Title: TUNEABLE ANTENNA ARRANGEMENT

FIELD OF THE INVENTION

The present invention relates to a tuneable antenna arrangement comprising a microstrip patch antenna means comprising conducting patch means.

STATE OF THE ART

Patch antennas are well known and widely used in modern microwave systems for transmitting and receiving microwave signals. They may in principle be of any shape, but rectangular patch antennas are most common. Fig. 1 shows a state of the art patch antenna which is rectangular and comprises a conducting patch disposed on a dielectric substrate which in turn is provided on a ground plane. Typically such antennas have a narrow bandwidth and a large size.

Tuneable antennas make it possible to avoid the fundamental gain-bandwidth limitation of electrically small antennas. A small and highly efficient antenna with a narrow instantaneous bandwidth may be tuned over a wide bandwidth. A single tuneable antenna may eliminate the need for multiple antennas covering several wireless standards.

MEM (MicroElectro Magnetic) electro-statically tuneable antennas are known but they are not cost effective due to a complex design (vacuum packaging) and in addition thereto they are slow. Semiconductor varactor tuned antennas have a poor efficiency

which mainly is due to a low Q-factor (Quality factor) of the semiconductor varactors, particularly above 10 GHz.

A tuneable antenna using a ferroelectric varactor as a tuning element is known from "Active integrated antenna on planar dielectric resonator with tuning ferroelectric varactor", by O. Yu. Buslov et al . , in Dig. Int. Microwave Symp., IMS'2007. Such tuneable antennas require external Voltage Controlled Oscillators (VCO) and typically the VCO and the antenna are connected via a microwave network, i.e. an interconnecting transmission line. This makes the interconnected oscillator- antenna network large in size, complex and not cost effective.

Active antennas integrating self-oscillating mixers are known from "HBT active antenna as a self-oscillating Doppler sensor", by M. J. Kelly et al . , in IEEE Proc. Microwaves Antennas and Propagation, vol. 147, No. 1, pp. 4347, 2000, and "Integration of self-oscillating mixer and an active antenna", by J. Zhang et al., in IEEE Micr. Guided Wave Lett., vol. 9, No. 3., pp. 117- 119, 1999. Due to integrated mixing functions such antennas may be used for both receiving and transmitting of microwave signals. However, these antennas and oscillators are not tuneable. In addition thereto phase locking is not achieved or facilitated. Moreover the design of such a network is such that it becomes large in size, complex and not cost effective. Due to the interconnections between the antenna and the oscillator they also have high losses which has a negative impact, particularly if they are used as receivers.

Thus, known arrangements all suffer from one or more of the following drawbacks: the have a narrow bandwidth, there is a

high phase noise they are not tuneable, large in size, complex and not cost effective. They often also have suffer from high losses .

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an antenna arrangement as initially referred to which is small, non complex and easy to fabricate and, which can be used for both transmitting and receiving microwave signals. Moreover it should be tuneable over a wide bandwidth. Particularly it is an object to provide an antenna arrangement as initially referred to which has low losses and which enables or facilitates phase locking and which has a low phase noise. It is a particular object to provide an oscillator and antenna system which provides self injection locking features.

Therefore a tuneable antenna arrangement is suggested which comprises a Self-Oscillating Mixer (SOM) arrangement which is electromagnetically integrated with or in a tuneable antenna means. The Self-Oscillating Mixer (SOM) arrangement is also tuneable and comprises or forms a number of tuneable oscillators. Tuning means are provided which are adapted to both tune the tuneable antenna means and the tuneable SOM arrangement. The tuneable antenna arrangement comprises an input terminal and an output terminal for input and output respectively of low frequency intermediate, baseband signals.

