Encyclopedia of radio electronics and electrical engineering / Antennas. Measurements, adjustment, coordination

 Comments on the article

Some amateur HF bands (160, 80 and 10 meters) have a wide relative bandwidth of almost 10%, and not every antenna performs satisfactorily on all frequencies of these bands. Replacing a narrow-band antenna with a broader one is far from the easiest and cheapest solution to the problem.

There is another possibility to significantly expand the operating frequency band of a narrow-band antenna - with the help of a specially designed matching device. The issues of creating such devices are considered in the published article.

Often, the antenna system with its matching device (CS) does not cover the desired frequency band for a given SWR. In this case, the antenna has its own band, and the SU has its own. And, it would seem, when connected in series, the total bandwidth (BW) will be less. But we take into account that the antenna and control system, as a rule, are resonant devices. Therefore, the BW of the antenna system can either narrow or expand, everything depends on the nature of the change in the reactivity jX(f) of the antenna and the control system.

Recall the technique of bandpass filters - a two-loop filter can have a wider band than a single loop. As you know, a properly made bandpass filter contains alternating series and parallel oscillatory circuits. We have one of the circuits - an antenna (with some approximation, this can be considered). Therefore, depending on the nature of the change in jXa with frequency (as in a serial or parallel LC circuit), it is necessary to choose the nature of the change in jXcу(f).

1. Broadband matching by a parallel LC circuit at the feed point

Near the resonant frequency, the equivalent circuit of a half-wave (λ/2) dipole fed at the center is a conventional series LC circuit. The same applies to λ/4 GP. If the first circuit (antenna) is serial, then to form a broadband two-circuit filter, a parallel LC circuit must be connected to it, tuned to the middle frequency of the matching range. It is connected in parallel to the supply cable and, accordingly, to the antenna. What this leads to is shown in Fig. 1, using the example of a λ / 2 dipole at 28 MHz, in parallel to which a parallel LC circuit is connected (capacitor with a capacitance of 500 pF and an inductance of 62 nH).

(click to enlarge)

The dependence jX(f) acquires an S-shaped character typical for broadband matching systems, and, with the correct setting, stops the zero value three times. This is a consequence of the mutual compensation of the reactivity of the antenna and the control system (our circuit). As a result, BW in terms of SWR <2 expands by more than one and a half times compared to a conventional half-wave dipole.

Dependence R(f) has an unusual form - at the middle frequency (where the LC circuit is tuned to resonance and does not affect in any way) R corresponds to the resistance of a simple dipole. With a detuning in any direction from the center frequency, the presence of an LC circuit leads to a transformation of the resistances and an increase in the total R. As a result, the dependence R(f) has two maxima, almost symmetrically located relative to the center frequency.

The reactance of the loop capacitor at the operating frequency usually lies in the range of 5 ... 20 ohms (rather large capacitance), the coil is selected based on the condition for obtaining resonance. Practice has shown that slightly better BW results are obtained if the resonant frequency of the LC circuit is slightly higher (by 10..15% of the absolute BW band) of the middle frequency of the range. The distance between the extreme zeros of the S curve on the graph jX(f) depends on the capacitance of the circuit capacitor. Its increase leads to the convergence of the extreme zeros and, accordingly, to the narrowing of the band. An excessive decrease in capacitance leads to an expansion of the S-curve to those frequencies where R already drops sharply, which again leads to a narrowing of BW. The optimal value of the loop capacitance is easy to select using MMANA, focusing on the shape of the S-curve of the jX(f) graph and the bandwidth BW on the SWR graph.

Good results are obtained using this termination for a λ/4 GR on the ground, powered by a 50 ohm cable. An increase in the active part of the input impedance from 37 ohms in the center to 50.. .60 ohms at the ends of the range provides two SWR minimums. On fig. Figure 2 shows an example of an 80 m GP to/A matching (GP resonance at 3,65 MHz) with a parallel loop tuned to 3,67 MHz with a loop capacitance of 7500 pF.

(click to enlarge)

SWR in the entire range of 3,5 ... 3,8 MHz does not exceed 1,4 with two distinct minima in the CW and SSB DX sections. With a decrease in the vertical height to obtain a resonance of 3,75 MHz, an increase in the frequency of the SU circuit to 3,78 MHz and a decrease in the capacitance of the capacitor to 5000 pF, it becomes possible to cover a band of more than 500 kHz.

