Center Operating Frequency Research Articles

A Novel Low-Profile Dual Circularly Polarized Dielectric Resonator Antenna

A novel dual-port dual-sense circularly polarized (CP) T-shaped dielectric resonator antenna is introduced. The antenna consists of a T-shaped dielectric resonator, a pair of microstrip-fed stubs printed on a substrate with a truncated ground plane, and a decoupling network. Circular polarization is obtained by the structure to excite multiple orthogonal modes. The antenna can radiate left-hand CP (LHCP) or right-hand CP (RHCP) fields depending on the feed port selected. The measured RHCP (LHCP) field at the boresight direction is more than 26 dB (25 dB) stronger than the LHCP (RHCP) counterpart at the center operating frequency. The measured results show that the antenna has usable bandwidths of 17.2% (4.98–5.92 GHz) and 17.9% (5.02–6.03 GHz) and peak gains of 3.2 and 3.3 dBic at two feed ports, respectively. The isolations between two feed ports are better than 22.5 dB over the whole operating band. In addition, the antenna has peak radiation efficiencies of about 89% and 91% for Ports 1 and 2, respectively.

Wideband substrate‐integrated monopole antenna

ABSTRACTA coaxial probe fed wideband low‐profile electric monopole cavity antenna with measured impedance bandwidth of 56% at a central operating frequency of 8 GHz is proposed. The antenna, based on a modified shorted square patch, effectively forms a substrate‐integrated cavity with four curved radiating slots at its periphery. The concave curvature of these four radiating slots provides a magnetic current loop mode while increasing bandwidth and reducing volume of the resonator. The proposed design may be easily fed using a 50 Ω probe feed and capacitive gap, and is robust to manufacturing tolerances, as parasitic modes are not excited. The design is compatible with applications requiring a vertically polarized signal with respect to the antenna surface. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1855–1857, 2016

Computation of Schenberg response function by using finite element modelling

Schenberg is a detector of gravitational waves resonant mass type, with a central frequency of operation of 3200 Hz. Transducers located on the surface of the resonating sphere, according to a distribution half-dodecahedron, are used to monitor a strain amplitude. The development of mechanical impedance matchers that act by increasing the coupling of the transducers with the sphere is a major challenge because of the high frequency and small in size. The objective of this work is to study the Schenberg response function obtained by finite element modeling (FEM). Finnaly, the result is compared with the result of the simplified model for mass spring type system modeling verifying if that is suitable for the determination of sensitivity detector, as the conclusion the both modeling give the same results.

Thermal connection and vibrational isolation: an elegant solution for two problems

Schenberg is a detector of gravitational waves resonant mass type, with a central frequency of operation of 3200 Hz. Transducers located on the surface of the resonating sphere, according to a distribution half-dodecahedron, are used to monitor a strain amplitude. To improve the performance of the detector it is essential to decrease the temperature, then it will be cooled down, this temperature could reach as low as 50 mK. This refrigerator produces vibration noise that could compromise the performance of Schenberg detector. In this work we the study such vibration noise and how it could be minimized proposing a new connection from the dilution refrigerator to the sphere suspension. The vibration attenuation is studied by finite element modeling (FEM) and an attenuation higher than 1024 is found, higher enough to note compromise the performance of Schenberg detector.

Optimal Design of a Center Support Quadruple Mass Gyroscope (CSQMG).

This paper reports a more complete description of the design process of the Center Support Quadruple Mass Gyroscope (CSQMG), a gyro expected to provide breakthrough performance for flat structures. The operation of the CSQMG is based on four lumped masses in a circumferential symmetric distribution, oscillating in anti-phase motion, and providing differential signal extraction. With its 4-fold symmetrical axes pattern, the CSQMG achieves a similar operation mode to Hemispherical Resonant Gyroscopes (HRGs). Compared to the conventional flat design, four Y-shaped coupling beams are used in this new pattern in order to adjust mode distribution and enhance the synchronization mechanism of operation modes. For the purpose of obtaining the optimal design of the CSQMG, a kind of applicative optimization flow is developed with a comprehensive derivation of the operation mode coordination, the pseudo mode inhibition, and the lumped mass twisting motion elimination. The experimental characterization of the CSQMG was performed at room temperature, and the center operation frequency is 6.8 kHz after tuning. Experiments show an Allan variance stability 0.12°/h (@100 s) and a white noise level about 0.72°/h/√Hz, which means that the CSQMG possesses great potential to achieve navigation grade performance.

