diff --git a/compile_linux.sh b/compile_linux.sh
index 9c8cb9c54..d70f9145f 100644
--- a/compile_linux.sh
+++ b/compile_linux.sh
@@ -52,14 +52,14 @@ if test "$1" = "d"; then
   echo "configuring for 64 bit debug"
   echo
 # You may add  --enable-adms to the following command for adding adms generated devices 
-  ../configure --with-x --enable-xspice --enable-cider --with-readline=yes --enable-openmp CFLAGS="-g -m64 -O0 -Wall -Wno-unused-but-set-variable" LDFLAGS="-m64 -g"
+  ../configure --with-x --enable-xspice --enable-cider --with-readline=yes --enable-openmp --enable-sp CFLAGS="-g -m64 -O0 -Wall -Wno-unused-but-set-variable" LDFLAGS="-m64 -g"
 else
    cd release
    if [ $? -ne 0 ]; then  echo "cd release failed"; exit 1 ; fi
   echo "configuring for 64 bit release"
   echo
 # You may add  --enable-adms to the following command for adding adms generated devices 
-  ../configure --with-x --enable-xspice --enable-cider --with-readline=yes --enable-openmp --disable-debug CFLAGS="-m64 -O2" LDFLAGS="-m64 -s"
+  ../configure --with-x --enable-xspice --enable-cider --with-readline=yes --enable-openmp --enable-sp --disable-debug CFLAGS="-m64 -O2" LDFLAGS="-m64 -s"
 fi
 if [ $? -ne 0 ]; then  echo "../configure failed"; exit 1 ; fi
 
diff --git a/compile_min.sh b/compile_min.sh
index 606642aed..0571eda07 100755
--- a/compile_min.sh
+++ b/compile_min.sh
@@ -53,14 +53,14 @@ if test "$1" = "d"; then
   echo "configuring for 64 bit debug"
   echo
 # You may add  --enable-adms to the following command for adding adms generated devices 
-  ../configure --with-wingui --enable-xspice --enable-cider --enable-openmp prefix="C:/Spice64d" CFLAGS="-g -m64 -O0 -Wall -Wno-unused-but-set-variable" LDFLAGS="-g -m64"
+  ../configure --with-wingui --enable-xspice --enable-cider --enable-openmp --enable-sp prefix="C:/Spice64d" CFLAGS="-g -m64 -O0 -Wall -Wno-unused-but-set-variable" LDFLAGS="-g -m64"
 else
    cd release
    if [ $? -ne 0 ]; then  echo "cd release failed"; exit 1 ; fi
   echo "configuring for 64 bit release"
   echo
 # You may add  --enable-adms to the following command for adding adms generated devices 
-  ../configure --with-wingui --enable-xspice --enable-cider --enable-openmp --disable-debug prefix="C:/Spice64" CFLAGS="-m64 -O2" LDFLAGS="-m64 -s"
+  ../configure --with-wingui --enable-xspice --enable-cider --enable-openmp --enable-sp --disable-debug prefix="C:/Spice64" CFLAGS="-m64 -O2" LDFLAGS="-m64 -s"
 fi
 if [ $? -ne 0 ]; then  echo "../configure failed"; exit 1 ; fi
 
diff --git a/configure.ac b/configure.ac
index 41ee600c1..ffa20400f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -158,6 +158,10 @@ AC_ARG_ENABLE([adms],
 AC_ARG_ENABLE([pss],
     [AS_HELP_STRING([--enable-pss], [Enable PSS Analysis, (experimental)])])
 
+# --enable-sp: enable S Parameter Analysis
+AC_ARG_ENABLE([sp],
+    [AS_HELP_STRING([--enable-sp], [Enable S parameter Analysis])])
+
 # --enable-relpath: Relative path for binary and data. Default is "no".
 # ngspice shared may want relative paths for spinit etc.
 AC_ARG_ENABLE([relpath],
@@ -1161,12 +1165,20 @@ if test "x$enable_cider" = xyes; then
     AC_DEFINE([CIDER], [1], [The CIDER enhancements])
 fi
 
+# Add S parameter analysis to ngspice.
+if test "x$enable_sp" = xyes; then
+    AC_MSG_RESULT([S parameter analysis enabled])
+    AC_DEFINE([RFSPICE], [1], [S parameter analysis])
+fi
+
 AM_CONDITIONAL([CIDER_WANTED], [test "x$enable_cider" = xyes])
 AM_CONDITIONAL([NUMDEV_WANTED], [test "x$enable_cider" = xyes])
 
 
 AM_CONDITIONAL([PSS_WANTED], [test "x$enable_pss" = xyes])
 
+AM_CONDITIONAL([SP_WANTED], [test "x$enable_sp" = xyes])
+
 AM_CONDITIONAL([SENSE2_WANTED], [test "x$enable_sense2" = xyes])
 
 # adms option
diff --git a/src/Makefile.am b/src/Makefile.am
index 5d43dd39e..087658425 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -185,6 +185,11 @@ ngspice_LDADD += \
 	maths/sparse/libsparse.la \
 	misc/libmisc.la
 
+if SP_WANTED
+ngspice_LDADD += \
+    maths/dense/libdense.la
+endif
+
 if !WINGUI
 if !NO_X
 ngspice_LDADD += frontend/help/libhlp.la
@@ -463,6 +468,11 @@ libspice_la_LIBADD += \
 	misc/libmisc.la \
 	$(LIBS)
 
+if SP_WANTED
+libspice_la_LIBADD += \
+    maths/dense/libdense.la
+endif
+
 libspice_la_CFLAGS = -shared
 libspice_la_LDFLAGS =  -shared -Wl,--version-script=$(srcdir)/tclspice.map
 if TCLWIN
diff --git a/src/maths/Makefile.am b/src/maths/Makefile.am
index 9bc84a2cf..959156909 100644
--- a/src/maths/Makefile.am
+++ b/src/maths/Makefile.am
@@ -1,6 +1,10 @@
 ## Process this file with automake
 
 SUBDIRS = cmaths ni sparse poly deriv misc fft
-DIST_SUBDIRS = cmaths ni sparse poly deriv misc fft
+DIST_SUBDIRS = cmaths ni sparse poly deriv misc fft dense
+
+if SP_WANTED
+SUBDIRS += dense
+endif
 
 MAINTAINERCLEANFILES = Makefile.in
diff --git a/src/spicelib/analysis/Makefile.am b/src/spicelib/analysis/Makefile.am
index be94ad40c..62ab58d1a 100644
--- a/src/spicelib/analysis/Makefile.am
+++ b/src/spicelib/analysis/Makefile.am
@@ -108,6 +108,14 @@ libckt_la_SOURCES += \
 		psssetp.c
 endif
 
+if SP_WANTED
+libckt_la_SOURCES += \
+		cktspdum.c		\
+		span.c	\
+		spaskq.c	\
+		spsetp.c
+endif
+
 
 AM_CPPFLAGS = @AM_CPPFLAGS@  -I$(top_srcdir)/src/include -I$(top_srcdir)/src/spicelib/devices
 AM_CFLAGS = $(STATIC)