Directional coupler for high frequency range

p0001The invention is based on a directional coupler for high-frequency range according to the preamble of claim 1.

p0002In high-frequency technology, in particular of radar technology, directional couplers are used in various applications, for example for coupling out a radio frequency signal (RF signal) or for coupling an RF calibration signal in a RF circuitry. For such applications, directional couplers are known which are carried out in different technologies, for example in<ul><li>so-called drop-in technique or</li><li>as tri-plate arrangements or</li><li>as waveguide coupler or</li><li>as coaxial couplers.</li></ul>

p0003Such couplers are generally constructed as discrete components and therefore spatially large and not cost-effective, especially in an industrial scale production of RF devices that must possess all the same electrical properties and must be physically small and mechanically robust. Such RF devices are, for example transmit / receive modules (T / R) modules for phased arrays. Such an antenna requires a large number, for example, several thousands of T / R modules, which must be arranged spatially close together, for example, at a pitch of about λ / 4, where λ the transmission / reception frequency, for example, several GHz means. It will be appreciated that such an arrangement has to be electrically highly accurately manufactured and adjusted, if a high-precision work of the antenna is required. For example, at each T / R module, at least one coupler which is inserted at a predetermined measurement point in the circuitry necessary to couple, for example, an RF signal for testing, calibration and / or measurement purposes. It is apparent that for suitable coupler also need to be highly accurate and also with each other must have the lowest possible predetermined tolerances of the electrical properties. However, this is at the couplers mentioned at best with a high degree of integration and reconciliation effort to reach, which cost unfavorable insbson-more in an industrial mass production.

p0004To avoid such drawbacks, it is natural to use couplers that are fully produced in integrated technology. Such a coupler includes a (main) waveguide, to which a further waveguide, for example, a λ / 4 waveguide, coupled, so that a pipe coupling occurs. In such couplers generally more passive components (reactances) are necessary to effect a proper coupling in or out of RF signals.

p0005Such couplers are therefore disadvantageously also technically complicated and therefore not cost-effective, especially for industrial scale production.

p0006The invention is therefore based on the object of specifying a generic coupler in a reproducible manner is economically and reliably produced with integrated line technology at predetermined tolerances of the electrical characteristics, particularly in an industrial mass production.

p0007This object is achieved by the features specified in the characterizing part of patent claim 1.

p0008Voreilhafte embodiments and / or embodiments of the invention are further claims.

p0009A first advantage of the invention is that the coupler is fully in line technology, such as microstrip technology which can be prepared which for the wavelength (frequency) is capable of guided signals. There are no discrete components required, which would otherwise be added to the circuit arrangement, for example by soldering, adhesive or bonding connections. This results advantageously not otherwise caused thereby electrical contact points at which disturbing reflections of the guided wave might occur.

p0010A second advantage is that virtually lossless coupler can be produced, that is, to the insulation path (isolation port) occurs almost no signal on that with an appropriate termination resistance (RF swamp) is otherwise converting heat to (loss). At the entrance occurs advantageously negligible reflection.

p0011A third advantage is that at high directivity (directivity) and high coupling attenuation are also wideband coupler manufactured.

p0012A fourth advantage is that no line coupling is present, so that no troublesome dispersion effects can occur.

p0013Further advantages result from the following description.

p0014The invention will in the following using an exemplary embodiment explained in more detail with reference to a figure schematically illustrated.

p0015The embodiment relates to a coupler in the high frequency range (X-band, that is 8 GHz to 12 GHz) for coupling an RF signal component in particular for testing, calibration and Meßzecke.

p0016The coupler is constructed completely in an appropriate for this frequency range microstrip line technology. The coupler advantageously has a, with respect to the ports P1 to P4, fully symmetrical construction, so that a coupler characterizing terms, such as through-path, coupling path, gate, insulated gate, can be selected. This is possible, for example, with the same so-called circuit layout of the coupler for flexible adaptation to other circuitry and / or layout requirements. For example, each of the four gates are used as insulated gate.

p0017In the example shown it is assumed that the port P1 is the input port, in which an RF input signal can be fed. The between the port P1 and the port P2 (output port) existing path is called a pass-through path. The between the ports P3 and P4 existing path is called a coupling path. Since the coupler is a so-called feedforward is used, there arises a coupled out signal (measuring signal) at the (coupling) port P3, which is explained in more detail. The port P4 is the insulated gate, at the most a negligible signal component leaks, which can be supplied as required in addition to an RF terminating resistor (RF swamp). Continuity and coupling path are microstrip waveguide. The coupling between these by means of a predetermined number of coupling capacitors C1 to C3, which are advantageously also be produced in microstrip Leitungstechnologle, for example, by a precisely predetermined line interruption (line gap) of a corresponding waveguide.

