Slot-coupled Microstrip Lines Research Articles

A Series of Ultra-low Permittivity ALaP4O12 (A = Li, Na, K) Metaphosphate Microwave Dielectric Ceramics for Ultra-wideband Dielectric Resonant Antenna Application.

The employment of ultra-low permittivity materials in the configuration of antennas has been demonstrated to augment the antenna bandwidth and diminish signal delay effectively. This study presents three ultra-low permittivity metaphosphate microwave dielectric ceramics (MWDCs). The ALaP4O12 (A = Li, Na, K) metaphosphate ceramics, which all belong to the monoclinic crystal system, exhibit extremely low permittivity (εr ≈ 5) and excellent quality factor (Q·f > 10,000 GHz) at a low sintering temperature (T < 950 °C). Terahertz time-domain spectroscopy indicates that the εr of ALaP4O12 at terahertz frequencies is comparable to that observed in the microwave band and its value remains stable over an extensive frequency range. Furthermore, the relationship between the crystal structure and the dielectric properties of ALaP4O12 has been analyzed through the lens of chemical bond theory. The highest Q·f value observed for LiLaP4O12 can be attributed to the high chemical bond strength and stability of its crystal structure. The lowest ionic polarizability per unit volume is exhibited by NaLaP4O12, which results in the lowest pore-corrected permittivity. The thermal expansion of the chemical bonds within KLaP4O12 is considerable, resulting in the highest coefficient of thermal expansion. Finally, the performance of a LiLaP4O12-based dielectric resonator antenna (DRA) excited by slot-coupled microstrip lines was designed and optimized by using different ceramic radius-to-height (RH) ratios. It was found that when the RH ratio of DRA reached 1.85, both the fundamental mode (HEM11δ) and the higher-order mode (HEM12δ) of DRA were simultaneously excited. The two modes overlap significantly, resulting in an ultra-wideband (UWB) of 46.8% (bandwidth = 7.93 GHz). Concurrently, the maximum radiation efficiency and gain of the DRA, obtained from the simulation, are 97.9% and 7.92 dBi, respectively. The findings of this study may inform the investigation of ultra-low permittivity phosphorus-based MWDCs and UWB DRAs.

Design and Fabrication of Wideband Dielectric Resonator Antenna Using Low Loss Ultra‐Low Sintering Temperature Li6B4O9 Microwave Dielectric Ceramic for Wireless Communication Applications

AbstractLow dielectric constant (ɛr), high quality‐factor (Q × f), and temperature stable microwave dielectric ceramics with ultra‐low sintering temperature are the preferred choice of researchers for the development of low‐cost and high‐performance dielectric resonator antenna (DRA), which have wide application prospects for wireless communication technology. In this work, wideband DRAs fabricated using ultra‐low sintering temperature, low‐loss, and high‐quality Li6B4O9 microwave dielectric ceramics are reported. Li6B4O9 ceramic synthesized via solid‐state reaction at sintering temperature of 620 °C demonstrates excellent microwave properties with optimum ɛr = 5.95, high Q × f = 38,700@12.4 GHz, and thermal coefficient of the resonant frequency (TCF ≈ −68.6ppm/○C). For the first time, performance comparison of two Li6B4O9‐based cylindrical DRAs with different ceramic aspect (radius to height) ratios excited by slot coupled microstrip line is realized. In the first DRA with ceramic aspect ratio of 0.864, DRA HE11δ mode is excited and bandwidth of 20.01% , 95% radiation efficiency, and 6.3 dBi maximum gain is attained. In the second DRA with ceramic aspect ratio of 2.367, slot and dielectric resonator resonances are merged to attain wide bandwidth of 38.15% over which antenna broadside radiation performance is preserved. The proposed DRAs can be utilized for high‐capacity, high‐speed wireless communication applications.

A High-Gain Dielectric Resonator Antenna With Plastic-Based Conical Horn for Millimeter-Wave Applications

A novel high-gain dielectric resonator antenna, featuring a peak realized gain of 11.3 dBi over a fractional bandwidth of 16.6% around 30 GHz, is presented. The proposed antenna structure, excited by a slot-coupled microstrip line, is composed of a cylindrical dielectric resonator and of a truncated plastic-based conical horn useful to enhance the gain. An annular perturbation notch is realized in the dielectric horn to achieve a better focusing of the RF energy along the antenna boresight direction, while reducing the sidelobe levels (SSLs). The presented antenna design achieves SSLs below −10 dB for both the E - and H -plane so to meet the requirements of next-generation 5G wireless communication protocols and of low-cost satellite and mobile systems.

Omnidirectional Dual-Polarized Antenna With Sabre-Like Structure

In this communication, a sabre-like dual-polarized antenna with omnidirectional patterns in the azimuthal plane is presented for low wind drag airborne applications. The proposed antenna consists of a thin cavity for the horizontal polarization and a coplanar waveguide-fed monopole for the vertical polarization. The colocated thin cavity and the monopole construct a compact sabre-like structure with low wind drag, and it is suitable for airborne use. Especially, a hybrid-feeding structure, including a capacitive slot-coupled microstrip line and an inductive probe, is proposed for impedance matching of the thin cavity to provide omnidirectionally horizontal polarization. In order to verify the proposed design, a prototype is fabricated and tested with the dimensions of $42 \times 29 \times 9$ mm3. ( $0.42\lambda _{0} \times 0.24\lambda _{0} \times 0.07\lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at 2.44 GHz.) The measured −10 dB reflection coefficient bandwidths of the two ports are 2.38–2.51 and 2.28–2.53 GHz. The measured gain variation in the azimuth plane is less than 3.60 and 3.45 dB for horizontal polarization and vertical polarization.

