# Measurement of parabolic antennas

• In my post A challenge for ingenuity I wrote:

If you are interested in how I built the "green" dots, please "like" this post. If you are not interested in this question - put any other rating, for example, "dislike".

If there are more likes, I'll create a thread about fine-tuning offset antennas with simple antenna measurements

Seven people voted "FOR". In addition, the following requests come to the PM:

Quote

I have a problem with my laminas antenna.

How can I measure the geometry of laminas and set it optimally?

Can you please explain to me step by step what I have to do and what I have to pay attention to...

Therefore, today I will begin a publication in which I will tell you about the Parabola 6.2 program - how to use it to determine the main parameters of a parabolic mirror and adjust the receiving unit to the maximum gain.

At the same time, I will help you optimally configure the Laminas 2700 antenna

But we will start with the Parabola 6.2 program for measuring parameters of parabolic antennas.

In this program, I implemented an exclusive algorithm for determining all geometric (and not only) parameters of an offset cut from a paraboloid of revolution in just three dimensions of the antenna mirror:

- height AB (major axis of the elliptical notch);

- width CD (minor axis of the elliptical notch);

- depth EH (perpendicular from the intersection of lines AB and CD).

Consider this using the CA - 1200 antenna as an example:

First of all, note that the vertices of the ACBD rhombus lie on the elliptical line that separates the parabolic part of the antenna from the bead. It can be flat or convex, but the points always lie on the points of change in curvature on the cross section of the antenna mirror.

You need to start marking the ACBD rhombus from the bottom point B, which is most easily determined visually.
When the rhombus is marked, pull thin threads between points AB and CD, which should barely touch each other at point E.
Take photographs of the antenna with the filaments stretched in front (the camera is on the continuation of the EH line) in profile (in the plane of the mirror cut on the continuation of the lines AB and CD).
Take a close-up photograph of points A, B, C, D and E so that the contact of the threads with the antenna and with each other is visible.
Post photos in this thread, and we will evaluate the accuracy of your constructions and the quality of the antenna surface.
See sample photos below:

• Today we will get acquainted with the program for determining the parameters of antennas that are necessary for their alignment - PARABOLA-6.2

When the program starts, a window opens in which you need to fill in a number of fields:

1 - the field where the name of the antenna is entered. It will be displayed in the header;

2 - field where the height of the antenna AB is entered in mm:

3 - field where the width of the CD antenna is entered in mm:

4 - field where the EH antenna depth is entered in mm, with an accuracy of tenths, which are separated by a comma ",":

5 - 9 - fields where the frequencies are entered in MHz, for which the gain factors and the width of the radiation pattern will be calculated for a given instrumentation:

8 - frequency for which the distribution of the electromagnetic wave power flow between the antenna mirror and the LNB will be calculated;

10 - the field where the desired MSUF (Mirror Surface Utilization Factor) is entered, from 60% for a normally tuned, 75% for a perfectly tuned single-dish antenna and up to 85% for the main mirror of two-dish antennas.

11 - checkbox and scale divider field for power flow distribution output inside the antenna opening angle alfa;

12 - button for entering the typed data;

13 - button for calculating the antenna profile;

14 - Help button

15 - button About the program - they are useful if you speak Russian:

The fields must be filled in in order, then the antenna parameters will be calculated immediately after filling in field 10.

If it doesn't, press 12:

To build an antenna profile, press 13:

After that, the checkbox Field 11 becomes active. If you mark it and press Profile 13, then the field strength distribution inside the mirror opening angle will be calculated. This distribution is derived by the variable density method - minimum values correspond to white, zero values - light brown, which gradually thickens, turns into black color of the absolute maximum at the antenna focus point F.

Note that the ray tube power flux-density AF is higher than the ray tube power flux-density BF for the same phases of the converging spherical wave (darker shade of brown and wider "white" band).

If you press button 14, the results can be saved to disk:

This is (after the name of the antenna):

- focal length F [mm]

- mirror opening angle Alfa [°]

- offset angle Fi [°]

- distance AG in a straight line from the top point of the parabolic surface of the mirror A to the aiming point G

- distance BG in a straight line from the lowest point of the parabolic surface of the mirror B to the aiming point G

- table for estimating antenna parameters for a given instrumentation:

- - first column - frequency, MHz

- - second column - antenna gain, dB

- - then three columns of the width of the main lobe of the radiation pattern at the level of -3dB:

- - - for even distribution of the incident field (RX mode)

- - - for cosine distribution (TX mode)

- - - for cos^2 distribution (TX mode)

The graph shows the coordinates of points in the X0Z system and distances in millimeters

The initial data (mirror measurement results) are signed in blue below in millimeters

