RU2571607C1 - Microstrip log-periodic antenna - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: compared to existing antennae, the present antenna has a width of a symmetrical distribution feeder at dipole connection points selected using the relationship b_n=b₀·τ2.6^(H-n-1), where n=0…N-1, where n=0 corresponds to the longest dipole and n=N-1 corresponds to the shortest dipole. The width of the symmetrical distribution feeder at the connection point of the shortest dipole b₀ is selected such that wave impedance of the symmetrical distribution feeder W_l is equal to the wave impedance of an exciting coaxial feeder W_f. The equivalent radius of stripline dipoles is selected using the relationship a_n=a₀·τ^2.5n, wherein the equivalent radius of the longest dipole α₀ is selected equal to half the maximum width of the symmetrical distribution feeder b₀.

EFFECT: high quality of receiving and transmitting radio signals in the centimetre wavelength range, reducing the standing-wave ratio in the exciting coaxial feeder to 1,1-1,7 in the entire operating frequency range at higher antenna gain values ranging from 9,4 to 12,7 dB.

9 dwg

Description

FIELD OF THE INVENTION

The invention relates to antenna technology and can be used as a broadband irradiator of mirror antennas in the organization of satellite communications and C-band radio monitoring.

The level of technology.

Known log-periodic vibrator antennas (LHLA) consist of a system of parallel vibrators located in the same plane, antiphase excited by a symmetrical distribution feeder, starting with the shortest vibrator. The lengths of the vibrators and the distances between them vary exponentially with the denominator τ, the period of the structure. The row-spacing coefficient σ represents the relative distance between adjacent vibrators [1]. Each period of the structure τ corresponds to a certain inter-row coefficient σ, at which maximum gain is achieved. The optimal values of a lie in the range from 0.12 to 0.19 [2].

The disadvantages of these antennas include the fact that the choice of the optimal inter-row coefficient with a period of structure close to unity leads, on the one hand, to an increase in the coefficient of directional action (KND), and on the other hand, to an increase in the coefficient of the standing wave (SWR) in the exciting coaxial feeder.

In existing versions of log-periodic antennas, acceptable SWR values (less than 1.8) are achieved using one of the following methods. So in [2, p. 344] to match the log-periodic vibrating antenna with a coaxial cable in the ultra-short (VHF) and decimeter (UHF) wavelength ranges, use a short-circuited loop less than, λ _max / 8, connected to the power points of the longest vibrator, and in the short-wave (KB) range - a jumper .

The disadvantage of such antenna options is that with a further increase in the frequency and transition to the centimeter range (SMW) wavelengths this becomes insufficient, since the jumper begins to play the role of heterogeneity, which can have a significant impact on the characteristics of the antenna. Therefore, in [3], it was proposed to additionally extend the distribution feeder for the shortest vibrator by a distance of 0.06λ _min . This measure allows you to slightly reduce the value of the SWR to 1.5-1.7 in a narrow frequency range. The authors of [4] propose a different matching method, which consists in using a symmetrical strip line, which is both a power line and a resistance transformer.

Among the known solutions, the closest in technical essence to the claimed device is a log-periodic vibrator antenna according to the patent of the Russian Federation No. 2356140 C1, IPC H01Q 11/10, published on 05/20/2009, Bulletin No. 14 [5]. This patent was selected by the authors as a prototype.

при условии, что W_ф=50 Ом, или

при условии, что W_ф=75 Ом, а отношение длины l_n плеча n-го симметричного вибратора логопериодической структуры к эквивалентному радиусу полоскового проводника вибратора a_n выбрано удовлетворяющим условию

, где n=1…N.The antenna contains a number of symmetric vibrators, powered by a symmetrical distribution feeder, which is the load for the exciting coaxial feeder, with each subsequent symmetric vibrator in the antenna powered opposite to the previous one, and the ratio of the shoulder lengths of adjacent vibrators and the ratio of the distances between them are selected according to the formation ratios of the optimal log-periodic vibrator . Symmetric vibrators and a symmetrical distribution feeder are made in the form of strip conductors located on both sides of the dielectric base, and the ratio of the wave resistance of the symmetric distribution feeder W _l to the wave resistance of the exciting coaxial feeder W _{f is} selected from the relations

provided that W _f = 50 Ohms, or

provided that W _f = 75 Ohms, and the ratio of the length l _{n of the} shoulder of the n-th symmetric vibrator of log-periodic structure to the equivalent radius of the strip conductor of the vibrator a _{n is} chosen to satisfy the condition

where n = 1 ... N.

