Fundamental TM Mode Research Articles

Broadband Metasurface Antenna Using Hexagonal Loop-Shaped Unit Cells

A broadband metasurface antenna with a novel hexagonal loop-shaped unit cell structure is presented. A hexagonal loop element array is proposed as the main metasurface radiator, which is aperture-fed through a microstrip line and a coupling slot. The bandwidth can be broadened from two perspectives. On the one hand, the proposed hexagonal loop element is capable of generating broadband radiating bandwidth. On the other hand, due to the shape of the hexagonal loop structure, gaps between unit cells lead to a larger equivalent capacitance. This larger capacitance significantly pulls the fundamental resonant frequency downward, compared with conventional square structures, consequently leading to the broad bandwidth. In the design, the broadband performance is achieved by utilizing five TM modes at five resonant frequencies in the operational band from 4.65 GHz to 8.3 GHz. Apart from the fundamental TM01 mode, only TM12 modes were excited in different parts of the metasurface layer at different frequencies. This has ensured that the proposed antenna can maintain a stable radiation pattern in the desired band. The operation of the proposed antenna is analyzed in detail. The proposed hexagonal metasurface antenna with an overall size of $1.1\,\lambda _{0} \times 1.1\,\lambda _{0} \times 0.06\,\lambda _{0}$ can achieve 56.3% fractional bandwidth and a gain ranging from 7 to 11 dBi, which can be employed in satellite, radar, and wireless communication systems.

Matched feeds for offset reflector antenna using circular microstrip patch antenna

This article presents two designs of matched feed for an offset fed reflector. Circular microstrip patch antennas are used in the proposed designs. Both the matched feeds achieve conjugate field matching by generating TM21 mode at an appropriate ratio to the fundamental TM11 mode. The first matched feed generates the required dual mode field distributions using a dual layer stacked patch antenna. The second matched feed is a novel design using centered circular array with the central element generating the required TM21 mode and the surrounding circular ring antenna elements operating in the TM11 mode. Both the designs are studied analytically using cavity model and are implemented in High frequency System Simulator (HFSS) and Computer Simulation Technology (CST). The matched feed designs are investigated for an offset reflector with the projected diameter, D = 50λ, focal length, F = 30λ and clearance height, H = 5λ operating at 20 GHz. The secondary field patterns of the offset reflector fed by the matched feeds are evaluated numerically using a MATLAB code based on geometrical optics technique and verified by HFSS-PO results. Offset reflector performance such as cross-polarization, −30 dB cross-polar bandwidth, gain, and first side-lobe level are investigated for the both matched feeds.

Subwavelength-grating-based compact and broadband TE-pass polarizer for slot waveguides on a SOI platform

We have numerically proposed a compact, broadband, and high-extinction-ratio (ER) TE-pass polarizer for vertical slot waveguides using a subwavelength grating slot (SWGS) waveguide on a silicon-on-insulator (SOI) platform. By carefully tailoring the equivalent material index, the TE fundamental mode (i.e., TE0) is supported in the SWGS waveguide, while the TM fundamental mode (i.e., TM0) is suppressed under the cutoff condition. Consequently, the input TE0 mode can pass through with negligible loss, whereas the injected TM0 mode will leak from the SWGS waveguide completely, realizing an efficient TE-pass polarizer. The proposed device only needs a single etching step, substantially reducing the fabrication difficulty compared with the previous counterparts. Moreover, thanks to the used SWGS configuration, such a device also exhibits a remarkable broadband property. From the results, the proposed polarizer with a total length of ∼56 μm has a high ER of 40.5 dB and an insertion loss (IL) of 0.42 dB at 1.55 μm, and its bandwidth is as large as ∼210 nm with ER>36 dB and IL<1 dB. In addition, fabrication tolerances to the key structural parameters are analyzed, and field evolution through the suggested polarizer is also presented.

