FR2713020A1 - Dipole type radiating element made of printed technology, matching adjustment method and corresponding network. - Google Patents

Abstract

The invention relates to a radiating element of the dipole type 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 consisting 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; said feed line (2) having 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 by a first length variable (11), and said slot (7) having a second end portion (10) projecting from the axis of said first end portion (9) of the feed line of a second variable length (12). ).

Description

Radiating element of the dipole type produced in printed technology,

  adaptation adjustment method and corresponding network.

  The field of the invention is that of telecommunication antennas up to

  frequencies of the order of the 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 dipole type radiating element as an omnidirectional transmitter or receiver antenna. The invention has many applications, such as, for example, field readings, the type of measurement of antenna patterns or electromagnetic compatibility measurement. The dipole-type radiating elements known from the state of the art generally consist of elements of two-wire lines, that is to say of cylindrical rods

  conductive, powered by a power line.

  These known radiating elements made of conductive rods have relatively wide-band performance, which makes them usable in many applications.

  However, several disadvantages are related to their use.

  Indeed, the supply lines (for example the coaxial lines) are

  generally asymmetrical, while the radiating elements are symmetrical.

  Therefore, in order for the radiation of these radiating elements to be acceptable, a balun should be used. A balun is traditionally represented as a transformer that involves localized or distributed impedances, and allows, when placed between a symmetrical radiating element and an asymmetrical feed line, to make the symmetrical currents on the radiating structure. Such a balun has the major disadvantage of requiring a setting to

always delicate point.

  Radiating elements consisting of cylindrical rods which are self-symmetrical are also known, so that they can be used without a balun. Obtaining such a characteristic of self-symmetry on these radiating elements can not, however, be

  achieved only at the expense of increased complexity of their structure.

  Another disadvantage of these known radiating elements of the rod-type dipole

  cylindrical is related to their adaptation to the power 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 element

  radiating 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. This is called double stub adaptation. Since the determination of the length of each stub (series or parallel) is empirical, the adaptation requires numerous welding / desoldering operations. Finally, in general, these known radiating elements of the dipole type with cylindrical rods have a relatively large size and a

  mechanical handling sometimes difficult.

  The purpose of the invention is notably to overcome these various disadvantages of

the state of the art.

  More specifically, an object of the invention is to provide a dipole type radiating element which has a large bandwidth and omnidirectional diagrams

  while having a small footprint and a very simple mechanical implementation.

  The invention also aims to provide such a radiating element of the type

  dipole that does not require the joint use of a balun.

  Another object of the invention is to provide such a radiating element of the type

  dipole which is easily adaptable to the power line to which it is connected.

  These objectives, as well as others which will appear subsequently, are achieved according to the invention by means of a dipole type radiating element consisting of: a substrate plate; a feed 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 constituted by two lateral strands separated by a coupling slot, and the vertical bar of said T constituting a ground plane for said feed line, said lateral strands constituting the radiating portion of said radiating element; said feed line having a first end portion extending along an axis intercepting the axis of said slot and protruding from said axis of the coupling slot by a first variable length, and said slot having a second portion of end protruding from the axis of said first end portion of the feed line by a second length

variable.

  The radiating element according to the invention is therefore produced in printed technology,

  which allows a considerable space saving and mechanical maintenance much easier.

  Moreover, the metal deposit comprises on the one hand the two lateral strands (forming the horizontal bar of the T) which constitute the dipole itself, and on the other hand an extension, in a direction orthogonal to these lateral strands (extension forming the T vertical bar), which is the ground plane for the power line. Thus, the presence of this ground plane associated with the power line ensures that the power supply is self-symmetric. In other words, the radiating element according to

  the invention does not require the joint use of a balun.

  In addition, the feed line feeds the two side strands via

of the coupling slot.

  Finally, in order to be able to implement the known principle of double stubs adaptation in the case of a radiating element produced by printed technology, the invention

  proposes an original realization of the stubs or sections of serial and parallel adaptation.

  Indeed, according to the invention: the series stub consists of the first end portion of the feed 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 feed line, and has the

second variable length.

  A suitable choice of these first and second variable lengths allows

  to adapt the radiating element to a wide band.

  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

  two lateral strands constituting the dipole itself.

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

  Advantageously, said feed line is a microstrip line.

  In an advantageous embodiment of the invention, the radiating element comprises first variable capacitance means connected between a ground plane and the end of said feed line located in said first end portion. the modification of the capacity of these first means has the same effect as a "physical" (that is, real) lengthening or

variable length.

  In another advantageous embodiment of the invention, the radiating element comprises second capacitance means connected between a ground plane and

  the end of said slot in said second end portion.

  Thus, we act on the second variable length as explained previously

  for the first variable length.

  In a preferred embodiment of the invention, the radiating element also comprises reflection means for suppressing radiation.

rear of said radiating element.

  In this way, the energy radiated by the radiating element is directed forward.