Similarly, λ/4 GP with its own resonance at 27,8 MHz is matched with a parallel circuit (capacitor capacitance 300 pF) in the 26...29,7 MHz band covering the MW and amateur bands.

In this way, it is possible to expand the bandwidth of any antenna that behaves at its resonant frequency like a series circuit. These include almost all antennas fed at the discontinuity of the current antinode (that is, most antennas), including loops with a perimeter of 1λ.

I note that in order to obtain optimal characteristics, it is desirable that the intrinsic (without SU) input impedance Ra of the antenna at resonance be somewhat lower than the wave impedance Zo of the transmission line used. The Zo/Ra ratio will give the value of the peak SWR at the center of the range. The bandwidth extension achieved by this method is 1,5...2 times.

The voltage on the loop does not exceed the output voltage of the transmitter, the reactive power of the loop capacitor must be at least the power of the transmitter. The SU circuit must be tuned to the middle frequency of the range before installation on the antenna and usually does not need further tuning. But adjustment within small limits (by stretching or compressing the loop coil turns) to the maximum BW will not hurt.

2. Broadband matching by serial LC circuit through A, 4 line segment

Despite all the advantages, the matching method described in the previous paragraph has disadvantages. Firstly, the Ra value in the middle of the range is determined by the antenna and cannot be changed, and secondly, the LC circuit located at the feed point is not always available for adjustment (near a dipole, for example). The method described below is devoid of these shortcomings. It is based on a curious property of a line segment with a length of λ/4: if you load it on a series LC circuit, then at the input of the line, the nature of the dependence jX(f) will correspond to a parallel circuit (above the resonant frequency, jX will be capacitive, and below - inductive).

If we connect an antenna with the nature of jX(f) change, as in a series circuit, through a line segment with a length of λ/4, then at the end of the segment we will obtain the jX(f) dependence, as in a parallel oscillatory circuit. Obviously, to expand the band (that is, the formation of a two-loop filter) between the parallel circuit (the end of the λ / 4 line segment) and the main feed line, it is necessary to turn on a serial circuit tuned to the middle frequency of the range. In this way it is also possible to transform Ra if the wave impedance λ/4 of the segment is not equal to Ra.

In this way, λ / 50 GP standing on the ground successfully agree with the 4 Ohm line. When connected through a segment of a 50-ohm cable with a length of λ / 4, the antenna resistance Ra \u37d 68 Ohm increases at the average frequency to 68 Ohm (providing a "hump" SWR 50/1,35 \u50d 4). Adding a serial LC loop allows you to get an S-curve jX(f) with two SWR minimums at the ends of the range and an extension of BW. This matching scheme looks like this: a 2,15 ohm power cable is connected directly to the GP (without SU). At a distance of λ / 900 (taking into account the shortening factor of the cable used), a serial LC circuit (L = 50 μH, C = 19,5 pF) tuned to the middle frequency of the range is included in the gap of the central wire of the cable. Next to the transmitter is a 450 ohm cable of arbitrary length. The vertical height of 3,5 m, matched in this way, has a bandwidth of more than 3,8 kHz with two distinct SWR minimums at XNUMX and XNUMX MHz.

The distance between the extreme zeros of the S-curve on the graph jX(f) depends on the capacitance of the circuit capacitor. A decrease in capacitance leads to the approach of extreme zeros and, accordingly, to a narrowing of the band. An excessive increase in capacitance leads to an expansion of the S-curve to those frequencies where R already drops sharply, which also leads to a narrowing of BW. The optimal value of the capacitor is easy to select in MMANA, focusing on the form of the S-curve of the jX(f) graph and the bandwidth BW on the SWR graph.

The advantages of this method (apart from the possibility of transforming Ra) include the availability of the contour during tuning. The disadvantages are a rather large inductance of the loop coil (reactance at an operating frequency of 100..300 Ohm), which requires a high design quality factor.

The reactive power of the circuit capacitor must be several times (in the loaded quality factor of the circuit) times higher than the transmitter power. The operating voltage of the capacitor is the same number of times higher than the voltage of the transmitter at the matched load.

