EP0654845A1 - Adaptable dipole radiating element in printed circuit technology, method for adjustment of the adaptation and corresponding array - Google Patents

Abstract

The invention relates to an adaptable dipole-type radiating element consisting of a substrate plate (1), of a feeder line (2) situated on the lower face of the said substrate plate (1), and of a metal deposition (3) situated on the upper face of the said substrate plate (1) and substantially T-shaped: the horizontal bar of the said T consisting of two lateral strands (5, 6) separated by a coupling slot (7), and the vertical bar (11) of the said T constituting an earth plane for the said feed line (2), the said lateral strands (5, 6) constituting the radiating part of the said radiating element. According to the invention, the said feed line (2) has a first end portion (9) extending along an axis intercepting the axis of the said coupling slot (7) and extending from the said axis of the coupling slot by a first variable length (l1), the said slot (7) has a second end portion (10) extending from the axis of the said first end portion (9) of the feed line by a second variable length (l2), and the radiating element comprises first and/or second variable-capacitance means, the said first variable-capacitance means being connected between an earth plane (6) and the end of the said feed line (3) situated in the said first end portion (9), the said second variable-capacitance means being connected between an earth plane and the end of the said slot situated in the said second end portion. <IMAGE>

Description

The field of the invention is that of telecommunications antennas up to frequencies of the order of a gigahertz.

More specifically, the invention relates to a radiating element of the dipole type. Indeed, it is still common in high frequency telecommunications to use such a radiating element of the dipole type as an omnidirectional transmitting or receiving antenna.

The invention has numerous applications, such as, for example, field readings, of the type of antenna diagram measurement or even measurement of electromagnetic compatibility.

The radiating elements of the dipole type known from the prior art generally consist of elements of two-wire lines, that is to say of conductive cylindrical rods, supplied by a supply line.

These known radiating elements consisting of conductive rods have relatively broadband performance, which makes them usable in many applications.

However, several drawbacks are linked to their use.

In fact, the supply lines (for example the coaxial lines) are generally asymmetrical, while the radiating elements are themselves symmetrical.

Consequently, in order for the radiation from these radiating elements to be acceptable, a balun should be used. A balun is traditionally represented as a transformer which involves localized or distributed impedances, and allows, when placed between a symmetrical radiating element and an asymmetrical supply line, to make the currents symmetrical on the radiating structure. Such a balun has the major drawback of requiring always delicate focusing.

Radiating elements are also known which consist of cylindrical rods which are self-symmetrized, so that they can be used without a balun. Obtaining such an autosymmetry characteristic on these radiating elements cannot however be obtained only at the expense of an increased complexity of their structure.

Another drawback of these known radiating elements of the dipole type with cylindrical rods is linked to their adaptation to the supply line to which they are connected.

Indeed, without such an adaptation, the energy emitted by a generator and transmitted to a radiating element by a supply line is not radiated by the radiating element but returned to the generator.

Generally, this adaptation is achieved through the use of two additional sections (or stubs) placed one in series and the other in parallel. We then speak of double stub adaptation. Now, the determination of the length of each stub (series or parallel) being empirical, the adaptation requires numerous welding / unsoldering operations.

Finally, in general, these known radiating elements of the dipole type with cylindrical rods have a relatively large size as well as sometimes difficult mechanical handling.

The invention particularly aims to overcome these various drawbacks of the state of the art.

More specifically, an objective of the invention is to provide a radiating element of the dipole type which has a large passband and omnidirectional patterns while having a small footprint and a very simple mechanical implementation.

The invention also aims to provide such a radiating element of the dipole type which does not require the joint use of a balun.

Another object of the invention is to provide such a radiating element of the dipole type which is easily adaptable to the supply line to which it is connected.

