Below is a description of the input sequence in OMNEC. Each input section reads data from INPUT.NEC, PARNR.NEC or from both files. Below all lines of the test example 4x6 elements are described. *********************************************************** *********************************************************** INPUT: CE 4x6 elements Not optimised This is just a comment line. Like in NEC2 this line may be preceded by any number of additional comment lines having CM as the first two characters. *********************************************************** PARNR: MO 1 This line tells OMNEC to use the modified wire radius when calculating matrix elements for the interaction between wire segments and to use a more modern value for the speed of light. Alternative: MO 0 Optimise with NEC2 in original form. *********************************************************** PARNR: GS 0 0 .001 .000 .000 .000 .000 .000 .000 This line has to be identical to the corresponding line in INPUT. It tells that the dimensions have to be scaled by a factor 0.001 To convert from millimetres to meters Alternative: GS 0 0 .02540000 .000 .000 .000 .000 .000 .000 To convert from inches to meters, so the antenna coordinates can be given in inches. *********************************************************** PARNR: FR 0 1 0 0 .1441E+03 .0000 .0000 .0000 .0000 .0000 This line has to be identical to the corresponding line in INPUT. It tells, exactly as in NEC2 what frequency to perform the calculation for. Alternative: FR 0 2 0 0 143.500 1.5000 .0000 .0000 .0000 .0000 Optimise for two frequencies at the same time. The first frequency is 143.5 and the second is 145.0 (increment=1.5). If more than one frequency is used the sum of the sum of squares from all frequencies is minimised. In this way the bandwidth should be improved. If more than one frequency is used, the number of points in the radiation pattern may be limited. *********************************************************** INPUT: GW 1 5 .000 -495. 0. .000 495. 0. 5.000 PARNR: GW 1 9 0 -1 0 0 1 0 These two lines specify the first wire. cols 3-5 ITAG, specifies the wire by associating this number to all segments that constitute this wire. cols 6-10 NS, number of segments for this wire. The value in INPUT.NEC is used, while the value in PARNR.NEC is not used at all. cols 11-20 X1,INPUT=.000 the X coordinate of end 1 of this wire is 0 X1,PARNR=0 keep the X koordinate fixed. cols 21-30 Y1,INPUT=-495. the Y coordinate of end 1 of this wire is -495 Y1,PARNR=-1 Optimise the Y coordinate. Increasing parameter number 1 will cause element end 1 to move away from the element midpoint. cols 31-40 Z1,INPUT=.000 the Z coordinate of end 1 of this wire is 0 Z1,PARNR=0 keep the Z koordinate fixed. cols 41-50 X2,INPUT=.000 the X coordinate of end 2 of this wire is 0 X2,PARNR=0 keep the X koordinate fixed. cols 51-60 Y2,INPUT=495. the Y coordinate of end 2 of this wire is 495 Y2,PARNR=1 Optimise the Y coordinate. Increasing parameter number 1 will cause element end 2 to move away from the element midpoint. cols 61-70 Z2,INPUT=.000 the Z coordinate of end 1 of this wire is 0 Z2,PARNR=0 keep the Z koordinate fixed. cols 71-80 RAD, The wire radius. The two ends of an element are changed in opposite directions in order to keep the element centred on the boom. *********************************************************** INPUT: GW 2 5 .000 -460. 660. .000 460. 660. 5.000 PARNR: GW 2 9 0 -2 3 0 2 3 Use parameter 2 to vary the length of wire 2, and use parameter 3 to vary the Z coordinate for wire 2. Since radiation is maximised in the Z direction this means that both length and position are optimised for this wire. *********************************************************** INPUT: GW 3 5 .000 -455. 1400. .000 455. 1400. 5.000 GW 4 5 .000 -450. 2000. .000 450. 2000. 5.000 GW 5 5 .000 -435. 3000. .000 435. 3000. 5.000 PARNR: GW 3 9 0 -4 5 0 4 5 GW 4 9 0 -6 7 0 6 7 GW 5 9 0 -8 9 0 8 9 Associate parameters 4 to 9 to these 3 wires. *********************************************************** INPUT: GW 6 5 .000 -460. 3600. .000 460. 3600. 5.000 PARNR: GW 6 9 0 -10 11 0 10 11 Optimise length an position for wire 6. Alternative for PARNR: GW 6 9 0 -10 0 0 10 0 Optimise length only for wire 6. This will cause an optimisation for a fixed boom length of 3.600 meters. *********************************************************** INPUT: GM 0 0 .000 .000 .000 1700. 1800. .000 .000 PARNR: GM 0 0 .000 .000 .000 12. 13. .000 .000 The antenna was placed with the midpoint of the reflector at the origin. Move the whole structure 1700 millimetres in the X direction and 1.8 millimetres in the Y direction. Optimise the position for this antenna by associating the parameters 12 and 13 to the X and Y shift respectively. Causes optimisation of the stacking configuration in combination with the GX option. When optimising a single antenna, remove these lines and the GX line. When optimising at a fixed stacking geometry, replace 12. and 13. in PARNR.NEC by 0. *********************************************************** INPUT: GS 0 0 .00100000 .000 .000 .000 .000 .000 .000 Has to be identical to the GS line in PARNR, see above. *********************************************************** INPUT: GX100 110 .000 .000 .000 .000 .000 .000 .000 Reflection of structure in coordinate planes. This will create new wires at the opposite side of the specified reflection plane(s). These new wires will be numbered by adding the 100 (cols 3-5) to the ITAG value of the original wires. Cols 8 to 10 specify the reflection planes. 110 means X and Y but not Z. First the structure, wires 1 to 6, is reflected along the X axis, producing a new identical 6 element antenna with the centre of each element at X=-1700 and Y=1800. The wires (elements) of this new antenna are numbered 201 to 206. Since the elements are along the Y axis the structure now corresponds to two yagis stacked above each other at 3.4 meters distance. Then the whole structure, wires 1-6 and 201-206, is reflected along the Y-axis, producing two new antennas at the other side of the XZ plane so the total structure becomes an array of 4 yagis at 3.4 vertical and 3.6 horizontal the new wires are numbered 201-206 and 301-306. *********************************************************** INPUT: GE 0 0 .000 .000 .000 .000 .000 .000 .000 End of structure section. *********************************************************** INPUT: FR 0 1 0 0 .1441E+03 .0000 .0000 .0000 .0000 .0000 Has to be identical to the corresponding line in PARNR.NEC, see above. *********************************************************** INPUT: EK 0 0 0 0 .0000E+00 .0000 .0000 .0000 .0000 .0000 Use the extended thin wire model of NEC2 (always do so!!) *********************************************************** INPUT: LD 5 1 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 2 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 3 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 4 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 5 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 6 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 101 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 102 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 103 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 104 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 105 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 106 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 201 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 202 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 203 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 204 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 205 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 206 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 301 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 302 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 303 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 304 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 305 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 LD 5 306 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000 To account for ohmic losses, which is essential in optimising yagis, all elements have to be loaded. The LD lines above specify aluminium as the element material. There are more options for LD - refer to the NEC2 manual. *********************************************************** INPUT: KH 0 0 0 0 .1500E+01 .0000 .0000 .0000 .0000 .0000 Use a simplified field approximation at segment separations above 1.5 wavelengths. *********************************************************** INPUT: EX 0 2 3 0 .1000E+01 .0000 .0000 .0000 .0000 .0000 PARNR: EX 0 2 5 00 50 0 0.05 Specify feed point. cols 3-5 Type of excitation 0=Voltage source (applied-E-field source) 5=Voltage source (current-slope-discontinuity) The other modes available in NEC2 are illegal in OMNEC cols 6-10 Number of wire to feed. The number has to be the same in both inputs and here 2 specifies the wire with ITAG=2 to be a radiator. cols 11-15 Segment number for segment to feed. The number is taken from INPUT.NEC while the number in PARNR.NEC is ignored. If this number = (NS+1)/2 the element is fed at its centre. Here with NS=5 (see above, GW 2 ...) the centre point is on segment 3. cols 21-30 INPUT: Real part of applied feed voltage. PARNR: Desired value for real part of feed impedance cols 31-40 Imaginary part of feed voltage. PARNR: Desired value for imaginary part of feed impedance cols 41-50 ZWEI, a weight factor giving the weight for the impedance error equation in the total least squares problem. Large values give impedances close to the desired value even if the cost is high in gain, while small values will give the desired impedance only if it can be obtained at a marginal loss of gain. *********************************************************** INPUT: EX 0 102 3 0 -.1000E+01 .0000 .0000 .0000 .0000 .0000 EX 0 202 3 0 .1000E+01 .0000 .0000 .0000 .0000 .0000 EX 0 302 3 0 -.1000E+01 .0000 .0000 .0000 .0000 .0000 PARNR: EX 0 102 0 00 50 0 0 EX 0 202 0 00 50 0 0 EX 0 302 0 00 50 0 0 Note that all image antennas have to be properly fed. When an antenna is reflected along the Y axis, the direction of the elements change sign so in order to be properly phased, these antennas have to be fed with a 180 degrees phase shift. Since the feed impedance is identical for identical antennas, there is no reason to include more equations doing the same thing. Therefore cols 41-50 is 0. *********************************************************** INPUT: RP 0 12 60 0 .9000E+02 .0000 .0004 .0003 .0000 .0000 Calculate radiation pattern. This line allows a compromise between computing speed and accuracy. The optimisation is done by a simultaneous minimisation of the power radiated in all directions except forward. The directions for which the field is calculated are controlled by the stepping parameters of this line. cols 3-5 NPPRT, a parameter to control radiation pattern listed in output file PATTERN.NEC. NPPRT=0 No radiation pattern in output. NPPRT=1 Pattern with theta=0, phi is stepped. NPPRT=2 Complete pattern, phi and thete stepped. NPPRT=3 Integrated pattern: Power radiated from 0 to phi (integrated over theta) as a function of phi. cols 6-10 NTH is the number of values of theta. Theta is a rotation around the Z-axis, and for a single yagi very few points are needed. For a stacking configuration like in this example, more points are needed. cols 11-15 NPH is the number of values for phi, the angle to the forward direction. phi=0 means forward and phi=180 degrees is backwards. cols 21-30 Largest value for theta. For a symmetric antenna there is no need to turn more than 90 degrees on theta. Continuing up to 360 degrees will just repeat the lobe pattern which does not help the optimisation. In this example the radiation pattern is calculated in 12 directions. The step size is 90/12=7.5 degrees and the radiated power is calculated with theta=3.75, 11.25, 18.75,.....,86.25 cols 31-40 Start value for phi. If this value is not 0, the summation excludes points near the forward direction, and the gain as calculated by integration becomes incorrect. The optimisation results in a broader main lobe and better suppression of the lobes above the start value. Do not use large numbers here. Try points on the main lobe of the initial structure. cols 41-50 GOVERT, a parameter putting more weight on the least squares equations above 30 degrees in phi. Large values should improve lobe suppression above 30 degrees at the expense of gain. By variation of this parameter it should be possible to find optimum G/T (?). cols 51-60 EFFWEI, a weight factor on an equation in the least squares fit for ohmic losses. With this parameter lower losses are obtained at the expense of gain. Lower losses means less current so this parameter tends to reduce Q and thereby it improves bandwidth. *********************************************************** INPUT: EN The last line - an end mark. *********************************************************** ***********************************************************