Photonic Bandgap Structures and Their Application to EMC Antennas

2/8/2017

Photonic Bandgap Structures and Their Application to EMC Antennas

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Photonic Bandgap Structures and Their Application to EMC Antennas  April 6, 2002  Item Media  Antennas, Articles, EMC Directory & Design Guide, EMC Directory & Design Guide, Technologies PBG structures have been explored as a way of reducing harmonics.

Vincente Rodríguez-Pereyra, Ph.D., ETS-Lindgren The concept of photonic structures has recently been applied to the study of the microwave frequency (MW) range [1, 2]. Photonic bandgap (PBG) structures are analogous to a crystal lattice. It is known that in natural crystals there are certain non-occurring or “impossible” energy levels. At these particular energy levels, electrons simply cannot exist. The observations derived from these electronic bandgaps can be extrapolated into the electromagnetic realm. Within the https://interferencetechnology.com/photonicbandgapstructuresandtheirapplicationtoemcantennas/

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photonic crystals, there are certain energy levels at which, as in natural crystals, certain photon Start Reading Nowexist. Available: The FREE 2016 are Automotive EMC Guide! by energies cannot [3] Photon energies related to frequencies Plank’s constant, E = hf.

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This equation indicates that since some energy levels for the photons in the photonic crystal are not possible, then the frequencies associated with these energy levels cannot propagate within the photonic crystal. Shares

Figure 1. The dielectric crystal structures tried by Yablonovitch.

Just how are these photonic crystals built? The analogous structure of natural crystals is instructive. In a natural crystal, ions are located in the sides or vertices of a geometrical lattice. Yablonovitch [3] tried locating dielectric spheres supported by foam, but his “dielectric crystals” failed to exhibit

Figure 2. A Bravais two-dimensional lattice dielectric

PBG characteristics (Figure 1a). The opposite

crystal that exhibits PBG behavior.

approach was followed, and holes were made in a dielectric block (Figure 1b). This

geometrical “Swiss cheese” does exhibit PBG properties. A much simpler PBG structure is introduced by Maradudin and McGurn in [4]. Maradudin’s PBG is a two dimensional Bravais lattice. Dielectric rods are introduced in a different dielectric background. The structure is placed between two conductive plates (Figure 2). This structure forbids the propagation of certain frequency bands. APPLICATIONS TO MW AND RF As noted above, these structures have been utilized in the 韘�eld of optics—e.g., as mirrors in lasers. Only recently have these concepts been applied to the lower spectrum frequencies. Filtering was one of the 韘�rst applications. Since they block certain bands, these structures can be used to block undesired frequencies. In some instances,

[1,2,5] the idea of the two-

Figure 3. A PBG constructed on a grounded dielectric substrate by drilling holes in the

dimensional Bravais type lattice is borrowed.

substrate.

Rasidic et al. [1] construct their lattice by drilling holes in the dielectric substrate along a microstrip line (Figure 3). A two-dimensional lattice works well since we know the direction in which the electromagnetic (EM) energy propagates. In Rasidic https://interferencetechnology.com/photonicbandgapstructuresandtheirapplicationtoemcantennas/

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et al., [1] the PBG structure is placed on the output of an ampli韘�er to 韘�lter undesired noise and Start Reading Available: FREE 2016 Automotive EMC Guide! harmonics. InNow Rasidic et al., The [2] another approach for creating a PBG structure along microstrip

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lines is introduced. Figure 4 shows that, in this case, the holes are etched on the ground plane of the structure. The measured results reported [2] are corroborated by numerical analysis in Figure 4 [6].

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Figure 4. A PBG constructed by etching holes on the ground plane of the microstrip line. The measured results and computed results using the FDTD technique show the "impossible" frequency band that did not propagate through the line.

In Rumsey et al., [5] three different PBG structures are lined together to create a broadband 韘�lter; Figure 5 shows these structures.

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Figure 5. A broadband 韘�lter constructed by cascading three PBG structures created by drilling holes on the substrate. The results presented in (5) are compared with the ones computed in (6).

USES IN EMC The use in EMC of PBG structures is not yet very widespread. In Rodriguez et al., [6] the possibility of using a PBG to reduce crosstalk in a microstrip line was introduced. The authors demonstrated that if a line carries a known frequency that could be coupled to a nearby line, the use of a PBG structure under the passive line reduces the coupling and consequentially improves transmission on the active line (Figure 6). The results for a series of cross-talk reducing techniques are compared.


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Figure 6. The use of PBG structures as a means of reducing coupline between printed cricut lines was presented in (6). The results for a series of cross-talk reducing techniques are compared.

