FI84947C - BREDBAND BALUN BYGGD IN I ANTENNEN. - Google Patents

Description

1 84947

BROADBAND BALUN BROWNBAND BALUN BYGGD IN I ANTENNA BUILT IN ANTENNA

The present invention relates to a new broadband balun built into a hollow symmetrical antenna, by means of which an asymmetrical antenna supply line (coaxial cable) can be connected to the symmetrical input terminals 5 of the antenna without disturbing the electrical symmetry of the antenna.

The symmetry of the supply is generally maintained if partial supply of the supply current to the outer surface of the metal sheath of the supply line can be prevented. In currently known balunes in use, this blocking of external surface currents is often implemented by increasing the impedance between the antenna supply terminals and the outer surface of the supply line sheath by means of additional components as high as possible compared to the antenna supply impedance. This solution is used e.g. In basooka and choke balunes. Known baluns also include baluns operating on the principle of 15 phase inversion and magnetic switching, which can also be used for impedance conversion at the same time. Many known structural solutions for baluns are based on the utilization of ferrite materials, an example of which is the so-called HP balun (Hewlett-Packard Applica- ____: 20 tion Note 86). Patented balunes are mentioned herein by U.S. Pat. Patents Nos. 3,656,071, 3,827,001, 3,846,721, 3,976,959 and 3,991,390, which were disclosed in Preliminary Study No. 204 / 88-04-12.

A: Balunes based on already known balun principles are also used inside the antenna. An example of this is the Marchand balun built into the antenna, which also acts as an impedance converter (N. Marchand, ‘; Transmission Line Conversion Transformers’, Electronics

Butter. 17, Dec. 1944).

2,84947

The worst shortcomings and disadvantages of known and currently used balunes are: - frequency dependence (also in broadband baluns) - impedance dependence 5 - rel. high switching attenuation - the formation of an additional mechanical structure in connection with the antenna

Ferrite-structured baluns also have the disadvantage of saturation at high power levels, which can crack 10 through transmissions. The problem with baluns using magnetic coupling is possible bias resonances, which reduce the available frequency range, especially in broadband baluns.

All the above-mentioned disadvantages of existing baluns 15 are avoided in the built-in broadband balun according to the invention, the characteristic points of which are set out in the claims. The structure of this balun and. . the operating principle will be explained in the following with the aid of FIGS. 1, FIG. 2 a) b), and FIG. First, the contents and main structural features of Figures 20 will be described.

FIG. 1 shows a balun according to the invention placed inside a rectangular symmetrical loop antenna 1 constructed of a tube. The element tube 1 is thought to be open-cut. The antenna feed points are marked with the letters 25 A, A 'and B, B'. Antenna supply cable (coaxial cable) 2

enters the antenna from the aperture C and passes in the right-hand branch of the antenna to the feed point. Inside the left branch of the antenna is a cable 3 corresponding to the diameter and characteristics of the supply cable, the sheath 30 of which is connected to the sheath of the supply line 2 at point 4 in the opening C

above. Cable 3 is referred to herein as a balancing cable. Connection of both cables at supply point A-B

3 84947 is identical for the sheaths (are mirror images of each other), but the inner wire of the balancing cable 3 is left free at both ends of the cable.

The structure of the antenna with the new balun as a whole (FIG. 1) comprises two symmetrical constructions: 1) An external actual antenna which connects to space with its radiation resistance and radiates energy. 2) A built-in balancing balun, 1. A "balun antenna" that does not communicate with space and does not emit energy. The supply line 10 comes out of the potential 0-point C of both of these constructions. It should be noted that the actual supply line is the dielectric material between the inner surface of the sheath of the supply line 2 and the center wire of the line. The outer surface of the sheath of the same wire 2 15 inside the antenna (in the right branch) is half the total length of the balun.

