Capacitive Patches Research Articles

Miniature Dual-Band Meander-Line Monopole Chip Antenna With Independent Band Control

A dual-band monopole chip antenna with an overall size of 5 × 3 × 2.1 mm3 is investigated for 2.4/5.2/5.8 GHz WLAN applications. The chip antenna has three substrates with four copper layers in total. It deploys a modified nonuniform folded meander line and capacitive loading patches to reduce the antenna size. A fundamental monopole mode and a higher order mode are excited to obtain the 2.4 GHz (2.40–2.48 GHz) and 5 GHz (5.150–5.350 GHz and 5.725–5.875 GHz) WLAN bands, respectively. The lower and upper bands can be independently controlled by the widths of the meander lines on the first and third layers, respectively. A prototype was fabricated and measured to verify the idea. A reasonable agreement between the measured and simulated results is observed. The measured 10 dB impedance bandwidths of the lower and upper bands are 5.3% (2.38–2.51 GHz) and 19.3% (5.14–6.24 GHz), respectively, fully covering the 2.4/5.2/5.8 GHz WLAN bands. The measured efficiency of the chip antenna is higher than 60% for the two bands.

Balanced triple‐mode substrate integrated waveguide bandpass filter

This Letter proposes a novel balanced triple-mode substrate integrated waveguide (SIW) bandpass filter for the first time. The new triple-mode resonator is realised by a square-shaped SIW cavity with a capacitive loading patch. The resonance of higher-order mode TE 301 can be controlled and shifted to that of modes TE 102 and TE 201 . High-performance common mode suppression, controllable bandwidth, compact size and quasi-elliptic differential mode response can be achieved. For demonstration, a balanced triple-mode SIW filter is designed, fabricated and measured.

Triple‐mode bandpass filter

triple‐mode bandpass filter

Miniaturised and harmonic‐suppressed rat‐race couplers based on slow‐wave transmission lines

In this study, a compact rat-race hybrid coupler with harmonic suppression based on slow-wave transmission lines (SW-TLs) is presented. Such artificial lines are implemented by periodic loading a host microstrip line with series meandered inductors and shunt patch capacitors. The presence of both loading elements has a twofold effect, i.e. phase velocity reduction (due to the enhancement of the effective inductance and capacitance of the periodic line), and the generation of a controllable stopband in the frequency response (due to the Bragg effect, inherent to periodicity). It is shown that by designing the unit cell of the periodic line with an electrical length of 45°, at least the first five harmonic bands of the rat-race coupler are efficiently suppressed, keeping the band of interest unaltered. Moreover, 79% size reduction, as compared to the ordinary coupler, is achieved in the reported SW-TL-based prototype.

Quad‐band linear to circular reflective polarisation transformer and its application in dual‐sense circularly polarised antenna design

This study presents the design and application of a novel quad-band reflective polarisation transformer (RPT) with linear to dual-sense circular polarisation (LP to DS-CP) conversion. The proposed reflector is a highly miniaturised () two-layered structure built on a thin dielectric substrate (0.005λ0, where λ0 is the free-space wavelength of the lowest frequency with zero reflection phase) and backed by a ground plane. The design consists of anisotropic capacitive patches due to which the reflection phase of the orthogonal components of the LP wave differs by +90° (yielding right-hand circularly polarised (LHCP)) at 2 GHz and by −90° (yielding right-hand circularly polarised (RHCP)) at 2.4, 3.5 and 5.8 GHz. Further, it is proposed that the CP sense can be controlled by introducing narrow rectangular slots on both sides of the two-layered RPT. These perturbations delay (or advance) the reflections by 180°, thereby converting RHCP component to LHCP (or vice-versa). This diversity principle is verified using full-wave and circuit simulations. A prototype of the RPT is fabricated and measured to validate these results. For practical verification, the RPT is placed behind a quad-band LP antenna operating exactly at the ±90° reflection phase frequencies. The polariser converts LP to RHCP at 2.4–2.55/3.38–3.6 GHz and LP to LHCP at 2, 5.8–5.92 GHz.