• une plaque de substrat;
• une ligne d'alimentation située sur la face inférieure de ladite plaque de substrat;
• un dépôt métallique situé sur la face supérieure de ladite plaque de substrat et sensiblement en forme en T : la barre horizontale dudit T étant constituée de deux brins latéraux séparés par une fente de couplage, et la barre verticale dudit T constituant un plan de masse pour ladite ligne d'alimentation, lesdits brins latéraux constituant la partie rayonnante dudit élément rayonnant;

   ladite ligne d'alimentation présentant une première portion d'extrémité s'étendant selon un axe interceptant l'axe de ladite fente et dépassant dudit axe de la fente de couplage d'une première longueur variable,
   ladite fente présentant une seconde portion d'extrémité dépassant de l'axe de ladite première portion d'extrémité de la ligne d'alimentation d'une seconde longueur variable, et
   ledit élément rayonnant comprenant des premiers et/ou des seconds moyens à capacité variable, lesdits premiers moyens à capacité variable étant connectés entre un plan de masse et l'extrémité de ladite ligne d'alimentation située dans ladite première portion d'extrémité, lesdits seconds moyens à capacité variable étant connectés entre un plan de masse et l'extrémité de ladite fente située dans ladite seconde portion d'extrémité.These objectives, as well as others which will appear subsequently, are achieved according to the invention using an adaptable radiating element of the dipole type and consisting of:

• a substrate plate;
• a supply line located on the underside of said substrate plate;
• a metal deposit located on the upper face of said substrate plate and substantially T-shaped: the horizontal bar of said T being consisting of two lateral strands separated by a coupling slot, and the vertical bar of said T constituting a ground plane for said supply line, said lateral strands constituting the radiating part of said radiating element;

said supply line having a first end portion extending along an axis intercepting the axis of said slot and projecting from said axis of the coupling slot by a first variable length,
said slot having a second end portion projecting from the axis of said first end portion of the supply line of a second variable length, and
said radiating element comprising first and / or second variable capacity means, said first variable capacity means being connected between a ground plane and the end of said supply line located in said first end portion, said second variable capacity means being connected between a ground plane and the end of said slot located in said second end portion.

The radiating element according to the invention is therefore produced in printed technology, which allows a considerable saving of space and a much easier mechanical maintenance.

Furthermore, the metal deposit comprises on the one hand the two lateral strands (forming the horizontal bar of the T) which constitute the dipole proper, and on the other hand an extension, in a direction orthogonal to these lateral strands (extension forming the vertical bar of T), which constitutes the ground plane for the supply line.

Thus, the presence of this ground plane associated with the supply line ensures that the supply is autosymmetrized. In other words, the radiating element according to the invention does not require the joint use of a balun.

In addition, the supply line feeds the two side strands via the coupling slot.

• le stub série est constitué de la première portion d'extrémité de la ligne d'alimentation qui dépasse de l'axe de la fente, et possède la première longueur variable ; et
• le stub parallèle est constitué de la seconde portion d'extrémité de la fente qui dépasse de la première portion d'extrémité de la ligne d'alimentation, et possède la seconde longueur variable.

In order to be able to implement the known principle of double stub adaptation in the case of a radiating element produced in printed technology, the invention proposes an original embodiment of the stubs or sections of series and parallel adaptation. According to the invention:

• the series stub consists of the first end portion of the supply line which protrudes from the axis of the slot, and has the first variable length; and
• the parallel stub consists of the second end portion of the slot which protrudes from the first end portion of the supply line, and has the second variable length.

A suitable choice of these first and second variable lengths makes it possible to adapt the radiating element over a wide band.

The radiating element according to the invention is also adaptable thanks to the first and / or second means with variable capacity. Indeed, the modification of the capacity of the first means has the same effect as an elongation or a "physical" (that is to say real) reduction in the first variable length. Similarly, one can act on the second variable length by modifying the capacity of the second variable capacity means.

Advantageously, said slot is of rectangular shape.

Preferably, the cumulative length of all of said two lateral strands is substantially equal to half the operating wavelength of said radiating element.

Thus, conventional values of radiation impedance are obtained for the two lateral strands constituting the actual dipole.

Advantageously, said two lateral strands are of the same length.

Advantageously, said supply line is a microstrip line.

In a preferred embodiment of the invention, the radiating element also comprises reflection means making it possible to suppress rear radiation from said radiating element.

In this way, the energy radiated by the radiating element is directed forward. This allows to gain approximately 3 dB on the maximum directivity of the radiating element.

The invention also relates to a network of radiating elements comprising at least at least two radiating elements according to the invention.