HEXA-BAND HIGH-ISOLATED DUAL-POLARIZED LOOP ANTENNA FOR MOBILE COMMUNICATIONS

This paper presents a broadband hexa-band dual-polarized loop antenna for mobile communications. Two orthogonal one-wavelength-perimeter modes of a rectangular loop are excited by two orthogonal feedings. One mode for vertical polarization is excited by a circular monopole, and the other mode for horizontal polarization is excited by a slot-coupled microstrip line. By optimizing the antenna structure and the orthogonal feedings, the orthogonal polarizations can be achieved in a wide bandwidth with high ports isolation. The overall size of the proposed antenna is only 58 × 53 mm 2 (0.43λ0 × 0.39λ0, λ0 is the free-space wavelength at 2.2 GHz). A prototype of the proposed antenna is built and tested. The measured bandwidth with reflection coefficient less than −10 dB is 61.4% (1.65-3 GHz) for both orthogonal polarizations, covering the DCS, PCS, UMTS, WLAN, LTE2300, and LTE 2500 operation. The measured ports isolation is better than 28 dB over the entire band. In addition, the radiation patterns, gains and diversity performance are also discussed.

A New Broadband Marchand Balun Using Slot-Coupled Microstrip Lines

In this letter, a new broadband Marchand balun is proposed using slot-coupled microstrip lines. The developed balun is connected by two sections of diamond-shape slot-coupled microstrips with short- and open-circuited terminations at specified ports. To achieve the broadband operation, the simple formulas have been derived to convert the conventional rectangular-shape slot-coupled microstrip to the diamond-shape counterpart. The measured results of the developed balun not only agree with the full-wave simulation results very well, but also resemble the calculated results by ideal coupled lines. The new Marchand balun developed in this letter has a 10 dB return loss bandwidth of 90%, while in this frequency range the amplitude imbalance varies from -0.37 dB to 0.32 dB, and the phase difference in the range of -180.4° ~ -181.8°.

Integrated multibeam dual-polarised planar array

A novel four-beam dual-polarised microstrip antenna array at the 10 GHz band is presented. By using a multilayered structure and multiport slot-coupled microstrip lines, two Butler matrix microstrip circuits corresponding to two orthogonal polarisations can be located on different substrate layers (above and below the ground plane) and integrated with a patch array. The antenna has eight input ports corresponding to two orthogonal polarisations and four beams. The theoretical design is based on the finite-difference time-domain (FDTD) method. The measured return loss and isolation characteristics exceed 10 and 23 dB, respectively, in the 9.7-10.3 GHz band. The radiation pattern is close to an ideal Butler pattern and the cross-polarisation level is lower than -18 dB in the beams. Details of the antenna and its characteristics are presented.

Numerical analysis of dielectric resonator antennas

A numerical analysis of various dielectric resonator antennas (DRAs): simple (single element) and complex shape configurations (stacked and embedded resonators) with different excitations (dipole, coaxial probe, slot-coupled microstrip line) using a time-harmonic surface finite element method (SFEM) is presented. Numerical results have been compared with those obtained using a volume time-domain finite-element method (TDFEM) and experiments. Measurements on return loss and radiation field patterns show a good agreement with computed ones. Copyright © 2000 John Wiley & Sons, Ltd.

An improved network modeling of slot-coupled microstrip lines

This paper proposes an analytical method for slot-coupled microstrip lines with a view to developing an improved network model, which reflects the effects of inclination angles and offset distances. The network model consists of two ideal transformers and an extended slotline. The turn ratios are calculated by applying the reciprocity theorem with the spectral-domain immittance approach. The corresponding network models for several different configurations of these slot-coupled microstrip lines are then explored and shown to yield accurate scattering parameters.

Scattering parameters of arbitrarily oriented slot-coupled microstrip lines

The reciprocity method is extended to analyse arbitrarily oriented slot-coupled microstrip lines. The case of uniaxially anisotropic dielectric substrates is considered. The exact Green functions for these anisotropic substrates are used to solve for the unknown slot electric field, from which scattering parameters of a four-port network for this structure are obtained by using the reciprocity theorem. Comparison of numerical results for parallel microstrip lines with other available measured and computed data shows good agreement. It is found that for arbitrarily oriented microstrip lines, by varying slot inclination the angle coupling level can be widely controlled, and there exists maximum coupling for a certain value of slot inclination angle. Effects of other parameters such as slot length and dielectric anisotropy are also investigated.

Mixed potential integral equation technique for hybrid microstrip-slotline multilayered circuits using a mixed rectangular-triangular mesh

In this paper, a mixed potential integral equation (MPIE) formulation for hybrid microstrip-slotline multilayered circuits is presented. This integral equation is solved with the method of moments (MoM) in combination with Galerkin's method. The vector-valued rooftop functions defined over a mixed rectangular-triangular mesh are used to model the electric and magnetic currents on the microstrip and slotline structures. An efficient calculation technique for the quadruple interaction integrals between two cells in the system matrix equation is presented. Two examples of hybrid microstrip-slotline circuits are discussed. The first example compares the simulation results for a microstrip-slotline transition with measured data. The second example illustrates the use of the simulation technique in the design process of a broadband slot-coupled microstrip line transition. >