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Design and Simulation of a Compact Planar Micro-strip Crossover for Beam forming Networks using HFWorks for SOLIDWORKS

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Introduction

Crossovers are very interesting passive devices in monolithic Integrated Circuits (IC) and antenna arrays. These devices maintain signal purity when transmission lines intersect. There are several types of crossovers. Printed planar crossovers are the most used thanks to their compact and simple structure.

In this article, a compact planar crossover is designed using the CAD SOLIDWORKS and simulated using the full wave 3D simulator HFWorks. An S Parameter analysis is conducted to investigate the electromagnetic behavior of this structure. Figure 1 shows the fabricated prototype of the proposed crossover.

Figure 1 – Fabricated Prototype of the Square Patch Crossover

The Model Geometry

This compact planar crossover example is formed of a square micro-strip patch excited by four perpendicular micro-strip lines. The square patch comprises two perpendicular rectangular slots and four arc-shaped slots. The resonance frequency of this structure is 2.4 GHz.
The overall size of the crossover is about 13 mm x 13 mm x 0.64 mm. The 3D model is represented in Figure 2.

Figure 2 – The 3D SOLIDWORKS Model of the Compact Planar Crossover (Front View)

The square patch crossover is constructed on a dielectric substrate with a relative permittivity of 10.2. The layer beneath the substrate has a very small thickness and is therefore considered as a PEC surface. An air box surrounds the crossover.
The structure parameters are summarized in Table 1.

The Geometry of the Crossover

Figure 3 – The Geometry of the Crossover

Table 1 - Structure Parameters

Parameter	Value (mm)
W	13
W1	0.2
W2	0.2
Wf	0.67
L	8.6
L1	8.4

Simulation Setup

The Scattering Parameter simulator was used. The frequency plan is defined with a small step and is uniformly distributed between 2 and 3 GHz.

This design is made of 4 wave ports. The ports are applied to small areas next to the micro-strip line's beginning and end.
The ground metal is considered as a Perfect Electric Conductor.

Meshing

The mesh needs to be fine enough on the ports and the conductor edges. The slots included inside the patch should be finely meshed as well. The figure below illustrates the meshed structure.

Figure 4 – The Meshed Model

Simulation Results

To validate the precision of HFWorks, we compare the results to measurements. The following figure depicts the simulated S parameters results S11, S21 and S31 using HFWorks and the measured results of the square patch crossover.

Figure 5 – Simulated and Measured S parameters of the Square Patch Crossover

The return loss is greater than 10 dB for 2.3 - 2.54 GHz while the insertion loss is less than 1 dB. The isolation is more than 13 dB as demonstrated in Figure5.

The simulated and measured results shows a bandwidth of 12% centered at 2.4 GHz.

HFWorks automatically computed the electromagnetic field. The distribution of the electric field at the resonance frequency 2.4 GHz is indicated in Figure6 with an incident power of 1W.

Figure 6 – Distribution of the Electric Field at 2.4 GHz

Conclusion

A planar micro-strip crossover is designed and simulated using the duo of SOLDWORKS and HFWorks. The simulated and measured data [1] are in good agreement. The resonance frequency is found at 2.4 GHz.

References

[1] B.Henin, A.Abbosh “Compact Planar Microstrip Crossover Based for Beam-forming Networks” Progress In Electromagnetics Research C, Vol.33, 123-132, 2012.

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