The PARABOLA-6.2 program is attached in the archive

__________________________________________________________________________________________________________________________________________________

Сегодня познакомимся с программой определения параметров антенн, которые необходимы при их юстировке - PARABOLA-6.2

При старте программы открывается окно, в котором необходимо заполнить ряд полей:

1 - поле, куда заносится название антенны. Оно будет отображено в заголовке;

2 - поле, куда заносится высота антенны AB в мм:

3 - поле, куда заносится ширина антенны CD в мм:

4 - поле, куда заносится глубина антенны ЕН в мм, с точностью до десятых долей, которые отделяются запятой ",":

5 - 9 - поля, куда заносятся частоты в МГц, для которых будут рассчитаны коэффициенты усиления и ширина диаграммы направленности при заданном КИП:

8 - частота, для которой будет рассчитано распределение потока мощности электромагнитной волны между зеркалом антенны и LNB;

10 - поле, куда заносится желаемый КИП (Коэффициент Использования Поверхности зеркала), от 60% для обычно настроенной, 75% для отлично настроенной однозеркальной антенны и до 85% для главного зеркала двухзеркальных антенн.

11 - чекбокс и поле делителя масштаба вывода распределения потока мощности внутри угла раскрыва антенны alfa;

12 - кнопка ввода набранных данных;

13 - кнопка рассчёта профиля антенны;

14 - кнопка Помощи

15 - кнопка О программе - они полезны, если Вы владеете русским языком:

Поля нужно заполнять по-порядку, тогда параметры антенны будут рассчитаны сразу же после заполнения поля 10.

Если этого не произошло, нажмите 12:

Для построения профиля антенны нажмите 13:

После этого чекбокс Поле 11 становиться активным. Если его отметить и нажать Профиль 13, то будет рассчитано распределение напряжённости поля внутри угла раскрыва зеркала. Это распределение выводиться методом переменной плотности - минимальным значениям соответствует белый цвет, нулевым - светло коричневый, который постепенно сгущаясь, переходит в чёрный цвет абсолютного максимума в точке фокуса антенны F.

Обратите внимание, что плотность потока мощности в лучевой трубке AF превышает плотность потока мощности в лучевой трубке BF для одинаковых фаз сходящейся сферической волны (более тёмный оттенок коричневого и более широкая "белая" полоса.

Если нажать кнопку 14, то результаты можно сохранить на диск:

Это (после названия антенны):

- фокусное расстояние F [mm]

- угол раскрыва зеркала Alfa [°]

- угол офсетности Fi [°]

- расстояние AG по-прямой от верхней точки параболической поверхности зеркала A до точки прицеливания G

- расстояние BG по-прямой от нижней точки параболической поверхности зеркала B до точки прицеливания G

- таблица оценки параметров антенны при заданном КИП:

- - первый столбец - частота, МГц

- - второй столбец - коэффициент усиления антенны, дБ

- - далее три столбца ширины главного лепестка диаграммы направленности по уровню -3дБ:

- - - для равномерного распределения падающего поля (режим RX)

- - - для косинусоидального распределения (режим TX)

- - - для распределения cos^2 (режим TX)

На графике даны координаты точек в системе X0Z и расстояния в миллиметрах

Снизу подписаны синим цветом исходные данные (результаты обмера зеркала) в миллиметрах

Программа PARABOLA-6.2 прикреплена в архиве

• Anfang nächster Woche soll es wärmer werden. Da werde ich sehen was sich bezüglich der Messungen machen lässt.

Punkt E ist eine gewisse Herausforderung, der Rest so hoffe ich, geht mit einem Lasermessgerät.

Am Punkt F in der Mitte der beiden Halbschalen ist klar, aber auch mittig der Klemme?

Das eigentliche Feed ist ja davor, die Befestigung ist ja schon am Hohlleiter.

Beide grüne Markierungen, oder grün und blau, antennenseitig?

It's supposed to get warmer early next week. I'll see what can be done about the measurements.

Point E is a bit of a challenge, the rest I hope is doable with a laser gauge.

At point F in the middle of the two half-shells is clear, but also in the middle of the clamp?

The actual feed is in front of it, the attachment is already on the waveguide.

Both green markings, or green and blue, on the antenna side?

В начале следующей недели должно потеплеть. Я посмотрю, что можно сделать с измерениями.

Точка E немного сложнее, остальное, я надеюсь, выполнимо с помощью лазерного датчика.

В точке F посередине двух полуоболочек все ясно, а посередине тоже хомут?

Собственно корма перед ним, насадка уже на волноводе.

Обе зеленые маркировки, или зеленая и синяя, со стороны антенны?

Wer nicht die Antennengröße und den ungefähren Standort angibt, postet sinnlos, sofern es um eine Signalerfassung geht.