FIG. 2 a) shows an enlarged view of the connection of the supply cable 2 and the balancing cable 3 at the supply terminals A-B of the antenna 1. From this figure it is further derived FIG. 2 b), in which the total power coming via the -f- supply cable is represented by an equivalent generator 5. The second equivalent generators 6 and 7 supply the partial powers propagating in the right and left inner branches of the antenna 1. The equivalent generator 6, on the other hand, represents the partial power 25 which inherently tends to unbalance the supply, and the equivalent generator 7 represents the balancing power supply according to the invention by which the power supply of the generator 6 (further through the outer surface of the supply line 2 outside the antenna) is blocked. The polarities of the equivalent generators 30 represent the situation in a figure during a half cycle. It should be emphasized here that the generator 5 represents the total power supplied to the antenna, which is entirely intended to be fed into space 4 84947 through the outer surface of the antenna 1 element, and the generators 6 and 7 represent the partial powers propagating between the inner surface of the antenna element 1 and the balancing in accordance with 5 arrangements.

FIG. 3 shows an enlarged connection of a balun according to the invention in the lower part of the antenna at the opening C. Aperture C is located in the center of the antenna element, which also houses the minimum voltage of the antenna. Inside the element, the sheath of the balancing cable 10 is connected to the sheath of the supply cable at a point 4, which is the mechanical center of the balancing antenna and at the same time the 0 point of its electrical voltages. The part of the supply line outside the antenna leaves perpendicularly from point 4.

15 THE BUILT-IN BROADBAND OF THE INVENTION

BALUN ACTIVITIES

It is assumed that the antenna 1 under consideration according to FIG. 1 is electrically of one wavelength. (For balun and antenna operation, this length is not a condition, 20 but with an electrical sample length of one wavelength, the initial consideration is more illustrative in terms of phases). Since the closed state of the balancing antenna (inside the element 1) is mainly air, the electrical length of the balancing antenna is also about one wavelength. (Again, this 25 length equivalence is not a condition for balun operation, as will be shown later).

5 ö 4 947

When the correct frequency transmission between the inner surface of the sheath of the supply line 2 (PIG 1) and the inner wire meets the feed point A-B of the antenna, the outer surface of the rectangular antenna acts as the actual antenna and loads the transmission with the radiation resistance of these 5 antennas. The current representing the radiant power of the antenna flows on the outer surface of the element 1 in the direction shown in FIG. 2 b) during one half period.

Part of the power supplied by the supply line 2 also switches to propagate in the space between the inner surface 10 of the right branch of the antenna element 1 and the outer surface of the sheath of the supply line 2 and tends to propagate further out of the opening C under the outer surface of the sheath. (This power component is, in a general sense, the asymmetry-causing component that produces harmful currents on the outer surface of the supply line sheath outside the antenna 15).

On the other hand, part of the power supplied by the supply line 2 is switched on in the space between the inner surface of the left branch of the antenna element 1 and the outer surface of the sheath of the balancing cable 3.

In the arrangement according to the invention, the electromagnetic fields representing the above-mentioned partial powers arriving at point 4 (FIG. 1) from the right and left are equal, but with a phase difference of 180 degrees, and cancel each other out at this point. Point 4 always forms an electrically neutral point (point 0 of the rivet-25 rivets). There is no asymmetry from the opening C to the outside of the antenna, perpendicular to point 4, to the outer surface of the sheath of the connected supply line (out of the opening C); · Generating currents and supply point A-B is balanced.

