Abstract:
A patient device that possesses a receiver array having particularly great reception sensitivity. The patient device possesses an E-field antenna and an H-field antenna, in each instance, where the H-field antenna is structured as a frame antenna. According to the invention, a main axis that runs through the E-field antenna forms an angle of less than 30 degrees to a normal line of an area generated by the frame antenna.

Description:
This application takes priority from German Patent Application DE 10 2008 002 587.9, filed 23 Jun. 2008, the specification of which is hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a patient device having an antenna array with polarization diversity. 
     2. Description of the Related Art 
     In the medical technology sector, what are called patient devices are increasingly being used, which can be carried along by the patient and usually receive medical or technical data from an implant, such as a heart pacemaker of a patient, for example, at regular intervals, by way of a wireless data connection, and keep these data available for monitoring by the physician, or transmit them directly to a suitable device, for medical monitoring. Since electro-medical implants can only be replaced by means of an operation, and therefore are supposed to remain in the patient&#39;s body for multiple years, operated by a battery, the additional power consumption to be expended for such a telemetry function represents a critical factor in implementation. In order to minimize the transmission power to be expended for reliable data transmission, a particularly sensitive reception array in the patient device is desirable. The present invention therefore has the task of indicating a patient device that possesses a reception array having particularly great reception sensitivity. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to meet the above-stated requirements, the invention indicates a patient device that has a transmitter/receiver device having an E-field antenna and a H-field antenna, in each instance, where the H-field antenna is configured as a frame antenna. According to the invention, a main axis that runs through the E-field antenna forms an angle of less than 30 degrees relative to the normal line of an area generated by the frame antenna. 
     This geometric arrangement possesses the advantage that the E-field antenna and the H-field antenna cannot reciprocally influence one another. In this connection, “main axis” is understood to mean the axis that extends for the greatest possible distance within the E-field antenna. 
     The least influence of E-field antenna and H-field antenna results if the main axis is approximately parallel, or, even better, precisely parallel to the normal line. 
     In the case of an embodiment variant that is preferred because of its particularly compact construction, the main axis runs through the generated area. Particularly preferably, the main axis runs through an area center of gravity of the generated area. 
     Preferably, the E-field antenna and/or the H-field antenna is/are electrically extended. This can be brought about, in the case of the E-field antenna, in known manner, for example by means of a coil at the feed point of the antenna, or by means of a capacitor attached to the tip of the E-field antenna; in the case of the H-field antenna, it can be brought about by means of providing multiple loop windings. 
     The E-field antenna can be structured as a rod antenna or as a helical antenna. 
     Particularly preferably, the E-field antenna and the H-field antenna have a resonance frequency between 300 MHz and 500 MHz. This frequency range is particularly suitable for the transmission of data from medical technology implants. 
     A particularly preferred embodiment of the patient device according to the invention possesses an antenna array having a particularly robust mechanical structure. In this connection, the E-field antenna is structured as a quarter-wave dipole having an antenna counterweight. In antenna technology, a “counterweight” is a metallic device connected with ground, which can be structured as a plate or star, and reflects the quarter-wave dipole, so that its emission behavior at least approximately corresponds to that of a half-wave dipole. In the preferred embodiment, the antenna counterweight serves, at the same time, to mechanically stabilize the H-field antenna, which is structured as a frame antenna, in that it is connected with the latter (in electrically insulated manner) at least at one point of the H-field antenna. 
     Particularly preferably, the transmitter/receiver device of the patient device is configured to select either the E-field antenna or the H-field antenna for reception during operation, in each instance, as a function of the reception strength of a received signal. Alternatively, however, it is also possible to sum up the signals of the two antennas. 
     At least one antenna, the E-field antenna or the H-field antenna, can have an adaptation network that can be tuned by a controller. This makes it possible to maximize the reception or transmission power, respectively, in that during operation, the adaptation of the E-field antenna and/or the H-field antenna can be corrected in accordance with the general conditions predetermined by the environment. 
     The tunable adaptation network can have a plurality of capacitors that can be switched in parallel, where the controller is configured to connect a partial amount (lying between none and all) of the capacitors with at least one of the E-field antenna and the H-field antenna, and to electrically insulate the remaining capacitors from at least one of the E-field antenna and the H-field antenna. 