p0018According to the figure, both the continuity and the coupling path comprising a series circuit of in each case an input conductor LE which is adjacent in each case to a gate P1 to P4, and a predetermined number of λ / 4 waveguides L4 which the electrical length of λ / 4 possess, wherein λ is the wavelength of the guided wave means. arising on the mentioned between Leitungsbschnitten LE, L4, L4, LE connection points VP, who are trained in management technology, for example, as so-called T-pieces, the coupling capacitors C1 to C3 are arranged between the paths.

p0019If now in the entrance P1 an RF signal (incident line wave) coupled, so this is passed through the through path to output port P2. In addition, via the coupling capacitors C1 to C3, an excitation of a line shaft in the coupling path. This line shaft can in principle propagate in the coupling path in two opposite directions, namely in the forward direction shown by the numeral 2, desired, that is, from the isolated port P4 in the direction of the (coupling) gate P3 (ie parallel to the direction of propagation of the Goal P1 incident line wave) or in the opposite thereto, unwanted reverse direction, which is represented by the numeral 1, that is, before the (coupling) port P3 in the direction of the insulated gate P4. Due to the described arrangement, it is achieved that all propagating in the forward direction 2 in the coupling path line waves overlap advantageously constructive, that is, between these is essentially a phase difference of 0 °. By contrast exists between the means of the coupling capacitors C1 to C3 coupled line waves that propagate in the reverse direction 1, always a phase difference of substantially 180 °, that is, there arises a destructive interference. The current in the reverse direction 1 line waves cancel each other (by interference) therefore mutually exclusive, so that at most a negligible signal component occurring at your isolated port P4.

p0020Due to the described symmetrical structure of the coupler, it can be seen that are excited by the guided in Vorwärtsrlchtung 2 in the coupling path line wave of these in turn guide waves in the passage path. This can now also vorteihafterweise superimpose constructively only in the direction of propagation of the incident wave line due to the symmetrical structure, that is, only to the (output) port P2 emerge. On the (input) port P1 can also most a negligible signal component emerge. This is generally referred to as a reflected portion.

p0021It is seen that the disengageable maximum at the (coupling) port P3 performance, which is characterized in the literature also by the so-called coupling loss, the capacity of the coupling capacitors C1 to C3 is dependent.

p0022By the number of stages of the coupler relative whose (frequency) bandwidth is adjustable. It is a step, which is outlined in phantom in the figure, each consisting of a λ / 4-line piece (in any path) and an associated coupling capacitor. The relative bandwidth becomes larger as the number of stages is increased.

p0023It is evident that the dimensioning of the components (piping elements LE, L4 and coupling capacitors), among others, the absolute value of the (coupling) Goal shown depends P3 coupled out performance. A precise dimensioning of the components is possible by means of a skilled worker network computing.

p0024Such couplers can be characterized by the relative sizes (relative) bandwidth, coupling attenuation (ratio of the (coupling) port P3 decoupled power to the (input) port P1 eingekoppleten performance) and directivity = 1 / directivity. The directivity refers to the ratio of the (coupling) port P3 decoupled power to the isolated port P4 coupled out performance.

p0025With the described arrangement, that is, three coupling capacitors C1 to C3, and two λ / 4 lines L4 in each path, for example in microstrip technology, a coupler produced, the X-band (8 GHz to 12 GHz) a relative bandwidth has about 20% and a directivity of more than 30 dB with a coupling attenuation of approximately 30 dB.

p0026Such couplers are therefore currently customary advantageously in UHF technology integrated circuits, for example, so-called MIC (Microwave Integrated Circuits) and MMIC (Monolithic Microwave Integrated Circuits) can be implemented. therefore advantageously otherwise required additional discrete components are avoided, thereby significantly lowering the manufacturing cost (coaxial couplers for example). In addition, such couplers are mechanically robust (insensitive to shock loading), reliable and reproducible manner, that is, within a predetermined tolerance range of the regulation by electric characteristics, particularly in an industrial mass production.

p0027The invention is not limited to the example described, but apply mutatis mutandis to other. So it is a skilled worker to transpose the arrangement shown in the figure by means of network theory, for example, in almost every Freuenzbereich.