Low-Profile and Wideband Microstrip Antenna Using Quasi-Periodic Aperture and Slot-to-CPW Transition

In this communication, we propose a new type of compact and wideband coplanar waveguide (CPW)-fed microstrip antenna. Very different from traditional microstrip antennas, the proposed design has the quasi-periodic radiating aperture fed through the slot-to-CPW transition. By optimizing the geometry of the quasi-periodic aperture and the slot-to-CPW transition, the fundamental TM10 mode and antiphase TM20 mode can be efficiently excited, coupled, and matched over a broad bandwidth. We have fabricated and characterized the proposed antenna, and found a good agreement between measurement and simulation results. Our experimental results show that despite the antenna has a thickness of only $0.052\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at the center frequency), it exhibits a −10 dB impedance bandwidth of 36.5% (3.96–5.73 GHz), a 3 dB gain bandwidth of 35.4% (4–5.72 GHz), and a maximum available gain of 10.45 dBi. Our findings may offer a feasible solution to realize wideband microstrip antennas using a single-layer substrate, with unique merits, such as low profile, low cost, and ease of fabrication.

A Compact Wideband Omnidirectional Circularly Polarized Antenna Using TM01 Mode With Capacitive Feeding

An omnidirectional circularly polarized antenna with compact size and wideband characteristic is presented and thoroughly investigated. The antenna consists of a shorted monopolar patch proximity-fed by a disk-loaded coaxial cable and two sets of curved branches sequentially located along the radiating edges. To achieve the compact size, the patch is excited to operate in the fundamental TM01 mode and the curved branches are designed with meander-line configurations. For a wideband operation, a capacitive feeding technique is employed with an additional resonance generated by the curved branches. By properly choosing the position of the stubs, a wide low-axial-ratio performance in the azimuth plane can be realized. To verify the design concept, an antenna prototype with overall size of 0.50 λL × 0.50 λL × 0.08 λL , where λL is the free-space wavelength at minimum operating frequency, has been fabricated and measured. The measurement shows that the antenna exhibits a wide operation bandwidth of 30% with a symmetric dipole-like pattern. The realized gain in the azimuth plane is around 0.5 dBic across this band.

Compact One-Sixth Mode Substrate Integrated Waveguide Based Antennas for Wireless Communication and Public Safety Systems

The authors have chosen a hexagonal SIW cavity and designed it to resonate at the fundamental TM01 mode at 5.9 GHz. The cavity is then bisected along its diagonal to produce a semi-hexagonal half-mode substrate integrated waveguide antenna, having a center frequency of 5.57 GHz lying within IEEE 802.11a WLAN U-NII 2C band. The half-mode SIW antenna depicts a gain of 5.5 dBi. A furthermore division of the full mode parent hexagonal resonator into six equal parts, each an equilateral triangle, constitutes the one-sixth mode of the parent cavity. This one-sixth mode SIW antenna operates at the resonating frequency of 5.4 GHz unlicensed band producing a gain of 5.38 dBi and finds suitable application in wireless communication systems. The antenna is further miniaturized with the inclusion of double T-shaped slot. This miniaturized antenna resonating at 4.96 GHz with a gain of 4.99 dBi is very apt in its use for public safety systems in the IEEE 802.11j 4.9 GHz band. Each of the structures is studied parametrically in great detail and the antenna prototypes are fabricated on Arlon AD270 substrate. HFSS software is used to simulate and analyze all of the antenna parameters. The simulated and measured results tallied against are found to be in good agreement with each other.

A 50‐Ω microstrip line fed shorted equilateral triangular microstrip antenna

AbstractFor the fundamental TM10 mode of an equilateral triangular microstrip antenna (ETMSA), along its height, the impedance value is maximum at the vertex, zero at the isocenter and finite value at the base. Along the base, the impedance remains constant in between 150 to 200 Ω, depending upon the design. Thus, 50‐Ω microstrip (MS) line cannot be used to directly feed an ETMSA at its base. Instead, either inset or impedance transformer is used to facilitate the 50‐Ω MS line feed. In this article, a simple MS line feed at the base is proposed using a single shorting post for impedance matching. By inserting a shorting post (via) closer to the edge of the base of an ETMSA, a wide range of impedances can be achieved at any of the edge by selecting proper shorting positions. A detailed investigation of an ETMSA with variation in shorting post position is carried out for the direct MS line feed. Experiments have been carried out to validate the concept.

