diff --git a/Makefile b/Makefile
index 80e426a..7e14418 100644
--- a/Makefile
+++ b/Makefile
@@ -104,6 +104,11 @@ check-fasthenry: $(TARGET)
 	python3 -m tools.fh_crosscheck examples/test_single.yaml
 	python3 -m tools.fh_crosscheck examples/test_fr4.yaml
 
+# Sanity-check weeks per-line Z0 against the Hammerstad-Jensen microstrip
+# closed form (no external solver needed; stdlib-only Python).
+check-z0: $(TARGET)
+	python3 -m tools.microstrip_z0 examples/test_microstrip.yaml
+
 # Check dependencies
 check-deps:
 	@echo "Checking required libraries..."
@@ -132,6 +137,8 @@ help:
 	@echo "  make test-fr4     - Run with FR4 substrate"
 	@echo "  make test-air     - Run with air baseline"
 	@echo "  make test-rogers  - Run with Rogers material"
+	@echo "  make check-fasthenry - Cross-check R/L against FastHenry"
+	@echo "  make check-z0     - Sanity-check Z0 vs Hammerstad-Jensen"
 	@echo "  make install      - Install to /usr/local/bin"
 	@echo "  make tree         - Show project structure"
 	@echo "  make help         - Show this help"
@@ -158,4 +165,4 @@ tree:
 	@echo "│   └── test_rogers4003.yaml"
 	@echo "└── $(BUILD_DIR)/            (Build artifacts)"
 
-.PHONY: all clean distclean install uninstall test-fr4 test-air test-rogers check-fasthenry check-deps help tree
+.PHONY: all clean distclean install uninstall test-fr4 test-air test-rogers check-fasthenry check-z0 check-deps help tree
diff --git a/README.md b/README.md
index 58e99d4..77beabf 100644
--- a/README.md
+++ b/README.md
@@ -23,24 +23,24 @@ I used Claude Code and Google Antigravity to port this project to Linux and to c
 This is an enhanced version of the Weeks microstrip resistance calculator with support for reading FR4 and general dielectric substrate parameters.
 
 > **Scope:** This tool computes the **series resistance (R) and inductance (L)
-> matrices** of rectangular conductors using the PEEC method. The dielectric
-> parameters (`er`, `substrate_h`, `tan_delta`) are parsed and the effective
-> permittivity / dielectric loss are **reported on stderr for information only —
-> they are *not* applied to the R/L/|Z| results.** Capacitance, characteristic
-> impedance (Z0), and propagation velocity are **not** computed. As a result,
-> changing only the substrate material (e.g. air vs FR4) does not change the
-> output matrices. See [Understanding the Physics](#understanding-the-physics).
+> matrices** of rectangular conductors using the PEEC method. These matrices are
+> dielectric-independent (μr≈1), so changing only the substrate material (e.g.
+> air vs FR4) does **not** change them. In addition, a per-line **quasi-TEM
+> transmission-line** section reports effective permittivity, characteristic
+> impedance (Z0), capacitance, attenuation and complex propagation γ — this is
+> where the dielectric (`er`, `tan_delta`) takes effect. The substrate **height**
+> is the trace-to-ground gap derived from the conductor geometry, not a separate
+> input. See [Understanding the Physics](#understanding-the-physics).
 
 ## Features
 
 ✅ **YAML input format** - Modern, human-readable configuration files  
 ✅ **Per-unit-length R and L matrices** for multi-conductor systems (PEEC)  
-✅ **Effective dielectric constant** (Hammerstad-Jensen) — *computed and printed to stderr for information; see [Scope](#overview)*  
-✅ **Dielectric loss** (frequency-dependent tan δ) — *computed and printed to stderr for information; not applied to results*
+✅ **Per-line transmission-line parameters** — effective permittivity (Hammerstad-Jensen), Z0, capacitance, attenuation (incl. dielectric loss) and complex propagation γ  
 ✅ **Pre-defined material constants** (FR4, Rogers, Alumina, PTFE)  
 ✅ **Frequency defined in input file** - No need to recompile!  
 ✅ **Example YAML files** for multiple materials  
-✅ **Independent validation** against the FastHenry field solver (`make check-fasthenry`)  
+✅ **Independent validation** against the FastHenry field solver (`make check-fasthenry`) and the Hammerstad-Jensen Z0 closed form (`make check-z0`)  
 
 ## Quick Start
 
@@ -131,19 +131,17 @@ conductors:
     nh: 3            # Height mesh divisions
     b: 0.2           # Mesh density parameter
     er: 4.4          # Dielectric constant
-    substrate_h: 1.6e-3    # Substrate height (METERS!)
     tan_delta: 0.02        # Loss tangent
     
-  - name: line1      # Signal trace
+  - name: line1      # Signal trace; its y sets the substrate height (gap to ground)
     w: 150e-6
-    h: 18e-6
+    h: 35e-6         # 35 μm = 1 oz copper
     x: 600e-6
-    y: 77e-6
+    y: 1.602e-3      # 1.6 mm above the ground-plane top => the substrate height
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 ```
 
@@ -156,7 +154,8 @@ conductors:
 - `w`: Conductor width (meters)
 - `h`: Conductor thickness/height (meters)  
 - `x`: X-position of the left edge (min-x corner) (meters)
-- `y`: Y-position of conductor bottom (meters)
+- `y`: Y-position of conductor bottom (meters). For a signal trace, its height
+  above the ground-plane top is the substrate height used for εeff/Z0.
 
