The dipole board antenna design principles and practice
please Click here to get our dipole antenna
Abstract：This paper describes horizontal and vertical directivity functions of dipole planar antenna， introduces the principles on the determination of main parameters and discusses two frequently used schemes for obtaining down ward inclined main lobe and zero points cancellation．Some points on which attention must be paid in system design are pointed out．
Dipole antenna with a reflector plate (hereinafter referred to as the dipole-board antenna) is widely used in domestic and international radio and TV broadcasts an antenna. The higher the antenna gain (four-story double dipole board antenna gain can be done 8 dB), wide bandwidth meter band deployment of f0 ± 50 MHz bandwidth, the VSWR band the SWR ≤ 1.05, decimeter band an antenna for television transmission of multiple TV channels, horizontal direction, the map does not roundness can be done ≤ ± 2dB, and easy to install, debug, simple, high efficiency antenna.
A dipole-board antenna directivity function Figure
1.1 single dipole antenna directivity function
（1）
式中 
Horizontal directivity function; Fv (Δ) = 1 for vertical directivity function; l for the sum of the length of the oscillator; λ is the wavelength; θ is the azimuth; Δ is the pitch angle.
Different arm length l, level of dipole antenna directivity shown in Figure 1.
Figure a different arm length l, level of dipole antenna pattern
Radio and TV broadcasts on the choice of the oscillator arm length l, omni-directional in order to obtain higher gain, while maintaining a level of principle, the general should choose l = (0.6 ~ 0.7) λ is. The actual use of the oscillator length should be for the resonant length, the general oscillator the actual length of 10 = 0.95l.
Vertical dipole antenna directivity function Fv (Δ) = 1 This means that the vertical dipole antenna pattern is a rotation on the axis of the oscillator.
1.2 single dipole board antenna directivity function
Level of the single dipole-board antenna directivity function can be used the method of images obtained from Figure 2.
Figure 2 with a dipole antenna and its mirror reflector
The y-axis looking down the line for the infinite reflector, A is the active oscillator, the current upward direction B to its mirror. Cut in the ideal conductor surface electric field strength to the component with zero boundary conditions, the direction of current mirror should be facing down. H is the oscillator from the distance of the reflection plate.
For the r13.gif (183 bytes) H-plane at any point P, the source oscillator and its mirror constitute a constant amplitude inverting dual antenna array, the array factor of the mode
Where φ = k (2Hcosθ)-π as a mirror to the current B to point P lag phase; k = 2π / λ is the free space propagation constant.
Multiplied by the directivity function principle, the level of single dipole-board antenna directivity function
（2
Can be seen from the above equation, the role of sounding board, the main radiation direction θ = 0 °, the original field strength increases 2sin (kH) times.
Sounding board to the radiation field of the dipole antenna by the array factor f1, (θ) = 2sin (kHcosθ) study. Figure 3 shows the g68-1.gif (262 bytes) for different values of the array factor f1 (θ) direction Fig.
Figure 3 H / λ value array factor f1 (θ) pattern
The figure shows, regardless of g68-1.gif (262 bytes) value is the number of zero radiation in the g68-2.gif (374 bytes) direction. Oscillator from the sounding board for the same wavelength λ, the greater of the distance H, the more the pattern of lobe.
To reduce the sidelobes and zero, while at the same time to guarantee a certain direction coefficient engineering generally the g68-3.gif (651 bytes) is appropriate.
