Antenna matching device

Abstract

The invention discloses an antenna matching device (20) comprising an antenna matching circuit (26), a load (24) and a contact (34) for connecting an antenna (30). The antenna matching circuit (26) is used to match a transmission signal (28) to an antenna (30), wherein the antenna matching circuit (26) outputs a matched transmission signal (32). The load (24) attenuates the matched transmission signal (32) such that an attenuated transmission signal (35) is provided at the contact (34), wherein the load (24) is inductively coupled in between the antenna matching circuit (26) and the contact (34) for connecting the antenna (30).

Description

[0001] Antenna matching device

[0002] Description

[0003] The invention relates to broadband data transmission in the shortwave range using antennas that are too short in relation to the transmission frequency.

[0004] Shortwave radios operate, for example, in the frequency range of 1.5–30 MHz. These are typically used, especially in maritime environments, i.e., on watercraft, particularly underwater vehicles, in combination with rod antennas (also known as vertical antennas) with lengths of 7–10 meters. The optimal length of the rod antenna corresponds to one-quarter of the wavelength (A / 4) of the transmitted signal. In the lower frequency range, the antennas are significantly shorter than A / 4 due to their physical length. In this case, rod antennas present impedances with high electrical Q factors. This high antenna Q factor, due to the Bode-Fano limit (a physical-technical relationship), results in an unavoidably narrow impedance matching.

[0005] For optimal power transmission from the transmitter to the antenna, an antenna tuning unit (ATU) with an antenna matching circuit is typically used. The antenna tuning unit is also referred to as an antenna matching device. The antenna matching circuit performs an impedance matching of the antenna to the 50 Q system impedance of the transmitter at the set operating frequency. In the lower frequency range, however, the high Q factor of the antenna impedance results in a narrowband match. This means that the available bandwidth, especially during transmission, is severely limited. For example, with a 7-meter whip antenna and a transmission frequency of 1.6 MHz, it is only about 8 kHz.

[0006] Current radio standards, such as MIL-STD 188-141 D and STANAG 4203 ED4, use signals in the 1.6–30 MHz range up to a bandwidth of 48 kHz. When transmitting a 48 kHz signal, a large portion of the transmission power would be reflected back at the ATU (Automated Transmission Unit) in the mismatched frequency range. This leads to an additional load on the transmitter's final stage and distortion of the transmitted signal. Large bandwidths are intended to allow the transmission of higher data rates of up to 240 kbit / s, surpassing existing communication methods such as teletype and telephony. This enables the use of other protocols such as IP (Internet Protocol) or FTP (File Transfer Protocol).

[0007] US 5,604,507 A shows an antenna with a front-mounted load for broadband tuning. It also discloses a resistive wire, which increases the electrical length of the antenna through the inductance it generates. The resistive component of the resistive wire increases the bandwidth. However, it does not represent inductive coupling (cf., for example, a transformer) of a load. Rather, the resistive wire itself forms an inductive and resistive load.

[0008] The object of the present invention is therefore to create an improved concept for antenna matching devices.

[0009] The problem is solved by the subject matter of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0010] Exemplary embodiments show an antenna matching device comprising an antenna matching circuit, a load, and a contact for connecting an antenna. The antenna matching circuit serves to adapt a transmitted signal to an antenna by means of the impedance matching described in the introduction. The antenna matching circuit outputs a matched, in particular impedance-transformed, transmitted signal. The load attenuates the matched transmitted signal, i.e., energy is extracted from the transmitted signal. At the contact, the antenna matching device provides the attenuated transmitted signal for transmission to the antenna. Furthermore, the load is inductively coupled between the antenna matching circuit and the contact for connecting the antenna. The idea is thus to widen the bandwidth of the transmission system (signal generator, antenna matching device, antenna) by deliberately introducing losses.This makes it possible to transmit broadband radio signals with a bandwidth of, for example, at least 48 kHz using rod antennas at low frequencies of, for example, 1.6 MHz. The distortion of the transmitted signal is so low that reliable data transmission is possible.