     Alternatively or in addition, for example as “fine-tuning,” the tunable adaptation network can contain a varactor diode. The controller is configured to predetermine a cut-off voltage of the varactor diode by way of an inductance. The capacitance of the varactor diode can be adjusted in step-free manner by means of the cut-off voltage. The inductance serves to uncouple the high-frequency antenna signal from the control voltage of the controller. 
     The E-field antenna and/or the H-field antenna can be connected with the transmitter/receiver device by way of a directional coupler. The directional coupler is configured to output a measurement signal to the controller. In this connection, the measurement signal indicates a measure of the power reflected or received by the E-field antenna and/or the H-field antenna. The measurement signal advantageously allows establishment of a regulation loop for adjusting the tunable adaptation network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures show: 
         FIG. 1  the antenna array of a first exemplary embodiment of the patient device according to the invention; 
         FIG. 2  the antenna array of a second exemplary embodiment of the patient device according to the invention; 
         FIG. 3  in two sub-figures, examples of how the antenna arrays can be mechanically combined with an electronic circuit of the patient device according to the invention, structured as a circuit board; 
         FIG. 4  a first variant of an adaptation network; 
         FIG. 5  a second variant of an adaptation network; and 
         FIG. 6  a block schematic of a transmitter/receiver device with adaptation network. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the antenna array of a first exemplary embodiment of the patient device according to the invention. An E-field antenna  11 , which is preferably structured as an electrically lengthened quarter-wave or helical antenna, is disposed in the center of a circular frame antenna  21 , in such a manner that the feed point  31  of the E-field antenna is positioned in the center of the frame antenna  21 . The frame antenna  21  can generally be structured also as a loop antenna, which then has two or more spirals. Of course, the frame antenna  21  can also assume other geometrical shapes, such as rectangular, square, triangular, or hexagonal. An antenna counterweight  41  is configured as a right-angle cross of two rigid metallic conductors, the intersection point of which is situated as close as possible to the feed point  31  of the E-field antenna  11 , on the side facing away from the E-field antenna  11 . The metallic conductors are electrically connected with the ground line to the feed point  31 , and are dimensioned in such a manner that they mechanically support the frame antenna  21 , from which they are electrically insulated. The antenna counterweight  41  can also be configured as a star of metallic conductors or as a continuous surface, for example. The frame antenna  21  is supplied by way of a feed line  51 , which contains a ground-shielded signal line. Preferably, the frame antenna  21  is structured in such a flat manner that the area it covers lies at least approximately in one plane. The frame antenna  21  is disposed relative to the E-field antenna  11  in such a manner that a main axis of the E-field antenna is at least approximately parallel to an area normal line of the area covered by the frame antenna  21 . On the basis of this arrangement, the result is achieved that the two antennas do not negatively influence one another. In this connection, “at least approximately parallel” means an angle of less than 30 degrees, but even better, less than 10 degrees. The effect striven for with the geometric arrangement is best if the main axis of the E-field antenna is oriented as parallel as possible to the normal line of the area covered by the H-field antenna, within the usual production tolerances. 
       FIG. 2  shows the antenna array of a second exemplary embodiment of the patient device according to the invention. In the case of this exemplary embodiment, the E-field antenna  12  is configured as a half-wave dipole, and for this reason, the feed point  32  is situated in the middle of the E-field antenna  12 . As a half-wave dipole, the E-field antenna  12  does not have an antenna counterweight. A mechanical connection of the E-field antenna  12  with the frame antenna  22  is therefore preferably made by means of non-conductive materials. Again, the frame antenna  22  is configured to be circular. The E-field antenna  12  is disposed relative to the frame antenna  22  in such a manner that the feed point  32  comes to lie at least approximately at the center point of the area covered by the frame antenna  22 . Again, the main axis of the E-field antenna  22  is at least approximately parallel to a normal line of the area covered by the frame antenna  22 . The statements made above concerning alternative shapes of the frame antenna  22  apply for this exemplary embodiment, as well. The feed line  52  connects the feed point  32  of the E-field antenna  12  with the frame antenna  22 . 
