Patent Description:
A patch antenna generally consists of a dielectric substrate sandwiched between a conductive and radiating patch on the top and a ground plane at the bottom of the substrate. Ordinary materials for the patch are copper and gold. Typically, the patch is a square, though it can have almost any shape, and it is fed close to one edge thereof. If it is resonant there will be a standing wave across it where the current is at maximum at the middle of the patch and the voltage will have maxima at the edges, see <FIG>. If the ratio of the current and voltage is properly matched the patch will radiate effectively. The feeding can be done in several ways but an electric connection port at an edge of the patch, such as by means of a microstrip connection, or a magnetic connection port through a slot under the patch, such as by means of a microstrip extending below the substrate to the slot, is common. Other feeders, such as a coaxial cable, are sometimes used as well.

In order to transmit a signal with both horizontal and vertical E-fields, or in order to send two different transmit signals with the same antenna, the patch antenna is realized as a dual-polarized antenna. Then, a further connection port is provided. An additional electric connection is made at another edge, adjacent to and perpendicular to the edge of the first connection. An additional magnetic connection is made by means of an additional slot perpendicular to and crossing the first slot. Thus, traditionally, dual-polarized antennas are realized as one patch independently fed by two transmit paths.

If two transmitters that can be turned on or off and are connected to a respective one of the connection ports, the transmitted power of the patch antenna is limited to the power from one of them. If both transmitters are active to transmit a diagonal polarization, the patch is forced to resonate in a diagonal direction which is not optimal. If it was, patches would be designed to resonate diagonally.

<CIT> discloses such a patch antenna having two electric connection ports connected to a single patch. The connection ports are connected to first and second excitation units of the patch, generating first and second linearly polarized waves, being orthogonal to each other. The generated output signal is divided into two signals, which are fed to the respective first and second excitation units.

It would be advantageous to increase the efficiency of the antenna. To address this issue, in a first aspect of the invention there is provided an antenna device comprising an antenna part having a patch with several edges, a first transmit path connected to a first connection port at a first edge of the patch, and a second transmit path connected to a second connection port at the first edge of the patch, wherein the first and second connection ports are located at a distance from each other along the first edge, and a first transmitter and a second transmitter connected to the antenna part.

By connecting both transmit paths at the same edge it is possible to obtain a mode where both connections are driven in phase. This gives a higher impedance at each port compared to when the patch is driven by one connection only. They can also be driven in a differential mode resulting in an orthogonal polarization compared to the first case.

In accordance with an embodiment of the antenna device, the first transmit path comprises a first signal combiner connected to the first and second transmitters and to the first connection port, wherein the second transmit path comprises a second signal combiner connected to the first and second transmitters and to the second connection port, wherein the first signal combiner is arranged to generate a difference between signals originating from the first and second transmitters, and wherein the second signal combiner is arranged to generate a sum of the signals originated from the first and second transmitters. By means of the signal combiners it is possible to use the antenna device to simultaneously transmit two radio frequency signals in orthogonal polarizations.

In accordance with an embodiment of the antenna device the first transmit path comprises a first phase shifter and the second transmit path comprises a second phase shifter. Thereby, a simple control of the transmitted signal is obtained.

In accordance with an embodiment of the antenna device, the first phase shifter is connected to the first signal combiner and to the first connection port, and wherein the second phase shifter is connected to the second signal combiner and to the second connection port.

In accodance with an embodiment of the antenna device, the first phase shifter is connected to the first transmitter and to the first and second signal combiners, and the second phase shifter is connected to the second transmitter and to the first and second signal combiners.

In accordance with an embodiment of the antenna device, it comprises a beam controller connected to the phase shifter of each transmit path. Thereby a controlled beamforming is possible. When the antenna device comprises multiple antenna parts, preferably, the patches of the antenna parts are arranged as an array of desired configuration.

In accordance with an embodiment of the antenna device the first and second transmit paths of each patch are arranged to feed the same transmit signal to the patch in several different modes, including a common mode and a differential mode.