Finally, the invention also relates to a method of adjusting the adaptation of a radiating element, characterized in that it comprises a first step of adjusting said first variable length and a second step of adjusting said second variable length.

Indeed, it is always necessary to adjust the values of the first and second variable lengths (of the serial and parallel stubs) that the principle of the double stub adaptation allows to calculate theoretically.

In an embodiment of the method according to the invention, said first step of adjusting the first variable length consists in modifying the value of the capacity of first means with variable capacity connected between a ground plane and the end of the line feed located in the first end portion,
and said second step of adjusting the second variable length consists in modifying the value of the capacity of second variable capacity means connected between a ground plane and the end of the slot located in the second end portion.

Advantageously, said first step of adjusting the first variable length also consists in partially cutting said first end portion of the supply line,
and said second step of adjusting the second variable length also includes partially plugging said second end portion of the slot with a conductive material.

• la figure 1 présente une vue en perspective d'un mode de réalisation préférentiel de l'élément rayonnant selon l'invention;
• la figure 2 présente un schéma électrique équivalent d'un élément rayonnant selon l'invention;
• la figure 3 présente un exemple de moyens à capacité variable pouvant être mis en oeuvre dans un élément rayonnant selon l'invention;
• la figure 4 présente une courbe de variation, en fonction de la fréquence, du rapport d'onde stationnaire pour un exemple d'élément rayonnant selon l'invention;
• la figure 5 présente, sur un abaque de Smith, le principe de l'adaptation double stub;
• la figure 6 présente un second mode de réalisation d'un élément rayonnant selon l'invention comprenant un réflecteur;
• la figure 7 présente un exemple de réseau comprenant plusieurs éléments rayonnants selon l'invention ; et
• la figure 8 présente une courbe de variation, dans un abaque de Smith, de l'impédance d'entrée pour un exemple d'élément rayonnant selon l'invention.

Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of non-limiting example, and the appended drawings, in which:

• Figure 1 shows a perspective view of a preferred embodiment of the radiating element according to the invention;
• FIG. 2 presents an equivalent electrical diagram of a radiating element according to the invention;
• FIG. 3 shows an example of variable capacity means which can be used in a radiating element according to the invention;
• FIG. 4 shows a variation curve, as a function of frequency, of the standing wave ratio for an example of a radiating element according to the invention;
• FIG. 5 presents, on a Smith chart, the principle of the double stub adaptation;
• FIG. 6 shows a second embodiment of a radiating element according to the invention comprising a reflector;
• FIG. 7 shows an example of a network comprising several radiating elements according to the invention; and
• FIG. 8 presents a variation curve, in a Smith chart, of the input impedance for an example of radiating element according to the invention.

The invention therefore relates to a radiating element of the dipole type produced in printed technology. Figure 1 shows a perspective view of an embodiment of such a radiating element.

As shown in this FIG. 1, the radiating element according to the invention mainly comprises a substrate plate 1, a supply line 2, and a metallic deposit 3.

The substrate plate 1 is for example a Duroid substrate of the Teflon green type, having a relative permittivity ε _r = 2.2 and a thickness h = 0.76 mm.

The supply line 2 is located on the underside of the substrate plate 1. It is, for example, a microstrip line of width w. This supply line 2 is connected to a connector 4 (for example of the SMA type) making it possible to connect the radiating element to a traditional coaxial cable (not shown).

The metal deposit 3 is located on the upper face of the substrate plate 1 and is T-shaped.

(la partie imaginaire de Z_r pouvant être annulée en retouchant légèrement la longueur L de la partie rayonnante). La longueur L et la largeur W de cette partie rayonnante 8 déterminent les propriétés mécaniques propres à l'élément rayonnant.The horizontal bar of this T of the metallic deposit, which is the radiating part 8 of the radiating element, consists of two lateral strands 5,6 separated by a coupling slot 7. The length L of this radiating part 8 is chosen to be equal at half the operating wavelength, so as to have a conventional impedance value, namely ${\text{Z}}_{\text{r}}\text{= 73 Ω + j 42 Ω}$

(the imaginary part of Z _r can be canceled by retouching slightly the length L of the radiating part). The length L and the width W of this radiating part 8 determine the mechanical properties specific to the radiating element.

