diff --git a/inputs.cc b/inputs.cc
index 0e64bf7..f5c0a9b 100644
--- a/inputs.cc
+++ b/inputs.cc
@@ -659,14 +659,14 @@ char LoadSDF(char *name)
 	return return_value;
 }
 
-int LoadPAT(char *filename)
+int LoadPAT(char *az_filename, char *el_filename)
 {
 	/* This function reads and processes antenna pattern (.az
 	   and .el) files that correspond in name to previously
 	   loaded ss .lrp files.  */
 
 	int a, b, w, x, y, z, last_index, next_index, span;
-	char string[255], azfile[255], elfile[255], *pointer = NULL;
+	char string[255], *pointer = NULL;
 	float az, xx, elevation, amplitude, rotation, valid1, valid2,
 	    delta, azimuth[361], azimuth_pattern[361], el_pattern[10001],
 	    elevation_pattern[361][1001], slant_angle[361], tilt,
@@ -674,21 +674,6 @@ int LoadPAT(char *filename)
 	FILE *fd = NULL;
 	unsigned char read_count[10001];
 
-	for (x = 0; filename[x] != '.' && filename[x] != 0 && x < 250; x++) {
-		azfile[x] = filename[x];
-		elfile[x] = filename[x];
-	}
-
-	azfile[x] = '.';
-	azfile[x + 1] = 'a';
-	azfile[x + 2] = 'z';
-	azfile[x + 3] = 0;
-
-	elfile[x] = '.';
-	elfile[x + 1] = 'e';
-	elfile[x + 2] = 'l';
-	elfile[x + 3] = 0;
-
 	rotation = 0.0;
 
 	got_azimuth_pattern = 0;
@@ -696,8 +681,11 @@ int LoadPAT(char *filename)
 
 	/* Load .az antenna pattern file */
 
-	if( (fd = fopen(azfile, "r")) != NULL ){
+	if( az_filename != NULL && (fd = fopen(az_filename, "r")) == NULL && errno != ENOENT )
+		/* Any error other than file not existing is an error */
+		return errno;
 
+	if( fd != NULL ){
 		/* Clear azimuth pattern array */
 
 		for (x = 0; x <= 360; x++) {
@@ -757,6 +745,7 @@ int LoadPAT(char *filename)
 		} while (feof(fd) == 0);
 
 		fclose(fd);
+		fd = NULL;
 
 		/* Handle 0=360 degree ambiguity */
 
@@ -823,13 +812,15 @@ int LoadPAT(char *filename)
 		azimuth_pattern[360] = azimuth_pattern[0];
 
 		got_azimuth_pattern = 255;
-	}else if( errno == EACCES ){
-		return errno;
 	}
 
 	/* Read and process .el file */
 
-	if( (fd = fopen(elfile, "r")) != NULL ){
+	if( el_filename != NULL && (fd = fopen(el_filename, "r")) == NULL && errno != ENOENT )
+		/* Any error other than file not existing is an error */
+		return errno;
+
+	if( fd != NULL ){
 
 		for (x = 0; x <= 10000; x++) {
 			el_pattern[x] = 0.0;
@@ -1009,8 +1000,6 @@ int LoadPAT(char *filename)
 				LR.antenna_pattern[x][y] = az * elevation;
 			}
 		}
-	}else if( errno == EACCES ){
-		return errno;
 	}
 	return 0;
 }
diff --git a/inputs.hh b/inputs.hh
index 3f66472..3c14514 100644
--- a/inputs.hh
+++ b/inputs.hh
@@ -5,7 +5,7 @@
 
 int LoadSDF_SDF(char *name, int winfiles);
 char LoadSDF(char *name, int winfiles);
-int LoadPAT(char *filename);
+int LoadPAT(char *az_filename, char *el_filename);
 int LoadSignalColors(struct site xmtr);
 void LoadLossColors(struct site xmtr);
 void LoadDBMColors(struct site xmtr);
@@ -14,4 +14,7 @@ void LoadUDT(char *filename);
 int loadLIDAR(char *filename);
 int loadClutter(char *filename, double radius, struct site tx);
 
+static const char AZ_FILE_SUFFIX[] = ".az";
+static const char EL_FILE_SUFFIX[] = ".el"; 
+
 #endif /* _INPUTS_HH_ */
diff --git a/main.cc b/main.cc
index dfc62a8..c96b966 100644
--- a/main.cc
+++ b/main.cc
@@ -1050,6 +1050,7 @@ int main(int argc, char *argv[])
 	    0, area_mode = 0, max_txsites, ngs = 0;
 
 	char mapfile[255], udt_file[255], ano_filename[255], lidar_tiles[4096], clutter_file[255];
+	char *az_filename, *el_filename;
 
 	double altitude = 0.0, altitudeLR = 0.0, tx_range = 0.0,
 	    rx_range = 0.0, deg_range = 0.0, deg_limit = 0.0, deg_range_lon;
@@ -1218,10 +1219,26 @@ int main(int argc, char *argv[])
 				strncpy(mapfile, argv[z], 253);
 				strncpy(tx_site[0].name, "Tx", 2);
 				strncpy(tx_site[0].filename, argv[z], 253);
-				if( (result = LoadPAT(argv[z])) != 0 ){
-					fprintf(stderr,"Error reading antenna pattern file\n");
+				/* Antenna pattern files have the same basic name as the output file
+				 * but with a different extension. If they exist, load them now */
+				if( (az_filename = (char*) calloc(strlen(argv[z]) + strlen(AZ_FILE_SUFFIX) + 1, sizeof(char))) == NULL )
+					return ENOMEM;
+				strcpy(az_filename, argv[z]);
+				strcat(az_filename, AZ_FILE_SUFFIX);
+				if( (el_filename = (char*) calloc(strlen(argv[z]) + strlen(EL_FILE_SUFFIX) + 1, sizeof(char))) == NULL ){
+					free(az_filename);
+					return ENOMEM;
+				}
+				strcpy(el_filename, argv[z]);
+				strcat(el_filename, EL_FILE_SUFFIX);
+				if( (result = LoadPAT(az_filename,el_filename)) != 0 ){
+					fprintf(stderr,"Permissions error reading antenna pattern file\n");
+					free(az_filename);
+					free(el_filename);
 					exit(result);
 				}
+				free(az_filename);
+				free(el_filename);
 			} else if (z <= y && argv[z][0] && argv[z][0] == '-' && argv[z][1] == '\0' ) {
 				/* Handle writing image data to stdout */
 				to_stdout = true;