Antenna definition

Equation

   You can use an equation instead of a number. The numeric operators MMANA-GAL supports are +, -, *, and /. You can use () to specify the calculation order.

5*2+1 = 11
1+5*2 = 11
(1+5)*2 = 12
5*(2+1) = 15
20/(3+7) = 2

Special constant below can also be used.

R  –  l ( lambda)  = wavelength (meter)
     I      –     1 inch (meter) 1 inch = 2.54 cm
     F      –      1 foot (meter) 1 ft = 12 inches

Example:
R/4       =    l/4
5*R/8   =  l5/8
30*F   = 30 feet
15*I  = 15 inches

The equation is calculated immediately. MMANA-GAL does not memorize the equation itself in the wire definition.


Antenna definition - Geometry table 

   MMANA-GAL provides you with a couple of ways to define the antenna.  The straightest way is to input the antenna coordinates in the form of a table.  Click on the Geometry tab, and you see an editor in the table format like a shreadsheet.  With the table, you can define the antenna parameters including wire dimension, sources, and loads (LCR load/termination).

   Place the cursor to the parameter box and input a numeric value using a keyboard.  Hit the return key to validate the selected value.  You can use a simple equation instead of a numeric value (see Equation).  Right click of the mouse gets you a pop-up menu, with which you can do insert, delete, and other primary operations.

 


Wire definition

Define the wires that compose the antenna:

X1

X-axis starting position of the wire (unit is meter or l)

Y1

Y-axis starting position of the wire (unit is meter or l)

Z1

Z-axis starting position of the wire (unit is meter or l)

X2

X-axis ending position of the wire (unit is meter or l)

Y2

Y-axis ending position of the wire (unit is meter or l)

Z2

Z-axis ending position of the wire (unit is meter or l)

Radius of the wire (unit is millimeter or l)

SEG 

Segmentation method

   Note that R is not the diameter, but the radius. Put a minus value to R for modeling the element that is composed of two or more pipes having different radiuses. 

  If you put 0 (zero) to R, the wire behaves as an insulated wire.  Using this trick, you can define a complex combination of wires.  The element consisting of two or more wires must be connected together if it is edited or if it is treated as the element variable in the optimization. However, you may want to treat separated wires as one element. MMANA-GAL  accepts zero radium (R=0) in the wire definition, and does not calculate the wire.

Adjustment when the wire radius is changed

  It is common for an antenna to have very different characteristics when the wires' radius is changed. Particularly in Uda-Yagi or Quad antenna, the radius affects not only the impedance but also the gain and F/B ratio. However, you may want to change the radius of the antenna which you are very happy with. You may want to change the combination of the pipes.

   Here is the commendable procedure to keep the original characteristics.
1. Change the radius and calculate once.**
2. Push the Resonance button in the Frequency characteristics window, and get the fo.
3. Use the fo as the design frequency in the antenna definition window.
4. Calculate the model again. If the antenna characteristics are close to the original's, step forward. 
5. In the antenna size window of the Edit menu, check Y-axis and Z-axis (uncheck X-axis to keep the boom length). Resize the antenna so that it matches the original frequency.
6. Calculate the model again.
7. Repeat 1 to 6 if needed.

   ** A broad band Uda-Yagi antenna would have two or more frequencies that give jX=0. The resonance frequency derived the frequency characteristics window is only one of them, and therefore the derived frequency is not always same as the original fo. Keep the following tendency in mind. 
  - When you enlarge the pipe radius, the resonance frequency is likely to decrease. When you shorten the pipe radius, the resonance frequency is likely to increase. It should be noted that this tendency is reversed in loop antennas.
  - When you get the element tapered, the resonance frequency is likely to increase. When you use a straight single pipe, the resonance frequency is likely to decrease.

  Following this procedure,  the original characteristics shold be back, otherwise you could optimize the antenna again. This procedure, however, presumes that the original antenna is resonant at the design frequency. If your element is a little bit capacitive with a hairpin match, adjust the element length first to be resonant and follows the procedure above. After you are finished, tune again the element with the hairpin match

   For a Uda-Yagi antenna, it is a usual way to place the boom in parallel to X-axis, the elements to Y-axis, and the height direction to Z-axis.  It is a good idea to place the source at Z = 0 or to place the center of the antenna at Z=0.  You can change the antenna height above the ground using the other parameter described later.  If your target is a vertical antenna, place the source at Z=0.  It is recommended that you place the center of the antenna at X=0 and Y=0.

   In order to connect two or more wires at one point, you must give them exactly same starting or ending position, that is, the wires must have the same X, Y, and Z values at the connecting point; otherwise they would be treated as separated wires, which are not what you expected.  For example, if you want to model a T-shape antenna having a vertical wire connected to the center of a horizontal wire, you must define three wires (not two wires), as shown below.


Height of the vertical antenna

   You must put zero to the Z-axis value of the source and set the ground height zero; otherwise, you would model an end-fed antenna and result in an incorrect calculation of the impedance.

   You may want to calculate the beam pattern of the antenna that is set up on the housetop of an apartment house. In such a case, put a*/ minus value to the media setting window in the real ground option.

