A HIGH FREQUENCY PACKAGE AND A METHOD RELATING THERETO

TECHNICAL FIELD

The present invention relates to a high frequency package comprising a microwave circuit arrangement, particularly, but not exclusively, an active circuit arrangement; even more particularly one or more MMICs (Monolithic Microwave Integrated Circuit), arranged in a waveguide structure having the features of the first part of claim 1.

The invention also relates to a method for providing a high frequency package comprising a microwave circuit arrangement, e.g. one or more active MMICs, and a waveguide structure including at least one waveguide port having the features of the first part of claim 19.

BACKGROUND

The use of high frequencies is steadily gaining more interest. Up to about 67 GHz coaxial cables can be used as interconnects between microwave components. For higher frequencies, above 67 GHz, waveguides need to be used.

Several problems are associated with the construction of a package containing a high-frequency circuit that needs to be interfaced to a waveguide port.

Normally, for such high frequencies, a separate waveguide transition provides the interface between the waveguide and the circuit. The waveguide transition converts the waveguide TE10 mode to a microstrip or coplanar mode. The second requirement is that the waveguide transition is sufficiently narrow to prevent leakage of waveguide modes into the circuit cavity. Such a leakage results in direct losses and appearance of resonances within the circuit cavity that can e.g. result in a positive feedback between the ports of the circuit (for example in the case of an amplifier) and therefore cause oscillations. However, a separate waveguide transition requires a bond-wire or a flip-chip connection. Such a connection contributes with a substantial reactance at high frequencies, causing extra losses and reduction in the achievable bandwidth. Another disadvantage of having a separate waveguide transition is that it complicates the packaging process as it requires extra steps associated with mounting and accurate alignment of the transition circuit with respect to the circuit, e.g. an MMIC. Yet another disadvantage in using bond-wire connections at high frequencies is that the bond-pad contact area of e.g. an active circuit such as an MMIC becomes very small at high frequencies and bonding often destroys the high-frequency pad affecting the yield of the process. Attempts to integrate the waveguide transition onto the circuit (e.g. MMIC) have shown not to be possible in most cases since the waveguide transition has to be sufficiently narrow in order to prevent leakage of waveguide modes into the circuit (e.g. MMIC) cavity. The width of the waveguide transition needs to be below λ/4 for the highest frequency. Active circuits generally require a plurality of RF and biasing contact pads which occupy a considerable amount of space and therefore cannot be made as small as would be required.

For example, an MMIC, however, cannot be made sufficiently narrow to match the width of the waveguide transition.

In "waveguide-to-microstrip transition at G-band using elevated E-plane probe", Electronic Letters, 20 ^th January 2011, Vol.47, No.2, p. l 15-116 by O. Donadio, K. Elgaid and R. Appleby a high frequency waveguide-to-microstrip transition is disclosed in which a substrate is used to realize the transition to the waveguide. It has a narrow width to stop waveguide modes. Such transitions require bond-wire or flip-chip connection or similar which at high frequencies would present a high reactance which is extremely difficult to compensate for.

SUMMARY

It is therefore an object of the present invention to provide a high frequency package comprising a circuit arrangement, e.g. comprising one or more active MMICs (Monolithic Microwave Integrated Circuit), or one or more active and/or passive circuits in general, and a waveguide structure comprising at least one waveguide port as initially referred to through which one or more of the above-mentioned problems can be overcome. Particularly it is an object of the present invention to provide a high frequency package through which the need to use bond-wire connections or flip-chip connections at the high frequency port(s) can be avoided. It is also a particular object to provide high frequency package having a high, optimized, yield not affected by bonding onto small bond-pad areas.

It is also an object to provide a high frequency package which can be easily packaged, and which does not require alignment of more than one circuit.

It is further an object to provide a high frequency package which is easy and cheap to fabricate, and which allows assembly in a fast and easy manner.

Particularly it is an object to provide a package comprising an improved MMIC RF connection avoiding losses due to the presence of bond-wires and external waveguide transitions.