3. Broadband matching of vibrators with gamma and omega matchers

Most antennas have the same jX(f) behavior as that of a series circuit. But the majority is not all. Part of the antennas near the resonance has the character of changing jX(f), as in a parallel circuit. First of all, these are antennas fed not in the vibrator gap, but in parallel to it, through a loop, according to the gamma and omega matching scheme.

Naturally, in order to form a two-loop filter in this case, it is necessary to turn on a serial LC-loop in series with the antenna. In principle, it already exists in an antenna with gamma matching - the inductance of the loop and the tuning capacitor connected in series with it just form the desired circuit. But necessary according to the scheme, and by no means according to the values ​​\uXNUMXb\uXNUMXbof (to expand the band) of the elements included in it. The length of the gamma matching loop is selected from the condition for obtaining the desired Ra, and only its inductance - what happens. It is extremely unlikely that it will match the desired one to provide an optimal bandwidth. Therefore, it is much easier to connect an additional inductor in series with the loop, reducing the tuning capacitor accordingly.

The idea for this design was proposed by RA9MB. A grounded GP from a tube with a diameter of 15 mm and a height of 2,66 m with such an agreement has a bandwidth of more than 4 MHz and covers the bands of 12 and 10 m. The gamma matching tube (also with a diameter of 15 mm) is located at a distance of 0,1 m from the GP and has length 0,5 m. A capacitor with a capacitance of 28 pF and an inductance coil of 0,65 μH are connected in series with the cable.

The design methodology for such an antenna is as follows:

- First, an antenna is developed with the usual gamma-matching for the middle frequency of the range. The length of the gamma-matching tube is selected from the condition for obtaining Ra, which is somewhat higher than the impedance of the transmission line Zc. The Ra/Z0 ratio will give the SWR value at the mid frequency. It must be less than allowed.

- Then, a series LC circuit (tuned to the center frequency) is connected in series with the tuning capacitor, providing bandwidth extension. Increasing the inductance of this circuit leads to narrowing of the extreme zeros of the S-curve (similar to how described above).

- Upon reaching the desired bandwidth, two capacitors connected in series (loop and tuning gamma matcher) are recalculated into one.

In this way, very low SWR can be obtained over a wide frequency band. Grounded GP 19,7 m high (pin diameter 40 mm, matching tube diameter 4 mm, its height 3,6 m, at a distance of 0,3 m from the GP, a 136 pF capacitor and an 8 μH coil are connected in series with the cable at the feed point) has an SWR of less than 1,25 over the entire range of 3,5 .... 3,8 MHz.

The same effect can be obtained on an antenna with omega matching. And in the same way - by turning on the coil between the series tuning capacitor and the power cable. The methodology for designing such an antenna is exactly the same as the above methodology for gamma matching (only instead of changing the length of the loop, you need to change the capacitance of the parallel capacitor). The matching loop parameters are chosen as described, the achievable bandwidth extension is 1,5...2 times compared to the band of the same antenna without a loop.

4. Broadband antenna matching with a parallel lumped element

In addition to the considered antennas with gamma and omega matchers, antennas with parallel inductance matching (hairpin match) behave as a parallel oscillatory circuit. This is understandable - a parallel matching element, together with the reactance of the antenna, forms a parallel oscillatory circuit tuned to the operating frequency. Here, to expand the bandwidth, it is enough to include a serial LC circuit between the antenna and the cable.

A vertical standing on the ground with a height of 2,37 m and a diameter of 10 mm, thus coordinated, has a bandwidth of 3,4 MHz at an average frequency of 27,5 MHz. A coil with an inductance of 0,25 μH is connected between the vertical and the ground, and a series circuit with parameters L = 1,5 μH and C = 18 pF is connected between the central conductor of the cable and the vertical.

Another type of antennas, which at resonance have the jX(f) dependence, as in a parallel circuit, are shortened vibrators with a coil in the antinode of the current. The power line for such antennas is connected to the coil taps, which ensures matching. Especially often shortened GPs do this - the coil at the base provides resonance at the desired frequency, and the tap - matching with a given Z0.

A series LC circuit between the supply line and the outlet of the extension coil allows you to greatly expand the bandwidth, which is especially important for shortened antennas, the bandwidth of which is fundamentally less than full-size ones. Figure 3 shows a shortened (only 13m high) 80m range vertical with two capacitive load wires at the top, matched in the manner described.