Suspended Microracetrack Resonator with Lateral Sub-wavelength-Grating Metamaterial Cladding for Mid-infrared Sensing Applications

A one-time etching suspended microracetrack resonator with lateral sub-wavelength-grating (SWG) metamaterial cladding is theoretically and experimentally demonstrated on commercial 340 nm-thick-top-silicon silicon-on-insulator (SOI) platform for mid-infrared (MIR) bio-chemical sensing applications. The suspended structure can offer a larger exposed area of waveguides with the testing chemicals as well as a decent sensitivity. And the one-time etching process also eases the fabrication. The suspended waveguide is optimized with a balance between propagation loss and the sensitivity. The suspended microracetrack resonator is experimentally measured at 2 μm wavelength and well fitted with an extinction ratio (ER) of 12.3 dB and a full-width-at-half-maximum (FWHM) of 0.12 nm, which corresponds to a quality factor (Q factor) of 16600. With the equivalent refractive index method and a specially developed numerical model, the expected sensitivities of fundamental TE and TM mode were calculated as 58 nm/RIU and 303 nm/RIU respectively. This one-time etching suspended microracetrack resonator shows great potential in MIR optical bio-chemical sensing applications.

Design of Compact F-shape Microstrip Antenna For Dual Polarized Broadband Response

Design of compact multiple slots cut F-shape microstrip antenna for broadband dual polarized response is presented. The multiple rectangular slots in F-shape patch, tunes the resonance frequency and impedance at second order TM20 mode with reference to the fundamental TM10 mode, that yields bandwidth of more than 500 MHz (>40%). Because of orthogonal current variations across TM10 and TM20 modes, F-shape patch yields dual polarized wideband response. The bandwidth of individual polarization is governed by the stub length in F-shape patch. Proposed antenna exhibits broadside radiation pattern over the bandwidth with gain of more than 6 dBi at two resonant modes.

Linear analysis of an X-band backward wave oscillator with a circular-edge disk-loaded cylindrical waveguide driven by an annular electron beam

An X-band backward wave oscillator (BWO) with a circular-edge disk-loaded periodic metallic slow wave structure (CDSWS) is proposed and studied numerically. The structure is the modified version of our previously modeled semi-circularly corrugated slow wave structure (SCCSWS). The CDSWS is energized by an intense relativistic electron beam (IREB) which is directed by a strong magnetic field. The electromagnetic (EM) wave of the slow wave structure (SWS) merges with the space charge wave of the beam under the guidance of the strong axial magnetic field. The inner wall contour of CDSWS is modeled by a finite Fourier series and the dispersion characteristics of different TM modes are solved by utilizing the linear Rayleigh-Fourier (R-F) technique, which is verified by a commercial EM solver. To study the temporal growth rate (TGR) for the fundamental TM01 mode, the dispersion equation is solved for the beam current of 0.1-1.0kA and the beam energy of 205-665kV. For the TM01 mode, the TGR that occurs at the unstable region, which provides a qualitative index of the strength of the microwave generation, is compared with those of the BWOs with sinusoidally corrugated SWS (SCSWS), disk-loaded SWS (DLSWS) and triangularly corrugated SWS (TrCSWS) for different beam parameters. The dimension of the CDSWS is determined by comparing the dispersion characteristics of fundamental TM01 mode with DLSWS and SCSWS. For the same set of beam parameters, an average of 3.5%, 7%, 1.5% and more than 50% higher TGR have been obtained with the proposed CDSWS than that of SCSWS, DLSWS, TrCSWS and SCCSWS respectively. Moreover, the presented structure also provides an advantage in the fabrication process and is less prone to RF breakdown since it has no sharp edges in the inner wall where the electric field intensity can be infinitely high.

Numerical Investigations of a Silicon Photonic TE-Pass Polarizer Consisting of Alternating Copper/Silicon Nitride Layers

We propose and investigate a silicon photonic TE-pass polarizer consisting of alternating layers made out of copper/silicon nitride (Cu/Si3N4). Based on a Si stripe waveguide, the launched dominant fundamental TE mode can normally pass through it with little influence, whereas the unwanted fundamental TM mode ends up in nearly zero output as it is gradually coupled into a plasmonic mode. Particularly, the polarizer with wedge-shaped Cu/Si3N4 structure can achieve extremely high extinction ratio (ER) of 52.34 dB and low insertion loss of 0.35 dB within an ultracompact device length of 2 μ m. It also presents a relatively wide operating bandwidth of 61 nm maintaining ER >20 dB. Furthermore, considering Si3N4 itself a good Cu2+ ion diffusion barrier and its good adhesion to copper, the device fabrication is reasonably practicable using complementary metal–oxide semiconductor (CMOS)-compatible technologies. Last but not the least, we first present and analyze the connection between mode property and device performance, which could provide a significant step forward for establishing and improving the polarization diversity systems of great importance in nanophotonic integrated circuits.