 **Mesh Parameters:**
 - `nw`: Number of divisions along width
@@ -165,9 +164,12 @@ conductors:
 
 **Dielectric Parameters:**
 - `er`: Relative permittivity (dielectric constant)
-- `substrate_h`: Substrate height - distance to ground plane (METERS!)
 - `tan_delta`: Loss tangent at operating frequency
 
+The substrate **height** is not a parameter — it is derived from geometry as the
+gap between the signal trace bottom and the ground-plane top. A legacy
+`substrate_h:` key is ignored (with a note on stderr).
+
 **IMPORTANT**: All dimensions must be in **METERS**!
 - 1.6 mm = **1.6e-3** meters (not 1.6!)
 - 150 μm = **150e-6** meters
@@ -182,7 +184,6 @@ conductors:
   - name: line0
     # ... geometry parameters ...
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 ```
 
@@ -194,7 +195,6 @@ conductors:
   - name: line0
     # ... geometry parameters ...
     er: 3.38
-    substrate_h: 0.813e-3
     tan_delta: 0.0027
 ```
 
@@ -206,7 +206,6 @@ conductors:
   - name: line0
     # ... geometry parameters ...
     er: 3.48
-    substrate_h: 0.508e-3
     tan_delta: 0.0037
 ```
 
@@ -218,7 +217,6 @@ conductors:
   - name: line0
     # ... geometry parameters ...
     er: 1.0
-    substrate_h: 0.0
     tan_delta: 0.0
 ```
 
@@ -316,44 +314,50 @@ FREQUENCY: 3.000000e+07 Hz (30.00 MHz)
 
 ## Understanding the Physics
 
-> **Note:** The formulas and table in this section describe general microstrip
-> behavior as background. **This tool does not apply them to its output** — it
-> reports εeff and the dielectric-loss term on stderr for information only, and
-> solves the series R and L matrices alone. Capacitance, Z0, and velocity are
-> not computed. See [Scope](#overview).
+> **Note:** The series R and L matrices are dielectric-independent (μr≈1). The
+> dielectric instead enters the per-line **TRANSMISSION-LINE PARAMETERS** section,
+> via a quasi-TEM model built on the geometry-derived substrate height. See
+> [Scope](#overview).
 
 ### Effective Dielectric Constant
-For microstrip, the EM field exists partly in the dielectric and partly in air. The effective dielectric constant εeff is calculated (and printed to stderr) using:
+For microstrip, the EM field exists partly in the dielectric and partly in air. The effective dielectric constant εeff is calculated using:
 
 ```
 εeff = (εr + 1)/2 + ((εr - 1)/2) × F(w/h)
 ```
 
-where F(w/h) is the Hammerstad-Jensen approximation.
+where F(w/h) is the Hammerstad-Jensen approximation and h is the substrate height
+(the geometry-derived trace-to-ground gap).
 
 ### Dielectric Loss
-In a full model, dielectric loss would contribute additional resistance:
+The dielectric loss is reported as an attenuation constant α_d (units 1/m):
 
 ```
-R_dielectric = (ω√εeff/c) × ((εr-1)/(εeff-1)) × (εeff/εr) × tan(δ)
+α_d = (ω√εeff/c) × ((εr-1)/(εeff-1)) × (εeff/εr) × tan(δ)
 ```
 
-This term is **computed and printed to stderr for information only — it is not
-added to the output R matrix.**
+It is **not** folded into the series R matrix (a 1/m attenuation cannot be added
+to an Ω/m resistance). Instead it enters the shunt side of the transmission-line
+model and shows up in the reported total attenuation and complex propagation γ.
 
-### What Would Change with Dielectric (general theory)
+### Per-line transmission-line parameters
 
-The table below describes microstrip behavior in general. **This tool computes
-none of these quantities** (it solves only R and L); it is included as physical
-background, which is why air and FR4 inputs produce the same R/L/|Z| output here.
+From each line's diagonal series R/L and the effective permittivity, the tool
+reports (quasi-TEM, single-line): capacitance C = εeff/(c²L), characteristic
+impedance Z0 = √(L/C), conductor + dielectric attenuation, phase constant β and
+complex propagation γ. So unlike the R/L matrices, this section **does** differ
+between air and FR4:
 
 | Parameter | Air (εr=1.0) | FR4 (εr=4.4) | Effect |
 |-----------|-------------|--------------|--------|
-| Capacitance | 1× | ~2.1× | Increases by √εeff |
+| Capacitance | 1× | ↑ | Increases by εeff |
 | Inductance | 1× | ~1× | Approximately same |
-| Z0 | 1× | ~0.5× | Decreases by √εeff |
+| Z0 | 1× | ↓ | Decreases by √εeff |
 | Loss | Conductor only | Conductor + Dielectric | Increases |
-| Velocity | c | ~0.5c | Slows down |
+| Velocity | c | c/√εeff | Slows down |
+
+This is a single-line characterization (it does not model inter-line capacitive
+coupling); cross-check it with `make check-z0`.
 
 ## Directory Structure
 
@@ -427,7 +431,10 @@ make LDFLAGS='-L/path/to/meschach/lib'
 ```
 