The matching scheme is shown in fig. 4. Mast diameters - 40 mm, capacitive load wires - 2 mm each. This very simple and convenient structurally (capacitive loads are combined with the upper tier of mast braces) antenna, despite its small size, has more than a solid band of 370 kHz (see Fig. 3), which is unattainable with normal matching even for full-sized antennas! And, very practical, it has two pronounced SWR minimums of 1,2 in both CW and SSB DX sections. The "hump" of the SWR in the center of the range, where its value reaches 1, corresponds to the little-used section of 8 ... 3,6 MHz.

The CS setting (Fig. 4) is carried out according to the following method.

1. Disconnect the lower output of the coil L1 from the ground. The L2C1 circuit is also temporarily disabled. The cable is connected between the ground and the lower terminal of the coil L1 disconnected from the ground.

2. By changing the inductance L1, set the zero reactive component of the input impedance of the antenna at the middle frequency of the range. The SWR will be high, but at this stage it does not matter.

3. Restore the connection of the lower output of the coil L1 with the ground. By connecting the cable to the tap L1 and moving the tap, they achieve an active part of the resistance of about 80 ohms (HF bridge). At the same time, they do not pay attention to the reactive part (there will be an inductive component). If there is no HF bridge, take a tap from about 1/4 of the coil turns. But then you have to do point 5.

4. Connect the serial circuit L2C1 (previously tuned to the middle frequency of the range). By changing the capacitance of the capacitor C1, a symmetrical S-shaped curve of the reactive part of the input resistance is obtained (or, equivalently, an SWR graph with two minima).

5. If the SWR value at a frequency of 3,65 MHz is above 2 or below 1,5, the L1 coil tap is incorrectly set. Move it a little and repeat step 4. And so several times, until the dependence of SWR on frequency becomes the same as in Fig. 3.

In fact, this is the procedure for tuning a conventional two-loop bandpass filter. If it is the 3,6 ... 3,7 MHz section that is important for you, then you can either shift the extreme zeros of the S-curve by increasing the inductance L2 and, accordingly, reducing the capacitance C1 (this will reduce the SWR "hump" in the middle, but at the same time will slightly increase the SWR at the edges), or use an antenna similar to the one described, but with a smaller size. So, with a GP height of only 8,2 m, it is possible to obtain a band of more than 150 kHz and two minimum SWR at frequencies of 3,525 and 3,625 MHz.

5. Expansion of the band of nonresonant vibrators with gamma and omega matchers

If the length of GP is noticeably different from X/4 (and the symmetrical dipole - from X/2), then with gamma and omega matching, the capacitance of the series matching capacitor is significantly reduced. Accordingly, its reactance increases, increasing the quality factor of the control system and narrowing the antenna band.

The solution is obvious: to increase the capacitance of the series capacitor, it is necessary to reduce the inductance of the shunt. Since its length is fixed, this can only be done by a noticeable increase in diameter. A direct increase in diameter is inconvenient constructively, therefore, they proceed in the same way as in the Nadenenko dipole - they replace the thick tube of the plume with a set of thin parallel wires. Arrange them in a circle around the vibrator, as shown in Fig. 5.

In the 14 MHz band, a grounded shortened GP with a height of 3,5 m and a diameter of 30 mm, with normal gamma matching with a loop from a tube with a diameter of 12 mm, has a band of about 200 kHz. When replacing the tube with a "skirt" of four wires with a diameter of 2 mm, located around the vibrator at a distance of 0,2 m, it has a band of more than 300 kHz.

For elongated GPs with a height of more than X / 4, when using a "skirt", the band also expands by one and a half to two times. Almost all antennas of medium-wave broadcasting stations are made as grounded openwork masts with a "thick" shunt-"skirt", the wires of which are located around the mast.

A model file of an existing broadcasting station antenna with a power of more than a megawatt, coordinated in the described way, can be found at qsl.net/dl2kq/mmana/4-3-12.htm (the latest in the MW-Broadcasting.maa list). The same page contains model files (with detailed dimensions, ratings and characteristics) of all antennas mentioned in this article, and many others.