It is a particular object to provide a high frequency package which can be used for high frequencies, e.g. above 67 GHz, without any risk of leakage of undesired waveguide modes into the circuit arrangement, e.g. a MMIC (cavity).

A most particular object is to provide a high frequency package which comprises one or more active circuits, e.g. MMICs, of arbitrary size, i.e. also large MMICs, and even more generally, circuits of many different kinds including hybrid circuits, and even more particularly a package which is not limited to the use of very thin substrates.

It is also an object to provide a high frequency package which is reliable and precise in operation.

Therefore a high frequency package as initially referred to is provided which has the characterizing features of claim 1. Still further it is an object to provide a method for providing a high frequency package comprising a circuit arrangement and a waveguide package having the features of the first part of claim 19 through which one or more of the above mentioned problems are overcome.

Therefor a method as initially referred is provided which has the characterizing features of claim 19.

Particularly it is an object to provide a method for providing an improved circuit RF performance, particularly an MMIC RF connection.

Advantageous embodiments are given by the respective appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described in a non-limiting manner, and with reference to the accompanying drawings, in which:

Fig. 1 is a view in perspective of a high frequency package comprising a waveguide split block assembly in an assembled state according to a first embodiment of the present invention,

Fig. 2 is a view in perspective of the high frequency package of Fig.1 in a non-assembled, or partly assembled, state,

Fig. 3 is a view in a somewhat enlarged scale of the of the bottom part of the waveguide split block of Figs. 1 and 2,

Fig. 4 is a view of the bottom part of the waveguide split block including waveguide-to microstrip transitions,

Fig. 4A is an enlarged view of the section indicated A in Fig.4, showing a waveguide-to-microstrip transition more in detail, Fig. 5 is a view in a somewhat enlarged scale of the of the top part of the waveguide split block of Figs. 1 and 2,

Fig. 5A is an enlarged view of the section indicated B in Fig.5, illustrating a blocking structure according to the invention more in detail, and

Fig. 6 is a schematic view in perspective of an alternative high frequency package in a non- assembled, or partly assembled, state according to the invention. DETAILED DESCRIPTION

Fig. 1 schematically illustrates a high (RF) frequency package 100 comprising a circuit arrangement, here a MMIC (Monolithic Microwave Integrated Circuit) (not shown in Fig. l ; cf. Fig.2) arranged in a waveguide structure according to one embodiment of the invention. It should be clear that the invention is not limited to MMIC circuits, but it may alternatively be other circuit arrangements, e.g. where one or several MMICs or hybrid circuits are connected, or mounted on a carrier and interconnected. The circuit arrangement comprising one or more circuits, active or passive, is in the following also simply denoted "circuit".

Figs. 1 and 2 illustrate a two-port device, an amplifier, but it can be extended to any circuit having various number and types of ports. Examples are frequency converters (mixers), power amplifiers, LNAs (Low Noise Amplifiers), signal sources (frequency multipliers) and different combinations of these components etc.

The waveguide structure comprises a waveguide split block assembly comprising a first waveguide block portion 10, in the shown embodiment comprising a bottom waveguide block portion with a first waveguide part 15 A comprising a channel forming the half of a first waveguide, and a second waveguide block portion 20, in the shown embodiment comprising a top waveguide block portion, with a channel forming a second waveguide part 15B, i.e. the other half, of said first waveguide. An embodiment with channels or waveguide parts forming a second waveguide are shown in Fig.2. It should be clear that the invention covers embodiments with one, two or more waveguides. In Fig.1 the waveguide split block assembly is illustrated in an assembled, closed state.

The waveguide split block assembly 10,20 comprises an E-plane split block assembly as opposed to an H-plane split block assembly. An E-plane split block assembly comprises a waveguide formed from two split-blocks wherein, when the blocks are connected or assembled, a rectangular waveguide is formed, the split being along the broad dimension of the rectangular cross-section of the waveguide, i.e. the waveguide structure is cut along the electric plane.