  This saves about 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 (serial and parallel stubs) as the principle of double adaptation.

  stub makes it possible to calculate theoretically.

  In a first advantageous embodiment of this method according to the invention, said first step of adjusting the first variable length consists in partially cutting said first end portion of the feed line, and said second adjustment step of the second variable length is to partially plug said second end portion of the slot with a conductive material. In a second advantageous embodiment of the method according to the invention, said first step of adjusting the first variable length consists in modifying the value of the capacitance of first variable capacitance means connected between a ground plane and the end of the feed line located in the first end portion, and said second step of adjusting the second variable length is to change the value of the capacity of second variable capacity means connected between

  a ground plane and the end of the slot in the second end portion.

  In other words, the first embodiment corresponds for example to one or more "manual" actions while the second embodiment corresponds to

  example to one or more "electronic" actions.

  Other features and advantages of the invention will appear on reading the

  following description of a preferred embodiment of the invention, given as a

  indicative and nonlimiting example, and the accompanying drawings, in which: - Figure 1 shows a perspective view of a preferred embodiment of the radiating element according to the invention; - Figure 2 shows an equivalent electrical diagram of a radiating element according to the invention; FIG. 3 shows an example of means with variable capacity that can be implemented 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 exemplary radiating element according to the invention; - Figure 5 shows, on a Smith chart, the principle of 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 curve of variation, in a Smith chart, of

  the input impedance for an example of a radiating element according to the invention.

  The invention therefore relates to a radiating element of the dipole type produced in printed technology. Figure 1 presents a perspective view of a mode of

  realization 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 feed line 2, and a deposit

metallic 3.

  The substrate plate 1 is for example a Duroid substrate of Teflon glass type,

  having a relative permittivity er = 2.2 and a thickness h = 0.76 mm.

  The feed line 2 is located on the underside of the substrate plate 1. It is for example a microstrip line of width w. This power supply line 2 is connected to a connector 4 (for example of the SMA type) making it possible to connect the element

  radiating to a conventional coaxial cable (not shown).

  The metal deposit 3 is located on the upper face of the substrate plate 1 and is T-shaped. The horizontal bar of this T of the metallic deposit, which is the radiating part 8 of the radiating element, consists of two strands. side 5, 6 separated by a coupling slot 7. The length L of this radiating portion 8 is chosen to be equal to half the operating wavelength, so as to have a conventional value of impedance, namely Zr = 73 Qf + j 42 Q (the imaginary part of Zr can be canceled by slightly retouching 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 are of the same length L / 2.

  The supply line 2 feeds the radiating part 8 (that is to say the two lateral strands 5, 6) via the coupling slot 7. This slot 7 is

example of rectangular shape.

  The vertical bar 11 of the T of the metal deposit 3 extends from the two strands

  side 5, 6 to connector 4.

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

  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 11 extending beyond the axis of the slot 7. This first length 11 of the end portion from the feed line 2

  constitutes a series 9 circuit-open stub.

  The coupling slot 7 has an end portion of length 12 extending beyond the feed line 2. This second length 12 of the end portion

  slot 7 constitutes a parallel stub 10 in-line slot circuit.

  Thus, the radiating element according to the invention comprises, although realized as 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 adaptation

  stub, on a wide band of frequencies.

  The principle of double stub adaptation is now explained briefly 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 chart on which

  the main stages of implementation of this principle appear.

  As shown in FIG. 2: the radiating part has an impedance Zr = Rr + j Xr; the length series stub 11 has an adjustable reactance X 1 (X 1 being a function of 11), and the parallel stub of length 12 has an adjustable susceptance B2 (B2 being

function of 12).

  The adaptation of the radiating element consists in making the input impedance Ze of

  this radiating element equal to the characteristic impedance Zc of the coaxial cable.

  Typically, Zc = 50 Q. This adaptation (ie the equality Ze = Zc) is achieved by a suitable choice of the reactance X 1 and the susceptance B2, that is, say lengths 11 and 12

serial and parallel stubs.

  As shown in connection with FIG. 5, the Smith chart makes it possible to

  determine the acceptable values of X1 and B2, starting from the value of Zr = 1 / Yr.

  The calculation steps are as follows: - the circle G = 1 is shifted by 180 degrees, for the passage in admittance: - from the point Yr, we add j B2 while moving along the circle with constant conductance, until 'at the intersection with the circle G = 1 shifted. The new value of the admittance is Y'L OR Y "L; - we take the symmetry of Y'L or Y" L to have the new value in impedance (namely Z'L or Z "L) which is 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 condition of perfect adaptation). The value X2 is therefore X 'or X ".

  It should be noted that the greater bandwidth is obtained when the reactive elements are chosen as small as possible, so that the quality factor of the circuit

adaptation 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 Figure 1.