A Modified Meander Line Microstrip Patch Antenna With Enhanced Bandwidth for 2.4 GHz ISM-Band Internet of Things (IoT) Applications

Internet of Things (IoT) based application requires integration with the wireless communication technology to make the application data readily available. In this paper, a modified meander shape microstrip patch antenna has been proposed for IoT applications at 2.4 GHz ISM (Industrial, Scientific and Medical) band. The dimension of the antenna is 40×10×1.6 mm 3 . The antenna design is comprised of an inverse S-shape meander line connected with a slotted rectangular box. A capacitive load (C-load) and parasitic patch with the shaped ground are applied to the design. Investigations show that the antenna designed with an inverse S-shape patch and connecting rectangular box in the microstrip line has a higher efficiency and gain compare to the conventional meander shape antenna. The C-load is applied to the feed line to match the impedance. Moreover, parametric studies are carried out to investigate the flexibility of the antenna. Results show that, the gain and efficiency can be improved through adjusting the rectangular box with applying parasitic element and the shaped ground. The parasitic element has high impact on the bandwidth of the antenna of 12.5%. The finalized antenna has a peak gain of -0.256 dBi (measured) and 1.347 dBi (Simulated) with 79% radiation efficiency at 2.4 GHz. To prove the efficiency and eligibility in IoT applications, the measurement of the power delivered and received by the antenna at 2.4 GHz is performed and compared with the results of a dipole antenna. The antenna is integrated with 2.4 GHz radio frequency module and IoT sensors to validate the performance. The antenna novelty relies on the size compactness with high fractional bandwidth that is validated through the IoT application environment.

Harmonic suppression in branch‐line couplers based on slow‐wave transmission lines with simultaneous inductive and capacitive loading

AbstractA compact branch‐line hybrid coupler with harmonic suppression based on slow‐wave microstrip lines is presented in this paper. These slow‐wave artificial transmission lines are implemented by simultaneously loading a host line with series inductors and shunt capacitors. By this means, the effective capacitance and inductance of the line are increased and, consequently, the phase velocity and signal wavelength are reduced. This slow‐wave effect, useful for device miniaturization, is applied to reduce the size of the coupler. Particularly, by implementing the reactive elements through capacitive patches and inductive strips, 64% size reduction, as compared to the conventional coupler, is achieved. Moreover, due to the filtering capability of the inductors and capacitors, the first and second harmonic responses of the coupler are completely suppressed. A detailed design methodology based on the schematic of the proposed slow‐wave transmission line is reported. The work includes a simple analysis to justify that two unit cells per transmission line section are necessary to suppress the harmonic bands leaving unaltered the coupler response in the region of interest. The fabricated device is fully planar, does not use vias, and the ground plane is kept unaltered.

Influence of laser fluence on structural, optical and microwave dielectric properties of pulsed laser deposited Ba0.6Sr0.4TiO3 thin films

Barium strontium titanate Ba0.6Sr0.4TiO3 (BST6) thin films are deposited by pulsed laser deposition method at different laser fluences keeping the oxygen pressure constant. X-ray diffraction analysis confirms the formation of single phase cubic BST6 thin films. The strain in the grown films have been investigated, and the results show that the strain is in increased under the application of varying laser fluences. It can be inferred that the laser fluence is an important parameter in tuning the dielectric/ferroelectric properties of the films under optimized conditions. The thin films microstructures have been studied using HRTEM, and the results shows the presence of (110) faceted planes of BST6 with dspacing ~ 2.72–2.79 A. The optical band gap of the BST6 thin films was calculated by applying the Tauc relation from the transmission spectra in the 190–2500 nm range. The BST6 thin films grown at 2 J cm−2 which shows the best microstructural and optical properties was selected for the microwave dielectric measurements by depositing a test circular patch capacitor. The microwave tunability and dielectric constant (er) of a well crystallized BST6 thin film were found to be ~ 56 and ~ 284%, respectively at 1 GHz making it suitable for applications in tunable microwave devices.

A Capacitive Coupled Patch Antenna Array With High Gain and Wide Coverage for 5G Smartphone Applications

In this paper, a novel capacitive coupled patch antenna array capable of providing high gain and 360° coverage in the elevation plane is proposed. The proposed antenna element is studied in detail using the theory of characteristic modes to enhance the bandwidth. It exhibits a uniform radiation pattern with a stable gain when integrated with the mobile phone chassis. These elements are positioned in the mobile phone chassis as a set of four sub-arrays each with 12 antenna elements to provide high realized gain around 16.5 dBi with each sub-array providing 90° coverage. The antenna array is fabricated, and the beam steering performance of the array is evaluated using a beam-steering test bed. The results show that it covers the frequency range of 24–28 GHz, which is a promising band for future 5G-based smartphone services as predicted and could be a strong candidate for 5G applications.

Size reduction and harmonic suppression in branch line couplers implemented by means of capacitively loaded slow‐wave transmission lines

AbstractA systematic approach for the design of compact branch‐line hybrid couplers with harmonic suppression is proposed in this article. The couplers are implemented by means of slow‐wave artificial transmission lines based on patch capacitors. It is shown in this article that the number of unit cells of the artificial lines should not be arbitrary. Specifically, it is demonstrated that to efficiently suppress the harmonic bands of the coupler and simultaneously keep the response of the coupler unaltered in the region of interest, two unit cells are required. Based on the proposed design methodology, a compact branch line coupler with 46% size, as compared to the ordinary counterpart, and efficient rejection of the first and second harmonic bands, is reported in this article. The designed coupler exhibits good performance in the region of interest, very similar to one of the conventional coupler.