H-plane split blocks suffer from the drawback of requiring a very good mechanical contact between the blocks in order not to prevent a current to flow.

According to the invention these drawbacks can be avoided by using an E-plane split block. In an E-plane split block, no current flows along the plane where the waveguide is split.

Although in the illustrated embodiment the first block portion is taken to be a bottom block portion, it should be clear that, in alternative embodiments, the split block portion disposition may be different, e.g. reverted, or the blocks may comprise two blocks disposed and formed in any other appropriate way.

Fig.2 shows the waveguide split block assembly in an open, non-assembled, or partly assembled, state. In one of the block portions, here the bottom block portion 10, a circuit arrangement comprising an active MMIC 30 is provided, the circuitry itself not being illustrated, since the invention is not limited to any specific circuitry, and supporting electronics also not being shown for reasons of clarity, and since it does not form part of the inventive concept. The bottom block portion 10 is adapted to receive said MMIC 30, and comprises a receiving cavity 31 (see Fig.3). In alternative embodiments the MMIC 30 is mounted onto the bottom block portion 10 in any other appropriate way, e.g. by soldering, gluing or similar. It should also be clear that the circuit does not have to be an MMIC; it may also be any other active (or passive) circuit or circuits. The MMIC 30, or, more generally, the circuit may be of any appropriate, arbitrary size. Probes comprising one or more waveguide-to-microstrip transitions 1 1, 12 are integrated onto

(here) the MMIC 30 at locations corresponding to respective inner ends of a first waveguide part (channel) 15A of a first waveguide and of a first waveguide part (channel) 16A of a second waveguide. It should be noted that the waveguides can be arranged in many different ways, and in alternative embodiments there may be one, two, three or more waveguides, and hence one or more ports. Probes as disclosed in Figs. 2,4,4A,6 comprising waveguide-to-microstrip transitions may thus be arranged in any desired number, one or more, and at any position(s) to form a transition between a waveguide and a circuit arrangement.

A second, input and/or output, waveguide is here correspondingly formed by a first waveguide part (channel) 16A provided in the bottom waveguide block portion 10 and a second waveguide part (channel) 16B provided in said second waveguide block portion 20.

The second waveguide block portion 20, here a top waveguide block portion, comprises a waveguide and/or cavity mode propagation blocking arrangement 22 (in the following denoted a blocking arrangement), which e.g. is arranged in a blocking arrangement recess 21 or similar, provided at a location corresponding to the location in the first waveguide block 10 adapted for reception of the MMIC 30, i.e. such as to be disposed opposite to the MMIC 30 in a mounted state (cf. Fig.1) of the high frequency package 100.

The blocking arrangement 22 comprises a high impedance surface comprising a periodic or quasi- periodic structure e.g. formed by a plurality of metallic pins 23 extending substantially perpendicularly to a bottom surface in said blocking arrangement recess 21 or similar, forming said high impedance surface, e.g. a corrugated surface, and arranged to face the MMIC 30. By means of the high impedance surface, e.g. the periodic or quasi-periodic structure, of said blocking arrangement 22, waveguide modes are blocked from leaking into the MMIC cavity from the waveguides. Thus no power in a form of a waveguide mode can propagate between the waveguide and the circuit cavity.

The presence of the waveguide modes are blocked through the use of said blocking arrangement 22, comprising the high impedance surface such as e.g. a periodic or quasi-periodic structure by means of removing, preventing the existence of, the E-field perpendicularly to the surface. This means among other things that bond wires do not have to be used at high RF-frequencies, and the RF performance of the circuit and the yield are considerably enhanced.

It thus becomes possible to avoid, eliminate, propagation into the circuit arrangement, here the active MMIC, of all other modes than a specifically desired mode, which is extremely advantageous since, as a rule, only one specific mode is generally wanted.