SEG specifies the method of segmentation.

Minus value or DM1, DM2

Tapering. 
The best results. It is recommended. 

0 

Automatic regular segmentation.
Not recommended to use. 

Positive value

Manual regular segmentation.
Not recommended to use. 


  If you want to use tapering, put a minus value. In summary:

-1

 The lengths of segments vary from (l/(SC*DM1)) to (l/DM2).
 This is default setting. 

-2: 

Tapering is applied only to the starting point.

-3

Tapering is applied only to the ending point.

 

Others:

    DM1: the interval of tapering start (= lambda/DM1)
   DM2: the interval of tapering end (=lambda/(SC•DM2))
   SC: the easing parameter (multiplier), 1 < SC < 3.  SC specifies how fast the tapering changes..
   EC: the number of segments at tapering-end point

    The value is used as DM1.  If you put 200, for example, tapering is done from (lambda/ (SC*200)) to (lambda/DM2).
   If you put 600,60 for example, tapering is done from lambda/600 to lambda/60.        

   EC is the number of segments (DM1 segments) at the terminals in tapering.  For example, when you put 2 to EC, MMANA-GAL preserves 2 segments with lambda/DM1 interval.  In most cases, EC is set to 1, but it should be set to different values in special cases.

   

   Care should be taken if you use -2 or -3 for partial tapering, because the pulse may not be generated at the center of the wire.  This is only the case, however, in making up a wire with two or more pipes having different radiuses, and therefore you should not see any fatal problem.

   If you  put zero to SEG.  In this case, the length of each segment is nearly equal to 1/DM2 multiplied by the wavelength.  

   If you want to divide the wire into the segments that all have equal length, put a positive value.  Putting value 10, for example, makes the wire segmented into 10 pieces.

    It is well known that the number of segments and the way of segmentation strongly affect the computation accuracy.  In particular, the accuracy is improved by fine tapering only around the bending point of the wire of, for instance, a loop antenna.  This kind of technique improves the accuracy even with small number of segments.

   The moment method divides a wire into pieces, called segments, and calculates the current flow on each segment. Thus, the calculation accuracy strongly depends on how the wire is divided into segments.

   It is said that the dipole or yagi antenna, which consists of simple straight wires, can successfully be modeled with simple equal segmentation. If the wire is bended (e.g., loop antenna), you should segment the wire into fine pieces; otherwise you will not get an accurate result.

   Tapering is one of the methods that improve the calculation accuracy. It divides the wire section near the bending point into small segments, but divides the other sections (straight sections) into large segments. If all the wires were divided into small segments, the computation time would become intolerably large. Tapering sometimes allows you to keep the calculation accuracy for the straight wire with small number of segments.

   To improve the calculation accuracy, it needs to have small segments, but the calculation would become unstable for too small segments (less than 0.001 lambda). It also is said that a thick wire (radius:segment > 4:1) cannot be calculated in good accuracy.

   If the calculation speed is regarded important, for example in the optimization, DM1 and DM2 can be set to the values smaller than those show above. It is a good idea to observe the margin beforehand. With small DM1 and DM2, the calculation error tends to be small in the gain and F/B ratio, but is relatively large in the impedance (jX).

   There is no exact criterion to judge the calculation accuracy. You could, however, checks how the impedance is affected by increasing or decreasing the number of segments. If the impedance does not change much, your modeling should be fine. You should see the current distribution in the antenna view window. If the current does not traverse smoothly, check your modeling again.. 


    When the lambda box is checked, MMANA-GAL uses the ratios to the wavelength for the wire dimension and radius (unit is lambda).  This is called the wavelength mode.  When the box is not checked, MMANA-GAL uses 'meter' as the unit for dimension and 'millimeter' as the unit for the radius.  However, MMANA-GAL uses 'meter' for the unit of program-internal representations.  Even you change the design frequency in the wavelength mode, the original dimensions are preserved.  If you want to change the design frequency by keeping the wavelength ratio unchanged, use the antenna size function of the Edit menu.

    When the Keep connected box is checked, the wires connected to the target wire are also changed their dimension to remain them connected to the target wire. It should be cumbersome to design Yagi or loop antennas by inputting all the positions of the elements in X-Y-Z dimension.  You can use the Edit element function in the Edit menu.  If you want to design a more complex antenna, you could use the edit wire function in the Edit menu.

    MMANA-GAL assumes in the Element edit (variables) that the element is symmetrical with respect to X-, Y-, or Z-axis, and determines the changing points of the elements. Thus, the elements that are not targets will not be changed as you expected. In such a case, the insulated wire helps.

Example1:
-Y                0                Y
-------------- --------------
In the Element edit, the element is divided into two wires.

-Y                       0                                Y
--------------===========--------------
If you define the insulated wire "=====", it behaves as one element. 
When you change the width of the element in the Element edit, only the outmost points are moved.

Example 2:
-Y     0     Y
--------------
If you change the width of this element, both end points are moved. You want to fix the right end point.
-Y                              0                                   Y
--------------=========================
Add the insulated wire "=====" at the right end of the element. When you change the width of the element in the Element edit, both end points are moved, but the right edge of the original element is fixed.