[0011] Inductive coupling introduces the losses between the antenna matching circuit and the antenna, resulting in the most undistorted frequency response possible. The antenna matching circuit and the antenna form a resonant circuit, which is coated by the load. Inductive coupling also offers further advantages. First, the load is subjected to a much lower voltage than if the resistor were placed directly in the circuit between the antenna matching circuit and the antenna connection. This allows the use of commercially available load resistors with good thermal coupling for cooling. Furthermore, inductive coupling eliminates the common-mode component, enabling the resistor to operate with respect to ground. Compared to a high-power resistor with cooling, the coils used for inductive coupling require significantly less installation space. This facilitates implementation in confined spaces (e.g., in enclosures, cabinets, etc.).(in the mast of a submarine).

[0012] In other words, the load is galvanically isolated from the antenna and the antenna matching circuit by inductive coupling. This has the advantage that the resistor is not exposed to the high voltages (common-mode voltages) in the antenna feed line (i.e., at the antenna contact). This would otherwise necessitate the use of special high-voltage resistors with low capacitive load and complex cooling. Such complex cooling typically introduces parasitic capacitances. Furthermore, the complex cooling can create space constraints. However, by coupling the load, a ground-referenced signal is now present, allowing the use of standard high-frequency load resistors, optionally with a standard heat sink. Inductive coupling can be achieved, for example, using two coupled coils. Such an arrangement of coils can also be described as a transformer.For inductive coupling, however, preferably no voltage transformation and therefore no resistance transformation takes place, but rather a 1:1 coupling occurs.

[0013] By selecting the appropriate inductance, a specific bandwidth can be achieved or predetermined for a given antenna and minimum transmission frequency. This allows the same load and the same (feed) line (e.g., coaxial cable) to be used for any antenna.

[0014] In further embodiments, a coil for inductive coupling (in particular the primary coil in the circuit between the antenna matching circuit and the antenna connection contact) has an inductance of less than 15 pH, preferably less than 10 pH, and more preferably less than 7 pH. Conventional transformers typically have a significantly higher inductance. Higher inductances reduce interference and improve the coupling between the coils. The advantage of the lower inductances is the reduced resulting capacitance, which would otherwise negatively affect the antenna matching device.

[0015] Preferably, both coils for inductive coupling have the same number of turns. Furthermore, both coils advantageously have the same inductance. Thus, the connected load is inductively coupled into the circuit between the antenna matching network and the antenna connection point without any (voltage) transformation. Using a coil arrangement with two coils of the same inductance and number of turns has the advantage that the turns of both coils can be wound on the same core. This arrangement is very small and therefore space-saving, which is advantageous for integration on watercraft, especially underwater vehicles.

[0016] In further embodiments, inductive coupling is achieved using two air-core coils. Preferably, the two coils are wound alternately on the same air core. This makes the best possible use of the limited available installation space. Particularly in submarines, but also on ships, the overall installation space of the antenna matching device is severely restricted due to the limited space available. Therefore, a small installation space for the antenna matching device is essential for practical integration, at least on watercraft. The core material "air" is advantageous for reducing losses due to the high field strengths in the coils compared to, for example, an iron core. Furthermore, air provides the necessary electrical insulation between the primary and secondary windings, as required here, especially when the windings of both coils are on the same (air) core.Furthermore, the low permittivity of air, i.e., its low electrical polarizability, ensures low stray capacitance between the windings. Excessive stray capacitance has a negative impact and distorts the signal.

[0017] Further embodiments show that the load is arranged separately from the antenna matching circuit. That is, the load can be located, for example, outside the housing of the antenna matching device, or at least away from other electronics that generate significant heat. This allows for simpler cooling or even eliminates the need for separate cooling altogether. In any case, the energy, and thus the heat, is dissipated to a designated location, preventing overheating of the antenna matching device. Furthermore, it is possible to relocate the generated heat, for example in a submarine, from the exterior to the interior, thereby reducing the submarine's thermal signature.

[0018] Preferably, the load can be connected remotely using a coaxial cable. The coaxial cable preferably has a characteristic impedance of 50 ohms. By using a coaxial cable with a characteristic impedance equal to the load impedance, the load can be operated remotely from the antenna matching circuit without any limitations. This reduces the thermal stress on the antenna matching circuit or antenna matching device. Therefore, when a 50-ohm coaxial cable is used, a (purely real) load, i.e., a resistive load, of 50 ohms is also advantageously used. 50 ohms is a popular choice because it corresponds to the most common impedance system in high-frequency technology.