This technical solution has a limitation in that the authors of the patent provide the SWR values of the excitation coaxial feeder of 1.3-1.7 in the operating frequency range with an overlap coefficient of more than 2 when reaching the LPC values in the lower and upper limits of 6-7.5 dB and 10-11.5 dB, respectively, it is proposed to choose strictly defined values of the parameter pair τ and σ, optimized for two of the possible standard values of the wave impedance of the exciting coaxial feeder W _f = 50 Ohms W _f = 75 Ohms. In addition, the values of the active and reactive components of the input resistance of the antenna are not constant, but oscillate with a sufficiently large amplitude within the operating frequency range [5]. As a disadvantage of this technical result, it should be noted that the optimization procedure is aimed only at reducing the SWR without a significant increase in the antenna gain.

SUMMARY OF THE INVENTION

The purpose of the proposed technical solution is to improve the quality of reception and transmission of radio signals in the centimeter wavelength range (in the C range) by improving the matching of the antenna with the exciting coaxial feeder and a significant increase in the antenna gain.

This goal is achieved by the fact that in the proposed log-periodic vibrator antenna containing a number of symmetrical vibrators, the ratio of the shoulder lengths and the distances between them are selected by the ratios of the optimal log-periodic structure, fed from a symmetric distribution feeder, the width of which at the points of connection of the vibrators is determined by the expression b _n = b ₀ · Τ2.6 ^{(Nn ~ 1)} , where n = 0 ... N-1, with n = 0 corresponding to the longest vibrator, and n = N-1 to the shortest one. The width of the symmetrical distribution feeder at the connection point of the shortest vibrator was chosen so that the wave resistance of this feeder was equal to the wave resistance of the exciting coaxial feeder. The calculation of the width of the symmetric distribution feeder was carried out in accordance with the expression [6]:

- эффективное значение диэлектрической проницаемости, а h - толщина диэлектрической пластины, ε - относительная диэлектрическая проницаемость (для выбранного в качестве диэлектрика материала подложки ФЛАН-2,8 ε=2,9, тангенс угла диэлектрических потерь tg(δ)=1,5·10^-3 и h=1,95 мм). Симметричный распределительный фидер и симметричные вибраторы выполнены фотохимическим (печатным) методом в виде полосковых проводников, расположенных с двух сторон от диэлектрического основания, причем эквивалентный радиус полосковых вибраторов определяется выражением a_n=a₀·τ^2,5n. Максимальное значение эквивалентного радиуса выбиралось из условия a₀=0,5b₀. Антенна питается возбуждающим коаксиальным фидером с волновым сопротивлением W_ф=50 Ом.Where

is the effective value of the dielectric constant, and h is the thickness of the dielectric plate, ε is the relative dielectric constant (for the FLAN-2.8 substrate material chosen as the dielectric, ε = 2.9, dielectric loss tangent tg (δ) = 1.5 10 ^-3 and h = 1.95 mm). The symmetric distribution feeder and symmetric vibrators are made by the photochemical (printed) method in the form of strip conductors located on both sides of the dielectric base, and the equivalent radius of the strip vibrators is determined by the expression a _n = a ₀ · τ ^2.5n . The maximum value of the equivalent radius was selected from the condition a ₀ = 0.5b ₀ . The antenna is powered by an exciting coaxial feeder with wave impedance W _f = 50 Ohms.

In FIG. 1 shows three projections of the design of the claimed log-periodic vibrator antenna.

In FIG. 2 shows a view of a microstrip printed circuit board of a log periodic antenna.

In FIG. 3 shows the geometric dimensions of the elements of the log-periodic antenna.