Design of Capacitively Loaded Coupled-Line Bandpass Filters With Compact Size and Spurious Suppression

This paper is focused on the synthesis of capacitively loaded coupled lines for the design of bandpass filters with compact size and spurious suppression. The filters consist of cascaded pairs of coupled lines periodically loaded with patch capacitors. The loading capacitances provide a slow-wave effect to the coupled lines useful for filter miniaturization, whereas periodicity introduces bandgaps that can be controlled in order to achieve spurious suppression. Filter design is achieved following an automated process based on aggressive space mapping (ASM) optimization. The two reported examples, a third-order filter with central frequency $f_{0} = 1.0$ GHz, 8% fractional bandwidth, and 0.1-dB ripple level and a fifth-order filter with central frequency $f_{0} = 1.8$ GHz, 8% fractional bandwidth, and 0.1-dB ripple level, demonstrate the potential of the proposed ASM-based design approach, as well as the effectiveness of the loading capacitances to reduce filter size and reject the spurious bands. Significant size reduction in both filters is achieved, whereas the out-of-band rejection is better than 30 and 45 dB in the third-order and fifth-order filters, respectively, up to at least $4f_{0}$ .

EBG-based transmission lines with slow-wave characteristics and application to miniaturization of microwave components

In this paper, artificial transmission lines implemented by means of electromagnetic band gaps and consisting of a host line periodically loaded with reactive elements (either shunt capacitances or series inductances) are presented. The considered implementations are restricted to microstrip lines either loaded with patch capacitors or with inductive slots (etched in the ground plane). It is demonstrated that these structures are useful for device miniaturization due to the slow-wave effect associated with the presence of the reactive elements. A prototype device example consisting of a microstrip power divider implemented by means of a 35.35 Ω slow-wave impedance inverter with inductive slots is reported. It is shown that, by virtue of the slow-wave effect, the length of the inverter is reduced by a factor of two. The performance of the resulting power divider is comparable to the one based on an ordinary inverter. The possibility to suppress spurious (harmonic) bands by means of the Bragg effect is also discussed.

Broadband True-Time-Delay Circularly Polarized Reflectarray With Linearly Polarized Feed

We introduce a new technique for designing low-profile circularly polarized reflectarray antennas with ultrawideband, true-time-delay responses. The proposed reflectarray uses the unit cells of ground-plane-backed, anisotropic miniaturized-element frequency selective surfaces as its spatial time-delay units (TDUs). Each TDU is composed of a stack of nonresonant rectangular-shaped capacitive patches featuring asymmetric gap spacings and separated from one another by thin dielectric substrates. The TDUs are designed to provide a reflection phase difference of 90° between the horizontal and vertical components of the incident wave over a wide bandwidth. This way, a linearly polarized incident field is converted to a circularly polarized radiated wave. A device prototype that operates at $X$ -band is designed, fabricated, and measured. Measurement results demonstrated that the reflectarray antenna provides a gain of 23.7 dB with variations less than 3 dB within the 8–12 GHz operating frequency range or equivalently 40% bandwidth. Time-domain measurement results demonstrate the suitability of this device for operation with wideband pulses. The reflectarray is also used in a multibeam antenna and it is shown that the structure provides a wide-angle scanning performance with a field of view of ±45°.

MAcro-Electro-Mechanical Systems (MÆMS) based concept for microwave beam steering in reflectarray antennas

We present a new approach to perform beam steering in reflecting type apertures such as reflectarray antennas. The proposed technique exploits macro-scale mechanical movements of parts of the structure to achieve two-dimensional microwave beam steering without using any solid-state devices or phase shifters integrated within the aperture of the antenna. The principles of operation of this microwave beam steering technique are demonstrated in an aperture occupied by ground-plane-backed, sub-wavelength capacitive patches with identical dimensions. We demonstrate that by tilting the ground plane underneath the entire patch array layer, a phase shift gradient can be created over the aperture of the reflectarray that determines the direction of the radiated beam. Changing the direction and slope of this phase shift gradient on the aperture allows for performing beam steering in two dimensions using only one control parameter (i.e., tilt vector of the ground plane). A proof-of-concept prototype of the structure operating at X-band is designed, fabricated, and experimentally characterized. Experiments demonstrate that small mechanical movements of the ground plane (in the order of 0.05λ0) can be used to steer the beam direction in the ±10° in two dimensions. It is also demonstrated that this beam scanning range can be greatly enhanced to ±30° by applying this concept to the same structure when its ground plane is segmented.

