EP1672735A1 - Antenna including magnetic and capacitive radiator - Google Patents

Abstract

The antenna has a combination of a magnetic beam (7, 20, 22) with a capacitive emitter (17a, 17b). The capacitive emitters are attached at the periphery of the magnetic emitters. A constructional structure is provided by a symmetry plane for an energy feeding input of a capacitive emitter and a magnetic emitter as well as a tunable auxiliary capacity. The energy feeding input and the auxiliary capacity and a co-ordination device are not in a symmetric plane to the auxiliary capacity.

Description

Technical area

The invention relates to an antenna, in particular a transmitting antenna.

Object of the invention

The object of the invention is to provide an antenna, in particular a transmitting antenna, with a good efficiency with small geometric dimensions.

Solution of the task

The object is achieved by a combination of at least one magnetic radiator with at least one capacitive radiator, which radiates predominantly the electric field. In a preferred embodiment, one of the capacitive radiators is connected to the periphery of one of the magnetic radiators.

A typical capacitive emitter (capacitive antenna) 1 is shown in FIG . The capacitive radiator 1 has two radiation arms 3a and 3b and two spacers 5a and 5b leading to the radiation arms 3a and 3b . A power supply takes place at the terminals 6a and 6b at the ends of the spacers 5a and 5b facing away from the radiation arms 3a and 3b . The electrical equivalent circuit of this capacitive radiator 1 shown in FIG 2. The equivalent circuit includes a switched with a radiation resistance R _E in series capacitance C _E.

Dipole or monopole antennas that predominantly emit an electric field are often used in a truncated form by shortening the radiation arms to a fraction of the optimum length (e.g., 1/10 of a wavelength). Such shortened radiation arms result in a high, capacitive input impedance.

The adaptation of capacitive emitters to a conventional 50 ohm coaxial cable requires an unrepresented matching network, which usually consists of coils and capacitors. Since coils can not be produced lossless, the efficiency is reduced by heat losses in the coil sometimes considerably.

A typical magnetic radiator (magnetic antenna) 7 is shown in FIG . The magnetic emitter 7 comprises a coil with preferably a single turn 9 and an adjustable capacitor 11 for a frequency tuning and a small coupling loop 13 for a power supply. To the two terminals 14a and 14b of the coupling loop 13 , a coaxial cable, not shown, or other high-frequency conductor is connected. The magnetic radiator works in resonance, ie the exact frequency must be adjusted by means of the capacitor 11 . A frequency range results from the maximum and minimum capacitance of the capacitor 11.

In Figure 4 , the electrical equivalent circuit diagram of the magnetic radiator 7 is shown. The equivalent circuit diagram shows a parallel resonant circuit consisting of an inductance L, a capacitance C, a radiation resistance R _M and a loss resistance R _V. In many cases, R _V is greater than R _M. This reduces the efficiency significantly. In addition, for many applications, the narrow working bandwidth of the magnetic radiator 7 is disadvantageous, ie the capacitor 11 must also be readjusted even with small frequency changes.

As already stated above, a combination of a magnetic radiator with a capacitive radiator is now carried out according to the invention.

Preferably, the capacitive radiator will be arranged at the periphery of the magnetic radiator. A preferred location results in a connection of the capacitive radiator in the region of the capacitor of the magnetic radiator. The capacitive radiator is then fed with the RF voltage (high frequency voltage) applied to the capacitor. In simple terms, the magnetic emitter makes an impedance matching for the radiation arms of the coupled electric radiator. The impedance matching is then dependent on the electrical distance from the Energieeinkopplungsort the magnetic radiator. Of course, a connection (coupling) of the electric radiator also at other locations of the periphery, mostly consisting of only one turn wire loop of the magnetic radiator, take place.

Preferably, the electric radiator, i. arrange its radiation arms in the immediate vicinity of the connection point of the capacitor of the magnetic radiator, wherein the concept of immediate proximity is usually dictated by design constraints. It should be noted, however, that a distance from the effective capacitance is at most λ / 16, where λ is the wavelength of the frequency to be radiated. The closer the electric radiation arms are arranged to the capacitor, the better is a coupling to the electric radiator and the smaller geometric dimensions can be selected at the same frequency.

Preferably, the radiation arms of the capacitive beam will be arranged lying in mutually parallel planes. These parallel planes can be placed parallel to the plane of the magnetic emitter. All radiation elements can also be arranged in a single plane. As explained below, an optimization of a forward / reverse ratio can then be achieved by an appropriate selection of the geometric dimensions of the magnetic and the capacitive radiator, resulting in a directional antenna.

By a capacitive load of the Strahlungsarmenden (Endkapazitäten) also a shortening of the radiation arms can be achieved.

Further advantages and variants of the inventive antenna will be apparent from the following detailed description.