Optional advantageous implementations are given by the appended sub-claims. It is an advantage that a tuneable SOM antenna arrangement is provided which is small, compact, efficient, tuneable over a wide bandwidth and which in addition thereto has

low losses. It is also an advantage that it can be used for both transmitting and receiving of microwave signals and that phase locking is facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 is a state of the art figure showing a patch antenna,

Fig. 2 is a top view of an antenna arrangement according to a first embodiment of the present invention,

Fig. 3 is a top view of an antenna arrangement according to a second embodiment of the present invention,

Fig. 4 is a top view of an antenna arrangement according to a third embodiment of the present invention,

Fig. 5 is a top view of an antenna arrangement according to a fourth embodiment of the present invention,

Fig. 6 is a cross-sectional view taken along A-A in any one of the embodiments 1, 2, 3 or 4,

Fig. 7 is a cross-sectional view taken for example along A-A according to another implementation of e.g. embodiments 1, 2 or 3,

Fig. 8 is a cross-sectional view taken along for example A-A in still another implementation of any of the embodiments 1, 2 or 3,

Fig. 9 is a cross-sectional view along A-A showing another implementation of for example any one of said embodiments above,

Fig. 10 is a cross-sectional view along B-B showing the implementation of e.g. the embodiment shown in Fig. 2,

Fig. 11 is a cross-sectional view along B-B in the second embodiment of Fig. 4 with asymmetric patch portions,

Fig. 12 is another example of a cross-section taken across the mixing arrangement,

Fig. 13 shows an arrangement according to the present invention comprising an array of antenna arrangement,

Fig. 14 shows an application example of a basic transmitter/receiver circuit as a sensor according to the state of the art,

Fig. 15 is a diagram illustrating the time variation of frequency of microwave signals generated by the SOM measured at the antenna, and

Fig. 16 shows an application example with the tuneable arrangement according to the present invention

comprising a tuneable self-oscillating mixer-antenna arrangement used as a sensor.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention a tuneable self -oscillating mixer antenna is provided. It incorporates one or more tuneable SOMs which act as self-oscillating mixers (up and down converting) which are electromagnetically integrated with an antenna, i.e. form an integral part of the antenna itself. The tuning devices, i.e. a DC bias device or network, provides tuning voltages to the arrangement, particularly the SOMs and the antenna means , so that their frequencies will be the same and change synchronously by the same amount. In the tuneable antenna arrangement according to the present invention, which includes an electromagnetically integrated SOM, the tuneable antenna means acts as a radiating/receiving antenna loading the SOM arr angement, and at the same time it acts as an external cavity (resonator) providing self phase locking of the SOM arrangement at a desired frequency and thus reduces the phase noise.

As discussed above Fig. 1 shows a rectangular patch antenna 1Oo comprising a conducting patch I ₀ deposited on a dielectric substrate 8o which in turn is arranged on a ground plane 9o. A plurality of embodiments will now be discussed with reference to the following figures.

A tuneable self -oscillating mixer-antenna arrangement according to the present invention consists of a microstrip patch antenna comprising, or split into, two portions which may have the same or different shapes, have the same sizes or not.

Fig. 2 shows a first embodiment in which the patch antenna means comprises a first patch portion I ₁ and a second patch portion 2 _lr which may be deposited on a dielectric substrate, for example high resistivity silicon, GaAs, fused silica or any other low permittivity, low microwave loss, material (not shown in the figure) . The first and the second patch portions I ₁ , 2 ₁ at opposite ends, are connected via two pairs of varactors, or tuneable capacitors, A ₁₁ , A ₁₂ , A ₁₁ ¹ , A ₁₂ ¹ and an intermediate strip 3i disposed between said first and second patch portions. Tuning contact means are provided for tuning the capacitance of the varactors and hence the resonant frequency of the patch antenna, and comprises DC bias contact means 5n, 5 _12ι 5n', 5 ₁₂ ' for application of a DC bias voltage.

A tuneable SOM arrangement 6i is connected between the first patch portion I ₁ and the second patch portion 2 ₁ . In one embodiment a semiconductor chip is provided which contains said SOM arrangement 6i.