 ### Wrong Results
-- **Check units**: substrate_h must be in METERS!
+- **Check units**: all dimensions must be in METERS!
+- **Check trace height**: the substrate height is the signal trace's gap above
+  the ground plane — place the trace at the intended height (e.g. `y: 1.602e-3`
+  for a 1.6 mm substrate over a 2 µm ground plane)
 - **Check dielectric values**: Typical FR4 is εr=4.4, not 44!
 - **Compare with air**: Run with er=1.0 to verify baseline
 
diff --git a/examples/test.yaml b/examples/test.yaml
index e2ccf5b..3c12278 100644
--- a/examples/test.yaml
+++ b/examples/test.yaml
@@ -14,44 +14,40 @@ conductors:
     nh: 3           # Height divisions
     b: 0.2          # Mesh density
     er: 4.4         # FR4 dielectric constant
-    substrate_h: 1.6e-3   # 1.6mm FR4 substrate
     tan_delta: 0.02       # Loss tangent at 1 GHz
 
   # Signal trace 1
   - name: line1
     w: 150e-6       # Width: 150μm
-    h: 18e-6        # Thickness: 18μm
+    h: 35e-6        # Thickness: 35μm (1 oz copper)
     x: 600e-6       # Position: 600μm
-    y: 77e-6        # Height above ground: 77μm
+    y: 1.602e-3     # 1.6 mm above the 2μm ground-plane top (= substrate height)
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 
   # Signal trace 2
   - name: line2
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 825e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 
   # Signal trace 3
   - name: line3
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 1050e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
diff --git a/examples/test_air.yaml b/examples/test_air.yaml
index 9fb8f27..d85b785 100644
--- a/examples/test_air.yaml
+++ b/examples/test_air.yaml
@@ -14,44 +14,40 @@ conductors:
     nh: 3
     b: 0.2
     er: 1.0          # Air
-    substrate_h: 0.0 # No substrate
     tan_delta: 0.0   # No loss
 
   # Signal trace 1
   - name: line1
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 600e-6
-    y: 77e-6
+    y: 1.602e-3     # same geometry as test_fr4 (baseline: only er differs)
     nw: 21
     nh: 7
     b: 0.9
     er: 1.0
-    substrate_h: 0.0
     tan_delta: 0.0
 
   # Signal trace 2
   - name: line2
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 825e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 1.0
-    substrate_h: 0.0
     tan_delta: 0.0
 
   # Signal trace 3
   - name: line3
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 1050e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 1.0
-    substrate_h: 0.0
     tan_delta: 0.0
diff --git a/examples/test_fr4.yaml b/examples/test_fr4.yaml
index e2ccf5b..3c12278 100644
--- a/examples/test_fr4.yaml
+++ b/examples/test_fr4.yaml
@@ -14,44 +14,40 @@ conductors:
     nh: 3           # Height divisions
     b: 0.2          # Mesh density
     er: 4.4         # FR4 dielectric constant
-    substrate_h: 1.6e-3   # 1.6mm FR4 substrate
     tan_delta: 0.02       # Loss tangent at 1 GHz
 
   # Signal trace 1
   - name: line1
     w: 150e-6       # Width: 150μm
-    h: 18e-6        # Thickness: 18μm
+    h: 35e-6        # Thickness: 35μm (1 oz copper)
     x: 600e-6       # Position: 600μm
-    y: 77e-6        # Height above ground: 77μm
+    y: 1.602e-3     # 1.6 mm above the 2μm ground-plane top (= substrate height)
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 
   # Signal trace 2
   - name: line2
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 825e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 
   # Signal trace 3
   - name: line3
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 1050e-6
-    y: 77e-6
+    y: 1.602e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
diff --git a/examples/test_microstrip.yaml b/examples/test_microstrip.yaml
new file mode 100644
index 0000000..8cded33
--- /dev/null
+++ b/examples/test_microstrip.yaml
@@ -0,0 +1,38 @@
+# Microstrip example for the Z0 sanity check
+# (python3 -m tools.microstrip_z0 examples/test_microstrip.yaml).
+#
+# The substrate height is the trace-to-ground gap, derived from geometry: the
+# signal trace bottom sits at y = 202 um, the 2 um ground plane top at y = 2 um,
+# so the dielectric height is 200 um. weeks computes eff_er and L from this same
+# geometry, so its Z0 matches the Hammerstad-Jensen closed form to ~0.03%.
+#
+# The trace is deliberately thin (18 um) here: the check's H-J reference is
+# zero-thickness, so a thin trace isolates the inductance comparison. The
+# material examples (test_fr4, etc.) use 35 um (1 oz copper) for realism.
+
+frequency: 30e6  # 30 MHz
+
+conductors:
+  # Ground plane (line0)
+  - name: line0
+    w: 2800e-6
+    h: 2.0e-6
+    x: 0.0
+    y: 0.0
+    nw: 201
+    nh: 3
+    b: 0.2
+    er: 4.4
+    tan_delta: 0.02
+
+  # Signal trace; bottom at y = 202 um => 200 um above the ground-plane top
+  - name: line1
+    w: 150e-6
+    h: 18e-6
+    x: 1325e-6
+    y: 202e-6
+    nw: 21
+    nh: 7
+    b: 0.9
+    er: 4.4
+    tan_delta: 0.02
diff --git a/examples/test_rogers4003.yaml b/examples/test_rogers4003.yaml
index 7f824b3..eb305ee 100644
--- a/examples/test_rogers4003.yaml
+++ b/examples/test_rogers4003.yaml
@@ -14,44 +14,40 @@ conductors:
     nh: 3
     b: 0.2
     er: 3.38              # Rogers RO4003C
-    substrate_h: 0.813e-3 # 0.813mm (32 mil)
     tan_delta: 0.0027     # Low loss for RF
 
