RU2382448C2 - Loop dipole - Google Patents

Abstract

FIELD: physics; radio.

SUBSTANCE: invention can be used in radio systems for different purposes as a standalone antenna or as a base for a radiating element when making multi-dipole antennae. According to the invention, the loop dipole has two parallel wires directly joined to each other at the ends. One of the wires is broken in the middle and a transmitter or a receiver is connected between the resulting opening. Both wires are inside a solid loop screening conductor filled with dielectric. A symmetrical (balance) screened feeder is used to connect the transmitter or receiver to terminals formed after breaking the wire in the middle.

EFFECT: reducing longitudinal size of the dipole by 1,2…1,5 times at a given central wavelength of the operating frequency range.

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Description

The proposed device relates to the field of antenna technology and can be used in radio systems for various purposes as an independent dipole, and as a basic radiating element in the construction of multi-dipole antenna systems.

The relevance of the development of loop dipoles due to their widespread use in the formation of directed radiation of electromagnetic energy in radio engineering and telecommunication systems. To meet the ever-increasing requirements for the overall mass parameters of dipole antennas, it is necessary to fully reduce the size of their radiating part. In this case, it is necessary to comply with the design and technological restrictions that apply at the enterprises of the radio industry.

The loop dipole is known, described in the USSR AS No. 52669, published on February 28, 1938 (the outdated term “loop-like” was used in the text of this AS). This dipole contains two parallel wires connected to each other at the ends directly or by means of end impedances. Each wire is open in the middle and a transmitter or receiver is included in the gap of one wire, and longitudinal resistance is included in the gap of the other. All resistances are generally complex in nature, including they can be negligible (this corresponds to the case of direct connection). The length of both wires can be selected over a wide range. However, the greatest, if not universal, application was made of a loop dipole with a wire length l equal to half the central wavelength λ _{C of the} operating frequency range f _L ... f _R with the center frequency f _C = 3 · 10 ⁸ / λ _c (f _L / f _C <f _R ):

раз по сравнению с их геометрической длиной, как это имеет место в закрытых (экранированных) коаксиальных или полосковых передающих линиях, заполненных высокодобротным диэлектрическим материалом с относительной диэлектрической проницаемостью ε_r.It is this circumstance that in some cases leads to unacceptable longitudinal dimensions of the loop dipole, since the application of any dielectric coatings to the wires does not give the effect of increasing the electric length of the open radiating wires in

times compared with their geometric length, as is the case in closed (shielded) coaxial or strip transmission lines filled with high-quality dielectric material with a relative permittivity ε _r .

Thus, the described loop dipole, characterized by a wire length l equal to λ _C / 2, in some cases has an unacceptable longitudinal size, which very significantly limits the scope of its use in antenna technology.

A loop dipole is also known, as described in US Pat. No. 2,238,914, published May 26, 1942. This dipole, as follows from FIG. 1 of the description of the aforementioned patent, contains two parallel wires connected to each other at the ends by means of short lengths of wires of the same diameter. One of the wires is open in the middle and a symmetrical (balanced) two-wire line is connected to the gap to supply the high-frequency energy of the transmitter or to remove the received high-frequency signal to the input of the receiver. The described dipole can be used both independently and as a basic radiating element of more complex antennas. In this case, the length l of both wires is chosen over a wide range, but its minimum value is λ _C / 2.

Thus, in some cases this loop dipole also has an unacceptable longitudinal size, which significantly limits the scope of its use in antenna technology.

Describing subsequent work on loop dipoles, it can be noted that since the publication of descriptions of the aforementioned loop dipoles (in the USSR - February 28, 1938, in the USA - May 26, 1942; that is, over a 70-year period), the light of hundreds of books and thousands of articles in which a large number of multi-dipole antennas using the aforementioned loop dipoles have been proposed and described. As a result, it can be stated that all single- and multi-dipole antennas described in the literature will have a longitudinal dimension of one of the elements — a loop dipole — equal to half the central wavelength λ _{C of the} operating range in free space (vacuum). It is this fact that is the limiting factor in the use of loop dipoles and more complex antennas based on them.