  In this example, the radiating element is characterized by the following geometrical quantities: substrate plate 1 Teflon-type Duroid type, with a relative permittivity of úr = 2.2 and a thickness h = 0.76 mm; feed 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 11 = 10.5 mm; and

  - parallel stub of length 12 = 10 mm.

  This curve makes it possible to calculate the bandwidth [f 1, f 2] of the radiating element, that is to say the frequency band for which the ROS is less than 2. This bandwidth can also be expressed as a percentage, obtained by division of width

  (f2-fl) of the bandwidth by the central frequency f3 of this bandwidth.

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

bandwidth.

  Figure 8 shows a variation curve, in a Smith chart, of

  the input impedance Ze for the previous example of radiating element.

  At frequencies f1, f2 and f3 defining the bandwidth, there are the input impedances Zel, Ze2 and Ze3, with: Zel = 25.55 n + j 5.53 Q and fl = 1.83 GHz; Ze2 = 48.97D + j 3.5Q and f2 = 2.33GHz;

  Ze3 = 37.22 Q + j 28.2 Q and f3 = 2.84 GHz.

  We will notice the presence of the loop which guarantees a weak dispersion in

  frequency and reflects the effectiveness of adaptation.

  During the experimental phase, there may be a slight mismatch of the radiating element and it is then necessary to adjust the lengths 11, 12 of the series and parallel stubs, these lengths 11, 12 being calculated beforehand thanks to the principle of

  the double stub adaptation described above.

  Many methods can be imagined for such an adjustment of

  the adaptation of the radiating element.

  A first example of such a method consists in: adjusting the length 11 of the series stub by partially cutting the end portion of the feed line protruding from the slot; and - adjusting the length 12 of the parallel stub by partially occluding with a conductive material, the end portion of the slot protruding from the supply line. A second example of such a method can be implemented if the radiating element comprises: first means 31 (FIG. 3) with variable capacity connected between a ground plane (for example one of the lateral strands 6) and the end 32 of the end portion of the feed line constituting the series stub 9; and second means (not shown) with variable capacity connected between a plane

  mass and the end of the slot constituting the parallel stub.

  These first and second means with variable capacity are for example, as shown in Figure 3, varactors 31 electronically controlled. Thus, the variation of the capacity of these means 31 with variable capacity has the same effect as an elongation or

  a decrease in the length of the corresponding stub 9.

  FIG. 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 for removing a back radiation of this radiating element. Indeed, the radiation of the single dipole 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 the excitation). These reflection means 61 are intended to increase the directivity of the set 62 produced by printed technology (and corresponding to the radiating element of the first mode

realization).

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

maximum directivity.

  It is clear that the reflector 61 can have many other forms than

that presented in Figure 6.

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

  network 71 comprises three radiating elements 72 and a reflector 73.

Claims (11)

  1. radiating element of the dipole type, characterized in that it consists of: a substrate plate (1); - a feed line (2) located on the underside of said substrate plate (1); a metal deposit (3) situated on the upper face of said substrate plate (1) and substantially T-shaped: the horizontal bar of said T being constituted by 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 feed line (2), said lateral strands (5, 6) constituting the radiating portion of said radiating element; in that said feed 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 of a first variable length (11), and in that said slot (7) has a second end portion (10) projecting from the axis of said first end portion (9) of the feed line   of a second variable length (12).   2. radiating element according to claim 1, characterized in that said slot (7) is rectangular in shape.   3. radiating element according to any one 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 of the operating wavelength of said radiating element.   4. Radiant element according to any one of claims 1 to 3, characterized in   what said two lateral strands (5, 6) are of the same length.   5. radiating element according to any one of claims 1 to 4, characterized in   said feed line (3) is a microstrip line.   6. radiating element according to any one of claims 1 to 5, characterized in   it comprises first variable capacity means (31) connected between a ground plane (6) and the end (32) of said feed line (3) located in said   first end portion (9).   7. radiating element according to any one of claims 1 to 6, characterized in   what it comprises second means with variable capacity connected between a plane of   mass and the end of said slot in said second end portion.   8. radiating element according to any one of claims 1 to 7, characterized in   it also includes reflection means (61) for deleting a   rear radiation of said radiating element.   9. Network of radiating elements characterized in that it comprises at least two   radiating elements (72) according to any one of claims 1 to 8.   10. Method of adjusting the adaptation of a radiating element according to one   any of claims 1 to 8, characterized in that it comprises a first step   adjusting said first variable length (11) and a second adjusting step   of said second variable length (12).   A method according to claim 10, characterized in that said first step of adjusting the first variable length is to partially cut said first end portion of the feed line, and in that said second step of adjustment of the second variable length is to partially occlude said second end portion of the slot with a conductive material.   The method according to claim 10, characterized in that said first step of adjusting the first variable length is to change the value of the capacitance of first variable capacitance means connected between a ground plane and the end of the line. in the first end portion, and in that said second step of adjusting the second variable length is to change the value of the capacitance of second capacitance means connected between a ground plane and the end of the slot in the second end portion.