Brief description of the drawings

Fig. 1

einen typischen kapazitiven Strahler,

Fig. 2

ein elektrisches Ersatzschaltbild des in Figur 1 dargestellten kapazitiven Strahlers,

Fig: 3

einen typischen magnetischen Strahler,

Fig. 4

ein elektrisches Ersatzschaltbild des in Figur 3 dargestellten magnetischen Strahlers,

Fig. 5

eine Ausführungsform einer erfindungsgemässen Antenne,

Fig. 6

ein elektrisches Ersatzschaltbild zu der in Figur 5 gezeigten Antenne,

Fig. 7

ein zum Ersatzschaltbild in Figur 6 modifiziertes, elektrisches Ersatzschaltbild,

Fig. 8

ein Strahlungsfeld im Fernfeld links und rechts eines kapazitiven Strahlers mit dem in der Papierebene liegenden Strahlungsarmen 29a und 29b in perspektivischer Darstellung mit den elektrischen Feldvektoren E _K (in der Papierebene) und den magnetischen Feldvektoren B _K1 und B _K2 (senkrecht nach vorne und nach hinten zur Papierebene stehend),

Fig. 9

ein Strahlungsfeld im Fernfeld links und rechts eines magnetischen Strahlers, dessen Windung in der Papierebene liegt, in perspektivischer Darstellung mit den elektrischen Feldvektoren E _M1 und E _M2 in der Papierebene sowie den magnetischen Feldvektor B _M senkrecht aus der Papierebene nach vorne stehend,

Fig. 10

ein Ausführungsbeispiel zu der in Figur 5 erklärten Antenne,

Fig. 11

ein Diagramm für ein Leistungsverhältnis P _E / P _M von abgestrahlter elektrischer P _E zu magnetischer Leistung P _M in Abhängigkeit von einer auf die Wellenlänge λ normierten wirksamen Länge ℓ der beiden kapazitiven Strahler bei einer Antennenresonanzfrequenz vom 14 MHz, gemäss Ausführungsbeispiel,

Fig. 12

ein Diagramm für einen Antennenwirkungsgrad W über einer normierten Strahlerlänge ℓ/λ einer auch dem Diagramm in Figur 11 zugrunde gelegten Antenne,

Fig. 13

ein Diagramm für eine Bandbreite B in Kilohertz über einer normierten Strahlerlänge ℓ / λ einer auch dem Diagramm in Figur 11 zugrunde gelegten Antenne,

Fig. 14

eine Variante des kapazitiven Strahlers einer in Figur 5 dargestellten Antenne,

Fig. 15

eine weitere Variante zu der in Figur 14 dargestellten Antenne,

Fig. 16

eine weitere Antennenvariante mit gegenüber Figur 10 anders angeordneten kapazitiven Strahlern,

Fig. 17

eine Antennenvariante zu der in Figur 16 gezeigten Antenne mit kapazitiven Strahlern, welche einen Winkel von 90° miteinander einschliessen,

Fig. 18

eine Antennenvariante zu der in Figur 5 dargestellten Antenne, wobei die beiden kapazitiven Strahler weder parallel zueinander angeordnet sind, noch miteinander fluchten,

Fig. 19

eine Antennenvariante zu der in Figur 17 dargestellten Antenne, wobei die beiden kapazitiven Strahler als Seitenverlängerung einer quadratischen Windung des magnetischen Strahlers ausgebildet sind und miteinander fluchten,

Fig. 20

eine Ausführungsvariante zur Antennendarstellung in Figur 16, wobei die beiden kapazitiven Strahler in einer Ebene senkrecht zur Ebene des magnetischen Strahlers liegen,

Fig. 21

eine Ausführungsvariante zur Antennendarstellung in Figur 16, wobei jeder kapazitive Strahler in einer voneinander distanzierten parallelen Ebene liegt, zu denen mittig der magnetische Strahler angeordnet ist,

Fig. 22

eine Antennenausführungsvariante für eine Antennenanordnung als sogenannte gedruckte Schaltung,

Fig. 23

eine Skizze, in der mögliche Anschlussorte eines kapazitiven Strahlers an einen magnetischen Strahler aufgezeigt werden,

Fig. 24

eine schematische Darstellung einer p-förmig ausgebildeten Antenne und

Fig. 25

eine Ansicht in Blickrichtung XXV der in Figur 24 dargestellten Antenne in technischer Ausführung.

The drawings used to explain the embodiments show in

Fig. 1

a typical capacitive radiator,

Fig. 2

an electrical equivalent circuit diagram of the capacitive radiator shown in Figure 1 ,

Fig. 3

a typical magnetic emitter,

Fig. 4

an electrical equivalent circuit diagram of the magnetic radiator shown in Figure 3 ,

Fig. 5

an embodiment of an inventive antenna,

Fig. 6

an electrical equivalent circuit diagram to the antenna shown in Figure 5 ,

Fig. 7

1 to the equivalent circuit diagram in Figure 6 modified, electrical equivalent circuit diagram,

Fig. 8

a radiation field in the far field left and right of a capacitive radiator with the lying in the paper plane radiation arms 29a and 29b in perspective view with the electric field vectors E _K (in the paper plane) and the magnetic field vectors B _K1 and B _K2 (perpendicular to the front and back to the plane of the paper),

Fig. 9

a radiation field in the far field to the left and right of a magnetic radiator whose winding lies in the plane of the paper, in perspective view with the electric field vectors E _M1 and E _M2 in the plane of the paper, and the magnetic field vector B _M perpendicular to the plane of the paper,

Fig. 10

an embodiment of the explained in Figure 5 antenna,

Fig. 11

a diagram for a power ratio P _E / P _M of radiated electrical P _E to magnetic power P _M as a function of a normalized to the wavelength λ effective length ℓ of the two capacitive radiator at a Antennenresonanzfrequenz of 14 MHz, according to the embodiment,

Fig. 12

a diagram for an antenna efficiency W over a normalized radiator length l / λ of an antenna also based on the diagram in Figure 11 ,

Fig. 13

a diagram for a bandwidth B in kilohertz over a normalized radiator length l / λ of an antenna also based on the diagram in FIG. 11 ,