In the example presented, the two lateral strands 5,6 have the same length L / 2.

The supply line 2 supplies the radiating part 8 (that is to say the two lateral strands 5, 6) via the coupling slot 7. This slot 7 is for example of rectangular shape.

The vertical bar 11 of the T of the metal deposit 3 extends from the two lateral strands 5, 6 to the connector 4.

This part 11 of the metal deposit 3 constitutes a ground plane for the supply line 2 situated on the other face of the substrate plate 1. In this way, the radiating element generates symmetrical currents on the radiating part 8. In other words, the radiating element of the invention is self-symmetrized.

The supply line 2 has at its end opposite to that connected to the connector 4, an end portion of length l1 extending beyond the axis of the slot 7. This first length l1 of the end portion of the supply line 2 constitutes a series 9 open-circuit stub.

The coupling slot 7 has an end portion of length l2 extending beyond the supply line 2. This second length l2 of the end portion of the slot 7 constitutes a parallel stub 10 short-circuited slotted line.

Thus, the radiating element according to the invention comprises, although produced in a printed technologist, a series stub and a parallel stub. These two series and parallel stubs allow the adaptation of the radiating element, according to the principle of double stub adaptation, over a wide frequency band.

The principle of the double stub adaptation is now briefly explained in relation to FIG. 2, which presents an equivalent electrical diagram of a radiating element according to the invention, and FIG. 5 which presents a Smith abacus on which the main ones appear. stages of implementation of this principle.

• la partie rayonnante présente une impédance ${\text{Z}}_{\text{r}}{\text{= R}}_{\text{r}}{\text{+ j X}}_{\text{r}}$
  
  ;
• le stub série de longueur l1 présente une réactance ajustable X₁ (X₁ étant fonction de l1) ; et
• le stub parallèle de longueur l2 présente une susceptance ajustable B₂ (B₂ étant fonction de l2).

As shown in Figure 2:

• the radiating part has an impedance ${\text{Z}}_{\text{r}}{\text{= R}}_{\text{r}}{\text{+ j X}}_{\text{r}}$
  
  ;
• the stub series of length l1 has an adjustable reactance X₁ (X₁ being a function of l1); and
• the parallel stub of length l2 has an adjustable susceptance B₂ (B₂ being a function of l2).

The adaptation of the radiating element consists in making the input impedance Z _e of this radiating element equal to the characteristic impedance Z _c of the coaxial cable. Typically, we have Z _c = 50 Ω.

This adaptation (that is to say the equality Z _e = Z _c ) is achieved by means of a suitable choice of the reactance X₁ and the susceptance B₂, that is to say of the lengths l1 and l2 of the stubs series and parallel.

.As presented in relation to FIG. 5, the Smith abacus makes it possible to determine the acceptable values of X₁ and B₂, from the value of ${\text{Z}}_{\text{r}}{\text{= 1 / Y}}_{\text{r}}$

.

• on construit le cercle G = 1 décalé de 180 degrés, pour le passage en admittance :
• à partir du point Y_r, on ajoute j B₂ en se déplaçant le long du cercle à conductance constante, jusqu'à l'intersection avec le cercle G = 1 décalé. La nouvelle valeur de l'admittance est Y'_L ou Y''_L;
• on prend le symétrique de Y'_L ou Y''_L pour avoir la nouvelle valeur en impédance (à savoir Z'_L ou Z''_L) qui se situe comme on l'a imposé sur le cercle G = 1 ;
• on soustrait la réactance j X' ou j X'' (puisque l'origine de l'abaque correspond à une condition d'adaptation parfaite). La valeur X₂ est donc X' ou X''.

The calculation steps are as follows:

• we construct the circle G = 1 offset by 180 degrees, for the transition to admittance:
• from the point Y _r , we add j B₂ by moving along the circle with constant conductance, until the intersection with the offset circle G = 1. The new admittance value is Y ' _L or Y''_L;
• we take the symmetric of Y ' _L or Y'' _L to have the new impedance value (namely Z' _L or Z '' _L ) which is located as we imposed on the circle G = 1;
• we subtract the reactance j X 'or j X''(since the origin of the abacus corresponds to a perfect adaptation condition). The value X₂ is therefore X 'or X''.

