// line07.c random spacings // version 0.7 - constants fed in defines // // compile with gcc -o line07 line07.c -lm // // This computes the off-axis lobes for a 1 dimensional phased array // normalized random spacing // // The array is NX points wide centered around x=0. // The distance from the center of the array to a ground station is gy // look at signal intensity along a line from X0 to X1 // Start with the simple minded assumption that all stations are // phased from the ground receiver, with an (r,-i) component // Then look at the change of intensity with distance. #define DISTANCE 1 #undef DISTANCE // -------------------- array definition -------------------------- // NX == number of cells in array // #define NX 32 #define NX 128 // SX1 == base spacing #define SX1 10.0 // SXF == random spread (uniform) in meters // #define SXF 0.5 #define SXF 3.0 // number of random spreads from 0 to SXF #define NSP 4 // SAM == amplitude increase, parabolic // #define SAM -1.0 #define SAM 0.0 // wavelength #define WL 0.008 // -------------------- ground spot -------------------------------- #define GY 6411000.0 // 6411km from m288 to equator #define GX 0.0 // -------------------- ground sweep ------------------------------- #define THRESH 0.02 // -1000/5000 #define X0 -1000000.0 #define X1 5000000.0 #define NBINS 1201 #define NPTS_PER_BIN 4999 // odd to get center lobe // -100/500 //#define X0 -100000.0 //#define X1 500000.0 //#define NBINS 1201 //#define NPTS_PER_BIN 499 // odd to get center lobe // -10/50 //#define X0 -10000.0 //#define X1 50000.0 //#define NBINS 1201 //#define NPTS_PER_BIN 49 // odd to get center lobe // -5/20 // #define X0 -5000.0 // #define X1 20000.0 // #define NBINS 1001 // #define NPTS_PER_BIN 49 // odd to get center lobe // -1/1 //#define X0 -1000.0 //#define X1 1000.0 //#define NBINS 1001 //#define NPTS_PER_BIN 9 // odd to get center lobe // 14/16 //#define X0 14000.0 //#define X1 16000.0 //#define NBINS 1001 //#define NPTS_PER_BIN 9 // odd to get center lobe #include #include #include // emitter array phase double r[NX][NSP]; double i[NX][NSP]; main() { int ix ; // array index int ir ; // random part index double gx ; // swept ground position double px ; // double x1[NX][NSP] ; // distance component for x double x0 ; // working distance from center double xx ; // distance component for x double x2 ; // squared distance component for x double y1 ; // distance component for y double y2 ; // squared distance component for y double ran ; // accumulating random part double xdd ; double sumr ; // working sum per point double sumi ; // working sum per point double mag ; // power magnitude double binmax ; // maximum sum per bin double binmin ; // minimum sum per bin double lbinmax ; // log maximum sum per bin double lbinmin ; // log minimum sum per bin double frac ; // fraction of sweep double rp, ip ; // downlink path phase int nbin, npt ; // ground index double length ; // length of beam in wavelengths double wavenum = 2.0 * 3.1415926535897932 / WL ; // wavenumber double tmp ; double s2 = 1.0 / ( (double) ( NBINS-1 ) ) ; double s1 = 1.0 / ( (double) ( (NBINS-1)*( NPTS_PER_BIN ) ) ) ; double s0 = 0.5 * ( s1 - s2 ) ; double nx2 = 2.0 / ( NX - 1 ) ; double sam = SAM * nx2 * nx2 ; double am ; double amsum ; // first, compute emitter array from intended ground spot ran = 0.0 ; x0 = 0.5*SX1*(1-NX%2) ; // 0.5 if even, 0.0 if odd // find the distances for( ix=0 ; ix < NX/2 ; ix++ ) { // array position with spreading for( ir= 0 ; ir < NSP ; ir++ ) { xdd = x0 + ran * ( (double) ir ) / ( (double) (NSP-1) ) ; x1[NX/2+ix][ir] = GX + xdd ; x1[NX/2-(ix+1)][ir] = GX - xdd ; } ran += SXF*(drand48()-0.5) ; x0 += SX1 ; } // next, find the conjugate real and imaginary parts for each array y1 = GY ; y2 = y1*y1 ; for ( ir=0 ; ir < NSP ; ir++ ) { amsum=0.0 ; for( ix=0 ; ix < NX ; ix++ ) { x2 = x1[ix][ir]*x1[ix][ir] ; // distance squared length = wavenum * sqrt( x2 + y2 ); px = ix + 0.5 * ( 1.0 - NX ) ; am = 1.0 + sam * px * px ; amsum += am ; r[ix][ir] = am * cos( length ) ; i[ix][ir] = -am * sin( length ) ; } // normalize for( ix=0 ; ix < NX ; ix++ ) { r[ix][ir] /= amsum ; i[ix][ir] /= amsum ; } } #ifdef DISTANCE for( ix=0 ; ix < NX/2 ; ix++ ) { printf("%12d",NX/2+ix ); for( ir= 0 ; ir < NSP ; ir++ ) { printf("%8.2f", x1[NX/2+ix][ir] ); } printf("\n" ); } printf("\n"); printf("random scale"); for( ir= 0 ; ir < NSP ; ir++ ) { xdd = SXF * ( (double) ir ) / ( (double) (NSP-1) ) ; printf( "%8.3f", xdd ); } printf("\n"); printf(" gx max(db)\n"); #endif //DISTANCE // now, compute the traverse for( nbin = 0 ; nbin < NBINS ; nbin++ ) { frac = ((double)nbin )/(double)(NBINS-1) ; gx = GX + X0 + frac*(X1-X0); printf( "%12.2f", gx ); for ( ir=0 ; ir < NSP ; ir++ ) { binmax = -1e30 ; binmin = 1e30 ; for( npt = 0 ; npt < NPTS_PER_BIN ; npt++ ) { frac = s0 + s1*npt + s2*nbin ; gx = GX + X0 + frac*(X1-X0) ; sumr = 0.0 ; sumi = 0.0 ; // compute the signal sum at the ground from all the antennas for( ix=0 ; ix < NX ; ix++ ) { xx = gx + x1[ix][ir] ; x2 = xx * xx ; length = wavenum * sqrt( x2 + y2 ); rp = cos( length ) ; ip = sin( length ) ; sumr += rp*r[ix][ir] - ip*i[ix][ir] ; sumi += ip*r[ix][ir] + rp*i[ix][ir] ; } mag = sumr*sumr + sumi*sumi ; if ( binmax < mag ) binmax = mag ; if ( binmin > mag ) binmin = mag ; } lbinmax = 10.0*(log(binmax)/log(10.0)); printf("%8.3f", lbinmax ); } printf("\n"); fflush(stdout); } }