Fig. 14

a variant of the capacitive radiator of an antenna shown in Figure 5 ,

Fig. 15

another variant of the antenna shown in Figure 14 ,

Fig. 16

a further antenna variant with respect to Figure 10 differently arranged capacitive radiators,

Fig. 17

an antenna variant to the antenna shown in Figure 16 with capacitive radiators, which enclose an angle of 90 ° with each other,

Fig. 18

an antenna variant to the antenna shown in Figure 5 , wherein the two capacitive radiators are arranged neither parallel to each other, nor aligned,

Fig. 19

an antenna variant to the antenna shown in Figure 17 , wherein the two capacitive radiators are designed as a side extension of a square turn of the magnetic radiator and aligned with each other,

Fig. 20

FIG. 16 shows a variant embodiment for the representation of the antenna , wherein the two capacitive radiators lie in a plane perpendicular to the plane of the magnetic radiator,

Fig. 21

16 shows an embodiment variant for the representation of the antenna , wherein each capacitive radiator lies in a mutually distant parallel plane, to which the magnetic radiator is arranged centrally,

Fig. 22

an antenna embodiment variant for an antenna arrangement as a so-called printed circuit,

Fig. 23

a sketch in which possible connection locations of a capacitive radiator to a magnetic radiator are shown,

Fig. 24

a schematic representation of a p-shaped antenna and

Fig. 25

a view in the direction of XXV of the antenna shown in Figure 24 in a technical design.

Ways to carry out the invention

The inventive antenna 15 shown in Figure 5 in one embodiment is a combination of a magnetic radiator with a capacitive radiator. The antenna 15 has two capacitive radiation arms 17a and 17b, two spacers 19a and 19b, a capacitor 22 adjustable in its capacitance value , a single circular turn 20 and a power input 21. The energy coupling 21 has two connections 23a and 23b . One of the ports 23b is preferably earthed here. The energy coupling 21 is electrically connected to a location 24 that can be set on the winding 20 . The two terminals 23a and 23b are usually connected to a coaxial cable, through which the transmission power is supplied. Concerning an optimal position of the coupling-in location 24 further details are given below.

The radiation arms 17a and 17b are electrically connected via a spacer 19a and 19b in the vicinity of the capacitor 22 located in the winding 20 with one of its terminals, so that they are supplied with the RF voltage present there. One end of each spacer 19a or 19b is electrically connected to the wire loop 20 and the other end is galvanically connected to one end of each radiation arm 17a or 17b at an angle of 90 °. The radiation arms 17a and 17b, the spacers 19a and 19b and the wire loop 20 lie here in one and the same plane, wherein the two radiation arms 17a and 17b are aligned with each other.

FIG. 6 shows an electrical equivalent circuit 25 to the antenna 15 shown in FIG. 5. The equivalent circuit 25 includes an inductance L with only one single turn 20. Further, the equivalent circuit 25 has a capacitance C of the capacitor 22, a capacitance C _{E of} the radiation arms 17a and 17b, a radiation resistance R _{E of} the capacitive Emitter, a radiation resistance R _{M of} the magnetic radiator and a loss resistance R _{V of} the entire antenna 15 on. The magnetic antenna, as a part of this combination ( Figure 5 ), fulfills a dual function: it emits a magnetic field and at the same time it transforms the RF voltage for the capacitive emitter, which radiates an electric field.

Figure 7 shows a map used, modified, electric for the subsequent estimates equivalent circuit diagram 27 that has emerged with the subsequent transformations of the illustrated in Fi gure 6 equivalent circuit diagram of the 25th The elements C _E , C, R _M and R _V have remained the same in the two equivalent circuit diagrams 25 and 27 . The resistance R _E ' is the transformed into a magnetic part of the antenna 15 radiation resistance R _{E of} the capacitive radiator.

A current i in the magnetic circuit of the antenna 15 is divided according to the equivalent circuit diagram 25 in FIG. 6 into the two partial currents i ₁ and i ₂ $$\mathrm{i}={\mathrm{i}}_1+{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}_2,$$

A capacitive reactance X _{C of} the capacitor 26 with the capacitance C results at a resonance frequency f $${\mathrm{X}}_{\mathrm{C}}=1/\left(2\cdot \mathrm{\pi }\cdot \mathrm{f}\cdot \mathrm{C}\right),$$

A capacitive reactance X _{CE of} the capacitive radiator with the radiation arms 17a and 17b with the capacitance C _E results at the resonance frequency f $${\mathrm{X}}_{\mathrm{C}\mathrm{e}}=1/\left(2\cdot \mathrm{\pi }\cdot \mathrm{f}\cdot {\mathrm{C}}_{\mathrm{e}}\right),$$

For the flowing in the capacitor 26 current i ₁ applies at a lying over the capacitor 26 voltage u $${\mathrm{i}}_{}$$$${\mathrm{}}_1=\mathrm{u}/{\mathrm{X}}_{\mathrm{C}},$$

In a capacitive emitter short in a variant radiation arms 17a and 17b of the capacitive reactance X _C is much larger than the radiation resistance R _E.