Single dipole plates vertically array factor f2 (Δ) can be used in the same way, Figure 4, the direct introduction of f2, (Δ) = 2sin (kHcosΔ)
t68-2.gif (2076 bytes)
Figure 4 vertically array factor f2, (△)
single dipole plate antenna vertical directivity function
g68-4.gif (1793 bytes) (3)
Two multi-storey multi-faceted dipole board antenna array directivity function
2.1 Array horizontal radiation field
Radio and TV broadcasts, the actual use of the dipole-board antenna is composed of multiple dipole board multilayer dipole board antenna array, each plate of two or four dipole. The antenna array on each four dipole board is installed from the top view shown in Figure 5.
t68-3.gif (2361 bytes)
Figure 5 four loaded dipole board antenna top view
The antenna array in the far zone to any point P on the level of field strength EP (θ) and the principle of superposition, according to the vector
g68-5.gif (1489 bytes) (4)
Where Ai is the i Vice antenna radiation field relative amplitude values; 14.gif (181 bytes) H (θ-εi) the level of the single dipole-board antenna directivity function; εi for the i-th antennas main radiation direction x-axis positive direction angle; φH i is the i Vice antenna axis origin is the reference phase angle due to the wave path difference caused by the space
φH i = kRcos (θ-εi)
R is the origin to the distance of the dipole; φK i is the input current phase angle of the i-th antennas, any one antenna can be the same floor entrance current reference, ahead of a positive lag is negative.
Offset the side-mounted as shown in Figure 6.
t68-4.gif (2444 bytes)
Figure 6 four side mounted dipole board antenna array top view
Figure 6 is not difficult to g68-6.gif (1004 bytes)
Where r is the offset of the center of the oscillator displacement.
Four suits dipole board antenna array directivity function in the calculation shown in Figure 5, taking into account the role of geometric symmetry of the reflector, in fact only need to calculate the dipole panels A1, A2 in the direction of the first quadrant diagram that is, can, the rest of the direction of the quadrant diagram which can be introduced.
Current and other pieces of dress-phase feed case, ignoring the phase function of f1 (θ), (4) can be simplified to
g68-7.gif (2872 bytes)
g69-1.gif (2484 bytes)
Relative field strength Ep (θ) mode (horizontal directivity function mode)
g69-2.gif (2273 bytes)
2.2 Array vertical radiation field
Order to enhance the directivity of the vertical pattern, increase the gain, coverage, as mentioned earlier, the actual use of the dipole-board antenna antenna array, each column in the vertical direction of multi-level cell antenna. The four-story one side of the vertical antenna array shown in Figure 7.
t69-1.gif (2385 bytes)
Figure 7 four-story vertical antenna array top view
Similar to the n-element antenna shown in Figure 7, the center equidistant d arranged in the same line equal to the current amplitude and current phase of bottom-up lag beta antenna array arithmetic sequence, known as uniform straight-line antenna array, the array factor
g69-3.gif (2369 bytes) (6)
Array factor f3 (Δ) on the impact of the vertical radiation field may be to discuss in Figure 8.
t69-2.gif (2872 bytes)
Figure 8 array factor of the f3 (△) pattern
In order to avoid the vertical direction in Figure grating lobes, the distance d between the unit antenna engineering generally does not exceed λ / 2.
For such a uniform vertical antenna array, vertical directivity function
g69-4.gif (2727 bytes) (7)
Consider, radio and television antennas commonly used mechanical tilting and layers of the current amplitude and phase ranging from feed law to the beam dump and zero fill. Mechanical downtilt shown in Figure 9. Vertical direction in this case the radiation field strength is calculated by
t69-3.gif (2115 bytes)
Figure 9 Mechanical tilting plate phase lag map
g69-5.gif (1122 bytes) (8)
Where g69-6.gif (418 bytes) for the vertical directivity function of the i-th antenna element; δ is the unit of the i-th antenna mechanical down tilt; φvi for a point of reference, due to the wave path difference caused by space radiation phase. Below a layer of mid-point of reference, tilting plate phase lag angle
g69-7.gif (899 bytes) (9)
Where L is the distance between layers, l is the dipole height of the board; Ai and φKi respectively, the relative value of the i-th antenna element entrance current amplitude and phase.
Antenna overall design must be noted that three dipole board
Non-circularity of the pattern of the 3.1 level
To the level of the transmitting antenna radiation field is rotating field, and the roundness of horizontal directional diagram there are two distinct concepts. Radio and television transmitting antenna requirements in the horizontal direction to the radiation, horizontal directional map-of-roundness ≤ ± 2 dB, which is important to note that one of the issues in the design.