In a second aspect of the invention there is provided a method of transmitting a radio frequency signal, comprising providing an antenna device comprising an antenna part having a patch with several edges, a first transmit path connected to a first connection port of a first edge of the patch, and a second transmit path connected to a second connection port of the first edge of the patch, wherein the first and second connection ports are located at a distance from each other along the first edge. Further, the method comprises generating a first transmit signal by means of a first transmitter connected to at least the first transmit path, and generating a second transmit signal by means of a second transmitter connected to at least the second transmit path and feeding the first and second transmit signals to the antenna part.

This method provides the same advantages and solve the same problems as the above antenna device.

In accordance with an embodiment of the method it further comprises generating a sigma signal comprising a sum of the first transmit signal and the second transmit signal; generating a delta signal comprising a difference between the first transmit signal and the second transmit signal; feeding the sigma signal to the first connection port; and feeding the delta signal to the second connection port, thereby transmitting a first radio frequency signal with a first polarization, and a second radio frequency signal with a second polarization orthogonal to the first polarization from the patch.

The invention will now be described in more detail and with reference to the appended drawings in which:.

A first structure of an antenna device <NUM>, shown in <FIG>, shows some principles for using two connection ports associated with the same edge of a patch. The antenna device <NUM> comprises an antenna part <NUM>, having a patch <NUM> with several edges. In the figures the patches are illustrated as square patches. Many different shapes are feasible as understood by the person skilled in the art, however rectangular or modified rectangular shapes are preferred. The antenna part <NUM> further comprises a first transmit path <NUM>, connected to a first connection port <NUM> of the patch <NUM>, and a second transmit path <NUM> connected to a second connection port <NUM> of the patch <NUM>. The first and second connection ports <NUM>, <NUM> are provided at a first edge <NUM> of the patch <NUM>, and they are located at a distance from each other along that first edge <NUM>. Referring to <FIG>, if the first connection port <NUM> is positioned at a distance d1 from one end of the first edge <NUM>, the second connection port <NUM> is positioned at a distance d2 from the same end, where d2>d1. There are no particular relations between d1 and d2 or between those distances and the total length L of the edge that are generally preferable, but the most desirable measures have to be determined for each individual situation as a part of the design work. They depend on impedance levels, which in turn depend on substrate thickness, dielectric permittivity, etc. It is of course impractical to have them too close since there is no room for the feeding terminals. Additionally, it should be noted that the expression "at a first edge", as used in the present application, includes positioning of the connection ports <NUM>, <NUM> anywhere from exactly on the first edge <NUM> to a position displaced from the first edge <NUM> but still from a perspective of operation associable with the first edge <NUM>. For instance, if coaxial feeding terminals are used, the connection ports <NUM>, <NUM> are typically positioned at a distance from the edge displaced towards the centre of the patch <NUM>. When microstrip feeds are used, the patch <NUM> is typically provided with insets at the sides of the microstrip in order to reduce the input impedance of the connection ports <NUM>, <NUM>.

A single antenna part <NUM> antenna device <NUM>, where the antenna device <NUM> comprises a transmitter <NUM> connected to the antenna part <NUM>, is a basic alternative for the antenna device <NUM>. However, for further operational alternatives each transmit path <NUM>, <NUM> of the antenna part <NUM> comprises a phase shifter <NUM>, <NUM>, and the antenna device <NUM> further comprises a beam controller <NUM> connected to the phase shifters <NUM>, <NUM> for controlling the phase of the transmit signals fed to the respective first and second connection ports <NUM>, <NUM>.

Further, an advantageous application of the present invention is as an antenna array with beamforming capability. Hence, as also shown in <FIG>, the antenna device <NUM> generally comprises further antenna parts <NUM> forming a one-dimensional or two-dimensional array. Each further antenna part <NUM> also comprises first and second transmit paths <NUM>, <NUM> respectively connected to first and second connection ports <NUM>, <NUM>, arranged at a first edge <NUM> of the patch <NUM>. Each transmit path <NUM>, <NUM> of each further antenna part <NUM> comprises a phase shifter <NUM>, <NUM> connected to the beam controller <NUM>. The phase shifters <NUM>, <NUM> are connected to the transmitter <NUM> as well.