For the current i ₂ in the capacitive radiator is approximately $${\mathrm{i}}_2=\mathrm{u}/{\mathrm{X}}_{\mathrm{C}\mathrm{e}},$$

By dividing the above equations for the currents i ₁ and i ₂ , the voltage u can be eliminated: $${\mathrm{i}}_1/{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}_2={\mathrm{X}}_{\mathrm{C}\mathrm{e}}/{\mathrm{X}}_{\mathrm{C}},$$

If the current i _{1 is} eliminated using equation (1) in equation (2), the current i _{2 is obtained} $${\mathrm{i}}_2=\mathrm{i}\cdot 1/\left[\left({\mathrm{X}}_{\mathrm{C}\mathrm{e}}/{\mathrm{X}}_{\mathrm{C}}\right)+1\right],$$

oder $${\mathrm{P}}_{\mathrm{E}}={\mathrm{i}}^2\cdot {{\mathrm{R}}^{\prime }}_{\mathrm{E}}\mathrm{\hspace{0.17em}}\mathrm{mit}\mathrm{\hspace{0.17em}}{{\mathrm{R}}^{\prime }}_{\mathrm{E}}=1/{\left[\left({\mathrm{X}}_{\mathrm{C}\mathrm{E}}/{\mathrm{X}}_{\mathrm{C}}\right)+1\right]}^2\cdot {\mathrm{R}}_{\mathrm{E}}.$$

This results in a radiated electric power P _E through the capacitive radiator $${\mathrm{P}}_{\mathrm{e}}={\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}_2^2\cdot {\mathrm{R}}_{\mathrm{e}}={\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot 1/{\left(\left({\mathrm{X}}_{\mathrm{C}\mathrm{e}}/{\mathrm{X}}_{\mathrm{C}}\right)+1\right)}^2\cdot {\mathrm{R}}_{\mathrm{e}}$$

or $${\mathrm{P}}_{\mathrm{e}}={\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot {{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}\mathrm{}\mathrm{With}\mathrm{}{{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}=1/{\left[\left({\mathrm{X}}_{\mathrm{C}\mathrm{e}}/{\mathrm{X}}_{\mathrm{C}}\right)+1\right]}^2\cdot {\mathrm{R}}_{\mathrm{e}},$$

R _E ' is shown in the equivalent circuit shown in Figure 7 . The current i flows through the transformed radiation resistance R _E ' and emits the same electrical power as the radiation resistance R _E shown in the equivalent circuit diagram in FIG. 6 , through which the current i ₂ flows.

Magnetic power output P _M is provided by the magnetic radiator formed by the winding 20 and the capacitor 22 .

With respect to the radiated electric power P _E in relation to the radiated magnetic power P _M applies $${\mathrm{P}}_{\mathrm{e}}/{\mathrm{P}}_{\mathrm{M}}=\left({\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot {{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}\right)/\left({\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot {\mathrm{R}}_{\mathrm{M}}\right)={{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}/{\mathrm{R}}_{\mathrm{M}}.$$

The antenna according to the invention, although containing a magnetic radiator, has a higher efficiency W and a larger bandwidth B compared to a "pure" magnetic radiator, as explained below, and can also produce a directional effect with a suitable choice of the antenna geometry. The ratio P _E / P _M increases with the length L of the capacitive radiator. In one particular length L of the capacitive radiator R _e '= R _M, is then P _E / P _M = 1, that is, the magnetically radiated power P _M is equal to the electrically radiated power P _E. The antenna 15 generates in this case a straightening effect (see embodiment).

The straightening effect of the antenna 15 according to the invention will be explained with reference to FIGS. 8 and 9 . FIG. 8 shows the electric and the magnetic radiation field E _K and B _K in the far field of a capacitive radiator with the radiation arms 29a and 29b, which lie in the plane of the paper. The electric far field to the left and right of the radiation arms 29a and 29b lies in the snapshot shown here in the plane of the paper, with the electric field E _K on the left as well as on the right side still pointing up. The far-field magnetic vectors B _k1 and B _K2 , generated by the two radiation arms 29a and 29b of the capacitive radiator, are pointing to the left side perpendicular to the plane of the paper (B _K1 ) and pointing to the right perpendicular to the plane of the paper (B _K2 ).

FIG. 9 shows a representation analogous to FIG. 8 , but for a magnetic radiator whose winding 31 lies in the plane of the paper. To the right of the turn 31 , the far-field electric vector E _M2 lies upward in the plane of the paper and on the left side of the turn 31 the far-field electric vector E _M1 lies down in the plane of the paper.

The magnetic far field vectors B _{M of} the magnetic radiator are both perpendicular to the paper plane and point to the front.

• Auf der linken Seite des elektrischen und des magnetischen Strahlers gilt nun für die Fernfeldstärke
  EK - EM1 und BK1 - BM
  und auf der rechten Seite des elektrischen und des magnetischen Strahlers gilt nun für die Fernfeldstärke
  EK + EM2 und BK2 + BM.

Since here an electric and a magnetic emitter work together, a superimposition of the far-field vectors shown in FIGS. 8 and 9 is to be carried out:

• On the left side of the electric and magnetic radiators now applies to the far field strength
  EK - EM1 and BK1 - BM
  and on the right side of the electric and magnetic radiators now applies to the far field strength
  EK + EM2 and BK2 + BM.

In a special case where the capacitive and magnetic radiators emit the same power, the radiation vectors on the right side of the antenna (y-direction in the paper plane) double and on the left side they compensate each other.

The inventive antenna, which is composed of a combination of a magnetic and a capacitive radiator, is a directional antenna.