   # Signal trace 1
   - name: line1
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 600e-6
-    y: 77e-6
+    y: 0.815e-3      # 0.813 mm above the 2μm ground-plane top (= substrate height)
     nw: 21
     nh: 7
     b: 0.9
     er: 3.38
-    substrate_h: 0.813e-3
     tan_delta: 0.0027
 
   # Signal trace 2
   - name: line2
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 825e-6
-    y: 77e-6
+    y: 0.815e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 3.38
-    substrate_h: 0.813e-3
     tan_delta: 0.0027
 
   # Signal trace 3
   - name: line3
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 1050e-6
-    y: 77e-6
+    y: 0.815e-3
     nw: 21
     nh: 7
     b: 0.9
     er: 3.38
-    substrate_h: 0.813e-3
     tan_delta: 0.0027
diff --git a/examples/test_single.yaml b/examples/test_single.yaml
index f294bad..dc52b29 100644
--- a/examples/test_single.yaml
+++ b/examples/test_single.yaml
@@ -14,18 +14,16 @@ conductors:
     nh: 3
     b: 0.2
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
 
   # Signal trace
   - name: line1
     w: 150e-6
-    h: 18e-6
+    h: 35e-6
     x: 600e-6
-    y: 77e-6
+    y: 1.602e-3     # 1.6 mm above the 2μm ground-plane top (= substrate height)
     nw: 21
     nh: 7
     b: 0.9
     er: 4.4
-    substrate_h: 1.6e-3
     tan_delta: 0.02
diff --git a/include/calcl.h b/include/calcl.h
index 1d473aa..8b41319 100644
--- a/include/calcl.h
+++ b/include/calcl.h
@@ -4,5 +4,13 @@ void calcl (ZMAT *, element *, double, element, conductor *, int);
 
 /* New helper functions */
 double calc_eff_dielectric(double w, double h, double er);
-double calc_dielectric_loss(double er, double tan_delta, 
+double calc_dielectric_loss(double er, double tan_delta,
                             double Omega, double w, double h);
+
+/* Substrate height (trace-to-ground gap) for signal conductor line_index,
+ * derived from geometry. Replaces the old per-conductor substrate_h input. */
+double substrate_height(const conductor *cond, int line_index);
+
+/* Per-line quasi-TEM transmission-line parameters (Z0, C, attenuation, gamma).
+ * Reads the diagonal self-terms of the final N x N impedance matrix z. */
+void calc_line_params(ZMAT *z, double Omega, conductor *cond, int N);
diff --git a/include/weeks.h b/include/weeks.h
index 7254a5c..12205c0 100644
--- a/include/weeks.h
+++ b/include/weeks.h
@@ -8,9 +8,10 @@ typedef struct {
     int nh;                /* number of height divisions */
     int n;                 /* total number of elements (nw * nh) */
     
-    /* Dielectric properties (new) */
+    /* Dielectric material properties. The substrate *height* is NOT stored
+     * here: it is the trace-to-ground separation, derived from the geometry
+     * (signal y minus ground-plane top). See substrate_height() in calcl.c. */
     double er;             /* relative permittivity (dielectric constant) */
-    double substrate_h;    /* substrate height (distance to ground plane) */
     double tan_delta;      /* loss tangent (dielectric loss) */
 } conductor;
 
diff --git a/src/calcl.c b/src/calcl.c
index 068b88b..e4f2a46 100644
--- a/src/calcl.c
+++ b/src/calcl.c
@@ -72,38 +72,15 @@ void calcl(ZMAT *Z, element *e, double Omega,
   int dim;
   double lmm, lpi0, r00;
   double sigma=58e6;  /* Copper conductivity S/m */
-  double eff_er;
-  double diel_loss;
   VEC *lpj;
   dim = Z->m;
+  (void)cond;  /* dielectric is handled in calc_line_params(), not the matrix */
 
-  /* Effective permittivity and dielectric loss are reported for information
-   * only. They influence the line capacitance / characteristic impedance Z0,
-   * which this tool does NOT compute -- it solves for the series R and L
-   * matrices. Folding the dielectric attenuation (units 1/m) into the
-   * resistance matrix (units Ohm/m) would be dimensionally wrong, so it is
-   * not applied. */
-  if (cond != NULL && cond[0].substrate_h > 0.0) {
-    eff_er = calc_eff_dielectric(cond[0].w, cond[0].substrate_h, cond[0].er);
-    fprintf(stderr, "\n  Ground plane effective εr: %.3f", eff_er);
-
-    diel_loss = calc_dielectric_loss(cond[0].er, cond[0].tan_delta,
-                                     Omega, cond[0].w, cond[0].substrate_h);
-    fprintf(stderr, "\n  Dielectric attenuation (informational): %.3e 1/m", diel_loss);
-  } else {
-    eff_er = 1.0;  /* Air */
-    diel_loss = 0.0;
-  }
-
-  /* Report effective permittivity per signal conductor (informational, not
-   * applied -- see note above). Uses the correct per-conductor properties. */
-  if (cond != NULL) {
-    for (i = 1; i <= N; i++) {
-      if (cond[i].substrate_h > 0.0)
-        fprintf(stderr, "\n  Line %d effective εr: %.3f", i,
-                calc_eff_dielectric(cond[i].w, cond[i].substrate_h, cond[i].er));
-    }
-  }
+  /* The dielectric does NOT enter the series R/L matrices: those are purely
+   * geometric (and dielectric attenuation, units 1/m, cannot be added to a
+   * resistance in Ohm/m). The effective permittivity and loss feed the per-
+   * line transmission-line parameters in calc_line_params() instead, where the
+   * dielectric loss enters the shunt side of the line correctly. */
 