The prototype of the invention is a loop dipole, described in the first mentioned USSR AS No. 52669. As already noted, this loop dipole has the same length l of both wires equal to half the average wavelength λ _{C of the} operating range. At the same time, the wires emitting electromagnetic energy into the surrounding space cannot be “folded into a meander”, as is often done to reduce the longitudinal dimensions of strip / microstrip shielded (that is, enclosed in a solid metal case - closed) transmission lines. As a result, it is not possible to reduce the longitudinal size of the loop dipole by the currently known design and technological methods.

The task of the invention is the creation of a loop dipole having a smaller longitudinal size l at a given central wavelength λ _C.

The solution to this problem is ensured by the fact that in a known loop dipole containing two parallel wires directly connected to each other at the ends, one of the wires is open in the middle and a transmitter or receiver is included in the gap formed, a solid loop shielding conductor filled with a dielectric is inserted inside which are the specified wires.

Figure 1 shows the proposed loop dipole; figure 2 - frequency response of its complex input impedance on the Smith diagram; figure 3 is a printed version of the inventive loop dipole on the insulator FR-4; figure 5 - calculated and measured frequency characteristics of the complex input impedance of the printed version of the loop dipole on the Smith diagram.

The proposed loop dipole (Fig. 1) contains two parallel wires 1 and 2, located after direct connection between each other at the ends inside the solid, initially hollow, looped shielding conductor 3 filled with a dielectric. Wire 2 is open in the middle and a transmitter is included in the gap with poles 4 and 5 or a receiver with a balanced (balanced) output or input, respectively. Typically, this inclusion is carried out using a shielded symmetric (balanced) two-wire feeder 6 with a wave impedance ρ _F.

где ω=2πf=2π·3·10⁸/λ - текущая круговая частота; f - текущая циклическая частота; λ - длина волны в вакууме. Под воздействием приложенного к клеммам 4 и 5 напряжения u(t) в непосредственно соединенных между собой по концам проводах 1 и 2 потечет гармонически изменяющийся во времени ток i(t)=I_maxcos(ωt+φ-ϕ_D) с комплексной амплитудой

The principle of operation of the inventive loop dipole is as follows. Let the voltage harmonically varying in time u (t) = U _max cos (ωt + φ) with a complex amplitude be supplied to terminals 4 and 5 of the loop dipole via feeder 6 from a symmetric (balanced) signal source with a real internal resistance R _S = ρ _F

where ω = 2πf = 2π · 3 · 10 ⁸ / λ is the current circular frequency; f is the current cyclic frequency; λ is the wavelength in vacuum. Under the influence of the voltage u (t) applied to the terminals 4 and 5, the current i (t) = I _max cos (ωt + φ-ϕ _D ) with a complex amplitude will flow harmonically varying in time directly connected to each other at the ends of wires 1 and 2

here ϕ _D = arctan (X _D / R _D ) is the argument of the complex input impedance Z _D = R _D + jX _{D of the} loop dipole measured (calculated) with respect to terminals 4 and 5 (Fig. 1) and taking into account the presence of a continuous loop shielding filled with a dielectric of conductor 3. The current i (t) flowing through wires 1 and 2 induces an electric charge harmonically varying in time on the walls of a continuous shielding conductor 3, the surface density of which on the outer surface of the shielding conductor 3 depends both on time t and on the longitudinal coordinate x ( -l / 2≤x≤l / 2). Since the change in the surface charge in time is equivalent to the existence of a conduction current on the same surface, it can be stated that the conductivity current i _E (t) flows on the outer surface of the shielding conductor 3, although the signal source is not connected to the ends of the shielding conductor 3. It is this current i _E (t) that will create electromagnetic radiation around the loop dipole, the intensity of which will depend both on the frequency f (wavelength λ) and on the current spherical coordinates of the observation point in the space surrounding the dipole.

