# Ku-band Circulators Manufactured by LTCC Technology

Camilla Kärnfelt, Norbert Parker, Vincent Laur, Richard Lebourgeois

► To cite this version:

Camilla Kärnfelt, Norbert Parker, Vincent Laur, Richard Lebourgeois. Ku-band Circulators Manufactured by LTCC Technology. Swedish Microwave Days 2023, KTH, Royal Institute of Technology, Stockholm, Sweden, May 2023, Stockholm, Sweden. [hal-04112222](https://hal-04112222)

HAL Id: hal-04112222

https://imt-atlantique.hal.science/hal-04112222

Submitted on 31 May 2023

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# Ku-band Circulators Manufactured by LTCC Technology

Camilla Kärnfelt(1), Norbert Parker(2), Vincent Laur(2), and Richard Lebourgeois(3)

(1) Lab-STICC UMR CNRS 6285, IMT Atlantique F-29238 Brest, France

(2) Lab-STICC UMR CNRS 6285, Université de Bretagne Occidentale, F-29200 Brest, France

(3) THALES Research & Technology, F-91767 Palaiseau Cedex, France

## Summary

This paper presents Ku-band miniaturized circulators based on special ferrite materials developed to enable manufacturing by Low Temperature Cofired Ceramics (LTCC) technology. Since three different materials are co-fired together, special care is taken for these materials to shrink equally during firing. Simulation results give 0.5 dB insertion loss and 14% -20dB bandwidth for the Spinel3800 based circulator including motherboard and SMD transitions.

## 1. Introduction

Ferrite based devices such as circulators are commonly used in RADAR applications and in Active Electronically Scanned Arrays (AESA). Their bulkiness limits the required miniaturization, especially for AESAs that contain a huge number of transmit/receive modules (TRX). One way to overcome this limitation is to develop ferrite and dielectric cofireable materials to manufacture surface mountable miniaturized circulators using LTCC technology.

## 2. Material development

To enable manufacturing according to LTCC production standards, two new ferrimagnetic powders; garnets derived from Yttrium Iron Garnet (YIG) and spinels derived from nickel-zinc ferrites, were developed. These two powders were formatted by tape-casting into sheets and matched to a tape casted VLF220Q4 dielectric material. Special care was taken for the materials to be compatible with silver metallization and allow sintering at 920°C, a strong project requirement. The materials' electrical and magnetic properties are given in Table 1.

<table><caption>Table 1. Circulator materials</caption><thead><tr><td>Material</td><td>ε<sub>r</sub></td><td>tanδ</td><td>4πMs (G)</td><td>ΔH (Oe)</td></tr></thead><tbody><tr><td>Garnet1900</td><td>21</td><td>3.10-3</td><td>1900</td><td>100</td></tr><tr><td>Spinel3800</td><td>13</td><td>1.10-3</td><td>3800</td><td>100</td></tr><tr><td>VLF220Q4</td><td>21</td><td>3.10-3</td><td>-</td><td>-</td></tr><tr><td>Teflon™</td><td>2.1</td><td>1.10-3</td><td>-</td><td>-</td></tr></tbody></table>

## 3. Circulator design

The circulator design was made by the help of Ansys HFSS™ electromagnetic simulator and based on the theory in [1]. From specification requirements, the maximum allowed circulator's dimensions are fixed at 7 mm × 7 mm × 3 mm and to simplify its integration it should be a surface mountable device (SMD). Figure 1 shows the 3D model of the circulator mounted on a motherboard, together with the simulation results for the complete structure using the two ferrite materials. Insertion losses thus considers the circulator and motherboard. The motherboard is a 13 mm × 13 mm × 0.203 mm Roger 4003C sheet.

<figure><img src="image_1.png" /><figcaption>Figure 1. a) Circulator 3D model, b) Spinel3800 simulation results and c) Garnet1900 simulation results</figcaption></figure>
The simulated S-parameters of these two circulators are compared in the Table 2. The Spinel3800 version of the circulator shows better results than the Garnet1900 ferrite version.

<table><caption>**Table 2.** Simulated performances of both circulators</caption><thead><tr><th></th><th>Spinel3800 Circulator</th><th>Garnet1900 Circulator</th></tr></thead><tbody><tr><td>Minimal IL</td><td>0.5 dB @ 16.4 GHz</td><td>0.57 dB @ 16.3 GHz</td></tr><tr><td>-20 dB Bandwidth</td><td>2.33 GHz (14%)</td><td>1.77 GHz (10.6%)</td></tr><tr><td>-20 dB Maximum IL</td><td>0.61 dB</td><td>0.71 dB</td></tr></tbody></table>

## 4. Manufacturing method

The manufacturing of these circulators is done as follows: a) laser cut out of inserts, via holes and alignment holes, b) via hole screen printing, c) stacking, d) lamination, e) ground plane screen printing, f) Y-junction screen printing, g) firing and h) dicing. The firing step implies a 15 % shrinkage. At this step, it is of utmost importance that the three materials dielectric tape, ferrite tape and silver paste all have the same shrinkage profile, or else deformation will occur and ferrite inserts may fall out.

<figure><img src="image_2.png" /><figcaption>**Figure 2.** Circulators’ manufacturing steps: a) laser cut out and via screen printing, b) stacking, c) lamination, d) ground plane screen printing, e) Y-junction screen printing, f) ground plane view after firing, g) top surface view after firing, h) final circuit after dicing.</figcaption></figure>

## 4. Results

Manufacturing of these first circulator samples proves the feasibility of the chosen LTCC approach. Some distortion can be seen after firing, so some fine tuning of tape features and manufacturing process will be necessary. Measurement are on its way.

## 6. Acknowledgements

The authors like to thank Rose-Marie Sauvage and the defense innovation agency of the French Ministry of Defense for founding of this project. The manufacturing equipment was partly financed by the European Union through the European Regional Development Fund (ERDF), by the French Ministry of Higher Education and Research, by Brittany and Rennes Métropole, through the CPER Project SOPHIE / STIC & Ondes. The laser equipment was funded by Brest Metropole “Fonds de Concours à la Recherche”, by the Finistère department council’s program “Aide aux Programmes de Recherche Emergants” and by Carnot Research funds.

## References

[1] D. Polder, “Viii. On the theory of ferromagnetic resonance”, *The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science*, vol. 40, no. 7, pp. 99-115, 1949.