Author: I. Goncharenko (DL2KQ - EU1TT), Bonn, Germany

See other articles Section Antennas. Measurements, adjustment, coordination.

Read and write useful comments on this article.

<< Back

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Emotions of the West and East 10.02.2008 American and Japanese psychologists, studying differences in the expression of emotions in the two peoples, handed out photographs of faces to Japanese and Americans and asked them to rate whether the photographed person had a cheerful or sad expression. And the photographs were "synthetic": sad eyes were mounted with a wide smile, or, conversely, the eyes were smiling, and the tips of the lips were lowered. The results of a survey of 120 people showed that when evaluating facial expressions, Americans look primarily at the mouth, while Japanese look almost exclusively at the eyes. Scientists have concluded that the Japanese traditionally restrain their feelings, their facial expressions are inactive, so you have to look at the eyes, the expression of which is more difficult to control than the expression of the mouth. By the way, Japanese emoticons, computer icons synthesized from the characters of a conventional keyboard, are very different from Western ones. Where we put :-) to communicate his cheerful mood, the Japanese draws (^ ^). The sad mood icon in the everyday life of our computer users looks like :-(, and the corresponding Japanese one looks like (; _;) (tears drip from the eyes). That is, in our version, when the mood changes, the mouth pattern changes, and in Japanese - the eye. Examples of Japanese emoticons: (^_^) - smile, joy, (^^) - sometimes a smile, sometimes something like "hee hee", a slight smile, (^.^) - a woman's smile, (^_^;) - nervous laughter, (^o^) - dying with laughter, \(^_^)/ - joy, (*_*) - admiration, (^L^) - happy, (^(^) - happy, (^_ ^)/ - greeting waving hand, (^_^)/~~ - greeting, (;_;)/~~ - waving goodbye, (-_-) - sour mine, sadness, sadness, mysterious smile, ( ^_~) - wink, (^_-) - wink, (o_o) - surprised, (O_O) - very surprised, (o_O) - bewilderment, surprise, (V_v) - unpleasant surprise, (> _>) - skepticism , (@_@) - awesomeness, (*^o^*) - excited, (*^.^*) - excited, (v_v) - sadness, (;_;) - tears, crying, (T_T) - tears , crying, (~~>.<~~) - tears, crying, ///_^ - emo, ^_\\\ - emo, (*^^*) - embarrassment, shame, (^_^;;; ;) - embarrassment (in a cold sweat), (^^') - what is shown in anime and manga with a drop (embarrassment), (^^;) - a variation on the theme of a drop, (>_< ) - angry, angry, (>.< ) - angry, angry, m(._.)m - apologizes, (?_?) -misunderstanding, confusion, question, (!_!) - shock, (^o^;> - "I'm sorry, I didn't understand", (-_-;) - illness, (-_-;)~ - illness, (x_x) - death, corpse, (+_+) - death, (+_+)~ - death, (%_%) - after a night at the computer, ^}{^ - love, (=__=) - sleepy or "tired :", (-.-)Zzz.. - sleep, (u_u) - sleep, (* ^)3(*^^*) - kiss, \=oo=/ - wear glasses, m(_)m - humble a bow of gratitude or apology, (=^_^=) - a cat, (=^.^=) - the same, (^..^) - a pig, ("\ (o_O) /") - Father Medved, Y ( O,,,,O)Y - Cthulhu, (x(x_(x_x(O_o)x_x)_x)x) - alive among zombies. If in Western emoticons the strength of emotions is expressed by the number of brackets)))))))))))))))))))))))))))))))))))))))), then in in "Japanese-style" emoticons, this can be expressed by the length of the underline: ^______________^.

Other interesting news:

▪ Abnormally high temperature recorded in Greenland

▪ An alternative to SMS messages will appear in Europe

▪ Fabric to keep you cool in the heat

▪ Sony Handycam FDR-AX4E 1K camcorder

▪ Explosive reagent

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Note to the student. Article selection

▪ article Work, carelessly. Popular expression

▪ article Can we control hunger and thirst? Detailed answer

▪ Lomonos article. Legends, cultivation, methods of application

▪ article IR relay control unit. Encyclopedia of radio electronics and electrical engineering

▪ article Overhead power lines with voltage above 1 kV. Overvoltage protection, grounding. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024