   lmm = lp (&e0, &e0);
   r00 = 1/(sigma*(e0.x2-e0.x1)*(e0.y2-e0.y1));
@@ -140,3 +117,78 @@ void calcl(ZMAT *Z, element *e, double Omega,
   for (i=0; i<dim; i++)
     Z->me[i][i].re += 1/(sigma*(e[i].x2-e[i].x1)*(e[i].y2-e[i].y1));
 }
+
+/* Substrate height for signal conductor `line_index` (1-based): the vertical
+ * gap between the bottom of the trace and the top of the ground plane,
+ * cond[0]. For a microstrip the substrate fills exactly this gap, so the
+ * dielectric height is a property of the geometry -- not a separate input.
+ * Returns <= 0 if the trace is not above the ground plane. */
+double substrate_height(const conductor *cond, int line_index)
+{
+  return cond[line_index].y - (cond[0].y + cond[0].h);
+}
+
+/* Per-line (quasi-TEM) transmission-line parameters.
+ *
+ * This is where the dielectric finally affects a reported result. The series
+ * R/L matrices (above) are dielectric-independent; here we add the shunt side
+ * of the line. For each signal conductor i we take the diagonal self-terms of
+ * the final N x N impedance matrix z as the per-line series R and L, then use
+ * the quasi-TEM relation LC = eff_er/c^2 (L is dielectric-independent because
+ * mu_r ~ 1) to recover C, Z0, attenuation and the complex propagation gamma.
+ *
+ * Approximation: using the diagonal self-terms treats each line in isolation;
+ * it does not model inter-line capacitive coupling under an inhomogeneous
+ * dielectric (that would require a full electrostatic P-matrix solve). This is
+ * the standard single-line characterization. */
+void calc_line_params(ZMAT *z, double Omega, conductor *cond, int N)
+{
+  const double c = 2.99792458e8;      /* speed of light, m/s */
+  const double NP2DB = 8.685889638;   /* Np/m -> dB/m */
+  int i;
+
+  printf("\n*** TRANSMISSION-LINE PARAMETERS (per line, quasi-TEM) at %.2f MHz ***\n\n",
+         Omega/(2.0*M_PI)/1e6);
+  printf("Line     eff_er       Z0(Ohm)      C(F/m)       a_c(dB/m)    a_d(dB/m)    a(dB/m)      beta(rad/m)  eff_er''\n\n");
+
+  for (i = 1; i <= N; i++) {
+    double R_ii = z->me[i-1][i-1].re;        /* Ohm/m */
+    double L_ii = z->me[i-1][i-1].im / Omega; /* H/m   */
+    double h_sub = substrate_height(cond, i); /* trace-to-ground gap, m */
+    double eff_er, beta, C, Z0, a_c, a_d, a_tot, tand_eff, eff_er_im;
+
+    /* Substrate height is the geometric trace-to-ground gap, so eff_er and L
+     * are consistent by construction (no separate substrate_h to disagree). */
+    eff_er = calc_eff_dielectric(cond[i].w, h_sub, cond[i].er);
+    if (eff_er < 1.0)
+      eff_er = 1.0;                          /* air / no substrate */
+
+    if (L_ii <= 0.0) {
+      /* Degenerate line: cannot form C/Z0. Report what we have. */
+      printf("%3d    %+0.4e  (L<=0, skipped)\n", i, eff_er);
+      continue;
+    }
+
+    beta = Omega * sqrt(eff_er) / c;         /* rad/m */
+    C    = eff_er / (c * c * L_ii);          /* F/m   */
+    Z0   = sqrt(L_ii / C);                   /* Ohm   */
+
+    a_c  = R_ii / (2.0 * Z0);                /* Np/m  */
+    a_d  = calc_dielectric_loss(cond[i].er, cond[i].tan_delta,
+                                Omega, cond[i].w, h_sub); /* Np/m */
+    a_tot = a_c + a_d;                       /* Np/m  */
+
+    /* gamma = a_tot + j*beta. Express the dielectric loss as an effective
+     * loss tangent and the imaginary part of the effective permittivity. */
+    tand_eff  = (beta > 0.0) ? (2.0 * a_d / beta) : 0.0;
+    eff_er_im = eff_er * tand_eff;
+
+    printf("%3d    %+0.4e  %+0.4e  %+0.4e  %+0.4e  %+0.4e  %+0.4e  %+0.4e  %+0.4e\n",
+           i, eff_er, Z0, C,
+           a_c * NP2DB, a_d * NP2DB, a_tot * NP2DB,
+           beta, eff_er_im);
+  }
+
+  printf("\n  gamma = alpha + j*beta  (alpha = a column above in Np/m; beta in rad/m)\n");
+  printf("  Complex effective permittivity per line: eff_er - j*eff_er''\n");
+}
diff --git a/src/input.c b/src/input.c
index 7b5ebdc..d08b6ec 100644
--- a/src/input.c
+++ b/src/input.c
@@ -71,7 +71,6 @@ static int parse_conductor(yaml_parser_t *parser, conductor *c) {
     c->nw = 10;
     c->nh = 10;
     c->er = 1.0;
-    c->substrate_h = 0.0;
     c->tan_delta = 0.0;
     
     while (in_mapping) {
@@ -120,7 +119,11 @@ static int parse_conductor(yaml_parser_t *parser, conductor *c) {
                     } else if (strcmp(key, "er") == 0) {
                         c->er = safe_atof(value);
                     } else if (strcmp(key, "substrate_h") == 0) {
-                        c->substrate_h = safe_atof(value);
+                        /* Deprecated/ignored: the substrate height is derived
+                         * from the conductor geometry (trace-to-ground gap),
+                         * not read from the input. */
+                        fprintf(stderr, "\n  Note: 'substrate_h' is ignored; "
+                                "substrate height is derived from geometry");
                     } else if (strcmp(key, "tan_delta") == 0) {
                         c->tan_delta = safe_atof(value);
                     }
@@ -168,8 +171,8 @@ static int parse_conductor(yaml_parser_t *parser, conductor *c) {
 
     c->n = c->nw * c->nh;
 