If you don't specify the antenna size and the approximate location, posting is useless if it's about signal acquisition.

• Punkt F sollte idealerweise in der Mitte des blauen Kreuzes liegen

Точка F должна быть в идеале в центре синего креста

• Hi strannik,

Nice, to have an extensive manual for Parabola6 now, in english, by the autor!

I always liked the graphic representation of the calculation outcome.

In this program, I implemented an exclusive algorithm for determining all geometric (and not only) parameters of an offset

I wondered about your calculation method for the focal length; I've never found an indication by you.

Do you indeed use an algorithm in the program, in the sense that you start with an estimate, and step by step refine the estimate till no further improvement is possible (I believe this was the original meaning of the term 'algorithm') ?

Greetz,

A33

• I wondered about your calculation method for the focal length; I've never found an indication by you.

Do you indeed use an algorithm in the program, in the sense that you start with an estimate, and step by step refine the estimate till no further improvement is possible (I believe this was the original meaning of the term 'algorithm') ?

No, you misunderstood.

I have compiled a system of four transcendental equations that relate the main parameters of a parabolic mirror. I solved this system ANALYTICALLY, and not numerically by selection. This formed the basis for the algorithm of the program for determining the parameters of the antenna from just three measurements of the height AB, the width CD, and the depth EH of the parabolic mirror.

Naturally, these parameters must be measured carefully, since otherwise measurement errors accumulate and multiply when solving the system of transcendental equations

_________________________________________________________________________________________________________________________________________________________

Нет, вы поняли неверно.

Я составил систему из четырёх трансцендентных уравнений, которые связывают между собой основные параметры параболического зеркала. Эту систему я решил АНАЛИТИЧЕСКИ, а не численными методами путём подбора. Это легло в основу алгоритма программы определения параметров антенны всего по трём измерениям высоты AB, ширины CD и глубины EH параболического зеркала.

Естественно, что эти параметры нужно измерять тщательно, так как иначе ошибки измерений накапливаются и умножаются при решении системы трансцендентных уравнений

• I have compiled a system of four transcendental equations that relate the main parameters of a parabolic mirror. I solved this system ANALYTICALLY, and not numerically by selection. This formed the basis for the algorithm of the program for determining the parameters of the antenna from just three measurements of the height AB, the width CD, and the depth EH of the parabolic mirror.

Ah yes, I remember doing something similar now, for calculating the focal length.

I used a step by step calculation, first defining the coordinates of three points of the dish (top, bottom, and center), taking the offset angle into account; and then solving a quadratic equation on those points. And I was glad having your program, to confirm my outcomes, and so the accuracy of my approach!

Since then I've derived a more simple, direct equation for the focal length of a flat-faced paraboloid dish.

And, by the way, also for a non-flat paraboloid dish; for which Paul Wade and John Legon in their days advised the 'water method'.

For the latter, I had formerly used an iterative algorithm: from a starting estimate, with many repeated corrective steps, reaching the actual (very accurate) value in the end.

So I do like repetitive algorithms like that, when I do not have simpler methods at hand. Though I now don't use them anymore for parabolic calculations, since I've found other more direct methods, also for other types of parabolic/paraboloid dishes (e.g. for multifeed dishes, or prime focus dishes with a hole at the center).

Greetz,

A33

• I used a step by step calculation, first defining the coordinates of three points of the dish (top, bottom, and center), taking the offset angle into account; and then solving a quadratic equation on those points. And I was glad having your program, to confirm my outcomes, and so the accuracy of my approach!

The PARABOLA-6.2 program is attached in the archive

• AB = 1934,92 mm

CD = 1800,00 mm

FA = 1853,25 mm

FB = 1100,65 mm

FC = 1476,55 mm

FD = 1476,10 mm

FE = 1174,05 mm

FG = 1262,05 mm

FH = 1333,70 mm

EH = 168,76 mm

Nicht eindeutige Werte wurden mehrfach gemessen und der Mittelwert gebildet. Herausfallende Extremwerte wurden dabei nicht berücksichtigt.

Ambiguous values were measured several times and the average was formed. Outstanding extreme values were not taken into account.

Неоднозначные значения измерялись несколько раз и формировалось среднее. Выдающиеся экстремальные значения не учитывались.

Wer nicht die Antennengröße und den ungefähren Standort angibt, postet sinnlos, sofern es um eine Signalerfassung geht.

If you don't specify the antenna size and the approximate location, posting is useless if it's about signal acquisition.

• Femi auf deine Empfangsergebnisse bin ich gespannt wenn es dann soweit ist.

Bei uns geht es stürmisch zu, erst nächste woche ist Besserung angesagt.