Calculate the efficiency

The efficiency W is given by $$\begin{array}{l}\mathrm{W}={\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot \left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}\right)/\left[{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="imgf0004.png"\; state="\{\{state\}\}">i</figure-callout>}}^2\cdot \left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)\right]\\ \mathrm{W}=\left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}\right)/\left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right),\end{array}$$

The efficiency increases with the length of the capacitive radiators 17a and 17b or 29a and 29b.

The bandwidth B results from a Q-factor Q according to the following relationship $$\mathrm{B}=\mathrm{f}/\mathrm{Q},$$

If X _CE >> X _C , the Q can be approximately calculated with $$\mathrm{Q}={\mathrm{X}}_{\mathrm{C}}/\left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right),$$

This gives the bandwidth B to $$\mathrm{B}=\mathrm{f}/\mathrm{Q}=\mathrm{f}\cdot \left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/{\mathrm{X}}_{\mathrm{C}},$$

oder $$\mathrm{B}={\mathrm{B}}_0\cdot \left({{\mathrm{R}}^{\prime }}_{\mathrm{E}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/\left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)$$

mit $${\mathrm{B}}_0=\mathrm{f}\cdot \left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/{\mathrm{X}}_{\mathrm{C}},$$

wobei B ₀ die Bandbreite der rein magnetischen Antenne ohne die kapazitiven Strahler ist. Die Bandbreite B vergrössert sich mit der Länge der kapazitiven Strahler.Extended with (R _M + R _V ) and reshaped results $$\mathrm{B}=\mathrm{f}\cdot \left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/{\mathrm{X}}_{\mathrm{C}}\cdot \left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/\left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)$$

or $$\mathrm{B}={\mathrm{B}}_0\cdot \left({{\mathrm{R}}^{\text{'}}}_{\mathrm{e}}+{\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/\left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)$$

With $${\mathrm{B}}_0=\mathrm{f}\cdot \left({\mathrm{R}}_{\mathrm{M}}+{\mathrm{R}}_{\mathrm{V}}\right)/{\mathrm{X}}_{\mathrm{C}}.$$

where B _{0 is} the bandwidth of the purely magnetic antenna without the capacitive radiators. The bandwidth B increases with the length of the capacitive radiator.

Instead of the galvanic connection, as stated above, the wire loop 20 with the two capacitive radiation arms 17a and 17b via the spacers 19a and 19b , a capacitive connection can be made for example by an insulating bushing. Such a connection is chosen if this is to be potential-free.

If the antenna 15 is to be used only for a narrow frequency band, for example, the rotary capacitor 22 may be omitted. The resonant frequency is then determined substantially by the capacitance C _{E of} the capacitive radiators 17a and 17b and the capacitance formed by the spacers. A slight frequency variation is possible when the capacitance C _{E is} due to a change in the dimensions of the electrical Emitter 17a and 17b or their position is changed. In this case, it is recommended to provide a mechanical adjustment of the capacitive radiator.

Underpinning the above embodiments is made with the following embodiment. An antenna 35 as a variant of the antenna 15 has a square frame 37 with a side length of 75 cm; gives a circumference of 3 m. Each frame side 39a to 39d has an L-shaped aluminum profile, the aluminum having a material thickness of 2 mm and the profile having flanges with dimensions of 50 mm and 30 mm, respectively. The frame acts as a single turn of the magnetic sub-antenna. In the frame 37 , a variable capacitor 40 is used analogously to the capacitance 22 . The variable capacitor 40 can be set in a capacitance range of 10 pF to 65 pF, whereby the antenna 35 receives an adjustable frequency range of 14 MHz to 30 MHz. For the calculation example, a capacitance value of the rotating capacitor 40 of 65 pF is selected, resulting in a resonance frequency f of 14 MHz.

The capacitive radiators 41a and 41b analogously to the capacitive radiators 17a and 17b are made of an aluminum profile with a respective length of 1.1 m. This results in a radiator length of 2.2 m. The two radiators 41a and 41b were connected next to the rotary capacitor 40 by means of two spacers 43a and 43b (each 15 cm) also made of aluminum. A loss resistance R _{V of} this antenna 35 has been determined from the measurement of the bandwidth B _{0 of} the purely magnetic antenna (frame 37 with rotary capacitor 40, without the two capacitive radiators 41 a and 41 b) to R _V = 0.15 Ω. For the representation in the diagrams, the total length l of the capacitive radiators was varied within a range of 0 to 4 m.

$${\mathrm{R}}_{\mathrm{M}}=197\cdot {\left(\mathrm{Umfang\; des\; magnetischen\; Strahlers}/\mathrm{\lambda }\right)}^4=197\cdot {\left(3/21,4\right)}^4=0,076\mathrm{\hspace{0.17em}}\mathrm{\Omega }$$

$${\mathrm{X}}_{\mathrm{C}\mathrm{E}}=\mathrm{Mittlere\; Wellenimpedanz}/\tan \left(\mathrm{\pi }\cdot \ell /\mathrm{\lambda }\right)=400/\tan \left(3,14\cdot \ell /21,4\right)$$

