---
title: Designing a High-Pass RF Filter for 5 GHz Applications: A Step-by-Step Guide
siteUrl: https://logzly.com/rffilterlab
author: rffilterlab (RF Filter Lab)
date: 2026-06-18T06:00:34.668781
tags: [highpass, rfdesign, electronics]
url: https://logzly.com/rffilterlab/designing-a-high-pass-rf-filter-for-5-ghz-applications-a-step-by-step-guide
---


Ever tried to listen to a radio station and heard a hiss that just wouldn’t go away? That hiss is often low‑frequency noise that a high‑pass filter can block. In today’s 5 GHz world—think Wi‑Fi 6E, automotive radar, and satellite links—getting that filter right can be the difference between a clean signal and a garbled mess. Let’s walk through a practical design, a [practical step‑by‑step guide](/rffilterlab/designing-a-highpass-rf-filter-for-5g-small-cells-a-practical-stepbystep-guide), that you can build in the lab or simulate on a laptop.

## Why a High-Pass Filter at 5 GHz?

A high‑pass filter (HPF) lets frequencies above a chosen cut‑off pass while attenuating everything below. At 5 GHz we usually want to reject:

* **DC and low‑frequency drift** from mixers or power supplies.  
* **Spurious signals** from nearby bands (2.4 GHz Wi‑Fi, Bluetooth, etc.).  

The result is a cleaner front‑end for amplifiers, mixers, or antennas. In my first graduate lab, I built a crude HPF with a single inductor and a stray capacitor. The filter worked, but the insertion loss was so high I could barely hear the signal. That taught me the value of a systematic approach—something I share on RF Filter Lab every week.

## Step 1: Define the Specifications

Before you pick parts, write down what you need. Typical specs for a 5 GHz HPF are:

| Parameter | Typical Value |
|----------|---------------|
| Cut‑off frequency (f_c) | 4.5 GHz (−3 dB point) |
| Pass‑band ripple | ≤ 0.5 dB |
| Stop‑band attenuation | ≥ 30 dB at 3 GHz |
| Insertion loss | ≤ 1 dB in the pass band |
| Impedance | 50 Ω (standard RF) |

These numbers give us a target shape for the filter response. If you need tighter ripple or deeper stop‑band, you’ll end up with more sections and a slightly larger board.

## Step 2: Choose the Filter Topology

For a simple HPF at microwave frequencies, two topologies dominate:

1. **L‑section (single series inductor, shunt capacitor).** Easy to build, but limited stop‑band performance.
2. **Chebyshev or Butterworth multi‑section (cascade of LC sections).** Better control of ripple and attenuation.

Because we want ≤ 0.5 dB ripple and at least 30 dB stop‑band, a 3‑section Chebyshev HPF is a good compromise. It gives us the sharp roll‑off we need without making the layout too crowded.

## Step 3: Calculate the Component Values

The classic design equations for a Chebyshev HPF start with a normalized prototype. I use the tables in Pozar’s *Microwave Engineering* and then scale them to our 5 GHz target.

1. **Normalize the prototype** to a 1 rad/s cut‑off and 1 Ω source/load.
2. **Scale frequency**: f_c = 4.5 GHz → scaling factor = f_c / 1 rad/s.
3. **Scale impedance**: 50 Ω source/load → multiply all reactances by 50.

The resulting values (rounded to standard parts) are:

| Section | Series Inductor (L) | Shunt Capacitor (C) |
|---------|--------------------|---------------------|
| 1 | 1.2 nH | 0.45 pF |
| 2 | 0.9 nH | 0.60 pF |
| 3 | 1.5 nH | 0.35 pF |

These are small values, so you’ll need high‑Q surface‑mount inductors (e.g., 0402 or 0201) and NP0 or C0G capacitors for low loss. In my lab I prefer the 0402 size because it gives a little more mechanical stability while still fitting on a compact board.

## Step 4: Simulate the Design

Before you solder anything, run a quick simulation. I use Keysight ADS or the free RF Toolbox in MATLAB. Set up a 50 Ω source and load, insert the three LC sections, and sweep from 1 GHz to 8 GHz.

Key things to check:

* **−3 dB point** should sit near 4.5 GHz.  
* **Ripple** in the pass band stays under 0.5 dB.  
* **Attenuation** at 3 GHz is at least 30 dB.  

For deeper insight into [testing and tuning high‑pass filters](/rffilterlab/testing-and-tuning-high-pass-filters-in-real-world-rf-systems-proven-techniques-for-better-signal-integrity), refer to our dedicated guide. If the ripple is too high, you can tweak the capacitor values by a few femtofarads. If the stop‑band isn’t deep enough, add a fourth section—just remember each extra part adds loss and layout complexity.

## Step 5: Layout Considerations

At 5 GHz even a short trace can act like an inductor. Keep these tips in mind:

* **Use microstrip on a low‑loss substrate** (Rogers RO4350B works well).  
* **Maintain 50 Ω line width** throughout the filter. A calculator can tell you the exact width for your board thickness.  
* **Place ground vias** close to each component to create a solid return path.  
* **Avoid right‑angle bends**; use mitered or curved traces to reduce reflections.  

When I first tried a layout with 90‑degree bends, the return loss jumped by 2 dB. A quick redesign with gentle curves brought the performance back on target.

## Step 6: Build and Test

Order the parts, assemble the board, and then measure with a vector network analyzer (VNA). Connect the VNA ports to the filter’s input and output, and record S‑parameters.

* **S21** shows insertion loss and pass‑band shape.  
* **S11** tells you how well the filter matches 50 Ω.  

If you see a dip in S21 around the cut‑off, double‑check solder joints and component orientation. Small parasitic inductances from the pads can shift the cut‑off by a few hundred megahertz.

## Step 7: Tune if Needed

Sometimes the real board behaves a bit differently from the simulation. A practical trick is to add a tiny trimmer capacitor (e.g., 0.1 pF) in parallel with the first shunt capacitor. By adjusting it you can fine‑tune the cut‑off without redesigning the whole board. I keep a small stash of these trimmers in my lab drawer—they’ve saved me more than one deadline.

## Step 8: Document the Design

Finally, write down what you did. Include:

* Schematic (PDF or PNG).  
* Layout files (Gerber).  
* Measured S‑parameters (CSV).  

Sharing this on RF Filter Lab helps others avoid the same pitfalls, and it builds a knowledge base we can all rely on.

Designing a high‑pass filter for 5 GHz may sound intimidating, but breaking it into clear steps makes it manageable. Define the specs, pick a suitable topology, calculate component values, simulate, lay out carefully, test, and fine‑tune. Follow this recipe and you’ll have a clean, low‑loss filter ready for any modern RF system.