In accordance with a second structure of the antenna device <NUM>, as shown in <FIG>, the antenna device <NUM> comprises two transmitters, i.e. a first transmitter <NUM> and a second transmitter <NUM>. The first transmitter is connected to the first transmit path <NUM>, and the second transmitter <NUM> is connected to the second transmit path <NUM>. When multiplied to an antenna array comprising several antenna parts <NUM>, the first transmitter is connected to the first transmit path <NUM> of each antenna part <NUM>, and the second transmitter <NUM> is connected to the second transmit path <NUM> of each antenna part <NUM>. The beam controller <NUM> is connected to the phase shifters <NUM>, <NUM> as in the firststructure.

In accordance with a third structure of the antenna device <NUM>, as shown in <FIG>, the antenna device <NUM> comprises one or more antenna parts <NUM>, and a first transmitter <NUM> and a second transmitter <NUM> connected to the/each antenna part <NUM>. More particularly, each antenna part <NUM> comprises a patch <NUM>, a first transmit path <NUM> connected to a first connection port <NUM> of the patch, and a second transmit path <NUM> connected to a second connection port <NUM> of the patch <NUM>. Like in the previous structure the connection ports <NUM>, <NUM> are both associated with one and the same edge of the patch <NUM>. The first transmit path <NUM> comprises a first phase shifter <NUM> connected to the first connection port <NUM>, and a first signal combiner <NUM> connected to the first phase shifter <NUM>. The second transmit path <NUM> comprises a second phase shifter <NUM> connected to the second connection port <NUM>, and a second signal combiner <NUM> connected to the second phase shifter <NUM>.

The first transmitter <NUM> is connected to both the first transmit path <NUM> and the second transmit path <NUM>. The second transmitter <NUM> is connected to both the first transmit path <NUM> and the second transmit path <NUM> as well. More particularly, the first and second transmitters <NUM>, <NUM> are connected to the signal combiners <NUM>, <NUM>. The first signal combiner <NUM> is a delta element, i.e. a subtractor arranged to generate an output signal, here called delta signal, constituting the difference between a first transmit signal received from the first transmitter <NUM> and a second transmit signal received from the second transmitter <NUM>. The second signal combiner <NUM> is a sigma element, i.e. an adder arranged to generate an output signal, here called sigma signal, constituting the sum of the first transmit signal and the second transmit signal.

Further, similar to the other structures, the antenna device comprises a beam controller <NUM>, which is connected to all phase shifters <NUM>, <NUM>.

When the antenna device <NUM> comprises several antenna parts <NUM>, arranged in an array, the first transmitter <NUM> is connected to the first and second transmit paths <NUM>, <NUM> of each antenna part <NUM>, and the second transmitter <NUM> is connected to the first and second transmit paths <NUM>, <NUM> of each antenna part <NUM>. The beam controller <NUM> is connected to the phase shifters <NUM>, <NUM> of all antenna parts <NUM> as in the other structures. More particularly, each antenna part <NUM> comprises a patch <NUM>, and first and second phase shifters <NUM>, <NUM> connected to the connection ports <NUM>, <NUM> of the patch <NUM>. The first signal combiner <NUM> is shared by all antenna parts <NUM>, i.e. the output <NUM> of the first signal combiner <NUM> is connected to the first phase shifter <NUM> of each antenna part <NUM>. Similarly, the second signal combiner <NUM> is shared by all antenna parts <NUM>, i.e. the output <NUM> of the second signal combiner <NUM> is connected to the second phase shifter <NUM> of each antenna part <NUM>.

In accordance with a fourth structure of the antenna device <NUM>, as shown in <FIG>, the antenna device <NUM> comprises one or more antenna parts <NUM>, and a first transmitter <NUM> and a second transmitter <NUM> connected to the/each antenna part <NUM>. More particularly, each antenna part <NUM> comprises a patch <NUM>, a first transmit path <NUM> connected to a first connection port <NUM> of the patch <NUM>, and a second transmit path <NUM> connected to a second connection port <NUM> at the patch <NUM>. Like in the previous structures the connection ports <NUM>, <NUM> are both associated with one and the same edge of the patch <NUM>. The first transmit path <NUM> comprises a first signal combiner <NUM> connected to the first connection port <NUM>, and the second transmit path <NUM> comprises a second signal combiner <NUM> connected to the second connection port <NUM>. Further, the first transmit path <NUM> comprises a first phase shifter <NUM> connected to the first signal combiner <NUM> as well as to the second signal combiner <NUM>, and the second transmit path <NUM> comprises a second phase shifter <NUM> connected to both the second signal combiner <NUM> and the first signal combiner <NUM>.