The radiation resistance R _{E of} the capacitive radiator, the radiation resistance R _{M of} the magnetic radiator and the capacitive reactance X _{CE of} the capacitive radiator can be calculated by means of known formulas of the antenna technology as follows (see, for example, Rothammel, Antennenbuch, DARC-Verlag, 12th edition, pages 73, 333 and 429-431): $${\mathrm{R}}_{\mathrm{e}}=197\cdot {\left(\mathrm{Total\; length\; of\; the\; cape},\mathrm{}\mathrm{spotlight}/\mathrm{\lambda }\right)}^2=197\cdot {\left(\ell /21.4\right)}^2$$

$${\mathrm{R}}_{\mathrm{M}}=197\cdot {\left(\mathrm{Circumference\; of\; the\; magnetic\; radiator}/\mathrm{\lambda }\right)}^4=197\cdot {\left(3/21.4\right)}^4=0.076\mathrm{}\mathrm{\Omega }$$

$${\mathrm{X}}_{\mathrm{C}\mathrm{e}}=\mathrm{Medium\; wave\; impedance}/\tan \left(\mathrm{\pi }\cdot \ell /\mathrm{\lambda }\right)=400/\tan \left(3.14\cdot \ell /21.4\right)$$

By means of the formulas (3), (4), (5) and (6), P _E / P _M , W, B can be calculated as a function of the length l of the capacitive radiators. ℓ / λ P _E / P _M W B [kHz] 0 0 0.34 18 0.05 0.03 0.34 18 0.1 0.4 0.41 21 0.15 1.94 0.6 30 0.2 9.06 0.78 55

The results of the calculations are shown graphically in the diagrams of FIGS. 11, 12 and 13 .

FIG. 11 shows the influence of an effective length ℓ of the two capacitive radiators 17a and 17b together with respect to the wavelength λ of a resonance frequency of 14 MHz of the antenna 35. The ordinate shows the ratio of radiated electrical to radiated magnetic power P _E / P _M , As might be expected, the value of the power ratio of P _E / P _{M increases} disproportionately with the length ℓ of the radiator arms.

Figure 11 can be interpreted as follows: If the capacitive radiators 17a and 17b are zero in length, only magnetic power is radiated (P _E = 0). The longer the capacitive radiators are designed λ compared to the wavelength 17a and 17b, the higher the proportion of the electrically radiated power P _E is. If P _E / P _M = 1, the same amount of electrical and magnetic power is radiated; this is the case for a length ℓ / λ = 0.124 (dashed line in FIG. 11) . With this radiator length, the antenna produces an optimal directivity (maximum directivity). The manufactured antenna almost fulfilled this condition. Measurements showed a forward / reverse ratio of about 12 db.

The efficiency W and the bandwidth B in kilohertz of an antenna 35 described above as a function of a radiator length ℓ / λ standardized here also to the wavelength λ is shown in FIGS. 12 and 13 . Both curves increase disproportionately over the length ℓ.

In FIGS. 14 and 15 , antenna variants 44 and 46 are shown with respect to the antenna 15 shown in FIG . The capacitive radiators, here designated 45a and 45b or 47a and 47b , can be shortened, in which, as indicated in FIG. 14 , an end plate 49a or 49b is arranged at the respective end of the radiator 45a or 45b . Preferably, this plate 49a or 49b will be circular in shape; but it can also be used a different contour. In Figure 14 , both plates 49a and 49b are formed identically. It However, differently shaped plates can be used and thus the lengths of the two capacitive radiators are formed differently long.

Instead of the end plates 49a and 49b , the capacitive radiators 47a and 47b can, as indicated in FIG. 15 , also be changed in their circumference, here thickened. Preferably, the thickenings will form a circular cylinder. However, other shapes, such as plates arranged in a rod longitudinal direction, may be used.

The capacitive radiators 17a / b, 41a / b, 45a / b and 47a / b in FIGS. 5, 10, 14 and 15 are always located on the outside of the turns 20, 37, 50 and 51 of the magnetic radiator. That does not have to be that way. A radiation arm 53a may also, as in the case of an antenna 52 shown in FIG. 16 , be arranged within a winding 54 of the magnetic radiator. A second capacitive radiator 53b is parallel to the radiator 53a. The base points of both radiators 53a and 53b lie on both sides of the connection locations of a capacitor 55.

The magnetic radiator 54 approximately shown in FIG. 16 as a square frame may also be circular. Also, at the free ends of the local capacitive radiators 53a and 53b to the plane of the circle of the magnetic radiator 54 and the antenna parts 53a and 53b perpendicular antenna parts can be arranged.

For reasons of space, the antenna part 53a directed downwards in FIG. 16 can also be divided into two or more antenna parts, which are then connected to the same location of the capacitive partial radiator 53a and perpendicular to the antenna part 53b and perpendicular to the plane in which the magnetic radiator 54 is located ,

Antennas sketched in FIGS. 5, 10 and 14 to 16 each have two aligned or parallel capacitive radiators 17a / b, 41a / b, 45a / b, 47a / b and 53a / b . That too does not have to be. It is also possible to work with non-parallel capacitive radiators 57a and 57b, as shown in an antenna variant 58 in FIG. 17 . This capacitive radiator 57 is also not arranged in the immediate vicinity of a rotary capacitor 59 here . In Figure 17 , the magnetic radiator has a square winding 60. However, this winding may also, as indicated in Figures 5, 14 and 15 , be circular. In Figure 17 , the two capacitive radiators 57a and 57b are at an angle of 90 ° to each other. This also does not have to be, as another antenna variant 62 in FIG. 18 shows, in which two capacitive radiators 61a and 61b have an angle different from 90 ° and deviating from a parallel or aligned arrangement.

In Figure 17 , the two capacitive radiators 57a and 57b are formed as side extensions of the square winding 60 of the magnetic radiator. These side extensions can now also be designed such that the capacitive radiators 63a and 63b are aligned with one another, as illustrated by a further antenna variant 64 in FIG. 19 .