If the sizes of the patch portions considerably exceed the size of the SOM arrangement 6 ₁ , particularly the semiconductor chip (which however not is necessary) , an opening 12i can be provided for e.g. as cut out portions in the respective first and second patch portions (below) the semiconductor chip comprising the SOM 6i. The patch portions li, and/or the opening 12i may in general have any desirable shape, for example circular, annular, triangular, polygonal or have patterns consisting of a combination of straight and curved lines etc. In particular embodiments the in- and output terminals (indicated in and out respectively in Fig. 2) are connected to the patch portions in a

symmetrical manner, cf. e.g. Figs. 2, 3, i.e. symmetrically with respect to the patch portions. The microwave signal at the output terminals of the SOM 6 _lr H ₁₁ , H12 may have a phase difference allowing optimum excitation of the symmetric patch portions, cf. e.g. Fig. 2 and Fig. 3.

The semiconductor chip with the SOM arrangement 61 may include an electronic circuit which in combination with the two patch portions act as a VCO. The frequency of the VCO is controlled by tuning, or applying a DC voltage, to the varactors A ₁₁ , 4 _i2 , 4n', 4i2 ^! . In an alternative embodiment the semiconductor chip contains an integrated VCO (or VCOs) and the tuneable patch resonator may be used as an external cavity for self locking of the frequency of the VCO and hence reduce the phase noise. The patch portions I ₁ , I ₁ may have connecting means H ₁₁ , H12 for connection of the chip containing the SOM. The chip may have connecting means, for example comprising contact pads, bumps etc. to facilitate DC and microwave connection, for example wire bonding or flip-chipping, with the two patch portions, I ₁ , ±2 cf. Figs. 2, 3, 4, 5, 9. The connecting means H ₁₁ , II12, • • • may be arranged to provide impedance matching or delay line functions between the SOM and the patch portions, cf. Fig. 5.

The intermediate strip 3i and the contact means 5n, 5i2, 5n', 5i2 ^! are used to supply the DC bias to the SOM arrangement 61, or to the semiconductor chip that contains the SOM. Particularly the intermediate strip 3 _lf with appropriate decoupling networks

(not shown) , is also used for extraction of the intermediate frequency signal when the tuneable self-oscillating mixer antenna 1Oi is used as a receiver. At reception of a signal comprising radio waves etc. received from free space, a mixing

is done in the SOM and a low frequency signal is output on the output port (out) . Alternatively, or additionally the intermediate strip 3i, with appropriate decoupling networks (not shown) , is also used for applying a low frequency modulation signal when the tuneable self-oscillating mixer antenna arrangement 1Oi is used as a transmitter. The varactors A ₁₁ , 4 _i2 , 4ii', 4i2 ^! also serve as decoupling capacitors allowing different combinations of the applied DC voltages for controlling the frequency of the SOM arrangement 61 and its DC bias supply.

Fig. 3 shows another implementation of an antenna arrangement IO2 according to the present invention. Corresponding means in the figure are given the same reference numerals as in Fig. 2 but with indices "2", "21" etc. instead of "1", "11" etc. The tuneable antenna arrangement IO2 of Fig. 3 differs from the one described in Fig. 2 substantially in that no opening is provided for the SOM arrangement, or particularly the semiconductor chip containing the SOM 62- In every other aspect the functioning and the construction are similar. Fig. 3 for exemplifying reasons illustrates the arrangement when operating as a transmitter wherein a low frequency signal f _in is input on the input port, mixed in the mixer, whereupon the antenna arrangement radiates.

Fig. 4 shows a tuneable antenna arrangement IO3 according to still another embodiment. Again similar means are given the same reference numerals as in Fig. 2 but indexed "3", "31", "32" etc.

Similar to the embodiment of Fig. 2 an opening 12 ₃ is provided for the semiconductor chip 63. The difference here is that the opening 12 ₃ is asymmetric and to a larger extent formed in patch portion I ₃ and the semiconductor chip 63 is asymmetrically located with respect to the patch portions I ₃ , 2 ₃ , (hence having

different shapes or peripheries) and only one connecting means II3 is illustrated in the figure since they also differ in form and size. This means that the input and output terminals are connected to the patches in an asymmetric manner and the phase difference in the output signal may be different from 180°.