Thus, by means of the blocking arrangement 22 comprising a high impedance surface e.g. comprising a periodic or quasi-periodic structure formed by metallic pins or similar, leakage between the waveguide and the circuit arrangement, here the MMIC, can actually be prevented, all undesired waveguide modes actually being suppressed, which is extremely advantageous, and completely different from so far known solutions used in different contexts and in which are aimed at absorbing undesired leaking waveguide modes. Through the present invention, the appearance of any cavity modes in the circuit cavity are reactively prevented. Through the use of a blocking arrangement comprising a high impedance surface, a periodic or quasi-periodic structure, boundary conditions are created which do not allow the existence of any undesired modes in the circuit cavity.

The blocking arrangement 22, the high impedance surface, the periodic or quasi-periodic structure, may be provided for in many different manners and comprise different arrangements as will be further discussed below with reference to Figs. 5,5A.

Instead of having separate transitions on a separate substrate for connecting an (active circuit) to a waveguide, probes 1 1, 12 are integrated onto the circuit 30 itself, hence forming said waveguide- to-microstrip transitions 1 1, 12, which is extremely advantageous as discussed above. A common substrate is used for the circuit arrangement and the transition or the transitions, i.e. the same substrate as for the circuit arrangement is used also for the probe(s) or transition(s). According to the invention it is avoided being limited to the thickness of e.g. an MMIC, the dielectric substrate, since no surface waves will be excited from any discontinuity, the transition being integrated with the circuit, on the same, common substrate. Thus, the use of thicker substrates is enabled, particularly not requiring a wafer thinning, which is an additional step in e.g. MMIC fabrication reducing the yield of the manufacturing process, although also such substrates also are covered by the present invention. That the use of thicker substrates is enabled at high frequencies, e.g. above 60 GHz, or even above 100 GHz, is extremely advantageous since thin substrates are very fragile, and, as referred to above, the inventive concept works for substantially any size and height of the circuit.

Since thicker substrates can be used conductor losses may also be reduced, since if a thicker substrate can be used, the microstrip can be wider. It should be clear that the inventive concept is applicable for different substrate thicknesses, from e.g. 50 μιη up to about 250 μιη or more, e.g. from about 100-200 to 250 μιη. It should be clear that the figures are not given for limitative purposes, but merely for exemplifying reasons, and the thickness may also assume other values. Additionally the location of the probes can be arbitrary, which may provide additional flexibility in the designing of circuits.

Fig.3 is an enlarged view of the first waveguide block portion 10 comprising a bottom waveguide block portion with a first waveguide part 15A of a first waveguide and first waveguide part 16A of a second waveguide. The first waveguide parts or channels 15A, 16A extend from, on opposite outer edges with respect to one another, displaced positions of the bottom waveguide block portion 10, to locations at diagonally displaced outer edges of a receiving portion 31 adapted for reception of a circuit, e.g. an active MMIC, such as to (here) each correspond to a diagonally opposite position of an outer edge of such a circuit (not shown in Fig.3) where the transition waveguide-to- microstrip will be located.

Fig.4 is an enlarged view of the first waveguide block portion 10 comprising a bottom waveguide block portion with the first waveguide part 15 A of the first waveguide and the first waveguide part 16A of the second waveguide with an active MMIC 30 mounted in the receiving portion 31 (see Fig.3). In positions (here) at outer edges of the MMIC 30 probes are integrated comprising said waveguide-to-microstrip transitions 1 1, 12, or other types of planar transitions, for example a coplanar waveguide. However, as also referred to above, the probe location can be selected arbitrarily.

Fig.4A is an enlarged view of the section indicated A in Fig. 4 for the purposes of more clearly illustrating a waveguide-to-microstrip transition 12 comprising a probe integrated onto, or with, the MMIC, on a common substrate.