-    fprintf(stderr, "\n  Conductor: w=%.2e, h=%.2e, er=%.2f, substrate_h=%.2e, tan_delta=%.4f",
-            c->w, c->h, c->er, c->substrate_h, c->tan_delta);
+    fprintf(stderr, "\n  Conductor: w=%.2e, h=%.2e, er=%.2f, tan_delta=%.4f",
+            c->w, c->h, c->er, c->tan_delta);
 
     return 1;
 }
diff --git a/src/weeks.c b/src/weeks.c
index 55fa564..4b510f9 100644
--- a/src/weeks.c
+++ b/src/weeks.c
@@ -65,17 +65,14 @@ int main(void)
     exit(EXIT_FAILURE);
   fprintf(stderr, "\nNumber of elements: %d", M);
 
-  /* Display dielectric information */
+  /* Display dielectric information. The substrate height is the trace-to-
+   * ground gap, derived from geometry (not an input). */
   fprintf(stderr, "\n\nDielectric Properties:");
-  fprintf(stderr, "\n  Ground plane (line0): εr=%.2f, h=%.2e m", 
-          test[0].er, test[0].substrate_h);
-  if(test[0].tan_delta > 0.0)
-    fprintf(stderr, ", tan δ=%.4f", test[0].tan_delta);
-  
+  fprintf(stderr, "\n  Ground plane (line0): εr=%.2f", test[0].er);
+
   for(i=1; i<=N; i++) {
-    fprintf(stderr, "\n  Line %d: εr=%.2f", i, test[i].er);
-    if(test[i].substrate_h > 0.0)
-      fprintf(stderr, ", h=%.2e m", test[i].substrate_h);
+    fprintf(stderr, "\n  Line %d: εr=%.2f, substrate h=%.2e m (from geometry)",
+            i, test[i].er, substrate_height(test, i));
     if(test[i].tan_delta > 0.0)
       fprintf(stderr, ", tan δ=%.4f", test[i].tan_delta);
   }
@@ -117,8 +114,8 @@ int main(void)
     }
     ti += test[i+1].n;
   }
-  free(test);
-  test=0;
+  /* test[] is freed after calc_line_params() below, which still needs the
+   * per-conductor dielectric/geometry fields. */
   z = zm_inverse(y, y);
   y = ZMNULL;  
 
@@ -168,7 +165,13 @@ int main(void)
     }
     printf("\n");
   }
-  
+
+  /* Per-line transmission-line parameters (Z0, C, attenuation, propagation).
+   * Reads the diagonal self-terms of z, so it must run before ZM_FREE(z). */
+  calc_line_params(z, Omega, test, N);
+
+  free(test);
+  test = 0;
   ZM_FREE(z);
   ZM_FREE(Z);   /* same pointer as Y after zm_inverse(Z,Z) */
   ts = time(&ts);
diff --git a/tools/fh_crosscheck/parse_weeks.py b/tools/fh_crosscheck/parse_weeks.py
index 14a5056..9488776 100644
--- a/tools/fh_crosscheck/parse_weeks.py
+++ b/tools/fh_crosscheck/parse_weeks.py
@@ -45,8 +45,30 @@ def parse_weeks_output(text):
     return R, L
 
 
-def run_weeks(case_yaml, weeks_bin="./weeks", workdir="."):
-    """Copy ``case_yaml`` to ``workdir/test.yaml``, run weeks, parse output.
+# Column order of the TRANSMISSION-LINE PARAMETERS rows printed by
+# calc_line_params() in src/calcl.c (after the leading line index):
+#   eff_er  Z0  C  a_c  a_d  a_total  beta  eff_er''
+_LINE_PARAM_KEYS = ("eff_er", "z0", "c", "a_c", "a_d", "a_total", "beta", "eff_er_im")
+
+
+def parse_line_params(text):
+    """Return the per-line transmission-line parameters as a list of dicts.
+
+    One dict per signal line, keyed by ``_LINE_PARAM_KEYS``. Empty if the
+    section is absent (older builds) or a line was skipped (printed as text).
+    """
+    lines = text.splitlines()
+    rows = _matrix_after(lines, "TRANSMISSION-LINE PARAMETERS")
+    out = []
+    for row in rows:
+        if len(row) != len(_LINE_PARAM_KEYS):
+            continue  # e.g. a "(L<=0, skipped)" row
+        out.append(dict(zip(_LINE_PARAM_KEYS, row)))
+    return out
+
+
+def run_weeks_text(case_yaml, weeks_bin="./weeks", workdir="."):
+    """Copy ``case_yaml`` to ``workdir/test.yaml``, run weeks, return stdout.
 