It is obvious that when the frequency f ^* occurs when the frequency f changes, at which the reactive component XD (f = f ^* ) of the input impedance Z _{D of the} loop dipole becomes equal to zero, and the real component R _D is equal to the wave impedance ρ _{F of the} two-wire feeder 6

it is precisely at this frequency f ^{* that the} energy supplied to the terminals 4 and 5 of the loop dipole will be completely radiated by the loop dipole into the surrounding space. In this case, the input reflection coefficient G at the terminals 4 and 5 of the loop dipole, defined as

will be equal to zero, and the input coefficient K _{cm.U of a} standing voltage wave, defined as

will be equal to one. In this case, the radiation intensity of the loop dipole as a function of spherical angular coordinates will be characterized by its spatial radiation pattern.

The calculation of the input resistance Z _{D of the} inventive loop dipole in the frequency band f _L ... f _R , taking into account the effect of radiation of energy into the surrounding space from the surface of a continuous shielding conductor 3 filled with a dielectric with a relative permittivity with ε _r , is a very complicated electrodynamic problem. The greatest difficulty is the task in the analytical form of the boundary conditions on the conductive surfaces of the metal elements of the loop dipole. Although the steps of the subsequent analysis using the Maxwell integro-differential equations are well known, specific step-by-step procedures do not allow obtaining analytical expressions for the frequency dependence of the complex input loop resistance of the loop dipole Z _D (f) = R _D (f) + jx _D (f) in closed form, suitable for subsequent analysis.

For this reason, to calculate the input resistance Z _{D of the} loop dipole, it is advisable to apply one of the developed programs of three-dimensional electrodynamic modeling. Such software products have shown their high efficiency in solving radiation problems of antennas formed by an arbitrary combination of metal-dielectric structures with very complex surfaces. Therefore, further, to analyze the input impedance and radiation characteristics of the inventive loop dipole, we use the highly effective WIPL-D software product, which is freely sold on the software market as an application (on a CD) for work: V.M. Kolundzja, JSOgnjanovic, and T.K.Sarkar, "WIPL-D: Microwave circuit and 3D EM simulation for RF and microwave applications. Software and User's manual", Norwood, MA: Artech House, 2005.

The first one was to analyze a loop dipole made of a piece of RK-50-2-25-A coaxial cable in a continuous shielding - a copper tube with an outer diameter of 2.8 mm. It is this shell that performs the function of a continuous shielding conductor 3 (Fig. 1) filled with a dielectric. To give the loop dipole the desired shape (in the form of an “elongated” loop), the length of the cable of the appropriate length is properly bent so that the distance between the axes of the parallel wires 1 and 2 is 10 ... 12 mm. This distance satisfies, on the one hand, the requirement of spacing the emitting parallel conductors of the loop dipole by a small amount compared to the wavelength, and on the other hand, the requirement of observing the minimum bending radius of a solid copper tube without breaking it in the bend by 360 °. In this case, the wires 1 and 2 are the internal conductor (core) of the RK-50-2-25-A coaxial cable located in the dielectric with ε _r = 2.3 ... 2.5. The results of the analysis of the input resistance Z _D (f) of this loop dipole for the size l = 100 mm are presented graphically in the Smith diagram (figure 2, position 7). They indicate that at R _D = ρ _F = 224 Ohms, the claimed loop dipole is very well matched (G≈0; K _cm.U ≈1) with the signal source at a frequency f ^* = 1.227 GHz. If a loop dipole - prototype were designed for this frequency, then according to formula (1) its length would have to be:

Thus, the results of the analysis indicate that the inventive loop dipole, made of a piece of cable with a rigid outer conductor (braid) at a frequency f _C = f ^* = 1.227 GHz, has a size l of 1.2 times smaller than that of the prototype.

A more significant reduction in size is possible if an initially hollow shielding conductor 3 of an insulator with a large ε _{r is} used as a filling. However, commercially available coaxial cables are dielectric filled with ε _{r of the} order of 2.5. Therefore, foil sheet dielectrics should be used and a looped dipole should be implemented in a printed version that meets current trends in the design of small-sized dipole antennas. In this regard, we analyzed a printed loop dipole made on two dielectric blanks G ₁ (Fig. 3, position 8) and G ₂ (Fig. 3, position 9) from FR-4 material (ε _r = 4.4; tgδ = 0.018 ), with a thickness of H = 1 mm. This imported double-sided foil-coated dielectric is used in LLC “Electroconnect” (630090, Novosibirsk, 4, Inzhenernaya St.; www.pselectro.ru) in the manufacture of printed circuit boards for electronic products.