Fig.5 is an enlarged view of the second waveguide block portion 20 comprising a top waveguide block portion with a second waveguide part 15B of a first waveguide and second waveguide part 16B of a second waveguide leading from, here, on opposite outer edges with respect to one another displaced positions of the top waveguide block portion 20, to locations, or positions, at outer edges of a blocking arrangement receiving cavity 21 adapted for reception of a blocking arrangement, or arranged to comprise a blocking arrangement 22, such as to each correspond to the corresponding positions in the first waveguide block portion 10 where the respective corresponding first waveguide parts 15A,16A end, and where the of the outer edges of an active circuit to be received therein, are located, i.e. at the positions of the waveguide-to-microstrip transitions 11, 12 (see Figs.2,4,4A).

The blocking arrangement 22 here comprises a high impedance surface comprising a periodic structure comprising a plurality of metallic pins 23 disposed in parallel. The pins 23 here have a square-shaped cross-section and protrude perpendicularly with respect to a plane parallel with a planar outer surface of the second waveguide block portion 20 adapted to, in a mounted state of the high (RF) frequency package 100 (cf.Fig. l), be disposed on a planar outer surface of the first waveguide block portion carrying the active circuit. In an advantageous embodiment the width W, the cross-sectional dimension, of the square shaped pins 23 is about 0.15λ, λ being the wavelength of the centre frequency, and the height H of the pins is about λ/4, i.e. about a quarter wavelength (cf. Fig.4A).

The high impedance surface, particularly the periodic or quasi-periodic structure, here comprising pins 23, may be provided for in many different manners. In one embodiment pins are glued onto a surface in a blocking arrangement recess 21. Alternatively pins may be soldered onto such a surface, or in the bottom of a receiving recess in the waveguide block portion 20. Still further a high impedance surface may be provided through milling and comprise pins, ridges, corrugations or other similar elements forming a periodic or quasi-periodic structure. The pins or similar may of course also have other cross-sectional shapes; rectangular, circular etc. Also the dimensions are of course not limited to the exemplifying figures indicated for exemplary reasons above but may vary, e.g. as discussed below. The high impedance surface, or the periodic, or quasi-periodic structure, here formed by the pins 23, prevents propagation of any undesired waveguide modes into the MMIC (cavity) and hence prevents the existence of any cavity modes in the circuit cavity. The width, or cross-sectional dimension/the height of the pins, corrugations or other elements of any appropriate kind, is determined by the desired signal frequency band. The higher the frequency band, the smaller the dimensions, and the dimensions scale linearly with the wavelength; the higher the frequency, the smaller the wavelength λ, and the smaller the dimensions. It should be clear that, for a frequency band, λ is the wavelength of the centre frequency of the corresponding frequency band.

Fig.5 A is an enlarged view of the section indicated B in Fig. 5 for the purposes of more clearly illustrating an example of a blocking arrangement 22 comprising a periodic structure formed by pins 23. The blocking arrangement 22 comprising a high impedance surface in one embodiment comprises an array of pins 23 with a cross section e.g. having the dimensions of about 0.1λ-0.2λ, in advantageous embodiments about 0.15λ x 0.15λ, and a height H of 0.15λ-0.3λ, in particularly advantageous embodiments about 0.25λ. Particularly the period is between approximately 0.25λ and 0.4λ, most particularly about 0.3λ.

In another exemplary embodiment the blocking arrangement comprises a high impedance surface, a periodic structure comprising a number of square shaped pins with the cross-sectional area dimension of (0.1λ-0.2λ) ² , particularly about (0.15λ) ² and a height of 0.15λ -0.3λ, in particularly advantageous embodiments about 0.25λ. In still other alternative embodiments the high impedance surface, a periodic or quasi-periodic structure, may comprise a plurality of concentrically disposed corrugations with grooves.

It should be clear that a high impedance surface, a periodic or a quasi-periodic structure, may also be provided through differently disposed corrugations in still other embodiments.