   Be sure:
- You cannot connect a source to the insulated wire.
- You cannot insert a lumped-constant load to the insulated wire.
MMANA-GAL does not check if these conditions are met.

 

  Sources (Feeding point)

Pulse     – Pulse position
Phase    – Phase of feeding
Voltage – Voltage of feeding

Use the following convention for defining pulse positions.

W#C(#)

Offset from the center of the wire

W#B(#)

Offset from the beginning position of the pulse assignment on the wire

W#E(#)

Offset from the ending position of the pulse assignment on the wire

 

 

Example :  

 

 W1C

 Center of wire 1

 W3C1

 One point ahead of the center of wire 3

 W2C-2

 Two points behind of the center of wire 2

 W2B

 The beginning position of wire 2 

 W5E3

 Three points behind of the ending position of wire 5

   Usually, the Phase is set to 0 for the antenna with one source.  For the antenna that uses 135 degree phased driven (e.g., HB9CV), put 135 to the Phase value at the second source.

   Voltage normally has the value of the inverse of the number of sources (1 / Feeding_point_#).  If you model an unbalanced driven antenna, put the ratios to the Voltage values.  The absolute quantity of Voltage has no special meaning, but it affects the amplitude of the current distribution view in the Geometry tab.

  From the very microscopic view, the wire is assumed isolated with a narrow gap at the source, and the two wires are driven from the end.  For the modeling of two or more wires driven at one source..

Loads (lumped-constant)

PULSE:

The position of the pulse

Type

LC, R+jX, or S

  To define the pulse position, use the same convention as the source. To select a loading type, hit the return key at the type box and get the pop-up menu.

  When you choose LC, you must put L (uH), C (pF), and Q as the parameters.  When you use only L, put 0 to C.  When you use only C, put 0 to L.  L and C generate a parallel resonant trap.  MMANA-GAL automatically calculates and displays the resonance frequency given by the L and C.  Once you defined the trap, MMANA-GAL automatically changes L or C to keep the resonance frequency constant (resonance keeping function), when you change C or L.  Put 0 to L or C in order to stop the automatic resonance keeping function, and then put your values to L and C again. Conversely, when you input the resonance frequency and either L or C, MMANA-GAL calculates the value of C or L.You normally have to put the Q value to the L or C.  Put 0 to Q if L or C has no loss.

  When you use R+jX type definition, input resistance R (Ohm) and reactance X (Ohm).  It is convenient for modeling a termination resistance or for putting some reactance regardless of the circuit type.

  When you select S, you put the S parameter (A0 - An and B0 - Bn) of the load.  Class n is automatically given to the input point.  Use this S method for the complicated circuit consisting of serial-parallel resonance circuit that is not affected by the frequency.   The S parameter can be obtained by applying the Laplace transformation to the lumped-constant circuit (S = jw). The coefficients of the numerators are A0 - An and those of the denominator are B0 - Bn.
        R+LS+(1/CS) 1 + RC•S + CL•S2
        Z = R+jwL+(1/jwC) --> R+SL+(1/SC) 
   Therefore, you can simulate it with A0=1, A1=RC, A2=CL, B0=0, B1=C, B2=0 (or A0=1/C, A1=R, A2=L, B0=0, B1=1, B2=0).
   The units for R, C and L are ohm, F, and H, respectively. The absolute values of this system tend to be very small, and therefore the exponential notation is recommended. For instance, 20pF is 20 • 10-12 = 20-12.
  You have the same results using S parameter or R+jX because they represent exactly the same lumped-constant load. However, R+jX must be adjusted its value according to the frequency. For this reason, it is hard to analyze a multi-band antenna using R+jX. The LC type of load is modeled with the fixed circuit configuration in MMANA-GAL, so MMANA-GAL automatically changes its notation to R+jX.

 

Samples load are given in the following models:

Loading coil

VDP40B.MAA in directory ...\ANT\SHORT\L

Loading capacitor

 MAGLOOP.MAA, MAGLOOPC.MAAin directory ...\ANT\\SHORT\Magnetic loops\

Trap

MULTDPH.MAA, MULTDPHW.MAA in directory ...\ANT\HF multibands\Trap\

Resistor termination 

T2FD.MAA, RHOMBIC.MAA, ABW1.MAA in directory ...\ANT\HF aperiodic\

S parameter 

MCQM.MAA in directory ...\ANT\HF multibands\LC in antenna

 


Pulse assignment

   The pluses are assigned to the wires in the order of the wire definition. The pulse is not assigned to the dead end of an independent wire. If the wire, on the other hand, is connected to the other wire, a pulse is assigned to the end point. As for the special case, if the wire has its Z value 0, a pulse is assigned to that point (a vertical antenna is a typical example).

    Care also should be taken for the current direction at the source. See the example of four wires below. This is the case of the feeding scheme for the double doublet or twin delta loop. It is a good idea to insert a short wire between two sets of wires, and to feed at the center of the inserted wire, as shown in the right figure.