Rectangular Waveguide T-Junction with SeptumMuhammad Fahd Waseem

Faculty of Electronics EngineeringGhulam Ishaq Khan Institute of Engineering Sciences and Technology

Topi, Swabi, PakistanEmail: muhammadfahd@ieee.org

Abstract—This is originally a course assignment done for theEE472 course (Reg. No. 2007157) at the GIK Institute, Pakistan,and was completed on the 4th of December, 2010. This is NOT aresearch paper, though every attempt has been made to keep theinformation in this document as accurate as possible. This paperis released under the Creative Commons Share-Alike license only.

This paper shows the results of a T-Junction applied to aRectangular Waveguide.

Index Terms—Waveguides, T-Junctions, Ansoft HFSS, Simu-lation, Electromagnetic Fields

I. INTRODUCTION

In this paper, a rectangular waveguide with a T Junction hasbeen designed and simulated in Ansoft HFSS. The design drewheavily from the official Ansoft HFSS getting started guide,which also includes a wave splitting septum in the design[1].

II. APPLICATION OF T-JUNCTIONS

Waveguide junctions are used when power in a waveguideneeds to be split or some extracted. T-junctions are the simplestof junctions, and also amongst the easiest implement. Theyare thus used in applications where cost is critical, but smallamounts off power bouncing off the ‘T-wall’ are acceptable,such as the distribution waveguides for radio transmitters.

III. MODES, S PLOTS, DISTRIBUTION OF FIELDS ANDJUSTIFICATION

A. ModesThe waveguide a and b dimensions are in inches, with

a=0.02286m and b=0.01016m. The two T-top-bar arms areformed from the rotated duplication of the main T-vertical-bar. The septum is in the middle. The waveguide is operatedat 10GHz. Using the equation:

fc =c

2

√(ma

)2+(nb

)2shows that the only mode possible is TE10 because any higherorder mode has a cutoff frequency greater than 10GHz.

B. S PlotsTwo S plots are shown, see Fig. 1:• With the septum right in the middle• With the septum slightly displaced to one side

C. Field PatternsOnly the E-field patterns are shown for simplicity in Fig.

2 & 3. The E-field pattern must be in TE10 mode. The fieldvectors are also faintly shown.

D. Justification

The E-field is zero at the boundaries of the waveguide, asexpected. The pattern of the field also matches TE10 patterns.The septum is splitting the wave power to the two ports, andas expected, the strength of the E-field vectors is decreasedafter the junction. This is also verified by the S Plot in Fig.1. For the asymmetric splitting septum, the E-field vectors arestronger in the direction of the higher power flow, as alsoexpected.

IV. CONCLUSION

Results were as expected. The field patterns matched theones expected.

ACKNOWLEDGMENT

The author would like to thank his teachers, instructorsand TAs without whom this work would neither have beenrequired, nor completed.

REFERENCES

[1] (2010, Nov) Getting started with hfss: A waveguide t-junction. [Online].Available: www.sunist.org/shared%20documents/References/TeeGSG.pdf

8.00 9.00 10.00 11.00 12.000.00

0.20

0.40

0.60

0.80

1.00

Freq [GHz]

Y 1

Ansoft CorporationXY Plot 1

WaveGuideT

04 Dec 2010 23:25:18 Y1mag(S(WavePort1:1,WavePort1:1))offset=0

Y1mag(S(WavePort1:1,WavePort1:1))offset=0.00508

Y1mag(S(WavePort1:1,WavePort2:1))offset=0

Y1mag(S(WavePort1:1,WavePort2:1))offset=0.00508

Y1mag(S(WavePort1:1,WavePort3:1))offset=0

Y1mag(S(WavePort1:1,WavePort3:1))offset=0.00508

Figure 1. S Parameter plot for the Port1 as Input and Ports 2 and 3 as Output

Figure 2. Field Distribution and E-field vectors for the septum at center

Figure 3. Field Distribution and E-field vectors for the septum offset