As a design example shown in Figure 5, the four suits and other pieces of the center of the antenna array with the phase-fed dipole board oscillator arm length l = 0.7λ oscillator from the reflection plate distance H = λ / 4 dipole were taken away from the tower axis distance R 1λ, 1.2λ, 1.5λ, according to equation (5) the calculated level of directivity diagram shown in Figure 10.
t70-1.gif (4083 bytes)
Note: l = 0.7λ H = λ / 4
(A) R = 1λ (b) R = 1.2λ (c) R = 1.5λ
Figure 10 Figure 5 level of antenna array pattern
Can be seen from Figure 10, the above given parameters, in order to meet the level of directional diagram roundness ≤ ± 2 dB, indicators, it must be such that R <1.2λ. This meter band antenna may be hard to do, but for sub-meter band TV antenna, due to the restrictions of the horizontal cross-section of the tower body, often difficult to achieve. In this case, in order to improve the level of directional engineering is often used Polygon transmitting antenna array. Design methods can be found in the literature [2].
3.2 vertical distortion of the pattern
When the layers are more uniform vertical antenna array, the vertical pattern is mainly determined by the array factor (6) f3 (Δ). (6) can be deduced from the direction of maximum radiation angle of pitch
Δmax = sin-1β/kd (10)
Layers of current when the same phase feed, beta = 0 ° radiation angle Δmax the the = 0 ° main radiation direction of the tower vertical vertical, called the positive side radio array.
beta <0 ° that is bottom-up antenna array layers current phase ahead of a phase angle, Δmax <0 °, the main radiation under the direction of tilt.
beta> 0 ° ie antenna array bottom-up layers of current phase lag a phase angle, Δmax> 0 °, the main radiation upturned.
Especially when β = kd, when the main beam is perpendicular to the ground, into the end-fire array.
Layers of current non-ideal phase, which is prone to. Between the main feed tube, between the sub-feeder electrical unequal length, the design by the length sub-feeder to achieve beam dump purpose, but the actual construction errors assembly, etc., make the vertical direction in Figure distortion.
Figure 11 is a configuration diagram of the antenna and cable systems in the FM antenna transformation for the Huangshan 701 1993. Two 10 kW FM transmitter operating frequency of the center frequency f1 = 91.5 MHz, f2 = 103.6 MHz, design center frequency f = 100 MHz, The whole antenna and feeding system design is surrounded by the dipole board in the form of pairs of two pairs fed four layers, each dipole board design for the double dipole, the distance between the dipole d = λ / 2. Side of the side view shown in Figure 12.
t70-2.gif (6663 bytes)
Figure 11 duplex doubly fed FM antenna and cable system configuration diagram
t70-3.gif (2358 bytes)
Figure 12 four-layer of dipole board antenna side view
Installation and commissioning of the standing wave measured in the two main feed pipe at the entrance than the WSR ≤ 1.05, due to objective reasons, the two main feed tube geometry such as long processing only made in the construction of the actual effect of the transformation very poor.
Later by MA3620 network analyzer as long as the two main feed tube electrical re-test results are shown in Table 1.
Table 1 the main feed tube phase electrical test results
Center frequency of the main feed tube of a feed tube 2 the main feed tube
100MHz 21 ° 332.2 ° 311.2 °
Seen from Table 1, the two-tier current-fed phase lag than the lower layers of 311.2 ° / 2 = 155.6 °. The upper and lower levels were equivalent for the unit oscillator, the spacing D = 4d = 2λ. Substituting (10)
g70-1.gif (1654 bytes)
The antenna array main lobe width g70-2.gif (1361 bytes)
This shows that the severity of the main beam upturned.