The distance between the top of the high impedance surface, e.g. the top of the pin surface, and the ground plane of the circuit arrangement should be less than λ/4, i.e. the gap should be smaller than the wavelength/4. . The gap may be filled with air and/or a dielectric. Since the high impedance surface, the periodic structure, also denoted texture, is so designed that it stops propagation of waves over a specific frequency band for which it is designed, the shape and dimensions and the arrangement of e.g. pins, posts, grooves, ridges etc. of the periodic structure are selected correspondingly as discussed above. The non-propagating or non-leaking characteristics between two surfaces of which one is provided with a periodic texture (structure), is e.g. known from P.-S. Kildal, E. Alfonso, A. Valero- Nogueira, E. Rajo-Iglesias, "Local metamaterial-based waveguides in gaps between parallel metal plates", IEEE Antennas and Wireless Propagation letters (AWPL), Volume 8, pp. 84-87, 2009. The non-propagating characteristic appears within a specific frequency band, referred to as a stopband. It is also known that such stopbands can be provided by other types of periodic structures, as described in E. Rajo-Iglesias, P.-S. Kildal, "Numerical studies of bandwidth of parallel plate cut-off realized by bed of nails, corrugations and mushroom-type EBG for use in gap waveguides", IET Microwaves, Antennas & Propagation, Vol. 5, No 3 _¾ pp. 282-289, March 2011. These stopband characteristics are also used to form so called gap waveguides as described in WO/2010/003808.

Any of the described periodic or quasi-periodic textures can also be used in the high frequency package of the present invention. Thus, according to the invention, by using a blocking arrangement comprising a high impedance surface or a periodic or quasi-periodic structure, undesired waveguide modes can be efficiently suppressed. Fig. 6 schematically illustrates another embodiment of a high (RF) frequency package 100' comprising a circuit arrangement, e.g. an MMIC, arranged in a waveguide structure.

The high frequency package 100' here, for example, comprises a frequency multiplier. The waveguide structure comprises a waveguide split block assembly comprising a first waveguide block portion 10', comprising a bottom waveguide block portion with a first waveguide part 15 A' comprising a channel forming the half of a waveguide here serving as an output waveguide, for an output signal, and a second waveguide block portion 20' comprising a top waveguide block portion with a channel forming a second waveguide part 15B', i.e. the other half of said output waveguide. A probe comprising a waveguide-to-microstrip transition or other type of waveguide-to-planar transition 11 ' is integrated onto the MMIC 30' as also discussed above. Further, the waveguide split block assembly 10,20 comprises an E-plane split block assembly, and in the bottom block portion 10' a circuit 30' is provided as also discussed with reference to the embodiment described with reference to Figs.1,2 above.

In this embodiment, however, a coax port 161 ' serves as input for an input signal, an input frequency, which hence is fed through a coaxial cable, or alternatively another waveguide.

The second waveguide block portion 20', here a top waveguide block portion, comprises a waveguide mode propagation blocking arrangement 22' as discussed with reference to Figs.2,5, 5A above.

Similar elements bear the same reference signs as in these Figures, but are provided with a prime sign, and will therefore not be further described herein. It should be clear that the invention is not limited to the specifically illustrated embodiments, but that it can be varied in a number of ways within the scope of the appended claims. It is a particular advantage that it discloses a solution allowing integration of a circuit arrangement, particularly an active circuit, with one or more waveguides, and without the need for any bond- wire or flip-chip interconnects. It is also an advantage that a package is provided having low losses at high frequencies.

Particularly it is applicable for in principle any circuit of an arbitrary size, and height, active or passive. The high impedance surface, the periodic or quasi-periodic structure, can be provided for in many different manners, comprising different shapes and sizes of elements, distances between elements, periods etc. and being made of different materials, and it is not limited to any specific frequencies. Also, the invention is not limited to MMICs, but it is applicable to circuits, e.g. also hybrid circuits, in general, and is also intended to cover other (active or passive) circuits. It is also not limited to any particular number or type of ports, nor to the arrangement and positions of such ports, there may be one, two, three or more ports serving as input and/or output ports, the probes being integrated onto the circuit, on the same substrate, as discussed above. There may also be a combination of such ports and coax ports as exemplified through the embodiment shown in Fig.6. Further, the invention covers different types of planar transitions.