6 84947

The invention further includes an important and novel additional function that further improves the efficiency of balancing. In order to determine the additional operation, the further situation is considered after the electromagnetic fields from the right and left 5 inside the element 1 have encountered at point 4 (FIG. 1). Seen from the outside, the fields vector-cancel each other at this point, but continue to progress as separate fields towards each other's feed points. The subfield from point B (right) arrives at point A and the field from point A arrives at point B, respectively. On the other hand, due to mismatch, the feed points are each other’s reflection points, so the fields that arrive through the rotation are reflected back toward their starting points. Since there is no matching resistance in the balun, the equilibrium of all reflections is created when the real power that can be connected from the 20 A and B points inside the element 1, to the 1st balun, corresponds only to the ratio consumed in the balun. low power dissipation. The vector interaction of the fields is then that the outgoing fields inside the element are attenuated. The same can also be expressed as the impedances of the 25 supply points (inside the antenna) changing in the direction attenuating the output powers. In this case, a two-part amplitude-symmetrical, half-phase standing wave is generated on the balun transmission line path (for the entire length of the antenna interior). On the other hand, it can be shown that the equivalent loss resistance of the built-in balun according to the invention is very low even at relatively high frequencies. Balun losses are the resistive and dielectric losses of a structural cable that can be kept small by material choices. Balun does not radiate, and 35 thus has no radiation resistance. Thus, thanks to the reflection function described above, the new balun prevents the useful power from being coupled to the balun / outer surface of the supply line jacket.

7 84947

It can also be shown that the good balancing operation described above remains the same even if the electrical length of the antenna / balun differs from the resonant length.

The result of the reset and reflection operation of the built-in new balun is that only a relatively small partial power corresponding to the balun's own losses can reach a) the balun in general and further b) only a small part of this partial power can still reach the sheath of the supply line outside the antenna. (O-point attenuation is always at point 4 10 FIG. 1).

Structurally, the new balun must emphasize the new arrangement that when the supply line 2 enters the antenna from the antenna voltage minimum point C, it further enters the balun element from point 0-15 of the standing wave of the balun. The actual supply line is between the inner surface and the inner wire of the cable 2 sheath. The outer surface of the sheath of cable 2 is half of the balun element. The other half of the balun element consists of the outer surface of the sheath of the balancing cable 3.

The functional advantages and novelty values of the built-in broadband balun according to the invention can now be summarized - in summary: - The built-in new balun is very broadband.

. Theoretically, it is infinitely wideband, and it never limits the bandwidth of the antenna connected to it.

- The new balun is not impedance dependent, i.e. its balancing function is equally good in matched and unmatched input. Even if the mismatch is significant, or the load β 84947 is highly reactive, the balun will still work just as effectively and block currents on the outer surface of the supply line sheath outside the antenna.

- The connection attenuation of the built-in balun is low.

5 This is due to the fact that, according to the above operation, the balun takes advantage of a new symmetrical impedance change generated by the reflections in connection with the balun, which dampens from the connection points A-B (FIG. 1) in the direction of the supply line and the sheath of the balancing cable 10.

- The supply line is brought into the antenna and the balun from the electrical 0 points of the antenna and the balun element.

- The new balun switches in parallel with the input A-B and automatically processes only the part of the power that can normally reach the balun during balun operation.

- The new balun also implements the physical symmetry of the feed points A and B (FIG. 1, FIG. 2), which contributes to the creation of the electronic symmetry realized by the balun.

- The new balun is mechanically invisible and does not need space outside 20 antennas.

li

Claims (5)

9 84947 Broadband balun built into a symmetrical hollow antenna, characterized in that the balun element inside the antenna consists half of the outer surface of the sheath 5 of the antenna supply line (2) running inside the second branch of the antenna and half of the outer surface of the balancing cable (3) inside the second branch of the antenna and a two-part amplitude-symmetric and half-phase standing wave is generated on the transmission path between the common outer surface of the sheaths and the inner surface of the antenna structure, with the center of symmetry at the point (4) . Balun according to claim 1, characterized in that the supply line supplying the antenna is introduced inside the antenna and the balun at the voltage minimum of the two-part standing wave generated in the balun inside the antenna. Balun according to Claims 1 and 2, characterized in that the supply line supplying the antenna is introduced inside the antenna and the balun at the voltage minimum generated on the outer surface of the integral element part of the antenna. Balun according to Claims 1 to 3, characterized in that the balun is connected mechanically and electrically 25 symmetrically parallel to the input terminals of the antenna. Balun according to Claims 1 to 4, characterized in that the currents representing the radiant power of the antenna do not pass through the components of the balun. 10 84947