A Quintuple-mode Wideband Bandpass Filter on Single Metallic Cavity With Perturbation Cylinders

A quintuple-mode wideband bandpass filter (BPF) on a single circular waveguide cavity with perturbation-oriented cylinders is proposed. These five resonant modes are the fundamental TM01 mode, a pair of TM11 degenerate modes, and a pair of TE11 degenerate modes. Three metallic cylinders are installed on the bottom of an intra-cavity to excite TM modes, and two coaxial feed probes are used to further separate the paired TE11 modes. A wide passband under the resonance of these five modes is achieved with 36% fractional bandwidth. To prove the validity, the proposed filter is fabricated using silver-plated aluminum metal cavity. The measured results are in good agreement with the simulated results.

A Dual-Mode, Dual-Port Pattern Diversity Antenna for 2.45-GHz WBAN

A dual-mode, dual-port pattern diversity antenna is presented for 2.45-GHz wireless body area networks. This antenna provides multiple radiation patterns as desired for both on- and off-body applications, namely an omniazimuthal radiation pattern directed along the body and a broadside radiation directed away from the body, respectively. This was achieved by exciting the fundamental TM11 mode in a classical circular patch antenna for off-body radiation and the TM01 mode in another circular patch antenna for on-body radiation, which was enforced by using a short circuit between the patch and the ground plane. The two antenna prototypes were finally stacked together into a single package, and the feed positioning had been optimized to offer negligible coupling between the two antenna ports that excite the two modes. The antenna performance has been evaluated in proximity to the body and found to be quite stable, compared to the performance in the free space. Moreover, the diversity performance of the antenna has also been evaluated in the form of an envelope correlation coefficient (ECC) and a diversity gain (DG). The ECC has been observed to be close to zero with a corresponding DG close to 10 dB at 2.45 GHz. This also suggests the suitability of the proposed antenna for diversity and multiple-input–multiple-output systems.

TE-Pass Polarizer Based on Epsilon-Near-Zero Material Embedded in a Slot Waveguide

A horizontal silicon slot waveguide TE-pass polarizer with thin indium–tin oxide (ITO) layer embedded in the slot region is proposed and investigated. Since the dispersion relation of the material can be tuned by properly adjusting the carrier concentration, ITO is able to act as epsilon-near-zero (ENZ) material with high absorption near 1.55- $\mu \text{m}$ wavelength. With thin ENZ material embedded in the slot waveguide, huge polarization-dependent loss between fundamental TE mode and TM mode can be induced. Therefore, the slot waveguide functions as a TE-pass polarizer with good performance. Our simulation shows that in a 3- $\mu \text{m}$ -long polarizer with 10-nm-thick ITO layer embedded in the slot region, insertion loss of 42 dB for TM mode, and 0.38 dB for TE mode can be achieved simultaneously. The polarizer possesses the advantages of low insertion loss, high extinction ratio, ultra-compact, broadband, and large fabrication tolerance.

On the properties of single-mode optical resonators

We study the quality factor of single-mode optical whispering gallery mode resonators using finite element method simulations, with a particular focus on the photonic belt resonator geometry. We experimentally observe a large difference between the quality factors of TM and TE modes in such resonators. Examining radiative losses, we conclude that the TM fundamental mode of single-mode resonators can have geometry related radiative losses caused by mode hybridization and coupling that limits their achievable quality factor. However, TE modes are free from mode hybridization radiative losses. This leads to much higher achievable Q factors for TE modes, only limited by fabrication and material quality. We experimentally observed photonic belt resonator quality factors on the order of one billion for TE modes, higher than in any other single mode optical resonator of similar dimensions.