In order to achieve the main feed tube and amplitude-phase feed, the main feed tube 2 were shortened. Shorten the length of the
Δ l = λε = 155.6 ° / 360 °
Where g70-3.gif (489 bytes) wavelength of the main feed tube; of f0 = 100 MHz, c = 3 × 108 m / s, the speed of light; εr = 1.08 SJUY-50-80-3-type main The feed tube dielectric constant into the specific data to be regarded as Δ l = 1.25 m. Now long two 91.5 MHz, the measured field strength are shown in Table 2.
Table 2 f = 91.5MHz main feed tube and so on long before and after the field strength measurement results
Pool gate Qimen Yi Xian, Huangshan District
Such as long ago / dB 18 23 66 68
Such as long / dB,> 46 53 74 77
4 beam dump and zero fill
In order to expand the coverage of radio and television, usually by increasing the transmitter power, the erection of a high transmitting antenna to achieve, but As noted earlier, the rate with the phase-fed multi-layer the dipole board antenna is a spherical surface, so if primary beam downtilt, the far field of the main beam in the design range can not be tangent to the ground, the radiation energy of a considerable portion of it will fall on the air losses, which pour into the umbrella of the reasons is the main beam. Main beam tilt angle formula
g71-1.gif (671 bytes)
The formula θH down tilt; HT antenna center height from the ground.
General high-power units to take θH ≤ 3 °, alpine units should be larger.
Order to improve the reception field strength of the far field, increase the gain, the same transmit power, the project commonly used method to solve the increasing antenna layers. However, the antenna array, the more layers, although the directional coefficient is increased, but the vertical direction the main lobe more narrow, the sidelobes increase, zero increase. Resulting in the formation of the launch pad around zero radiation with more. Thus zero fill is designed multi-transmit antenna must be considered one of the issues.
Beam down-dip and zero filled, but the results will be ideal and easy installation and commissioning is usually equal amplitude ranging phase feed and mechanical downtilt.
Ranging from 4.1 constant amplitude phase feed method
To the the dipole board antenna layers fed to sites ranging from the phase current can be adjusted according to equation (10), the main radiation direction of the vertical directivity pattern. As noted earlier, to make the main beam tilt down, the whole of β <0, meaning that they make the upper layers of the antenna current phase advance, the lower lag.
Uniform vertical antenna array amplitude and phase, the tilting angle can be used (10) to calculate the vertical antenna array of pieces ranging from the phase difference feed, tilting angle can be used (8) Order, Ai = 1, δ i = 0, the numerical calculation obtained.
Ranging from equal amplitude-phase feed can also play a 0:00 fill the role. Uniform amplitude and phase vertical antenna array, for example, the vertical directivity function g71-2.gif (2108 bytes) (11)
β = 0 ° the main radiation the angle Δmax = sin-1 (beta / kd) = 0 °, the width of the main lobe 2Δ0.5 = 0.88λ/nd, the maximum radiation field strength relative value
E (Δmax) = nsin (kH) (12)
Zero radiation point by equation (11) molecule is zero while the denominator is not zero to obtain
Δ0 = ± π / 2 and Δ0 = sin-1 (Kλ / nd)
(K ∈ non-zero integer) (13)
Number of zeros of the first quadrant
K ≤ nd / λ
(K, take a small positive integer) (14)
More on style visible uniform linear antenna array layers n, the greater the distance d between the oscillator, the higher the frequency, zero more.
beta <0 ° the main beam downtilt the main radiation angle Δmax = sin-1 (beta / kd) (15)
The relative values of maximum radiated field strength
g71-3.gif (1198 bytes) (16)
The same can be obtained zero
Δ0 = ± π / 2 and Δ0 = sin-1 (Kλ / nd + β / kd)
(K ∈ non-zero integer)
Number of zeros of the first quadrant
K ≤ nd / λ (1-β/kd)
(K to take a small positive integer) (17)
(13) into (11), can be obtained β = 0 ° vertical array of zero field strength level of increase. However, equation (12) and (16) can be seen in the case of H ≤ λ / 4, the main radiation field strong decline, which means that this 0:00 fill at the expense of the maximum gain obtained. (15) shows, the magnitude of down-dip in the main beam is relatively significant. In addition, the amplitude and the phase difference of this and other methods able to fill the amplitude and phase fed first, second zero, but it will generate a new zero, see (17). Engineering, often ranging from the phase difference to achieve the beam down-dip and zero fill.