In the exemplary embodiments illustrated so far, the magnetic and the capacitive radiators lie in one plane. That too does not have to be. In FIG. 20 , another antenna variant 68 is shown as viewed from above, that is to say in the plane of the drawing of the preceding examples from the upper leaf side downwards. One turn of the magnetic radiator now appears only as a line 65, wherein the winding parts extending to the rear through the plane of the drawing are marked as arrow ends 66a and 66b for three-dimensional clarification. In addition to a variable capacitor 67 , two capacitive radiators 69a and 69b extend in a plane perpendicular to a plane in which the winding 65 of the magnetic radiator lies.

In Figure 21 , another antenna embodiment 70 is shown in which the two capacitive radiators 71a and 71b are arranged in parallel planes to the plane of the magnetic radiator such that the plane of the magnetic radiator 72 lies between the two planes of the capacitive radiator.

FIG. 22 shows an antenna arrangement 75 for, for example, resonance frequencies above 300 MHz. A square winding 73 and two capacitive radiators 74a and 74b are embodied here as printed circuit traces of a printed circuit 85 . As a capacitance 76 , the two adjacent supply lines 83a and 83b act here to the two capacitive radiators 74a and 74b. At each transition of a feed line 83a or 83b into the square winding 73 of the magnetic beam, an opening 84a or 84b is formed in the printed circuit. The two openings 84a and 84b are plug-in connections for a capacitive trimmer for fine adjustment of the resonance frequency f. Power is fed to antenna 75 at port 81a and ground at port 81b .

Areas of application of an analogous to the antenna 75 formed in Figure 22 , if this antenna is printed on a film, for example, a theft protection of sales objects, which carry this cheap to manufacture antenna. The printed antenna can also be coupled with simple electronics. The printed antenna would then receive supply energy for the coupled electronics (chip) from a transmitter which is arranged, for example, in the vicinity of a cash register or an outlet of a department store. The chip could then be one Create a goods identification signal, which is received and processed by the sender. A scanning of purchased goods at the cash register would thus be omitted; All goods in a shopping cart would be recognized by radio technology without removal and charged.

The connections for the capacitive trimmer need not be designed as breakthroughs; only soldering points can be present.

The resonant frequency f determining capacity can be generated by a corresponding arrangement of the leads to the radiation arms. Often, however, a fine adjustment of this resonance frequency f is desired. A fine adjustment can now, as described above for the antenna 75 , be made with the soldered capacitive trimmer. Further capacitive trimmers are indicated in FIGS. 5, 10, 14, 15, 17 to 21 and 23 .

However, the antenna 15 illustrated in FIG. 5 may be modified such that the rotary capacitor 22 (capacitive trimmer) is removed and the two free ends 87a and 87b of the winding 20 now formed are connected to an insulating tab (not shown) for mechanical stability. On the spacer 19b approximately in its lower third is perpendicular to the extension of the spacer 19b (not shown) plate arranged. On the spacer 19a another (also not shown), along the spacer adjustable plate is arranged, which plate engages over the plate on the spacer 19b . In order to fine-tune the resonant frequency f, the distance between the two plates is changed relative to one another, the capacitance value being greater, the larger the plate extension is formed and the smaller is their mutual distance. It can now be fixed to one of the plates on the spacer in question, while the other on its spacer slidably formed via a clamp mount is formed. If the resonant frequency f is not selected to be too high, the spacers 19a and 19b may be formed as threaded rods, on which both or only one of the plates can then be changed by turning in the position.

If the plates are formed as tabs, the capacitance value can also be changed by pivoting the tabs against each other.

The capacitive radiators should be arranged in the vicinity of the connection locations of the variable capacitor; ie the electrical connection locations (eg spacers) 78a and 78b of the capacitive radiator 79 should be in the vicinity of the base points 77a and 77b of the rotary capacitor 79 (FIG. 23). However, they can also be arranged at a distance from the foot points 77a and 77b , ie in the region A ₁ and A ₂ . Preferably will one choose a symmetrical distance? It does not make sense to arrange the connection locations between the energy supply points 80a and 80b ; ie not between the points 24 or 80a and the grounding point 23b or 80b. A shift in the connection locations changes the RF voltage applied to the capacitive radiators. The greater a distance from the points 24 or 80a and 23a or 80b is selected, the greater the impedance value.

The constructive structures of the antennas 5, 10, 14 to 22 shown above each have a plane of symmetry relating to the at least one capacitive radiator and the at least one magnetic radiator. If such a symmetrical arrangement is selected, then the feed location for the transmission power is voltage-neutral. A voltage neutrality at the feed location should be given so that no so-called mantle waves can arise on an energy supply line. Namely, such cladding waves would change the radiation characteristics, the gain and the quality of the antenna. In addition, this characteristic would also change if changes in the location of the energy supply are made.

It may now be apparent, for example, that the antenna can no longer be constructed symmetrically due to the environment, because, for example, a downwardly directed antenna part of a capacitive radiator would touch the ground analogously to FIGS. 16 or 20 in a design variant. In such a case, one would make the respective antenna part correspondingly smaller and provided with a terminal capacity (such as 47a or 47b of Figure 15) or with multiple sub-radiators. In this case, you would also move the feeder until it is voltage-neutral.

