of multilayer printed wiring board radiating device, it is relatively easy to tune in order to yield a high bandwidth.

Furthermore, at an operating frequency up to 12 GHz, the high level of integration that is facilitated by this technology makes sure that radiators 142 can be replaced well within a pitch of half a wavelength. Thus, this enables extreme scan angles (beam agility) without grating lobes occurring. Moreover, as patch radiator 143 is backed by a metallic cavity 18, it has much better directivity than what can usually be achieved by patch radiators, while surface waves are suppressed. This contributes to offering good scan performance. The stripline feed circuit 13 is slot-coupled (non galvanic) to each patch radiator 143.

Figure 3 shows more in details the offset layer. In this example, the offset layer 11 is adapted for an array of 256 channels. For X band the basic radiator grid pitch is approximately 15 mmx15 mm. Thanks to this offset layer 11 , the T/R modules 2 do not have to be aligned to the radiator grid, thus facilitating for areas that can accommodate, for example, supporting structure, cabling, coolant manifolds, etc. The purpose of the offset layer 11 is thus to enable more flexibility in the mechanical design, as the T/R modules 2 are not any longer required to be aligned with their respective radiators 143, which have to be positioned in a fixed grid. For this purpose, which can be summarize as correcting the alignment error, the offset layer (11) introduces a phase matched offset on each channel comprising a radiator element 143 and its respective input/output connector 111 such as the phase matched offset decouples the grid of the radiator element 143 and the grid of its respective external module 2.

Figures 4a and 4b show the advantage of the offset layer to facilitate for space behind the antenna array for auxiliary functions.

The advantage applies to both horizontal and /or vertical offset even if the figure only shows vertical offset.

Figure 4b shows an antenna multilayer 1 connected to T/R modules 2 contained in standard racks comprised between structural support 3 comprising, if needed, cooling manifold and cabling or printed wiring. Thus, the structural support is adapted to receive the T/R modules 2, the latter not having to be aligned to their respective antenna radiator. By this way, the available space behind the radiator array can be utilized to maximum efficiency.

This is allowed by the specific structure of the antenna multilayer 1 of this invention allowing as shown by Figure 4b the radiators 142 not to be aligned with the feed connectors 111 due to the positional error correction function of the offset layer 11 within the multilayer antenna 1.

Thus, the offset layer 11 facilitates the interconnection between T/R channels 2 and their respective radiators, which do not have to be aligned. This enables more design freedom. The mandatory pitch between individual radiators no longer dictates the physical layout of the front end electronics directly behind the radiating array. This greatly enhances freedom of antenna system architecture, e.g. better modularity and scalability. Figure 5 shows in more detail the calibration layer containing a testpulse distribution network and couplers for each of the 768 channels 51 in this example. This testpulse signal is being injected into each channel using couplers. This is a very convenient and cost effective way to keep the antenna calibrated at all times.

Within the radar industry, integrated calibration is rarely done because of manufacturing difficulties. In e.g. waveguide technology, it means that a full testpulse distribution circuit must be interlaced with all the active radiator channels (at least several thousands of channels), adding many more parts and making assembly much more complicated and requiring an even higher level of accuracy.

Most other systems rely on a separate external system for calibration. This is very simple but has a major disadvantage: calibration has to take place periodically to ensure a continuous, stable performance. This means, in case an external system is used, that this system must be positioned very accurately in front of the antenna, and removed afterwards to allow an unobstructed field of view. This is a very inconvenient procedure, which can not be executed at all times, in particular during severe weather, in particular in maritime applications.

However, an integrated calibration layer 12 can be used very frequently and under all circumstances keeping the antenna 1 calibrated at all times for maximum performance.

The complete assembly is based on known production processes, tailored to obtain the structures and features required for this application. It consists of a sequence of photolithographic, 3D Machining, galvanic and laminating processes to create the desired multilayer printed wiring board radiating devices. The sequence in which these process steps take place is a crucial factor and determines the feasibility of the design. This multilayer printed wiring board radiating device design has inherent structural integrity. From a mechanical point of view, a multilayer printed circuit board is a laminated, polymer composite panel. The thickness of a panel as described is more than about 10 millimetre. Hence, it is very rigid and does not usually require additional structural backup, thus simplifying the mechanical design of the radiating device.

The use of such a multilayer printed wiring board radiating device in Active phased array antennae is interesting as it facilitates connection with any kind of T/R modules as shown by Figures 4a and 4b.

Thus, applications are primarily radar, but could also include wireless telecommunication applications. In terms of radar, this could be applied in, for example S-Band and X-Band radar systems, but the invention is also suitable for a wide range of other frequency bands. In general, the higher frequency bands will benefit more due to smaller feature sizes, which are proportional to the wavelength.