Electromagnetic Simulation Software

Simulating a Beam Scanning Substrate Integrated
Waveguide Leaky Wave Antenna in XFdtd
Introduction
In this example, XFdtd is used to simulate the performance of a substrate integrated
waveguide (SIW) leaky wave antenna with transverse slots. The design was taken fromthe paper by Liu, Jackson, and Long [1]. The antenna operates like a transverse slottedrectangular waveguide, but is designed in SIW for reduced cost, size, and for easierintegration with planar circuits. Results for S-parameter performance, antenna gain,and efficiency are computed.
Device Design and Simulation
A top view of the entire antenna is shown in Figure 1 where the green material
represents copper and the red is a dielectric (relative permittivity = 2.25 and loss
tangent of 0.001). The device is approximately 310 mm in length, 40 mm in width, and
1 mm in height. The copper microstrip layer at the top of the device has transverse
slots spaced at regular intervals and tapered at the ends. At each end of the device a
nodal waveguide port is connected to a tapered microstrip line that connects to the SIWportion. In the top layer are a number of transverse slots, more easily seen in Figure 2.
The edges of the top microstrip layer are terminated with vias. The layers are shown inangled views in Figures 3 through 5 where all parts are shown in Figure 3, the substrate
is visible in Figure 4, and the vias in Figure 5.

Figure 1: A top view of the 3D CAD model of theantenna shows input and output ports at the ends
attached to tapered microstrip lines and a centermicrostrip section with numerous slots.

Figure 2: A detailed view of one end of the antennashows the tapered slots and the curved via pathlocated under the microstrip line.

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Simulating a Beam Scanning Substrate Integrated Waveguide Leaky Wave Antenna in XFdtd

Figure 3: An angled view of the antenna from one port
shows the nodal waveguide port attached to the tapered line, the thickness of the substrate layer, and aportion of the slotted top layer.

Figure 4: With the top microstrip layer removed, thesubstrate and some of the vias are visible in the antenna
structure.

Figure 5: In this figure the substrate layer has been removed and the ground plane and vias are visible.

Figure 6: The S-parameters show good return loss fromabout 10.4 GHz up to 12.5 GHz while the S21 has between -6 to -2 dB of loss in the same region.

The device is simulated by applying a frequency-limited signal to the waveguide port
at one end. The S-parameter results are shown in Figure 6 and it can be seen thatthe device has good operating performance from 10.4-12.5 GHz and a few smallerfrequency bands below 10.4 GHz. Below 10 GHz the response is cutoff.
The antenna produces several beams which range from near broadside to near end firedepending on the frequency. These beams are generally narrow and fan-shaped. At
10.2 GHz, the beam is quite narrow and peaks at about 8.6 dBi at theta=70 degrees in
the YZ plane as shown in Figure 7 in a polar plot. The 10.2 GHz pattern is shown asa three-dimensional plot from the same angle as the polar plot of Figure 7 in Figure 8.
A different perspective of the 10.2 GHz three-dimensional pattern is shown in Figure
9. At 10.8 GHz, the peak gain increases to 11.1 dBi and the beam shifts to a peak attheta=49 degrees in the YZ plane as shown in Figures 10, 11, and 12.

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Simulating a Beam Scanning Substrate Integrated Waveguide Leaky Wave Antenna in XFdtdFigure 7: A polar plot of the gain pattern at 10.2 GHz in
the YZ plane (along the length of the antenna) shows anarrow beam at theta=70 degrees with a gain of about
8.6 dBi.

Figure 8: The gain pattern of the antenna at 10.2 GHz
is shown here in a three-dimensional view overlaid on
the antenna geometry.

Figure 9: The gain pattern of the antenna at 10.2 GHz
is shown from an angled three-dimensional view todemonstrate the fan shape of the pattern.

Figure 10: A polar plot of the gain pattern at 10.8 GHzin the YZ plane of the antenna shows a beam at theta=49 degrees with a peak gain of 11.1 dBi.