Bis Dato werde ich mir die nötigen Gerätschaften besorgen,

somit kann ich nachkontrollieren ob ich letzte Woche die Antenne richtig eingemessen und optimiert habe.

It's going to be stormy for us, and things won't get better until next week.

To date I will get the necessary equipment,

so I can check if I measured and optimized the antenna correctly last week.

Location:

48.14*N, 9.2*E

• What was the antenna you measured? If it is Laminas AS-1800 then should be :

AB=1935mm

CD=1800mm

EH=170mm

then the offset angle =21.5 (exactly as stated by manufacturer)

• Die von dir zitierten Werte sind meine Messwerte.

Jene der Antenne sind ja auch ok, nur der Brennpunkt F könnte vielleicht optimiert werden.

Hier sehe ich Abweichungen der Messung und dem Programm parabola6.

The values you quoted are my readings.

Those of the antenna are also ok, only the focal point F could perhaps be optimized.

Here I see deviations in the measurement and the parabola6 program.

Приведенные вами значения - это мои показания.

С антенной тоже все в порядке, разве что фокус F можно было бы оптимизировать.

Здесь я вижу отклонения в измерении и программе parabola6.

Wer nicht die Antennengröße und den ungefähren Standort angibt, postet sinnlos, sofern es um eine Signalerfassung geht.

If you don't specify the antenna size and the approximate location, posting is useless if it's about signal acquisition.

• The values you quoted are my readings.

Except from antenna's depth, where instead of 170mm you've measured 168.76mm

• Ich weiß, Könnte dem Heizelement, der Last am LNB-Arm oder beiden geschuldet sein.

I know, could be due to the heating element, the load on the LNB arm, or both.

Я знаю, Может быть из-за нагревательного элемента, нагрузки на плечо LNB или из-за того и другого.

Wer nicht die Antennengröße und den ungefähren Standort angibt, postet sinnlos, sofern es um eine Signalerfassung geht.

If you don't specify the antenna size and the approximate location, posting is useless if it's about signal acquisition.

• could be due to the heating element, the load on the LNB arm, or both.

Did you make a string test of your antenna? If it is warped, then all the measurements and precise adjustments have a little sense.

• To date I will get the necessary equipment,

so I can check if I measured and optimized the antenna correctly last week.

You write that you will check the results of your measurements [Laminas 2700 antennas] next week...

Perhaps you did not carefully read the first post of this topic, where I asked to publish here photos of measurement points and measurement results (as shown in the photos below):

You need to start marking the ACBD rhombus from the bottom point B, which is most easily determined visually.
When the rhombus is marked, pull thin threads between points AB and CD, which should barely touch each other at point E.
Take photographs of the antenna with the filaments stretched in front (the camera is on the continuation of the EH line) in profile (in the plane of the mirror cut on the continuation of the lines AB and CD).
Take a close-up photograph of points A, B, C, D and E so that the contact of the threads with the antenna and with each other is visible.
Post photos in this thread, and we will evaluate the accuracy of your constructions and the quality of the antenna surface.

Unfortunately, I didn’t see the materials for measuring your antenna in the topic ...

You are new to the forum, and you still don’t know that I have a negative (whatever that means) attitude to ignoring my requests.

I hope you understand me correctly

• Except from antenna's depth, where instead of 170mm you've measured 168.76mm

I don't quite understand the negative coordinate of point B...

Please show a photo of this point on the antenna and AB measurement

• Did you make a string test of your antenna? If it is warped, then all the measurements and precise adjustments have a little sense.

Hallo Strannik,

du hast recht , hätte ich machen sollen

fehlen dir noch irgendwelche werte/ fotos ?

## Images

Location:

48.14*N, 9.2*E

• I don't quite understand the negative coordinate of point B...

Me neither I am only sure that offset angle of Laminas 1.8m is 21.5* (it comes from antenna's datasheet), the rest of measured data come from other owners of that antenna (I do not even remember who provided this data to me long time ago). So, if AB=1935mm, CD=1800mm and offset angle is 21.5* and no negative coordinate of point B, then the depth EH suppose to be something about 164,4mm. 164,4mm not so close to 168,76 and even further from 170mm. And this great Parabola6 calculator by strannik clearly shows mistakes and helps to solve them.

This incorrect depth measurement most likely comes from antenna's warpage. More antenna warped - bigger EH.

So, that brings me to the point which I already said earlier .... before any measurements and adjustments, antenna's shape should be corrected.

Which one is pulled first?

What are those lines in the photo that I marked with a "?" ?

Measurements should be taken with a taut (without bends) tape measure.

Show the measurement of AB as a whole and points A and B in close-up

Are the distances AC and CB equal?

Are the distances AD and DB equal?

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