Also, PBG structures have been explored at a way of reducing harmonics in printed microstrip antennas. Speci韘�cally, a three0dimensional PBG is used as the substrate of the antenna. The use of these structures in EMC antennas is a totally new idea. These structures are virtually invisible at some frequencies, and behave like conductors (not allowing certain frequencies to propagate through) at other frequencies, so their use in broadband antennas appears quite promising. EMC antennas are usually very broadband. Designing broadband antennas is a challenge. When certain parts of the antenna are modi韘�ed to improve performance, performance at certain other frequencies may degrate. Figure 7 shows how PBGs’ structure could be used as beam-forming strucutures at certain operating frequencies without affecting other frequencies at which they would be virtually invisible. The horn antenna in Figure 7 operates at a given low frequency. As the frequency increases, higher order modes are launched from the feed cavity. These modes may not radiate or may do so with a split beam. Locating a PBG structure in the cavity could reduce higher order modes and could https://interferencetechnology.com/photonicbandgapstructuresandtheirapplicationtoemcantennas/

Figure 7. A theoretical use of a PBG in increasing the frequency band of a standard horn antenna. 5/12

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allow for an effective pattern at higher frequencies, Reading Nowthe Available: Automotive EMC hence increasing band ofThe theFREE horn2016 without affecting lowGuide! frequencyStart behavior.

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LIMITATIONS OF PBG STRUCTURES As with every technology, PBG structures have their limitations. Although two-dimensional PBGs are rather easy to construct, three-dimensional PBGs are not easy to manufacture. Also, prior knowledge of the antenna 韘�elds is needed for using PBGs effectively in the design of EMC antennas. (Still, this can be obtained via numerical simulation). Another limitation of PBGs relates

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to their size. To stop the propagation of energy effectively, the PBG must be “electrically large” (ideally in韘�nite). A small PBG structure will attenuate the propagating wave but will not totally stop its propagation. This limitation is especially signi韘�cant in printed circuit design where the PBG may occupy a much larger area than a 韘�lter made up of lumped elements. CONCLUSIONS The present work has explored the basic principles of PBGs and has demonstrated some of their applications. A great deal of work remains to be done in this area, especially to determine if these structures can be utilized ef韘�ciently to increase the performance of broadband antennas vital to EMC. Some of the limitations of PBG structures have been explored as well. REFERENCES 1. Rasidic et al. “Broad-Band Ampli韘�er Using Dielectric Photonic Bandgap Structure.” IEEE Microwave Guided Wave Letters, Vol. 8, No. 1, January 1998. p. 13. 2. Rasidic et al. “Novel 2D Photonic Bandgap Structure for Microstrip Lines.” IEEE Microwave Guided Wave Letters, Vol. 8, No. 2, February 1998. p. 69. 3. Yablonovitch. “Photonic Bandgap Strucutres.” J. Opt. Soc. Am. B., Vol. 10, No. 2, February 1993, pp.283-295. 4. Maradudin et al. “Photonic Band Structure of a Truncated, 2D, Periodic Dielectric Medium.” J.

Opt. Soc. Am. B., Vol. 10, No. 2, February 1993, pp. 307-313. 5. Rumsey et al. “Photonic Bandgap Structures Used as Filters in Microstrip Circuits.” IEEE Microwave Guided Wave Letters, Vol. 8, No. 10, October 1998. 6. V. Rodriguez-Pereyra, A. Z. Elsherbeni, and C. E. Smith. “Photonic Bandgap Structures for Minimizing the Coupling Between Microstrip Lines.” 1999 IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, Orlando, Florida, July 1999.

Vincente Rodríguez-Pereyra attended the University of Mississippi, where he obtained his BSEE, MS, and Ph.D. in 1994, 1996 and 1999, respectively. Beginnnig in 1994, he was a research assistant at the Electrical Engineering Department at the University of Mississippi. From August 1999 to May 2000, he was a Visiting Assistant Professor of Electrical Engineering and Computer https://interferencetechnology.com/photonicbandgapstructuresandtheirapplicationtoemcantennas/

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Science at Texas A&M University-Kingsville. In May 2000, he joined ETS-Lindgren as an RF and Start Reading Now engineer. Available: The FREE 2016 Automotive EMC Guide! electromagnetics

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Dr. Rodríguez’ primary interest is Numerical Methods in Electromagnetics—especially as applied to antenna and RF/MW absorber design. Dr. Rodriguez is the author of more than 15 publications, including journal and conference papers, as well as contributions to texts. Dr. Rodríguez is a member of the ACES and the IEEE and several of its technical societies. He can be reached at [email protected]. Shares

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