This zero fill, and its mechanism is the use of layers of different feed phase, so that the layers of the electric field vector β = 0 ° uniform vertical array of zero at the formation of non-zero overlay at the same time pressure due to the direction of the upper layers of the primary radiation The lower tower vertical and perpendicular to the layers of the electric field vector superimposed the results of dumping under the direction of maximum radiation.
4.2 mechanical beam tilt and zero fill
This method is used on the radio and TV broadcasts is relatively more. That the the dipole board assembly process, the use of mechanical methods, will be on the first and the second dipole plate downward, tilt the board of the main radiation direction and the horizontal direction to form a negative angle between δ.
Four-story double dipole board FM antenna, and other sites with similar feed, the design center frequency f = 100 MHz (λ = 3 m), the oscillator spacing d = λ / 2 storey 2d = λ, the highest level dipole board δ = 15 ° mechanical downtilt, spent the interval between layers, and its structure is shown in Figure 13.
t72-1.gif (2543 bytes)
Figure 13 upper inclined four-layer dual-dipole board antenna array structure
Vertical directivity function of the x-z coordinate system origin located at the midpoint of the second layer A2, layers of wave path difference are the origin as a reference, excluding the f2 (Δ) and dual dipole phase function of the board, listed
g72-1.gif (7098 bytes) (18)
Where k = 360 ° / λ = 360 ° / 3 = 120 ° for the propagation constant;
f1 (Δ) = 2sin (90 ° cosΔ) cos (90 ° sinΔ) dual dipole-board vertical directivity function;
f2 (Δ) = 1 +2 cos (360 ° sinΔ) board for the next three-dipole array factor;
α = 120 ° (5.9sinΔ-0.4cosΔ) is the highest layer of the origin as a reference, due to the wave path difference caused by the lag phase angle.
Midpoint coordinates (x, z) is the highest level
g72-2.gif (2590 bytes) (19)
The modulus of the vertical directivity function
g72-3.gif (2325 bytes) (20)
Obviously, the top layer for mechanical downtilt make (19) δ = 0 into (18) may be organized
| FV '(Δ) | = 8sin (90 ° cosΔ) cos (90 ° sinΔ) × cos (180 ° sinΔ) cos (360 ° sinΔ) (21)
(21) the rectifiable winner radiation direction Δmax = 0 ° mode the maximum
| FV '(0 °) | max = 8, = 14.48 ° and zero Δ01, Δ02 = 30 °, Δ03 = 48.59 °, Δ04 = 90 °
Second zero into the tilt of the array of vertical directivity function (20), we can obtain g72-10.gif (1136 bytes), the first, second zero to the maximum value of the vertical array
g72-6.gif (2467 bytes)
Tilt array | 14.gif (181 bytes) V '(0 °) | = 7.36, Δ ≈ 2.8 °, the directivity function of the mold to obtain the maximum
| FV '(2.8 °) | max = 7.66
This means that the main beam tilt array tilt of about 2.8 °, while the gain and the value of upright compared, a decrease of the
g72-8.gif (1973 bytes)
Vertical direction as shown in Figure 14.
t72-2.gif (4230 bytes)
Figure 14 four-story double dipole board FM antenna vertical directivity pattern
Example, the dump can be achieved under mechanical beam down-dip, but not the formation of relatively large inclination, but also gain drop of the main radiation direction, zero filled with relatively large amplitude.
In summary, discussion, projects in order to obtain relatively large beam dump and the ideal zero-filling effect, usually combining the above two methods use the common calculation method can be used (8).
please Click here to get our dipole antenna
Our other product:
