***************** * * * HDL_ANT * * version 2.1 * * * ***************** copyright 1994,1995,1996 Paul Wade N1BWT Version 2.1 with option for the metric-impaired -> fixes roundoff error problem with Version 2.0. Any licensed radio amateur may use this program without charge; all other persons must send $73 to the ARRL Foundation, 225 Main St., Newington, CT 06111 HDL_ANT does the calculations needed to successfully implement several microwave antennas: horns, parabolic dishes, and metal-plate lenses. It also does the calculations involved in setting up an antenna range for antenna gain measurement. More detailed explanations of the antennas and measurements may be found in the series of QEX articles entitled 'Practical Microwave Antennas,' in the September, October, and November 1994 issues. An additional article, 'More on Parabolic Dish Antennas,' in the December 1995 issue of QEX, gave the descriptions for Offset dishes, Penny feeds, and the use of sun noise to measure antenna performance and receiver noise figure. All dimensions are in millimeters, since one mm. is about the accuracy required for antennas to work well at 10 GHz. However, there is an option for dimensions in inches, for the metric-impaired. MENU CHOICES: H For horn antennas, HDL_ANT will design an 'optimum' horn with a specified gain (between 10 and 25 dB) for any frequency - use menu entry 'H' for this option. It will then create a PostScript template file which may be used to print a paper template for horn construction. The paper template is attached to a sheet of copper or brass which is cut and folded on the template lines, then soldered together and soldered to a waveguide. See menu entry 'P' for more details on printing a PostScript file. E Menu entry 'E' is used to calculate the gain and other parameters for an existing horn - perhaps one you found at a hamfest. It can also create a template, to duplicate a horn known to have good dimensions. D Parabolic dish calculations are under menu entry 'D'. The most important dish dimension is the focal length, and the easiest way to find it is to measure the depth of the dish in the center, measured from a straightedge across the rim of the dish. HDL_ANT then calculates the focal length and f/D ratio, to allow selection of the best feed antenna - see the QEX series for details on feedhorn selection. For smaller dishes, HDL_ANT can also generate a PostScript template file; the printed template is used to check the accuracy of the parabolic curve of the dish. If it is not a good fit, sometimes a template for a slightly larger or smaller f/D ratio gives a better fit, since dishes sometimes have a flat area or large hole in the center which yields a misleading depth measurement. L Menu entry 'L' is used to design metal-plate lens antennas. These are normally fed by a horn; if an appropriate horn is not already available, then the 'H' entry may be used to design the horn. It may take a few trials to find a good combination of horn and lens. Note that the 'optimum' horns designed under the 'H' entry of the HDL_ANT program do not usually have the matched E-plane and H-plane phase centers needed for good lens performance; some adjustment of horn dimensions can improve the phase center matching. The lens design does not create templates since the lens curves are all simple circles which can be drawn more accurately with a compass. R Antenna range design is selected by menu entry 'R'. HDL_ANT calculates the minimum length and measurement height required for a specified maximum antenna aperture, and then calculates the height of the source antenna needed to have the RF field peak at the measurement height. C If a noise figure meter is used to measure antenna gain as described in the November 1994 QEX article, then it is necessary to convert noise figure readings into antenna gain. Menu entry 'C' makes these calculations. P Menu entry 'P' is a short explanation of how to print PostScript files. I Menu entry 'I' is this summary of information about HDL_ANT. U Menu entry 'U' allows you to select dimensions in either millimeters or inches. HDL_ANT defaults to millimeters. O Menu entry 'O' is a new feature for version 2.0 which does calculations for oval-shaped offset-fed parabolic reflectors. This routine uses a curve-fitting algorithm to find the focal point and tilt angle for aiming the dish. Required input data are the dimensions of the large and small axis of the oval, and the depth and location of the deepest point in the reflector, measured along a straightedge placed across the rim on the large axis. For offset reflectors that are not oval shaped, please read my article in QEX, December, 1995 on offset dishes for suggestions. There is an option to design a rectangular feedhorn as descibed in Menu entry 'F'. F Menu entry 'F' is a new feature for version 2.0 which will design a rectangular feedhorn for a dish with a specified f/D using a straightline approximation to the G3RPE curves. The approximation is accurate to about 2% for f/D < 0.8, and about 6% for larger f/D. It will then create a PostScript template file which may be used to print a paper template for horn construction as described for Menu Entry 'H'. The feedhorn dimensions generated by the approximation do not necessarily have equal E- and H-plane phase centers, so you may need to adjust the axial length of the horn to find a length that matches the phase centers to within 0.1 wavelengths without reporting any errors in the phase center routines. Also, the feedhorn dimensions assume a reflector which has symmetrical illumination angles in both planes. For reflectors requiring assymetrical illumination, run this option once for each illumination angle ( or equivalent f/D ), note the dimensions, and adjust the horn dimensions to use the appropriate one in each plane. Make sure the E-plane matches the normal polarization, i.e., E-plane horizontal for horizontal polarization, or E-plane vertical for vertical polarization. N Menu entry 'N' is a new feature for version 2.0 which calculates receiver noise figure by comparing noise received from cold sky and warm ground. : Q 'Q' for Quit ends the program. The source file, HDLANT21.CPP, was compiled using Borland C++ version 4.0. Any part of it may be modified or used as part of another program by any amateur radio operator, provided that credit is given and provided there is no charge for its use. Send problems, suggestions, and comments to Paul Wade, N1BWT. Expect support commensurate with the cost of the program!