[0019] In further embodiments, the antenna matching device has a switchable bypass, i.e., a bypass around the load, to disconnect the load so that the antenna matching circuit is connected to the antenna terminal without the load. This means the load can be switched on or off. The bypass can, for example, bridge the inductance for inductive coupling of the load. Thus, the antenna matching circuit can be designed for a wide frequency range, for example, a frequency range from 1.5 MHz to 30 MHz. However, with a selected antenna, for example, a 7-10 m whip antenna, it may be sufficient to attenuate the transmitted signal in the lower frequency range with the load. For example, it is sufficient to attenuate the transmitted signal in the frequency range up to 5 MHz, preferably up to 4 MHz, and more preferably up to 3.5 MHz when using a 7-10 m whip antenna.At higher frequencies, the desired bandwidth of more than 48 kHz is achieved even without attenuation of the transmitted signal, and the load can be bypassed. This means that no inductive coupling of the load occurs at these frequencies. Therefore, switching from a narrowband to a broadband transmission channel can be remotely controlled. The switching is accomplished by disabling or activating the bypass. Advantageously, the switching occurs in the lower frequency range (e.g., up to 5 MHz for the antenna described above). In the upper frequency range, high efficiency can be achieved in both the narrowband and broadband transmission channels, even without a load. The switching can be performed, for example, in the antenna matching network. Thus, higher efficiency can be achieved for narrowband applications with the bypass engaged.

[0020] Furthermore, a watercraft, in particular a manned submarine, comprising an antenna and the antenna matching device according to one of the preceding claims is disclosed, wherein the antenna is connected to the contact. Preferably, the antenna is a rod antenna with a length of 7-10 m. Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. They show:

[0021] Fig. 1 : a schematic circuit diagram of a system with an antenna matching device with a load connected in series with an antenna matching circuit;

[0022] Fig. 2: a schematic circuit diagram of a system with an antenna matching device with a load connected in parallel to an antenna matching circuit;

[0023] Fig. 3: a schematic circuit diagram of a system with an antenna matching device with a load inductively connected in a circuit between the antenna matching circuit and the contact for connecting the antenna;

[0024] Fig. 4: a schematic circuit diagram of a system with an antenna matching device with a load inductively connected in a circuit between the antenna matching circuit and the contact for connecting the antenna, wherein the load can be bypassed;

[0025] Fig. 5: a schematic representation of the system on a submarine as an example of a watercraft.

[0026] Before exemplary embodiments of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0027] Fig. 1 shows a schematic circuit diagram of a system 22 with an antenna matching device 20, which includes a load 24 and an antenna matching circuit 26. The load 24 is connected in series with the antenna matching circuit 26. The load 24 is represented as an ohmic resistor. The antenna matching circuit 26 serves to match a transmit signal 28 to an antenna 30, with the antenna matching circuit 26 outputting a matched transmit signal 32. The transmit signal 28 can be provided by a signal generator 33. The load 24 overlays the matched transmit signal 32. Thus, the antenna matching device 20 can provide an overlaid transmit signal 35 at a contact 34 for connecting the antenna 30. By overlaying the transmit signal, the bandwidth of the system 22 is increased.

[0028] In this application, a series resistor offers the advantage that a relatively low resistance value in the range of approximately 20-100 Ω is required for damping. A disadvantage of the series resistor is the high common-mode voltage it experiences during operation. Using 500 W of transmit power, this results in voltages of several kilovolts. Simultaneously, high losses occur in the resistor, necessitating adequate cooling.

[0029] Fig. 2 shows a schematic circuit diagram of system 22 in a further embodiment. In contrast to the representation in Fig. 1, the load 24 is not connected in series, but in parallel with the antenna matching circuit 26. A parallel resistor (to ground) with the same effect as the series resistor in Fig. 1 is in the range of 15–100 kΩ. This would significantly restrict the selection of suitable high-power resistors.

[0030] Fig. 3 reveals a schematic circuit diagram of a preferred embodiment of the system 22. In contrast to the embodiments shown in Fig. 1 and Fig. 2, the load 24 is inductively coupled between the antenna matching circuit 26 and the antenna 30. The inductive coupling avoids the disadvantages of connecting the load 24 in series and in parallel, as shown in the embodiments according to Fig. 1 and Fig. 2. The inductive coupling is achieved, for example, by means of two coupled coils 38. Such an arrangement of the coils can also be referred to as a transformer, whereby preferably no voltage transformation and thus no resistance transformation takes place, but rather a 1:1 coupling occurs.