Log-periodic vibrator antenna (see Fig. 1) contains a number of symmetrical vibrators 1 connected to a symmetrical distribution feeder 2, which are made in the form of strip conductors on both sides of the dielectric base 3. An excitation coaxial feeder 4 is laid along one of the conductors of the symmetric distribution feeder 2. The braid 5 of the exciting coaxial feeder 4 is in contact with one of the conductors of the symmetrical distribution feeder 2 at the connection point of the smallest of the vibrators, and the central silt 6 of the exciting coaxial feeder 4 is in contact with the opposite conductor of the symmetrical distribution feeder 2. On the side of the largest of the vibrators, the conductors of the symmetric distribution feeder 2 are connected by a short-circuit loop 7.

The principle of operation of such an antenna is as follows. An electric signal with a frequency f _n , n = 0 ... Ν-1, which is resonant for the nth vibrator, is supplied to the antenna through a symmetric distribution feeder. Vibrators located at the beginning of the antenna and short in comparison with the resonating, as well as located at the end of the antenna and long in comparison with the resonating, practically do not emit, since the currents branching into them are small in amplitude due to the large value of the reactive component of the input resistance of the vibrators .

The resonant n-th antenna vibrator is excited most intensively by the voltage wave in the symmetric distribution feeder, since the magnitude of the reactive component of its input resistance is minimal, and the input resistance itself is practically active. On both sides of the resonating vibrator there are vibrators acting as directors and reflectors, the current amplitudes in which are comparable with the current amplitude in the resonating vibrator due to the small reactive component of their input resistance. Thus, there is a so-called active region of the antenna, in the composition of which, as a rule, from three to five vibrators are present.

When the operating frequency changes in the direction of decreasing, the next longer vibrator begins to resonate with respect to the previously considered case and the active region moves along the antenna to its end. On the contrary, with increasing frequency, the active region shifts to the top of the antenna [7]. To coordinate the antenna with the exciting coaxial feeder and stabilize the SWR within the specified limits of 1.1-1.7, as well as to provide the specified value of the directivity gain, we optimized the geometry of the strip vibrators and the symmetric distribution feeder, which was carried out at a given period of the structure τ and the corresponding optimal value inter-row coefficient σ.

Analysis of existing electrodynamic models of LPVA showed that in the known optimal structures it is assumed that the vibrator as an element of the antenna is infinitely thin and ideally conducting electric current; the amplitude distribution of the current is sinusoidal along a symmetrical vibrator; the complex equivalent input impedances of individual vibrators are represented by the sum of the complex intrinsic resistance of the vibrator and the complex introduced resistance from the other vibrators of the system, taking into account the mutual electromagnetic coupling between them; all elements of a multivibrator antenna are fed from individual feeder lines and are consistent with them [1, p. 341], or the distribution feeder is matched with the resonating element and two neighboring elements, and the influence of the remaining elements is not taken into account [1, p. 19].

These assumptions do not allow an accurate estimate of the width of the active region of the antenna, the induced radiation power of all vibrators on the element under consideration, as well as the directional properties of the VLBF such as the width of the radiation pattern (LW), directional coefficient (KND), gain (KU) and relative level of side lobes (UBL).

It is known that the LPVA is supplied by one distribution feeder, and individual antenna elements are loads included in its various sections. Moreover, the complex equivalent input resistances of the emitters in a complex way depend on the frequency due to the presence of electromagnetic coupling between them and are not complex conjugate values of the input resistance of the feeder in the sections under consideration. In [8], a method was proposed for calculating the amplitude-phase current distributions along the LPVA, in which the influence of the distribution feeder and the resistance value of the ohmic loss of the elements are taken into account. In [9], the influence of the distribution feeder on the characteristics of the LPAA radiation is taken into account and a mathematical model of the radiation field and the polarization properties of the LPAA in the far zone is presented.