The first transmitter <NUM> is connected to both the first transmit path <NUM> and the second transmit path <NUM>. Correspondingly, the second transmitter <NUM> is connected to the first transmit path <NUM> and, via the second phase shifter <NUM>, to the second transmit path <NUM>. More particularly, the first transmitter <NUM> is connected to the first phase shifter <NUM>, and, via the first phase shifter <NUM>, to the second signal combiner <NUM>. The second transmitter <NUM> is connected to the second phase shifter <NUM> and, via the second phase shifter <NUM>, to the first signal combiner <NUM>. Similar to the third structure, the first signal combiner <NUM> is a delta element, and the second signal combiner <NUM> is a sigma element.

Further, similar to the other structures, the antenna device <NUM> comprises a beam controller <NUM>, which is connected to all phase shifters <NUM>, <NUM>.

The first structure of the antenna device <NUM> is operated as follows. For each antenna part <NUM>, <NUM>, first and second transmit signals from the transmitter <NUM> are fed to the patch <NUM>, <NUM> via the first and second transmit paths <NUM>, <NUM>, <NUM>, <NUM>. The signals originate from the same source. If the first and second transmit signals are fed to the patch <NUM>, <NUM> in common-mode, that is with the same phase and the same amplitude, the patch <NUM>, <NUM> works similar to a patch of the prior art having a single port at the edge, but the impedance in each connection port <NUM>, <NUM>, <NUM>, <NUM> is twice the impedance of the single port. However, the total power transmitted by the patch <NUM>, <NUM> is doubled as well. That is, the power from both transmit signals is added in phase and thereby the transmitted power is doubled. The total transmitted power is the sum of the power in both connection ports <NUM>, <NUM>, <NUM>, <NUM> since they work in parallel. The radio frequency signal transmitted from the patch <NUM> will have a y polarization, see <FIG>.

If the first and second transmit signals are fed to the two ports <NUM>, <NUM> in differential mode, i.e. the same amplitude but opposite polarity, which means a phase difference of <NUM> degrees, there will be a current maximum in the symmetry plane of the ports <NUM>, <NUM>, as shown in the right hand scheme of <FIG>. In this case as well the transmitted power will be the sum of the power of both ports <NUM>, <NUM>. The radio frequency signal transmitted from the patch <NUM> will have an x polarization, see <FIG>. Thus, for both polarizations, i.e. x as well as y polarization, of the resulting transmitted radio frequency signal, the output power will be the sum of the power of the two ports <NUM>, <NUM>.

In addition to controlling the relative phase between the first and second transmit signals fed to each patch <NUM>, <NUM>, the beam controller <NUM> differentiates the phases of the antenna parts <NUM>, <NUM> in relation to each other in order to obtain a desired beam forming to the final signal transmitted from the antenna device <NUM>. Since this is done according to methods well known to the person skilled in the art it will not be further described herein.

In the secondstructure, shown in <FIG>, when two transmitters <NUM>, <NUM> are used to transmit the same signal, the total power delivered by the two transmitters <NUM>, <NUM> is transmitted by the patch <NUM>. A first transmitter Tx1, <NUM> is included in the first transmit path <NUM> of each antenna part <NUM> and it is connected to the first phase shifter <NUM> of each antenna part <NUM>, which first phase shifter <NUM> in turn is connected to the first port <NUM>. A second transmitter Tx2, <NUM> is included in the second transmit path of each antenna part <NUM> and it is connected to the second phase shifter <NUM> of each antenna part <NUM>, which second phase shifter <NUM> in turn is connected to the second port <NUM>. The first and second transmitters <NUM>, <NUM> are transmitting the same signal, and the phase controller <NUM> controls the phases of the phase shifters <NUM>, <NUM> to form the beam direction and also to determine the polarization.