It should be noted that the greatest bandwidth is obtained when the reactive elements are chosen to be as small as possible, so that the quality factor of the adaptation circuit remains low.

FIG. 4 shows a variation curve, as a function of frequency, of the standing wave ratio (ROS) for an example of a radiating element as shown in FIG. 1.

• plaque de substrat 1 Duroïd type verte téflon, de permittivité relative ε_r = 2,2 et d'épaisseur h = 0,76 mm ;
• ligne d'alimentation 2 de largeur w = 2,16 mm ;
• partie rayonnante (dipôle) 8 de longueur L = 55 mm et de largeur W = 10 mm ;
• stub série de longueur l1 = 10,5 mm ; et
• stub parallèle de longueur l2 = 10 mm.

In this example, the radiating element is characterized by the following geometric quantities:

• substrate plate 1 Duroid green teflon type, with relative permittivity ε _r = 2.2 and thickness h = 0.76 mm;
• supply line 2 of width w = 2.16 mm;
• radiating part (dipole) 8 of length L = 55 mm and width W = 10 mm;
• stub series of length l1 = 10.5 mm; and
• parallel stub of length l2 = 10 mm.

This curve makes it possible to calculate the passband [f₁, f₂] of the radiating element, that is to say the frequency band for which the ROS is less than 2. This passband can also be expressed as a percentage, obtained by dividing the width (f₂-f₁) of the passband by the center frequency f₃ of this passband.

In this example, the bandwidth is substantially between f₁ = 1.83 GHz and f₂ = 2.84 GHz. With a central frequency f₃ = 2.33 GHz, this bandwidth is equal to 44%. The radiating element according to the invention therefore has a wide pass band.

FIG. 8 presents a variation curve, in a Smith chart, of the input impedance Z _e for the previous example of a radiating element.

${\text{Z}}_{\text{e2}}\text{= 48,97 Ω + j 3,5 Ω et f₂ = 2,33 GHz ;}$

${\text{Z}}_{\text{e3}}\text{= 37,22 Ω + j 28,2 Ω et f₃ = 2,84 GHz.}$

At frequencies f₁, f₂ and f₃ defining the passband, we have the input impedances Z _e1 , Z _e2 and Z _e3 , with:

${\text{Z}}_{\text{e1}}\text{= 25.55 Ω + j 5.53 Ω and f₁ = 1.83 GHz;}$

${\text{Z}}_{\text{e2}}\text{= 48.97 Ω + j 3.5 Ω and f₂ = 2.33 GHz;}$

${\text{Z}}_{\text{e3}}\text{= 37.22 Ω + j 28.2 Ω and f₃ = 2.84 GHz.}$

Note the presence of the loop which guarantees low frequency dispersion and reflects the efficiency of the adaptation.

During the experimental phase, there may be a slight mismatch of the radiating element and it is then necessary to adjust the lengths l1, l2 of the series and parallel stubs, these lengths l1, l2 being calculated beforehand thanks to the principle of adaptation double stub described above.

• des premiers moyens 31 (figure 3) à capacité variable connectés entre un plan de masse (par exemple un des brins latéraux 6) et l'extrémité 32 de la portion d'extrémité de la ligne d'alimentation constituant le stub série 9 ; et/ou
• des seconds moyens (non représentés) à capacité variable connectés entre un plan de masse et l'extrémité de la fente constituant le stub parallèle.

To allow such an adjustment of the lengths l1, l2 the radiating element comprises:

• first means 31 (FIG. 3) with variable capacity connected between a ground plane (for example one of the side strands 6) and the end 32 of the end portion of the supply line constituting the series stub 9; and or
• second variable capacity means (not shown) connected between a ground plane and the end of the slot constituting the parallel stub.

These first and / or second variable capacity means are for example, as shown in Figure 3, varactors 31 controlled electronically. Thus, varying the capacity of these variable capacity means 31 has the same effect as lengthening or decreasing the length of the corresponding stub 9.

Thus, such an adjustment of the adaptation of the radiating element consists in modifying the capacities of the first and / or second means with variable capacity, which is equivalent to a modification of the lengths 11, 12 of stubs.