In the method proposed by the authors for calculating the terminal currents of the vibrators, according to the induced EMF method, the terminal current of the i-th vibrator is determined by the expression:

- элементы матрицы, обратной по отношению к матрице собственных и взаимных сопротивлений вибраторов с учетом омических потерь,

- комплексная амплитуда клеммного напряжения i-го вибратора.Where

- elements of the matrix inverse to the matrix of intrinsic and mutual resistances of the vibrators, taking into account ohmic losses,

- the complex amplitude of the terminal voltage of the i-th vibrator.

Terminal voltages are determined by a recurrence relation of the form:

- комплексная амплитуда напряжения на входе симметричного распределительного фидера, Z_вхi - комплексное входное сопротивление i-го вибратора с учетом влияния симметричного распределительного фидера, γ=α+jβ - комплексный коэффициент распространения волны в симметричном распределительном фидере, α - коэффициент затухания в симметричном распределительном фидере, β - коэффициент фазы в симметричном распределительном фидере, S_i-1 - расстояние между i-ым и (i-1)-ым вибраторами. Входящее в данное рекуррентное соотношение комплексное входное сопротивление Z_вхi определяется выражением видаwhere i = 0 ... (N-2),

is the complex voltage amplitude at the input of the symmetric distribution feeder, Z _Вi is the complex input resistance of the i-th vibrator taking into account the influence of the symmetrical distribution feeder, γ = α + jβ is the complex wave propagation coefficient in the symmetric distribution feeder, α is the attenuation coefficient in the symmetric distribution feeder , β is the phase coefficient in the symmetric distribution feeder, S _i-1 is the distance between the i-th and (i-1) -th vibrators. Included in this recurrence relation, the complex input impedance Z _Vxi is determined by an expression of the form

- комплексное входное сопротивление i-го вибратора с учетом его электромагнитной связи с другими вибраторами антенны, а

- комплексное входное сопротивление сечения симметричного распределительного фидера в месте подключения i-го вибратора.Where

- the complex input resistance of the i-th vibrator, taking into account its electromagnetic coupling with other antenna vibrators, and

- complex input impedance of the cross section of the symmetric distribution feeder at the connection point of the i-th vibrator.

задано выражением видаIntegrated input impedance of the i-th vibrator

given by an expression of the form

where Z _ij are the elements of the matrix of intrinsic and mutual resistances of the vibrators, and the complex input impedance of the cross section of the symmetric distribution feeder is determined by a recurrence relation of the form

The mathematical model of the LPAA radiation field in the far zone is the sum of the complex amplitudes of the electric field strengths from all antenna elements under the assumption that the radius of the LPAA element is infinitesimal, the gap between the terminals is small and the element’s shoulders are aligned.

The complex amplitude of the electric field of an individual LPVA element is determined by an expression of the form [10]:

, r - расстояние от клемм самого длинного элемента до клемм i-го элемента, R - расстояние от клемм самого длинного элемента до точки наблюдения, а комплексная амплитуда напряженности электрического поля ЛПВА в дальней зоне:where (θ, φ) are the spherical coordinates,

, r is the distance from the terminals of the longest element to the terminals of the i-th element, R is the distance from the terminals of the longest element to the observation point, and the complex amplitude of the LPVA electric field in the far zone:

The antenna gain in the direction of maximum radiation can be calculated in accordance with an expression of the form:

where E _max - the maximum value of the amplitude of the electric field of the antenna.

The polarization diagram and the ellipticity coefficient of the antenna are determined by expressions of the form:

This electrodynamic model was the basis for model studies of directional and polarization properties, as well as the electrical characteristics of a patented antenna in a MathCAD environment, the results of which are presented in FIG. 4-9. An analysis of the results showed that the shape of the radiation pattern remains virtually unchanged in the entire operating frequency range and there is a slight increase in the width of the beam with an increase in the operating frequency (see Fig. 4-5). The polarization diagram is a regular figure eight, and the polarization characteristic is straight in the entire frequency range, which indicates the linear nature of the polarization of the radiated antenna wave (see Fig. 6). The gain values are in the range from 9.4 to 12.7 and on average decrease with increasing operating frequency (see Fig. 7).