Fig. 5 shows a tuneable antenna arrangement 1O ₄ according to another embodiment. Corresponding reference numerals are used, with index "4", "41" etc. It comprises a section of a coplanar waveguide with a signal strip and two ground planes. A semiconductor chip 64 is provided which here is symmetrically located with respect to the patches I ₄ , 2 ₄ and the intermediate signal strip 3 ₄ .

It provides for impedance matching between the chip by and the patches I ₄ , 2 ₄ . An intermediate frequency IF is output. As in the preceding embodiments the varactors 4 _4i , 4 ₄₂ , ... and the IC are DC biased (DC bias contact means 5' ₄ i, 5' ₄ 2, 5 _4i , 5«) .

Figs. 6-9 show different implementations of cross-sections along A-A in Figs. 2, 3, 4 or 5, or more generally show different implementations of cross-sections e.g. with the locations of the connection via capacitors etc. between the first and second patch portion and the strip being different as discussed above.

Fig. 6 shows an example of a tuneable self -oscillating mixer antenna (cross-section thereof) which includes an etched ferroelectric film 7A sandwiched between the strip 3A and patch portions IA, 2A forming the varactors 4i, 42.

Fig. 7 shows a cross-section of another implementation of a tuneable an tenna arrangement according to the present invention wherein, in addition to a patterned ferroelectric film 7B as in Fig. 6, thin dielectric (low permittivity) films 1OB, 1OB are provided on portions of the interface patch portion IB; 2B, substrate 8, ferroelectric film 7B, among other things to facilitate a particularly good control of the fabrication process. The thin dielectric films may comprise SiC>2 or similar.

Fig. 8 shows still another implementation similar to Figs. 6 and 7 but wherein the ferroelectric film 7C is not patterned, but substantially uniformly disposed between the first and second patch portions 1C, 2C and the strip 3C for example transversely in at least one direction across the antenna arrangement.

Fig. 9 shows another implementation wherein the varactors, here 14i, 14 ₂ are in the form of tuneable chip capacitors, semiconductor chips, ferroelectric chips, MEM chips or any other type of varactors. They may be provided with, for example, mounting means, pads, bumps for connection to the patches ID, 2D, cf. e.g. Figs. 2, 3, 4, 5 containing connecting means Hi, II12; H3; H4 (mounting means, pads, bumps or similar are not shown in the figure but it should be obvious how they are disposed or could be disposed) .

Fig. 10 (e.g. cross-section B-B of Fig. 2 or Fig. 4) shows a first patch portion IE, second patch portion 2E with a central strip 3E on which a semiconductor chip 6E is disposed. The substrate 8 may comprise a dielectric substrate on which a semiconductor chip 6E is provided on top.

If, on the other hand, the substrate is semiconducting, the semiconductor chip with the mixing arrangement 6E may also be provided on top as in Fig. 10, but it may also/alternatively be integrated in the substrate. Thus, although not shown, the semiconductor chip with SOM arrangement may also be integrated monolithically in the substrate if the substrate consists of a semiconducting material.

Fig. 11 shows another cross-section B-B e.g. taken through the part of the arrangement IO3 (Fig. 4) comprising a SOM arrangement 6E (63) . The patch portions IF, 2F may particularly correspond to patch portions I3, 2 ₃ and the strip 3F may correspond to strip 3 ₃ .

Fig. 12 shows still another embodiment of a cross-section through the SOM arrangement, e.g. as in Fig. 2 not showing any connecting means, i.e. the section not being made through the connecting means.

In an alternative embodiment (not shown) all components and means discussed are monolithically integrated into a semiconductor substrate for example of Si, GaAs, GaN, SiC etc. using semiconductor monolithic integrated circuit fabrication processes .

Generally, for any implementation, a combined SOM arrangement, particularly semiconductor chip, may be provided which handles both the transmitting and the receiving functionality. Alternatively different or distinct mixer arrangements or semiconductor chips are provided for the receiving and the transmitting functionality respectively (not shown) .