A Dual-Band, Inductively Coupled Miniaturized-Element Frequency Selective Surface With Higher Order Bandpass Response

We present a new approach for designing dual-band miniaturized-element frequency selective surfaces (MEFSSs) with independent control of the frequencies of operation of each band. The proposed device is composed of 2-D periodic arrays of subwavelength inductive wire grids and capacitive patches separated by dielectric substrates. The structure is built on an inductively coupled MEFSS that uses capacitively loaded dielectric spacers as its main resonators. The two operating bands of this MEFSS correspond to the first and second resonant frequencies of its constituting resonators. By judiciously choosing the locations where the resonators are loaded and the load values, the frequencies of the first and second resonances can be controlled individually. In this way, a dual-band MEFSS with independent frequency bands of operation can be obtained. Using the equivalent circuit model of this MEFSS, a synthesis procedure is developed that can be used to synthesize the dual-band MEFSS from its system-level performance indicators. A prototype of the proposed dual-band MEFSS with second-order bandpass response at each band is designed, fabricated, and experimentally characterized. The measurement results of this device show a stable frequency response with respect to the angle of incidence up to ±45° for both the TE and TM polarizations of incidence.

A broadband, circular-polarization selective surface

We introduce a new technique for designing wideband circular-polarization selective surfaces (CPSSs) based on anisotropic miniaturized element frequency selective surfaces. The proposed structure is a combination of two linear-to-circular polarization converters sandwiching a linear polarizer. This CPSS consists of a number of metallic layers separated from each other by thin dielectric substrates. The metallic layers are in the form of two-dimensional arrays of subwavelength capacitive patches and inductive wire grids with asymmetric dimensions and a wire grid polarizer with sub-wavelength period. The proposed device is designed to offer a wideband circular-polarization selection capability allowing waves with left-hand circular polarization to pass through while rejecting those having right-hand circular polarization. A synthesis procedure is developed that can be used to design the proposed CPSS based on its desired band of operation. Using this procedure, a prototype of the proposed CPSS operating in the 12–18 GHz is designed. Full-wave electromagnetic simulations are used to predict the response of this structure. These simulation results confirm the validity of the proposed design concept and synthesis procedure and show that proposed CPSS operates within a fractional bandwidth of 40% with a co-polarization transmission discrimination of more than 15 dB. Furthermore, the proposed design is shown to be capable of providing an extremely wide field of view of ±60°.

Compact Dual-Mode Substrate Integrated Waveguide Coaxial Cavity for Bandpass Filter Design

This letter proposes a new compact filtering building block. It consists of two via holes embedded into a substrate integrated waveguide (SIW) cavity connected to capacitive metal patches at the top layer. This topology provides two coaxial modes performing a doublet filtering configuration. The proposed dual-mode SIW coaxial cavity is studied in detail and guidelines for the filter design are given. As will be shown, the proposed building block presents a high degree of design flexibility, which allows for the design of multiple kind of bandpass filter (BPF) responses, including both narrow- and wide-band BPFs along with transmission zero generation. As a verification, several filters are designed and implemented at 8 GHz.

A new approach to design compact tunable BPF starting from simple LPF topology using a single T‐DGS‐resonator and ceramic capacitors

ABSTRACTIn this article, a novel very compact DGS lowpass filter (LPF) and reconfigurable bandpass filter are proposed. The designed filter consists of one T‐DGS resonator, which is excited by 50 ohm microstrip line, placed on top layer between the input and output of the proposed structure. The selected filter topology has several advantageous compared with the other previous works such as the compactness and its simple design. The addition of compensated patch capacitor improves the low insertion loss and ultra‐wide stopband with 15 dB attenuation from 2.2 to 3.6 GHz. The size of the proposed single T‐DGS LPF‐BPF is less as (0.023 λg × 0.044 λg) with λg = 0.263 m. The tunable bandpass filter (BPF) is extracted from LPF topology using variable Chip Monolithic Ceramic Capacitors and J‐inverter technique. Finally, the measured, EM‐ and field simulation results are presented and discussed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1142–1148, 2016

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%.

X-band Band-pass Frequency Selective Surface for Radome Applications

A low profile multi layer miniaturized unit cell frequency selective surface (FSS) with second-order band-pass response is design. The metallic layers in the form of capacitive patches and inductive grids are separated by dielectric substrates. The non-resonant sub-wavelength unit cells with unit cell dimensions and periodicities on the order of 0.15λ. The overall thickness of approximately 0.03λ is designed which is useful at lower frequencies with long wavelengths. The FSS exhibit a stable frequency response to different angles of incidence and polarizations. The analysis and synthesis of the FSS is done using equivalent circuit method and simulated using CST microwave studio at X-band.