Wideband Linear-to-Circular Polarization Converters Based on Miniaturized-Element Frequency Selective Surfaces

We introduce a new technique for designing wideband polarization converters based on miniaturized-element frequency selective surfaces (MEFSSs). The proposed structure is a two-dimensionally anisotropic periodic structure composed of arrays of subwavelength capacitive patches and inductive wire grids separated by thin dielectric substrates. The structure is designed to behave differently for field components of the two orthogonal polarizations and transmits a circularly polarized wave once illuminated by a linearly polarized plane wave. Using equivalent circuit models for MEFSSs, a synthesis procedure is developed that can be used to design the polarization converter from its required bandwidth and center frequency of operation. Using this procedure, a prototype of the proposed polarization converter operating within the X-band is designed, fabricated, and experimentally characterized using a free-space measurement system. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS-based polarization converter operates in a wide field of view of $\pm45^{\circ}$ with a fractional bandwidth of 40%.

A Millimeter-Wave Filtering Monopulse Antenna Array Based on Substrate Integrated Waveguide Technology

A millimeter-wave filtering monopulse antenna array based on substrate integrated waveguide (SIW) technology is proposed, manufactured, and tested in this communication. The proposed antenna array consists of a filter, a monopulse comparator, a feed network, and four antennas. A square dual-mode SIW cavity is designed to realize the monopulse comparator, in which internal coupling slots are located at its diagonal lines for the purpose of meeting the internal coupling coefficiencies in both sum and difference channels. Then, a four-output filter including the monopulse comparator is synthesized efficiently by modifying the coupling matrix of a single-ended filter. Finally, each SIW resonator coupled with those four outputs of the filter is replaced by a cavity-backed slot antenna so as to form the proposed filtering antenna array. A prototype is demonstrated at Ka band with a center frequency of 29.25 GHz and fractional bandwidth of 1.2%. Our measurement shows that, for the H-plane, the sidelobe levels of the sum pattern are less than -15 dB and the null depths of the difference pattern are less than -28 dB. The maximum measured gain of the sum beam at the center operating frequency is 8.1 dBi.

The Analysis of a Wideband Strip-Helical Antenna with 1.1 Turns

A wideband strip-helical antenna with 1.1 turns is analyzed numerically and experimentally. By replacing the traditional wire helix with wide metallic strip, the forward traveling current on the strip helix with about one turn smoothly decays to the minimum value at the open end of the helix. Therefore, the strip helix can excite a wideband circular polarization (CP) wave with 50-ohm impedance matching. The proposed antenna is printed on a hollow-cylinder with a substrate relative permittivity ofεr=2.2and a thickness ofh=0.5 mm. A 50 Ω coaxial cable is directly connected to excite the strip-helical antenna without any additional impedance matching section. The ground plane is placed below the antenna in order to provide a directional radiation pattern. To demonstrate this method, a prototype of 1.1-turn strip-helical antenna is tested. The test shows that the proposed antenna can reach an overlapped bandwidth of 46% with height of 0.52λ0, whereλ0is the wavelength in free space at the center operation frequency.

Design of a Wideband Circularly Polarized Strip-Helical Antenna With a Parasitic Patch

A wideband strip-helical antenna with a parasitic circular patch for circular polarization is designed in this paper. A strip-helix with 2.5 turns and a pitch angle of 5° is placed over a ground plane and coaxial probe-fed by a 50- $\Omega $ SMA connector. A parasitic patch is electromagnetic-coupled to the open end of the strip-helix with an extremely small distance. By combining the strip-helix with the parasitic patch, two nearby circularly polarized (CP) resonances are produced and a wide axial ratio (AR) bandwidth is obtained. The strip-helix can excite a CP resonance in axial mode, while the parasitic patch can generate another nearby one in fundamental mode. Radiation characteristics of the proposed design, including current distributions, reflection coefficient (S11), AR, and radiation patterns, are studied. Measured results shows that the proposed antenna has an impedance bandwidth (S11 ≤ − 10 dB) of 53%, an AR bandwidth (AR ≤ 3 dB) of 44%, and a peak gain of 9.4 dBi in its volume of $0.43\lambda _{0} \times 0.43\lambda _{0} \times 0.25\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space at the center operation frequency.

Epsilon-Negative Transmission-Line-Based Annular-Ring-Loaded Circular Microstrip Antenna With Improved Performances

A novel epsilon-negative transmission line (ENG TL)-based annular-ring-loaded (ARL) circular microstrip antenna (CMSA) is proposed in this letter. Compared to a conventional CMSA, the proposed structure offers improved impedance bandwidth by exciting the TM11 modes on both the driven CMSA and the coupled ENG TL-based annular ring. Due to the enlarged radiation aperture, the gain is correspondingly enhanced. Moreover, the proposed structure exhibits lower levels of radiation along the horizon and toward the backside as compared to conventional CMSA. The mutual coupling characteristics of the proposed antenna are also investigated, and the simulated results show that the E-plane mutual coupling between the proposed ENG TL-based ARL CMSAs decreases much more rapidly with spacing than that for conventional CMSAs. To validate the proposed concept, prototypes with a center operating frequency of 6.5 GHz are fabricated and tested. Good agreements are achieved between simulation and measurement.