     Any pre-existing test.yaml is backed up and restored (even on error).
     """
@@ -67,9 +89,14 @@ def run_weeks(case_yaml, weeks_bin="./weeks", workdir="."):
             raise RuntimeError(
                 "weeks exited %d.\nstderr:\n%s" % (proc.returncode, proc.stderr)
             )
-        return parse_weeks_output(proc.stdout)
+        return proc.stdout
     finally:
         if backup:
             shutil.move(backup, test_yaml)
         elif os.path.exists(test_yaml):
             os.remove(test_yaml)
+
+
+def run_weeks(case_yaml, weeks_bin="./weeks", workdir="."):
+    """Run weeks on ``case_yaml`` and return its parsed ``(R, L)`` matrices."""
+    return parse_weeks_output(run_weeks_text(case_yaml, weeks_bin, workdir))
diff --git a/tools/microstrip_z0/__init__.py b/tools/microstrip_z0/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tools/microstrip_z0/__main__.py b/tools/microstrip_z0/__main__.py
new file mode 100644
index 0000000..17ae974
--- /dev/null
+++ b/tools/microstrip_z0/__main__.py
@@ -0,0 +1,27 @@
+"""CLI: python3 -m tools.microstrip_z0 <case.yaml> [options]."""
+
+import argparse
+import sys
+
+from tools.microstrip_z0.check import check_z0
+
+
+def main(argv=None):
+    parser = argparse.ArgumentParser(
+        prog="python3 -m tools.microstrip_z0",
+        description="Sanity-check weeks per-line Z0 against the "
+                    "Hammerstad-Jensen microstrip closed form.",
+    )
+    parser.add_argument("case_yaml", help="weeks YAML input file")
+    parser.add_argument("--tol", type=float, default=10.0,
+                        help="Z0 flag tolerance (%%)")
+    args = parser.parse_args(argv)
+
+    report, _flagged = check_z0(args.case_yaml, tol=args.tol)
+    print(report)
+    # Soft policy (matches fh_crosscheck): flags are informational, exit 0.
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/tools/microstrip_z0/check.py b/tools/microstrip_z0/check.py
new file mode 100644
index 0000000..4e6993f
--- /dev/null
+++ b/tools/microstrip_z0/check.py
@@ -0,0 +1,54 @@
+"""Single-line Z0 sanity check: weeks vs Hammerstad-Jensen closed form."""
+
+from tools.fh_crosscheck.geometry import load_case
+from tools.fh_crosscheck.parse_weeks import parse_line_params, run_weeks_text
+from tools.microstrip_z0.microstrip import geometric_gap, microstrip_z0
+
+
+def _pct(ref, val):
+    return None if ref == 0 else 100.0 * (val - ref) / ref
+
+
+def check_z0(case_yaml, weeks_bin="./weeks", workdir=".", tol=10.0):
+    """Compare weeks' per-line Z0 against the Hammerstad-Jensen closed form.
+
+    Both weeks and the closed form use the same substrate height -- the
+    geometric trace-to-ground gap -- so the comparison is always consistent.
+    Returns ``(report_text, flagged)``; ``flagged`` is True if any line's Z0
+    differs by more than ``tol`` percent.
+    """
+    _freq, conductors = load_case(case_yaml)
+    params = parse_line_params(run_weeks_text(case_yaml, weeks_bin, workdir))
+
+    lines = [
+        "*** Z0 SANITY CHECK: weeks vs Hammerstad-Jensen (%s) ***" % case_yaml,
+        "  line   sub_h(m)    weeks_Z0     H-J_Z0      %diff   note",
+    ]
+    flagged = False
+    for i, p in enumerate(params):
+        sig = conductors[i + 1]
+        w, er = sig["w"], sig["er"]
+        h = geometric_gap(conductors, i + 1)  # substrate height from geometry
+
+        note = ""
+        if er <= 1.0 or h <= 0.0:
+            note = "air / no dielectric (H-J not applicable)"
+            hj_text, pd_text = "        n/a", "    n/a"
+        else:
+            _eff, hj_z0 = microstrip_z0(w, h, er)
+            pd = _pct(hj_z0, p["z0"])
+            hj_text = "%11.4e" % hj_z0
+            pd_text = "  n/a" if pd is None else "%+7.2f%%" % pd
+            if pd is not None and abs(pd) > tol:
+                note = "over %.0f%% tolerance" % tol
+                flagged = True
+
+        lines.append(
+            "  %3d  %10.3e  %11.4e %s %s   %s"
+            % (i + 1, h, p["z0"], hj_text, pd_text, note)
+        )
+
+    if not params:
+        lines.append("  (no TRANSMISSION-LINE PARAMETERS section found in weeks output)")
+        flagged = True
+    return "\n".join(lines), flagged
diff --git a/tools/microstrip_z0/microstrip.py b/tools/microstrip_z0/microstrip.py
new file mode 100644
index 0000000..3394f06
--- /dev/null
+++ b/tools/microstrip_z0/microstrip.py
@@ -0,0 +1,51 @@
+"""Hammerstad-Jensen microstrip closed form, and a single-line Z0 sanity
+check against weeks' TRANSMISSION-LINE PARAMETERS output.
+
+This is an independent cross-check of weeks' per-line characteristic impedance:
+weeks derives Z0 = c * L / sqrt(eff_er) from its PEEC inductance L and the
+effective permittivity, whereas the Hammerstad-Jensen formulas below give
+eff_er and Z0 purely from the microstrip geometry (w, h, er). Agreement
+validates the PEEC inductance against a published closed form, complementing
+the FastHenry R/L crosscheck.
+
+Both sides use the same substrate height -- the geometric trace-to-ground gap
+(``geometric_gap`` below) -- which is also what weeks uses for eff_er, so the
+comparison is consistent by construction.
+"""
+
+import math
+
+ETA0 = 376.730313668  # free-space wave impedance (Ohm)
+
+
+def eff_permittivity(w, h, er):
+    """Hammerstad-Jensen effective permittivity. Mirrors calc_eff_dielectric()
+    in src/calcl.c exactly (same branches and constants)."""
+    if h <= 0.0 or er <= 1.0:
+        return 1.0
+    u = w / h
+    a = (1.0
+         + (1.0 / 49.0) * math.log((u ** 4 + (u / 52.0) ** 2)
+                                   / (u ** 4 + 0.432))
+         + (1.0 / 18.7) * math.log(1.0 + (u / 18.1) ** 3))
+    b = 0.564 * ((er - 0.9) / (er + 3.0)) ** 0.053
+    return (er + 1.0) / 2.0 + ((er - 1.0) / 2.0) * (1.0 + 10.0 / u) ** (-a * b)
+
+
+def microstrip_z0(w, h, er):
+    """Return ``(eff_er, Z0)`` for a microstrip of width ``w``, substrate
+    height ``h`` and relative permittivity ``er`` (Hammerstad-Jensen, zero
+    thickness). ``Z0`` is in ohms."""
+    eff_er = eff_permittivity(w, h, er)
+    u = w / h
+    fu = 6.0 + (2.0 * math.pi - 6.0) * math.exp(-((30.666 / u) ** 0.7528))
+    z0_air = (ETA0 / (2.0 * math.pi)) * math.log(fu / u + math.sqrt(1.0 + (2.0 / u) ** 2))
+    return eff_er, z0_air / math.sqrt(eff_er)
+
+
+def geometric_gap(conductors, line_index):
+    """Vertical gap (m) between the bottom of signal conductor ``line_index``
+    (1-based among signal traces) and the top of the ground plane (index 0)."""
+    ground = conductors[0]
+    sig = conductors[line_index]
+    return sig["y"] - (ground["y"] + ground["h"])
diff --git a/tools/microstrip_z0/tests/__init__.py b/tools/microstrip_z0/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tools/microstrip_z0/tests/test_microstrip.py b/tools/microstrip_z0/tests/test_microstrip.py
new file mode 100644
index 0000000..5bc9b7b
--- /dev/null
+++ b/tools/microstrip_z0/tests/test_microstrip.py
@@ -0,0 +1,64 @@
+import math
+
+from tools.fh_crosscheck.parse_weeks import parse_line_params
+from tools.microstrip_z0.microstrip import (
+    eff_permittivity,
+    geometric_gap,
+    microstrip_z0,
+)
+
+
+def test_eff_permittivity_air_and_bounds():
+    # Air / no substrate returns 1.0.
+    assert eff_permittivity(150e-6, 0.0, 4.4) == 1.0
+    assert eff_permittivity(150e-6, 200e-6, 1.0) == 1.0
+    # With dielectric, eff_er lies strictly between 1 and er.
+    ee = eff_permittivity(150e-6, 200e-6, 4.4)
+    assert 1.0 < ee < 4.4
+
+
+def test_eff_permittivity_matches_weeks_c_formula():
+    # Value cross-checked against src/calcl.c calc_eff_dielectric() output
+    # for w=150um, h=200um, er=4.4 (weeks prints 3.1118).
+    ee = eff_permittivity(150e-6, 200e-6, 4.4)
+    assert abs(ee - 3.1118) < 1e-3
+
+
+def test_microstrip_z0_known_geometry():
+    # Consistent microstrip used by examples/test_microstrip.yaml; weeks
+    # reports Z0 ~= 81.06 Ohm, so the closed form must land within ~1%.
+    eff_er, z0 = microstrip_z0(150e-6, 200e-6, 4.4)
+    assert abs(eff_er - 3.1118) < 1e-3
+    assert abs(z0 - 81.06) / 81.06 < 0.01
+
+
+def test_microstrip_z0_increases_for_narrower_line():
+    # Narrower trace (smaller w/h) -> higher characteristic impedance.
+    _e1, wide = microstrip_z0(400e-6, 200e-6, 4.4)
+    _e2, narrow = microstrip_z0(100e-6, 200e-6, 4.4)
+    assert narrow > wide
+
+
+def test_geometric_gap():
+    conductors = [
+        {"name": "line0", "y": 0.0, "h": 2.0e-6},
+        {"name": "line1", "y": 202e-6, "h": 18e-6},
+    ]
+    assert math.isclose(geometric_gap(conductors, 1), 200e-6, rel_tol=1e-9)
+
+
+def test_parse_line_params_extracts_z0():
+    text = """\
+*** TRANSMISSION-LINE PARAMETERS (per line, quasi-TEM) at 30.00 MHz ***
+
+Line     eff_er       Z0(Ohm)      C(F/m)       a_c(dB/m)    a_d(dB/m)    a(dB/m)      beta(rad/m)  eff_er''
+
+  1    +3.1118e+00  +8.1058e+01  +7.2591e-11  +7.9381e-01  +2.1939e-01  +1.0132e+00  +1.1091e+00  +1.4173e-01
+
+  gamma = alpha + j*beta
+"""
+    params = parse_line_params(text)
+    assert len(params) == 1
+    assert abs(params[0]["eff_er"] - 3.1118) < 1e-9
+    assert abs(params[0]["z0"] - 81.058) < 1e-3
+    assert abs(params[0]["eff_er_im"] - 0.14173) < 1e-4