       FIG. 3  shows, in two sub-figures, how the antenna arrays can be combined with an electronic circuit of the patient device according to the invention, structured as a circuit board. In the first partial figure, an E-field antenna  13   a  is attached at the center of an edge of a circuit board  63   a , on which the electronic circuit of the transmitter/receiver device as well as any other components such as adaptation networks and the like are applied, so that the main axis of the E-field antenna  13   a  is oriented at least approximately parallel to a plane described by the circuit board  63   a . A frame antenna  23   a  is attached in the lower region of the circuit board  63   a , perpendicular to its two surfaces. The frame antenna  23   a  is made from a rigid conductive material, so that no additional mechanical stabilization is required. The feed points of both the E-field antenna  13   a  and of the frame antenna  23   a  lie on the circuit board, so that particularly simple connection with the electronic circuits of the transmitter/receiver device is possible. As was already the case above, the main axis of the E-field antenna  13   a  is oriented at least approximately parallel to a normal line of an area covered by the frame antenna  23   a.    
     In the exemplary embodiment shown in the second partial figure, the E-field antenna  13   b  is disposed perpendicular to the circuit board  63   b . The frame antenna  23   b  lies in a plane with the circuit board  63   b , and encloses this in one half of the frame antenna  23   b . Here again, the E-field antenna  13   b  is disposed at least approximately parallel to an area normal line of the area covered by the frame antenna  23   b . Again, the feed points of the two antennas lie on the circuit board  63   b.    
       FIG. 4  shows a first variant of an adaptation network. The circuit example only shows an adaptation network for an E-field antenna  14 , which is electrically lengthened by the inductance  34  switched between the E-field antenna  14  and the directional coupler  24 . Other antennas, such as, in particular, an H-field antenna, can be connected with the transmitter/receiver device to which the E-field antenna  14  is connected by way of the directional coupler  24 . In order to make adaptation of the E-field antenna  14  changeable, and thus to be able to adapt the E-field antenna  14  to changing emission and reception conditions, three capacitors  44  are disposed between the antenna line and ground, in switchable manner, in the example. In this connection, the capacitors  44  are structured so that they can be connected with the antenna line by way of switches, preferably transistors. A controller  54  receives a signal from the directional coupler  24 , which signal represents a measure of the adaptation of the antenna, particularly in the transmission case. The controller  54  strives to minimize the (power) signal received from the directional coupler  24 , or to lower it below a predetermined amount, in that it changes the antenna adaptation dynamically, by way of suitable switching signals for the switches disposed on the capacitors  44 . Of course, the exemplary embodiment is not restricted to a number of three capacitors  44 . It is advantageous if the capacitors  44  demonstrate capacitance values that increase in binary manner, so that the greatest possible number of different capacitance values can be combined from a minimal number of capacitors  44 . 
       FIG. 5  shows a second variant of an adaptation network. The second exemplary embodiment differs from the first in the manner in which the variable capacitance for adaptation is implemented. Fundamentally, it is also possible to combine the two variants with one another. The adaptation network of the second variant comprises a varactor diode  45 , which is switched between ground and a capacitor  65  in the cut-off direction. A second connector of the capacitor  65  is connected with the antenna line. The varactor diode  45  has a variable capacitance that depends on the amount of the cut-off voltage by way of the varactor diode  45 . The cut-off voltage, and thus the adaptation of the antenna, is set by the controller  55  as a function of the signal made available by the directional coupler  25 , which signal represents a measure of the adaptation of the antenna. The changeable cut-off voltage brings about a change in the capacitance of the varactor diode. The second inductance  75  serves to uncouple the high-frequency transmission or reception signal, respectively, from the direct voltage source disposed in the controller, which generates the cut-off voltage. 
       FIG. 6  shows a block schematic of a transmitter/receiver device having an adaptation network. The transmitter/receiver device comprises an RF circuit  96 , which contains a power amplifier to generate the transmission signal, among other things. The transmitter/receiver device is preferably switchable between a transmitting and a receiving mode, in half-duplex operation. Accordingly, the RF-circuit  96  also comprises switching components required for reception, such as a low-noise amplifier and the like. The transmission signal of the RF-circuit  96  is given to the adaptation network  86  by way of a measurement circuit  26 , which is preferably structured as a directional coupler. At the same time, the measurement circuit  26  generates a measurement signal for the controller  56 , which determines, using the measurement signal, how well the antenna  16  connected with the adaptation network  86  is adapted. The controller  56  generates suitable control signals for the RF-circuit  96  and the adaptation network  86 , in order to change the adaptation of the antenna in such a manner that the adaptation is optimized or brought to a specific value.