This guide extends the ideal-component LPF design introduced in the previous article by replacing ideal inductors and capacitors with real Murata component S-parameter data imported into uSimmics (formerly QucsStudio). The goal is to quantify the performance gap between ideal and real components and demonstrate how switching to a low-loss component grade closes that gap.
- What You’ll Learn
- Background: The Gap Between Ideal and Real Components
- Why Use Real Component Models?
- Components and S-Parameter Acquisition
- Procedure: Placing S-Parameter Components in the Schematic
- Simulation Results — Standard Grade
- Optimization: Switching to Low-Loss Component Grades
- Re-Simulation Results — Low-Loss Grade
- Analysis and Design Implications
- Summary
- Related Articles
What You’ll Learn
- Why real components differ from ideal ones (parasitic inductance and parasitic capacitance)
- How to download and import Murata S-parameter data (.s2p) into uSimmics (formerly QucsStudio)
- How the standard-grade components (GRM03, LQP03TG) affect LPF insertion loss
- How switching to low-loss grades (GJM03, LQP03HQ) improves performance
- How to quantitatively compare component grades in simulation
Background: The Gap Between Ideal and Real Components
The previous article (LPF Design Guide Using uSimmics (formerly QucsStudio) [2026]) designed a 915 MHz LPF using ideal lumped components. This article replaces those ideal components with real Murata parts to produce a simulation that more closely reflects actual hardware performance.
Why Use Real Component Models?
The capacitors and inductors available as lumped components in uSimmics (formerly QucsStudio) are ideal — they have no loss and no parasitic behavior. Real components include the following parasitic elements that become significant at GHz frequencies:
- Parasitic inductance (ESL): Inductance in the electrodes and leads of chip capacitors
- Parasitic capacitance: Inter-winding capacitance in chip inductors
- DC resistance (DCR): Winding resistance of inductors, contributing to insertion loss
These parasitics increase passband insertion loss and alter attenuation characteristics, especially above a few hundred MHz.
Components and S-Parameter Acquisition
This simulation uses Murata chip capacitors (GRM03 series) and chip inductors (LQP03TG series) — standard parts widely used in wireless device design.
S-parameter download: Visit Murata’s SimSurfing portal to download S-parameter data (Touchstone .s2p format) for each part.
Standard-Grade Component List
| Part Number | Type | Value |
|---|---|---|
| GRM0332C15R6BA01 | Chip capacitor | 5.6 pF |
| GRM0332C14R1BA01 | Chip capacitor | 4.1 pF |
| GRM0334C11R5BA01 | Chip capacitor | 1.5 pF |
| LQP03TG15NJ02 | Chip inductor | 15 nH |
| LQP03TG10NJ02 | Chip inductor | 10 nH |
| LQP03TG3N7B02 | Chip inductor | 3.7 nH |
Procedure: Placing S-Parameter Components in the Schematic
Place the real-component LPF in parallel with the ideal-component LPF on the same schematic, then run a single S-parameter simulation to compare both.
- Open the LPF schematic from the previous article in uSimmics (formerly QucsStudio).
- From the Components panel under system components, select s-parameter file.
- Place an s-parameter file component on the schematic and double-click to open its properties.
- Set Ports to
2. - Under File, select the downloaded .s2p file for the corresponding Murata part.
- Repeat for each component (C1, C2, C3, L1, L2, L3).
- Wire up the real-component LPF, connect it in parallel with the ideal-component circuit, and configure the S-parameter simulation to cover both.
Simulation Results — Standard Grade
Comparing S21 of the ideal LPF (red) and the standard-grade real-component LPF (blue):
At first glance, the real-component LPF appears to show higher attenuation at high frequencies, which might seem beneficial. However, a closer look at the passband (824–915 MHz) reveals that the real-component LPF has noticeably higher insertion loss.
Root Cause Analysis
With GRM03 capacitors and LQP03TG inductors, the passband insertion loss increases by approximately 2 dB compared to the ideal simulation. The main contributors are:
- Equivalent series inductance (ESL) in capacitors increasing high-frequency loss
- DC resistance (DCR) and inter-winding capacitance in inductors
- Equivalent series resistance (ESR) in capacitors
A 2 dB passband degradation is meaningful — in a real application it can push performance outside specification.
Optimization: Switching to Low-Loss Component Grades
To reduce passband insertion loss, switch to lower-loss component grades:
- Capacitors: GRM03 → GJM03 (reduced DC resistance and ESR)
- Inductors: LQP03TG → LQP03HQ (higher Q factor, lower loss)
Low-Loss Grade Component List
| Part Number | Type | Value |
|---|---|---|
| GJM0335C1E5R6BB01 | Low-loss chip capacitor | 5.6 pF |
| GJM0335C1E4R1BB01 | Low-loss chip capacitor | 4.1 pF |
| GJM0335C1E1R5BB01 | Low-loss chip capacitor | 1.5 pF |
| LQP03HQ15NH02 | High-Q chip inductor | 15 nH |
| LQP03HQ10NH02 | High-Q chip inductor | 10 nH |
| LQP03HQ3N7B02 | High-Q chip inductor | 3.7 nH |
Re-Simulation Results — Low-Loss Grade
After switching to GJM03 capacitors and LQP03HQ inductors, the simulation shows performance approaching the ideal component results.
| Metric | Standard Grade | Low-Loss Grade |
|---|---|---|
| Insertion loss vs. ideal | ~2 dB gap | ~1 dB gap |
| Passband compliance | Risk of failing spec | Within spec |
The low-loss grade reduces the performance gap to approximately 1 dB.
Analysis and Design Implications
This result demonstrates the importance of selecting the appropriate component grade for the target performance specification. Simulating with ideal components alone masks the real-world performance gap. Real-component S-parameter simulation reveals it.
Benefits of incorporating real-component simulation into the design flow:
– Accurate performance prediction before fabrication
– Quantitative comparison of component grades
– Cost-vs-performance trade-off evaluation at the design stage
Summary
Real-component S-parameter simulation in uSimmics (formerly QucsStudio) is a critical tool for RF filter design that demands tight performance tolerances. Iterating component grade selection in simulation — standard grade first, low-loss grade if needed — is a systematic way to meet specification while controlling BOM cost. Combining ideal-component simulation with real-component simulation is the foundation of a reliable filter design methodology.
Comment