Design of Wideband Dual-Polarized Planar Antenna Using Multimode Concept

A wideband dual-polarized planar antenna is designed and analyzed by using the theory of characteristic modes (TCM). The eigenvalue, eigencurrent, characteristic pattern, and modal weighting coefficient are analyzed to bring physical insight to this kind of antenna. The results demonstrate that there are two modes resonant in the operating band for each polarization, which have been combined to form a wider frequency band. A bandwidth of 60.2% (1.72–3.2 GHz) for VSWR < 1.5 with high isolation of 32 dB is achieved simultaneously. The size of the radiator structure is 0.33λ0× 0.33λ0× 0.22λ0(λ0refers to the center operating frequency).

A Quadruplet-Resonator-Based Ferrite-Free Choke for Suppressing Noise Currents on Cable Shielding

This paper presents a novel technique for suppressing cable noise currents, the quadruplet-resonator-based ferrite-free choke (QR-based FFC), to eliminate the gigahertz (GHz) electromagnetic interference caused by noise currents flowing on the cable shielding. This problem is difficult to handle with conventional ferrite materials since their permeabilities dramatically degrade when the operating frequency goes up to several GHz. In this paper, with the aid of QR surrounding on the cable shielding, the FFC forms bandstop responses against the noise currents. The corresponding equivalent lumped circuit model is proposed and investigated. Furthermore, the synthesis procedure is established using microwave filter theory. The QR-based FFC can achieve a high-level current suppression at the desired frequency band. This technology is experimentally verified: a given design example is demonstrated at the operating center frequency of 2.57 GHz. The frequency range of 3-dB current suppression is measured from 2.47 to 2.75 GHz (FBW $= $ 10.8%), where the highest suppression level is up to 36 dB. The FFC-added cable also demonstrates a good result in the reduction of far-field radiation, where the reduction level of radiation peak gain is measured as 7 dB compared with that of a bare cable.

A dual polarized, Ku-band patch antenna using hybrid LTCC-PCB technology

This work presents the design and fabrication of a wideband dual polarized patch antenna to be used in an array for applications such as satellite communication. Our proposed patch is made of 591 Green Tape made by Low Temperature Co-Fired Ceramic and Rogers RT5870, and is designed to work in the frequency range of 10.7–12.7 GHz. Our result shows that the one layer patch antenna increases the bandwidth up to 17% in simulation and 12.3% in experiment related to the center operation frequency band. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:202–206, 2016

Compact continuously tunable microwave photonic filters based on cascaded silicon microring resonators

We propose and experimentally demonstrate a photonic approach to achieving tunable bandpass microwave photonic filters (MPFs) based on cascaded microring resonators (CMRRs). The optical spectrum of the silicon CMRRs could offer two bandpass response to separately filter the optical carrier and one of the sidebands generated by the phase modulation. Thus we could achieve a bandpass MPF. Moreover, as the central frequencies and bandwidths of the two bandpass response can be tuned by adjusting the laser wavelength and voltages applied on one MRR, the central operating frequency or 3-dB bandwidth of the MPF can be continuously tuned in wide ranges respectively. A proof-of-concept experiment illustrates a central frequency tuning range from 19GHz to 40GHz, and a wide bandwidth tuning range from 5.5GHz to 17.5GHz.

Inductively-Coupled Miniaturized-Element Frequency Selective Surfaces With Narrowband, High-Order Bandpass Responses

We introduce a new technique for designing miniaturized-element frequency selective surfaces (MEFSSs) with narrowband, bandpass responses of order $N\ge2$ . The proposed structure is composed of two-dimensional periodic arrays of subwavelength inductive wire grids separated by dielectric substrates. A simple equivalent circuit model, composed of transmission line resonators coupled together with shunt inductors, is presented for this structure. Using this equivalent circuit model, an analytical synthesis procedure is developed that can be used to synthesize the MEFSS from its desired system-level performance indicators such as the center frequency of operation and bandwidth. Using this synthesis procedure, a prototype of the proposed MEFSS with a second-order bandpass response, center frequency of 21 GHz, and fractional bandwidth of 5% is designed, fabricated, and experimentally characterized. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS has a stable frequency response with respect to the angle of incidence of the EM wave in the $\pm40^\circ$ range for both TE and TM polarizations of incidence.

A single layer ultra-miniaturized FSS operating in VHF

In this paper, we propose an ultra-miniaturized FSS element, which is composed of interwoven and convoluted dipoles printed on one side of a dielectric substrate. The design procedure is briefly presented. Simulations results show that the element size is reduced to 0.016λ0×0.016λ0, where λ0 is the wavelength in vacuum at the resonant frequency. The thickness of FSS is only 0.0008λ0. Due to the ultra-miniaturized size, the proposed FSS exhibits excellent angle-stability under both TE and TM polarizations. Furthermore, wide-band performance is also achieved, with a fractional bandwidth 73.5% under normal incidence. When the incidence angle reaches up to 75°, the central operating frequency is only shifted by 0.36%. Based on plasmon resonance, the induced currents on metallic pattern are analyzed to explain the miniaturization performance.