Figure 11: The gain pattern of the antenna at 10.8
GHz is shown here in a three-dimensional view
overlaid on the antenna geometry.

Figure 12: The gain pattern of the antenna at 10.8 GHz
is shown from an angled three-dimensional view todemonstrate the fan shape of the pattern.

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Simulating a Beam Scanning Substrate Integrated Waveguide Leaky Wave Antenna in XFdtd

The pattern broadens slightly and increases in peak gain at 11.5 GHz where themain lobe direction changes to theta=28 degrees and the maximum gain is 12.7 dBi
as shown in Figures 13, 14, and 15. At 11.7 GHz the maximum gain is 14 dBi at anangle of theta=19 degrees as shown in Figures 16, 17, and 18. Finally, at 12 GHz, themaximum gain is 14.2 dBi at an angle of theta=13 degrees as shown in Figures 19, 20,and 21.

Figure 13: A polar plot of the gain pattern at 11.5
GHz in the YZ plane of the antenna shows a beamat theta=28 degrees with a peak gain of 12.7 dBi.

Figure 14: The gain pattern of the antenna
at 11.5 GHz is shown here in a three-dimensional view overlaid on the antenna geometry.

Figure 15: The gain pattern of the antenna at 11.5 GHz is shown from an angled
three-dimensional view to demonstrate thefan shape of the pattern.

Figure 16: A polar plot of the gain pattern at
11.7 GHz in the YZ plane of the antenna showsa beam at theta=19 degrees with a peak gainof 14 dBi.

Figure 17: The gain pattern of the antenna
at 11.7 GHz is shown here in a three-dimensional view overlaid on the antenna geometry.

Figure 18: The gain pattern of the antenna at 11.7 GHz is shown from an angled
three-dimensional view to demonstrate thefan shape of the pattern.

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Simulating a Beam Scanning Substrate Integrated Waveguide Leaky Wave Antenna in XFdtd

Figure 19: A polar plot of the gain pattern at 12 GHz in
the YZ plane of the antenna shows a beam at theta=13
degrees with a peak gain of 14.2 dBi.

Figure 20: The gain pattern of the antenna at 12 GHz
is shown here in a three-dimensional view overlaid on
the antenna geometry.

Figure 21: The gain pattern of the antenna at 12 GHz is shown from an angled three-dimensional view to demonstrate the fan shape of the pattern.

The radiation efficiency is computed in the paper using a theoretical approach for aslotted rectangular waveguide which does not consider the system mismatch or thepower lost in other ports. A value comparable to this theoretical one is computed in
XFdtd and is labeled the standalone radiation efficiency. The theoretical radiation
efficiency from the paper is plotted in Figure 22 along with the standalone radiation
efficiency from XFdtd and the XFdtd system efficiency, which includes both themismatch loss and the power lost in the second waveguide port.

315 S. Allen St., Suite 416 | State College, PA 16801 USA | +1.814.861.1299 phone |+1.814.861.1308 fax | sales@remcom.com | www.remcom.com

Simulating a Beam Scanning Substrate Integrated Waveguide Leaky Wave Antenna in XFdtd

Figure 22: Shown is the radiation efficiency for the antenna. The theoreticalresult from the paper [1] is for a slotted rectangular waveguide. The XFdtd
results are for the system efficiency which includes the mismatch loss andloss in the second port, and the standalone efficiency which is only for radiation and does not include other losses.

Reference:[1] J. Liu, D. R. Jackson, and Y. Long, “Substrate Integrated Waveguide (SIW) LeakyWave Antenna With Transverse Slots,” IEEE Trans. Antennas Propag., vol. 60, no. 1, pp.
20-29, Jan. 2012.
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315 S. Allen St., Suite 416 | State College, PA 16801 USA | +1.814.861.1299
phone | +1.814.861.1308 fax | sales@remcom.com | www.remcom.com
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