Thus, the antenna 15 shown in Fig. 5 may be formed as a p-shaped antenna 90 under a task of its symmetry as shown in Figs. 24 and 25 , with no electrically conductive transition between the linear portion 91 and the abutting thereof circular section 92 is more; there is a gap 93 here. By "ρ-shaped" is meant a shape according to the Greek letter rho. At the free end of the circular part, a straight antenna section 94 is arranged perpendicular to the linear part of the "ρ"'s. The straight portion 94 together with the linear part 91 forms a capacitance which is adjustable by changing the gap width d . The circular portion 92 is the magnetic radiator and the linear and the straight portion 91 and 94 form the capacitive radiator. The energy feed 95 takes place at the apex of the circular part 92. Such an antenna has a good directivity. It is inexpensive to manufacture and could thus preferably be used in the transmission of information records in ad hoc networks, such as For example, they are used between vehicles (car-to-car) or used in any mobile or portable use.

Instead of a p-shaped design, which is particularly suitable for high frequencies (from about 100 MHz), a b-shaped design can be made, which is particularly suitable for low frequencies (below 10 MHz). In the case of the b-shaped design, in order to increase the mechanical stability to a straight rod or to a flat element, a semicircular part can be welded or soldered.

The magnetic emitter has, as shown in Figure 3 , a capacity. The electric radiator, as shown schematically in FIG. 1 , now also forms a capacitance with its radiation arms. A capacity resulting from the mechanical construction, formed by the radiating arms of the electric radiator, can now be designed using a plurality of radiating arms with and without changes to the arm ends (see for example the end plates 49a and 49b in FIG . that it just corresponds to the predetermined capacity of the magnetic radiator. For coordination purposes, a partial capacity can then be provided. However, an effect of tuning can also be achieved by making geometrical distances between the units forming the electric radiator. Such a trained antenna consisting of a combination of at least one magnetic radiator with at least one capacitive radiator is characterized by a compact, raummässig reduced structure, which also usually can also be produced inexpensively.

Claims (8)

Antenna, in particular transmitting antenna (15, 35, 44, 46, 52, 58, 62, 64, 68, 70, 75), characterized by a combination of at least one magnetic beam ( 7, 11; 20, 22; 39a-39d, 40) 50, 51, 73 ) having at least one capacitive radiator ( 1; 3a, 3b; 17a, 17b; 41a, 41b; 45a, 45b; 47a, 47b; 61a, 61b; 74a, 74b ). Antenna ( 15, 35, 44, 46, 52, 58, 62, 64, 68, 70, 75 ) according to claim 1, characterized in that one of the capacitive radiators ( 1; 3a, 3b; 17a, 17b; 41a, 41b 45a, 45b, 47a, 47b, 61a, 61b, 74a, 74b ) is connected to the periphery of at least one of the magnetic radiators ( 7, 11, 20, 22, 39a-39d, 40, 50, 51, 73 ). Antenna ( 15, 35, 44, 46, 52, 58, 62, 64, 68, 70, 75 ) according to claim 1 or 2, characterized by a construction with a plane of symmetry relating to the at least one capacitive radiator ( 1; 3b, 17a, 17b, 41a, 41b, 45a, 45b, 47a, 47b, 61a, 61b, 74a, 74b ) and the at least one magnetic radiator ( 7 , 11, 20, 22, 39a-39d, 40, 50). 51, 73 ) and a power supply ( 13, 14a, 14b, 21, 23a, 23b, 24, 81a, 81b ), and preferably a tunable auxiliary capacitor, wherein the power supply ( 13, 14a, 14b; 21, 23a, 23b, 24; 81a, 81b ), and in particular the additional capacity and an additional capacity tuning means do not have the plane of symmetry. Antenna ( 15, 35, 44, 46, 52, 58, 62, 64, 68, 70, 75 ) according to one of claims 1 to 3, characterized by a capacity of the at least one magnetic radiator, which only by a structural design of at least a capacitive radiator is formed and thus eliminates the capacity as an independent component. Antenna ( 15, 35, 44, 46, 52, 58, 62, 64, 75) according to one of claims 1 to 4, characterized in that at least one magnetic and at least one capacitive radiator in planes parallel to each other, preferably in the same plane, are arranged, wherein preferably geometric dimensions of the capacitive and one of the magnetic radiators are chosen such that a specifiable, in particular maximum forward / Rückwärtsstrahlungsverhältnis can be achieved. An antenna ( 15, 35, 44, 46, 52, 58, 62, 64, 68, 70, 75 ) according to any one of claims 1 to 5, characterized by a power supply (21) coupled in the at least one magnetic radiator . Antenna ( 15, 35, 44, 46, 52, 58, 64, 68, 70, 75 ) according to one of claims 1 to 6, characterized in that at least one capacitive radiator with at least two radiation arms ( 17a, 17b, 41a, 41b 45a, 45b, 47a, 47b, 53a, 53b, 57a, 57b, 63a, 63b, 69a, 69b, 71a, 71b, 74a, 74b ), the radiation arms preferably being parallel to one another. Antenna (44, 46) according to one of Claims 1 to 7, characterized in that at least one of the radiation arms (45a , 45b; 47a , 47b) of the at least one capacitive radiator has a rod-shaped initial part electrically connected to at least one magnetic radiator and an end part has, wherein the outer contour (49a, 49b, 47a, 47b) of the end portion relative to the outer contour of the initial part is increased in order to reduce a longitudinal extent (ℓ _a , ℓ _b ) of the capacitive Strahlungsarms.

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