Bandwidth Enhancement of Three-Stage Doherty Power Amplifier Using Symmetric Devices

This paper proposes a design scheme for extending the bandwidth of a three-stage Doherty power amplifier (DPA) based on symmetric devices for broadband applications. The proposed bandwidth enhancement scheme provides an optimized solution for the load combiner parameters while operating the auxiliary power amplifier (PA) at lower current values as compared to the main PA at saturation. The proposed scheme promises 30.3% fractional bandwidth in terms of efficiency enhancement up to 9.54-dB back-off. The proposed design methodology is validated with the design of a broadband three-stage DPA using three 10-W packaged GaN HEMT devices. Measurement results show more than 51.6% drain efficiency at 6-dB output power back-off (OPBO) over the entire frequency range from 700 to 950 MHz. At 9.54-dB OPBO, the drain efficiency is better than 50.2% over this 250-MHz band. The peak drain efficiency at saturation is better than 60.04% over the entire band of operation. Measurement with 5-MHz WCDMA modulated signal shows the average drain efficiency of about 57.6% at 33.97-dBm average output power at the center frequency of operation. The corresponding adjacent channel power ratio is better than ${-}{\hbox{45.6}}$ dBc after applying digital predistortion. The circuit is realized with microstrip technology, which can be easily fabricated using conventional printed circuit processes.

Novel Polarization-Reconfigurable Converter Based on Multilayer Frequency-Selective Surfaces

In this paper, a novel polarization-reconfigurable converter (PRC) is proposed based on a multilayer frequency-selective surface (MFSS). First, the MFSS is designed using the square patches and the grid lines array to determine the operational frequency and bandwidth, and then the corners of the square patches are truncated to produce the phase difference of 90° between the two orthogonal linear components for circular polarization performance. To analyze and synthesize the PRC array, the operational mechanism is described in detail. The relation of the polarization states as a function of the rotating angle of the PRC array is summarized from the principle of operation. Therefore, the results show that the linear polarization (LP) from an incident wave can be reconfigured to LP, right- and left-hand circular polarizations by rotating the free-standing converter screen. The cell periods along x- and y-directions are the same, and their total height is 6 mm. The fractional bandwidth of axial ratio (AR) less than 3 dB is more than 15% with respect to the center operating frequency of 10 GHz at normal incidence. Simultaneously, the AR characteristics of different incidence angles for oblique incidence with TE and TM polarizations show that the proposed PRC has good polarization and angle stabilities. Moreover, the general design procedure and method is presented. Finally, a circularly shaped PRC array using the proposed PRC element based on the MFSS design is fabricated and measured. The agreement between the simulated and measured results is excellent.

Gain enhancement of a wide‐slot antenna using dual‐layer, bandstop frequency selective surface as a substrate

ABSTRACTA technique for enhancing the gain of a conventional wide‐slot antenna over the wide frequency band using a dual‐layer, low‐profile, bandstop frequency selective surface (FSS) is presented in this article. The dual‐layer FSS exhibits transmission below −10 dB and a linear phase variation with frequency in the range of 4–7 GHz. Unit cell dimension on the order of 0.2λ is used for the FSS layers with respect to the center frequency of operation. The FSS is used as a substrate below the antenna that allows in‐phase reflection of radiated waves leading to enhancement in its gain in the broadside direction over entire operating band. An improvement of upto 3‐dBi gain is achieved over 4–6.5 GHz frequency band with a peak gain of 8.4 dBi. Spacing between the antenna and FSS layers is much less than the conventional quarter wavelength value. Simulation and measurement results are presented in each case. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2016–2020, 2015

A finite element approach to modelling fractal ultrasonic transducers

Piezoelectric ultrasonic transducers usually employ composite structures to improve their transmission and reception sensitivities. The geometry of the composite is regular with one dominant length scale and, since these are resonant devices, this dictates the central operating frequency of the device. In order to construct a wide bandwidth device it would seem natural therefore to utilize resonators that span a range of length scales. In this article, we derive a mathematical model to predict the dynamics of a fractal ultrasound transducer; the fractal in this case being the Sierpinski gasket. Expressions for the electrical and mechanical fields that are contained within this structure are expressed in terms of a finite element basis. The propagation of an ultrasonic wave in this transducer is then analysed and used to derive expressions for the non-dimensionalized electrical impedance and the transmission and reception sensitivities as a function of the driving frequency. Comparing these key performance measures to an equivalent standard (Euclidean) design shows some benefits of these fractal designs.