• l'ajustement de la longueur l1 du stub série consiste également à découper partiellement la portion d'extrémité de la ligne d'alimentation dépassant de la fente ; et
• l'ajustement de la longueur l2 du stub parallèle consiste également à boucher partiellement, avec un matériau conducteur, la portion d'extrémité de la fente dépassant de la ligne d'alimentation.

This "electronic" adjustment process can possibly be supplemented by a "manual" adjustment such as:

• adjusting the length 11 of the series stub also consists in partially cutting the end portion of the supply line projecting from the slot; and
• adjusting the length 12 of the parallel stub also consists in partially plugging, with a conductive material, the end portion of the slot protruding from the supply line.

Figure 6 shows a second embodiment of a radiating element according to the invention. In fact, this second embodiment differs from the first only in that it comprises reflection means 61 making it possible to suppress rear radiation from this radiating element. Indeed, the radiation of the dipole alone 62 is omnidirectional except in the axis of the dipole. However, for certain applications, it is desired to direct the radiated energy towards the front of the dipole (that is to say on the side opposite to the excitation).

These reflection means 61 aim to increase the directivity of the assembly 62 produced in printed technology (and corresponding to the radiating element of the first embodiment).

These reflection means 61, in the case where they consist of a reflector (in the absence of an ideally undefined defector plane), make it possible to gain approximately 3 dB on the maximum directivity.

It is clear that the reflector 61 can have many other shapes than that presented in FIG. 6.

FIG. 7 shows an example of an array 71 of radiating elements 72 according to the invention. The networking of radiating elements also makes it possible to obtain increased directivity and can therefore be combined or not with a reflector. In this example, the network 71 comprises three radiating elements 72 as well as a reflector 73.

Claims (10)

Adaptable radiating element, of the dipole type and consisting of: - a substrate plate (1); - a supply line (2) located on the underside of said substrate plate (1); - a metal deposit (3) located on the upper face of said substrate plate (1) and substantially T-shaped: the horizontal bar of said T being made up of two lateral strands (5, 6) separated by a coupling slot ( 7), and the vertical bar (11) of said T constituting a ground plane for said supply line (2), said lateral strands (5, 6) constituting the radiating part of said radiating element; characterized in that said supply line (2) has a first end portion (9) extending along an axis intercepting the axis of said coupling slot (7) and projecting from said axis of the coupling slot d 'a first variable length (l1),
in that said slot (7) has a second end portion (10) projecting from the axis of said first end portion (9) of the supply line of a second variable length (12),
and in that it comprises first (31) and / or second variable capacity means, said first variable capacity means (31) being connected between a ground plane (6) and the end (32) of said supply line (3) located in said first end portion (9), said second variable capacity means being connected between a ground plane and the end of said slot located in said second end portion. Radiating element according to claim 1, characterized in that said slot (7) is of rectangular shape. Radiating element according to either of Claims 1 and 2, characterized in that the cumulative length of all of said two lateral strands (5, 6) is substantially equal to half the operating wavelength of said radiating element . Radiating element according to any one of Claims 1 to 3, characterized in that said two side strands (5, 6) are of the same length. Radiating element according to any one of Claims 1 to 4, characterized in that the said supply line (3) is a microstrip line. Radiating element according to any one of Claims 1 to 5 ', characterized in that it also comprises reflection means (61) making it possible to suppress rear radiation from said radiating element. Array of radiating elements characterized in that it comprises at least two radiating elements (72) according to any one of claims 1 to 6. Method for adjusting the adaptation of a radiating element according to any one of claims 1 to 6, characterized in that it comprises a first step of adjusting said first variable length (l1) and a second step d adjustment of said second variable length (12). Method according to claim 8, characterized in that said first step of adjusting the first variable length consists in modifying the value of the capacity of first variable capacity means connected between a ground plane and the end of the line of feed located in the first end portion,
and in that said second step of adjusting the second variable length consists in modifying the value of the capacity of second variable capacity means connected between a ground plane and the end of the slot located in the second end portion . Method according to claim 9, characterized in that said first step of adjusting the first variable length also consists in partially cutting said first end portion of the supply line,
and in that said second step of adjusting the second variable length also consists in partially plugging said second end portion of the slot with a conductive material.

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