ADS-B Patch Antenna on RF Controlled Impedance PCB

In exploring options for high-quality antennas, recent searches have highlighted the importance of using low loss and controlled impedance board stock for creating effective ADS-B patch antennas. These antennas are notable for their ability to receive signals from great distances, making them ideal for ADS-B aircraft tracking systems.

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With this particular design, my ADS-B receiver is conveniently placed on my windowsill, successfully picking up aircraft signals from over 200 kilometers away.

Design Considerations

Corner Cutting

The antenna features a standard rectangular patch configuration, utilizing circular polarization. This design choice provides increased flexibility for mounting options in various environments.

Optimization with Slots

The inclusion of side slots in my antenna design expands its bandwidth while also lowering the operational frequency. Thus, these slots can be effectively used to fine-tune the antenna's characteristics.

Selection of PCB Material

Different manufacturers such as Rogers, Isola, and Panasonic produce a range of RF PCB types, each with distinct RF parameters. Therefore, designing an antenna for a specific type like Rogers C will require a new design if you decide to use something like Isola I-Tera MT40.

To evaluate the most cost-effective board stock, I submitted a simple design for manufacturing quotes from three different PCB companies (Eurocircuits, Ourpcb, Pcbonline). Here’s what I found:

• Not all manufacturers carry the advertised stock.
• Some may not have the necessary setup to utilize it.
• Prices can vary significantly.

The highest cost board was Rogers C, primarily due to set-up fees from manufacturers. Below is a comparative cost list, with the ROC material set as 1:

• ROC = 1
• ROB = 0.44
• I-Tera MT40 = 0.32
• IS400 = 0.36
• FR4 generic = 0.18

As a result, RF boards can be two to four times more expensive than standard boards, although this cost difference diminishes significantly with larger orders.

Prototype Specifications

The prototype patch antenna was constructed using Rogers B, which boasts the following RF parameters:

• Permittivity Dk = 3.66
• Loss Df = 0.
• Dielectric width Dw = 0.508 mm
• Cu 1 Oz = 36 um
  

In contrast, the standard FR4 board exhibits a loss factor of 0.016, as compared to the ROB board’s 0. This substantial difference is critical, as the goal is to ensure the antenna is adept at radiation rather than dissipating energy as heat.

Conformal Mounting on Aircraft

This PCB antenna is designed for optimal use in aerospace applications. Its lightweight design (only 23 grams) allows for easy conformance with the aircraft's skin, and its circular polarization lets it be mounted virtually anywhere on the fuselage for versatile signal reception.

The preferred mounting strategy involves positioning the antenna in the interior of an RF window made of fiberglass reinforced epoxy. If the antenna contacts the glass, it will experience a slight detuning of approximately 500 kHz, which is generally manageable.

Tuning and Calibration

During initial testing, I discovered the prototype's measurements were significantly off. After some manual trimming with traditional tools, I achieved a fine-tuned structure.

The current VSWR stands at an ideal 1.0 at the target frequency, featuring a 3 dB bandwidth of around 30 MHz. The patch antenna's narrow bandwidth implies there may not be a need for additional bandpass filtering, thereby simplifying the design of the ADS-B receiving system.

The antenna's impedance is finely tuned at 49.7 Ohm, reflecting its high performance.

Further Development and Prototyping

Testing and measurement will continue to refine the tuned antenna before proceeding with manufacturing additional prototypes. For those wishing to outsource the fabrication, Eurocircuits is a suitable option as they offer direct quoting from uploaded designs. With each piece generally costing around 150 Euros, the project represents a notable commitment.

Inquiries and Production Orders

If you are interested in acquiring this antenna design, feel free to reach out. Once enough interest is indicated, I will arrange for a batch production with Eurocircuits.

La voila!

Herman

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For further information on the Quadrifilar Helix Antenna, please don’t hesitate to contact us.