Modelling of measured optical properties of Pd–Au alloy ultrathin film for room temperature hydrogen sensing

A theoretical framework is presented to describe optical properties of palladium gold alloy ultra‐thin film of thickness about 5 nm. Density functional theory is employed to calculate complex dielectric function of hydrogen loaded Pd3Au alloy. Using Bruggeman's effective medium theory, the effective dielectric function of hydrogenated alloy is calculated in case of non‐uniform diffusion of hydrogen starting from very low concentration. Reflectance of deposited film on silica substrate is calculated using transfer matrix method and results are compared with the measured reflectance of sputter deposited thin film of alloy on identical substrate. The change of reflectance with hydrogen concentration is also calculated and verified experimentally. In both the cases, hydrogen loaded films show low reflectance due to reduction of the available electronic states near Fermi level compared to unloaded films. From TEM images and Grazing Incidence X‐ray diffraction analyses, crystal structure of the deposited alloy film is predicted. Using this alloy a four‐layered plasmonic waveguide is designed for room temperature hydrogen sensing. Analytical calculations show that absorption loss of fundamental TM mode of the waveguide at 633 nm changes almost linearly with hydrogen concentration variation. The loss will decrease about 5 dB/100% atomic concentration of hydrogen for 10 µm device length.

Surface plasmon polaritons one-way mode converter based on parity-time symmetry broken system

In this paper, we have proposed a novel periodic surface plasmon polariton (SPP) waveguide to realize a one-way mode converter which is based on a parity–time (PT) symmetry broken system, and it converts the fundamental TM mode to the first-order TM mode in only forward direction. Periodic gain potentials are put in place to construct the system mentioned in periodic SPP waveguide. Further, as the mode converter contains gain and loss material, light signals will be amplified when it propagates forward, and they will be attenuated toward when they propagate backward. The unidirectional mode converter has wide applications in nonlinearity induced isolation, mode insensitive element and on-chip mode locked laser.

Broadband Slot Cut Rectangular Microstrip Antenna

Variation of E-shaped Microstrip antenna, a broadband rectangular Microstrip antenna cut with three unequal length rectangular slots is proposed. A detail analysis to study the effects of rectangular slots that realizes broader bandwidth is presented. The slot reduces resonance frequencies of orthogonal higher order TM02, TM11 modes and along with fundamental TM10 mode, yields more than 450MHz (>45%) of bandwidth. The realized bandwidth in the proposed configuration is more than the bandwidth obtained in equivalent rectangular patch antenna with U-slot or pair of rectangular slot i.e. E-shaped patch antenna. The proposed configuration gives broadside radiation pattern over the bandwidth with a peak broadside gain of more than 8 dBi.

Triple Band E-shaped Microstrip Antenna

The triple frequency design of E-shaped Microstrip antenna backed by E-shaped ground plane is proposed. The pair of rectangular slots that realizes E-shaped structure in patch as well as the ground plane reduces the resonance frequencies of TM02 and TM12 modes and along with fundamental TM10 mode yields triple frequency response. At each frequency, proposed antenna yields 1 to 2% of VSWR bandwidth. The slots in ground plane and patch modify the surface current distribution at higher order modes to give broadside radiation pattern at each frequency. To increase the gain suspended variation of defected ground plane backed radiating patch is proposed which gives more than 1 to 5 dBi of gain at each frequency. The proposed works clearly explains the functioning of defected ground plane triple band antenna in terms of patch resonant modes. This will be useful as similar work to get an insight into functioning of defected ground plane backed antenna is not available in the literature.

Mode hybridization and conversion in silicon-on-insulator nanowires with angled sidewalls.

The mode property and light propagation in a tapered silicon-on-insulator (SOI) nanowire with angled sidewalls is analyzed. Mode hybridization is observed and mode conversion between the TM fundamental mode and higher-order TE modes happens when light propagates in a waveguide taper which is used very often in the design of photonic integrated devices. This mode conversion ratio is possible to be very high (even close to 100%) when the taper is long enough to be adiabatic, which might be useful for some applications of multimode photonics. When the mode conversion is undesired to avoid any excess loss as well as crosstalk for photonic integrated circuits, one can depress the mode conversion by compensating the vertical asymmetry in the way of reducing the sidewall angle or introducing an optimal refractive index for the upper-cladding. It is also possible to eliminate the undesired mode conversion almost and improve the desired mode conversion greatly by introducing an abrupt junction connecting two sections with different widths to jump over the mode hybridization region.