When comparing the analyzed printed version of the loop dipole with figure 1, it can be noted that the loop shielding conductor 3 is implemented by two parallel printed loop loops 10 and 11 (figure 3). To ensure the equipotentiality of the surfaces of the conductors 10 and 11 on each workpiece G ₁ and G ₂ four through metallized holes 12 with a diameter of 0.8 mm are provided. The width W of these conductors is 3 mm, and the width w of the printed conductors 13 located under the shielding conductors 10 and 11, which implements the printed loop method of the shielding conductor 3 (Fig. 1), was 0.6 mm. In this case, the conductors 13 are printed analogues of parallel wires 1 and 2 (Fig. 1) and are located above / below the conductors 10 and 11 symmetrically so that the distance between their center lines is 7 mm. After combining the blanks G ₁ and G ₂ (for orientation, one of the corners of the blank is beveled) and soldering through metallized holes 12, a printed version of the inventive loop dipole is formed.

The results of the analysis of the input resistance Z _D for the size l = 100 mm are presented in Fig. 4 (position 14 is a solid line and shaded circles), which implies that at R _D = ρ _F = 166 Ohms the proposed printed version of the loop dipole is ideally matched with a signal source at a frequency f ^* = 0.968 GHz. If a loop dipole prototype was implemented at this frequency, then according to (1) it would have the size

Thus, the results of the analysis of both the “cable” and the printed versions of the proposed loop dipole indicate a noticeable decrease in the longitudinal dimension l at the same frequency f ^* = f _C. This allows us to recommend the proposed loop dipole for use in compact antenna devices of both printed strip and volumetric tubular designs. In addition, the proposed loop dipole has a lower value of the material component R _D (f ^* ) of the input impedance at resonance compared to the classical value of the input impedance of the prototype loop dipole equal to 4 · 73.1 = 292.4≈300 Ohm. This makes it possible to simplify the execution of the matching-balancing device when supplying the proposed loop dipole with a coaxial cable (unbalanced single-wire shielded transmission line). As for the radiation patterns and the level of cross-polarization radiation, according to the analysis by the WIPL-D program, these characteristics of the proposed loop dipole correspond to the same characteristics of the prototype loop dipole. In other words, the introduction of a loop shielding conductor 3 (Fig. 1) filled with a dielectric does not impair the polarization and directional characteristics of the loop dipole.

For experimental confirmation of the health of the proposed loop dipole, the printed version depicted in FIG. 3 was examined. The input impedance Z _D was measured by the Tatarinov method (described, for example, in the work: Sazonov D.M., Gridin A.N., Mishustin B.A. Microwave Devices. - M .: Higher School, 1981, pp. 33-34) on the installation using a klystron generator G3-22, a measuring line P-122 and a specially made balancing device in a printed version, easily interfaced with the proposed loop dipole. All devices and components were connected with a 75 Ohm cable according to the block diagram shown in the work: Drabkin A.L., Zuzenko V.L., Kislov A.G. Antenna feeder devices. - M .: Soviet Radio, 1974, p. 433, Fig. XX.1.

The results of experimental studies of the frequency response of the complex input impedance Z _D (f) presented on the Smith diagram (Fig. 4, position 15 — open circles) indicate a successful solution of the problem posed — the realization of a loop dipole with a longitudinal dimension l of one and a half times smaller than at the dipole prototype [see formula (6)], at the same central wavelength λ _C , and about the prospects of the proposed loop dipole for practical use in dipole antenna devices of radio and telecommunication systems.

Claims (1)

A loop dipole for emitting electromagnetic energy into the surrounding free space, containing two parallel wires directly connected to each other at the ends, while one of the wires is open in the middle, and a transmitter or receiver is included in the gap formed, characterized in that a continuous loop shield is inserted into it a conductor filled with a dielectric, inside which wires are located.

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