Fig. 12 schematically illustrates a SOM arrangement 6. It should be clear that the IC chip (transistors) may have any of the standard forms. The tuneable patch antenna, Fig. 2, 3, 4, 5, may be used as a tuneable resonator which in combination with the IC chip (transistors) may act as a tuneable SOM. Alternatively, the IC chip (transistors) and an LC tank based on (i.e. ferroelectric) varactors implemented on the substrate 8 may constitute a SOM and the tuneable patch comprising of parts I ₁ , 2i etc. varactors A ₁₁ , 4 ₂ i etc. may act as an external tuneable resonator (cavity) for self injection locking of the SOM to stabilise the frequency of the SOM and thus reduce the phase noise .

Fig. 13 schematically illustrates an implementation with a tuneable antenna arrangement according to the present invention which comprises an array 100 of antennas 1On, ... , 1O ₄₄ arranged for beam forming (retrodirective, beam scanning etc.) and/or for free space microwave power combiners by proper phase locking of the antennas in the array. In general the antenna arrangement according to the present invention also may have individual applications in sensors, radio tags (RFIDs), security or safety systems, etc.

Fig. 14 is a simplified illustration of a typical, known, system used for measurement of the distance between an antenna 30 and an object 0. It consists of basic components VCO 90, power amplifier 101, low noise amplifier 110, mixer 120, circulator 130 and the antenna 30, i.e. 7 individual components.

The VCO generates microwave signals with time dependent frequency as schematically shown in Fig. 15. It is supposed that the frequency measured at ti is fi. The time interval the signals travel to the object 0 and back to the antenna 30 is given as:

Id Id _r τ = — = —Vε v c ₀

wherein d is the distance between the antenna 30 and object 0, v is the average velocity of the microwave signals in the medium between the antenna and the object, ε is the average dielectric permittivity and Co is velocity of light in vacuum. During the time interval t ⁼ t2~ti the frequency of the microwave signals will change from fi to t ₂ , cf. Fig. 15. For reasons of simplicity the time delays in amplifiers and circulator are ignored (they may the measured/calibrated correctly) . At the moment t ₂ the mixer will receive signals with frequencies fi and f _2r producing a low intermediate frequency F=fi-f ₂ . This frequency is measured by a frequency meter (not shown) and it is proportional to the time interval

X =FIv _f

wherein v _f is the speed of changing frequency generated by the VCO. This speed is known for the given VCO. Hence, from the formulas given above, the distance d will be determined using the measured intermediate frequency F and the velocity v _f as :

If for example it is assumed that the frequency of the VCO is tuned from 5.2 to 5.6 GHz for 1.0 μs, then v _f =4 10 ¹⁵ Hz/s. If the distance d=5.0 cm, then the frequency F at the output of the mixer 120 will be in the range 1.25 MHz. In case the medium has a permittivity ε the minimum distance will be ε times smaller or the intermediate frequency may be ε 1/2 times larger. In alternative implementations the electronic devices may have different technical implementations. However, the main function is to compare the frequencies of two signals and provide an output signal which is proportional to the distance d. The output signal may have an electrical, optical, magnetic or any other format suitable for a computer control system.

The system described above includes several separate components and is not cost effective for many sensor or RFID applications. Even if all components were integrated on a single chip, the integration of the antenna itself makes the chip size rather large and economically not affordable. Additionally, most of the components, for example VCO, use lumped inductors which make the chip size even larger.

According to the present invention the number of critical components can however be reduced and a higher degree of integration and cost effectiveness can be achieved for such applications. The circuit topology of an implementation based on the inventive concept is shown in Fig. 16.

The tuneable SOM-antenna combination IO5 in Fig. 16 also acts as a mixer 9O ₅ for the waves reflected (RE waves) from the object O producing the intermediate frequency. The frequency of the SOM is controlled/scanned (as in Fig. 14) when the distance from the fixed object is measured. Alternatively the frequency may be fixed to measure the speed of an object.

It should be clear that the invention is not limited to the particularly illustrated embodiments but that it can be varied in a number of ways and also used for several different applications .