More particularly, as illustrated in <FIG>, showing one antenna part <NUM> of the antenna device <NUM>, when the phase difference between the first and second phase shifters <NUM>, <NUM> is zero then the patch becomes polarized in the y-direction. When the phase difference is <NUM> degrees the patch <NUM> becomes polarized in the x-direction. In both polarizations, the total transmitted power will be the sum of the power of both antenna paths. In contrast, in the prior art antennas where two ports are arranged at different edges of the patch, usually the ports are alternatively activated, causing transmission with x or y polarization, or they are activated in common causing transmission with diagonal polarization with the power of one transmit signal in both cases, since when both ports are activated they do not add in phase.

The beam forming is provided with the same phase controller <NUM> by providing phase differences between the antenna parts <NUM> according to any suitable common technology beam forming method as known to the person skilled in the art.

The third structure of the antenna device operates as follows. The first transmit signal output from the first transmitter <NUM> is fed to the first signal combiner <NUM> and to the second signal combiner <NUM>. The second transmit signal output from the second transmitter <NUM> is fed to the second signal combiner <NUM>. For each antenna part <NUM>, the delta signal output from the first signal combiner <NUM> is fed to the first phase shifter <NUM> of the first transmit path <NUM>, and further to the first connection port <NUM> of the path <NUM>. The sigma signal output from the second signal combiner <NUM> is fed to the second phase shifter <NUM> and further to the second connection port <NUM>. The first and second phase shifters <NUM>, <NUM> may be used to mutually phase shift the delta and sigma signals in order to change polarity on the radio frequency signals transmitted from the patch <NUM> or, in case of several antenna parts <NUM>, in order to steer the beam transmitted from the antenna device <NUM>.

If the delta signal is denoted txΔ, the sigma signal is denoted txΣ, the first transmit signal is denoted tx1, and the second transmit signal is denoted tx2, then: <MAT> <MAT>.

Thus, the first transmit signal tx1 is received in common mode at the first and second connection ports <NUM>, <NUM>, and the second transmit signal tx2 is received in differential mode. Consequently, as explained above, the first transmit signal tx1 is transmitted from the patch <NUM> as a radio frequency signal in y polarization and the second transmit signal tx2 is transmitted in x polarization from the patch <NUM>. Both signals are transmitted simultaneously. If desired, by means of the phase shifters <NUM>, <NUM> the polarization of the transmitted signals can be switched such that the first transmit signal tx1 is transmitted in x polarization and the second transmit signal tx2 is transmitted in y polarization.

Similar to the third structure the fourth structure of the antenna device <NUM> generates two simultaneously transmitted radio frequency signals, which are sent with orthogonal polarizations, i.e. x and y polarizations, one originating from the first transmitter <NUM> and the other originating from the second transmitter <NUM>. A difference in comparison with the third structure, caused by the shifted positions of the signal combiner <NUM>, <NUM> and the phase shifter <NUM>, <NUM> of each transmit path <NUM>, <NUM>, is an improved isolation between the transmit signals tx1 and tx2.

As obvious to the person skilled in the art, the antenna device can be used to receive radio frequency signals as well. In the antenna devices <NUM>, <NUM> according to the third and fourth structures, the inherent isolation between the two polarisations in the patch <NUM>, <NUM> makes the transmitted signal tx1 independent of the impedance in the transmitter TX2. This allows for transmitting and receiving signals simultaneously in different polarisations, or in time-division mode, without suffering from poor impedance matching in the path that is not active.

Consequently, in accordance with the present invention, an antenna array is designed that can make use of a number of beamforming channels to control both beam direction and polarization while transmitting power from all channels in both polarizations. By using two transmitters and incorporating the signal combiners one can control the polarization of the two transmitters relative to each other.

One advantage of this solution over previous solutions is that it allows to transmit twice the power in two polarizations.

Claim 1:
An antenna device comprising an antenna part (<NUM>) having a patch (<NUM>) with several edges, a first transmit path (<NUM>) connected to a first connection port (<NUM>) at a first edge (<NUM>) of the patch, a second transmit path (<NUM>) connected to a second connection port (<NUM>) at the first edge of the patch, wherein the first and second connection ports are located at a distance from each other along the first edge, and a first transmitter (<NUM>) connected to at least the first transmit path, characterized in that the antenna device further comprises a second transmitter (<NUM>) connected to at least the second transmit path.