[0031] The load 24 is arranged remotely from the antenna matching circuit 26 and optionally also remotely from the antenna matching device 20. A line 36, for example a coaxial cable, is used for this separation.

[0032] Fig. 4 shows a schematic circuit diagram of system 22 in a modified embodiment. In addition to the embodiment shown in Fig. 3, the antenna matching device has a bypass 40 with which the load 24 can be bypassed. The bypass 24 can be activated, for example, by means of two switches, a first switch 42 and a second switch 44. Switching the switches 42 and 44 disconnects the coils 38, so that the load 24 is no longer inductively coupled between the antenna matching circuit and the antenna. This means that the matched transmit signal 32, and not the vaporized transmit signal 35, is provided at contact 34. Suitable high-frequency relays, for example, can be used as switches.

[0033] Fig. 5: A schematic diagram of the antenna matching device 20 on a submarine 46 as an example of a watercraft. The submarine 46 dives below the water's surface 48 and travels, for example, at periscope depth. The antenna 30 is extended so that it can radiate above the water's surface 48.

[0034] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding method, such that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also constitute a description of a corresponding block, detail, or feature of a corresponding device. The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be readily apparent to those skilled in the art.Therefore, it is intended that the invention be limited only by the scope of protection of the following patent claims and not by the specific details presented herein by way of description and explanation of the exemplary embodiments.

[0035] Reference symbol list:

[0036] 20 Antenna matching device

[0037] 22 System 24 Last

[0038] 26 Antenna matching circuit

[0039] 28 transmission signal

[0040] 30 antenna

[0041] 32 adapted transmit signal 33 transmit signal generator

[0042] 34 Contact for connecting the antenna

[0043] 35 vaporized transmission signal

[0044] 36 Management

[0045] 38 coupled coils 40 bypass

[0046] 42 first switch

[0047] 44 second switch

[0048] 46 Watercraft

[0049] 48 Water surface

Claims

Patent claims 1. Antenna matching device (20) with the following features: - an antenna matching circuit (26) for matching a transmit signal (28) to an antenna (30), wherein the antenna matching circuit (26) outputs a matched transmit signal (32); - a load (24) to vaporize the adapted transmit signal (32); - a contact (34) for connecting an antenna (30), wherein the antenna matching device (20) is configured to provide a vapor-coated transmit signal (35) at the contact (34), wherein the load (24) is inductively coupled between the antenna matching circuit (26) and the contact (34) for connecting the antenna (30).

2. Antenna matching device (20) according to claim 1, wherein a coil (38) for inductive coupling has an inductance of less than 15pH, preferably less than 10pH, more preferably less than 7pH.

3. Antenna matching device (20) according to one of the preceding claims, wherein both coils (38) for inductive coupling have the same number of turns.

4. Antenna matching device (20) according to one of the preceding claims, wherein the inductive coupling is carried out by means of two air coils (38).

5. Antenna matching device (20) according to claim 4, wherein the two coils (38) are wound alternately on the same air core.

6. Antenna matching device (20) according to one of the preceding claims, wherein the load (24) is arranged remotely from the antenna matching circuit (26).

7. Antenna matching device (20) according to claim 6, wherein the load (24) is remotely connected by means of a coaxial cable (36).

8. Antenna matching device (20) according to one of the preceding claims, wherein the antenna matching device (20) has a switchable bypass (40) to disconnect the load (24) so ​​that the antenna matching circuit (26) is connected to the contact (34) for connecting the antenna without the load (24).

9. Antenna matching device (20) according to one of the preceding claims, wherein the load (24) has an ohmic resistance of 50 ohms.

10. Antenna matching device (20) according to one of the preceding claims, wherein the antenna matching circuit (26) is designed for a frequency range from 1.5 MHz to 30 MHz.

11. Antenna matching system (22) with the following features: - the antenna matching device (20) according to one of the preceding claims; - an antenna (30) which is connected to the contact (34) for connecting the antenna.

12. Antenna matching system (22) according to claim 11, wherein the antenna (30) is a rod antenna with a length of 7-10 m.

13. Watercraft (46) comprising the antenna matching system (22) according to one of claims 11 or 12.

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