Analysis of the frequency dependence of the active and reactive components of the input resistance of the LPVA (Fig. 8) allows us to conclude that both components remain almost unchanged in the entire operating frequency range, and the active component makes small fluctuations around a value of 50 Ohms, corresponding to the wave resistance of the exciting coaxial feeder and the reactive component is capacitive in nature with an average absolute value of 10 ohms. The presence of a small reactive component of the input resistance of the LPVA indicates a small mismatch of the antenna with the exciting coaxial feeder. The values of the SWR also remain stable and lie in the declared range from 1.1 to 1.7 (see Fig. 9). Thus, the claimed configuration of the LPVA allows reaching gain values of 9.4-12.7 dB with SWR values from 1.1 to 1.7.

The technical result is to reduce the standing wave coefficient (SWR) in the exciting coaxial feeder to values of 1.1-1.7 in the entire operating frequency range with an achievable level of antenna gain from 9.4 to 12.7 dB.

LIST OF USED LITERATURE

1. Petrov B.M., Kostromin G.I., Goremykin E.V. Log-periodic vibratory antennas: a textbook for universities. - M .: Hot line - Telecom, 2005 .-- 239 p.

2. Rothammel K. Encyclopedia of antennas. Volume 1, 2. Edition 11 rev. - M.: DMK Press, 2011 .-- 812 p.

3. Yatskevich V.Α., Alexandrov V.S. Design of log-periodic vibrator antennas // Antennas, Vol. 7-8, 2005 .-- p. 3-12.

4. Bondarev V., Kalenov R. Coordination of a log-periodic antenna in a wide frequency range // Modern Electronics, No. 2, 2012. - p. 52-56.

5. Patent of the Russian Federation No. 2356140 C1, IPC H01Q 11/10, published May 20, 2009, Bulletin No. 14.

6. Design of microwave strip devices: a training manual. - Ulyanovsk: Ulyanovsk State Technical University, 2001. - 129 p.

7. Kocherzhevsky G.N., Erokhin G.Α., Kozyrev N.D. Antenna-feeder devices: Textbook for universities. - M .: Radio and communications, 1989 .-- 351 p.

8. Volkhonskaya E.V., Korotey E.V., Kuzhekin D.V. Calculation of the electrical parameters of a multi-element antenna taking into account the interaction of elements through a feeder line. Journal of Radio Engineering No. 2, 2013. Geographically-distributed security systems (magazine in the journal "Radio Systems") - p. 103-106].

9. Volkhonskaya E.V., Korotey E.V., Kuzhekin D.V. Comparative analysis of the directed properties of LPVA of the GSM-900 standard according to the results of model and full-scale experiments. Journal of Radio Engineering No. 2, 2014. Geographically distributed security systems (magazine in the journal "Radio Systems") - p. 95-98.

10. Markov G.T., Sazonov D.M. Antennas: A textbook for students of radio engineering majors. - M .: Energy, 1975 .-- 528 p.

Claims (1)

A log-periodic vibrator antenna containing a series of symmetrical vibrators made in the form of thin rectangular metal conductors on the surface of the dielectric base, the ratio of the lengths of the arms and the distances between them is selected according to the ratios of the optimal log-periodic structure, which are in phase fed from the symmetric distribution feeder formed by two flat conductors located on both side of the dielectric base, powered by an exciting coaxial feeder, with Connections at the connection point of the shortest of the vibrator, wherein the terminals of the longest vibrator attached shorted stub length λ _max / 8, characterized in that the width of the distribution feeder symmetrical dipoles at the points of attachment selected ratio b _n = b ₀ · τ ^{2,6 (Nn -1)} , where n = 0 ... N-1 and n = 0 corresponds to the longest vibrator, and n = N-1 to the shortest one, the width of the symmetrical distribution feeder at the connection point of the shortest vibrator b _{0 is} chosen so that the wave impedance symmetric p of the distribution feeder W _{l was} equal to the wave impedance of the exciting coaxial feeder W _f , and the equivalent radius of the strip vibrators was selected from the relation a _n = a ₀ · τ ^2.5n , and the equivalent radius of the longest vibrator a _{0 was} chosen equal to half the maximum width of the symmetrical distribution feeder b ₀ .

Images