Iet Microwaves Antennas & Propagation最新文献

The design of three-dimensional (3D)-printed heterogeneous ceramics exhibiting isotropic and anisotropic dielectric permittivities at microwave frequencies is studied for dielectric resonator antenna (DRA) applications. The heterogeneous ceramics are engineered by using periodic structures made up of subwavelength unit cells filled with zirconia ceramic and air. Ceramic stereolithography (CSLA) allows the 3D printing of a one-piece ceramic block mixing isotropic and anisotropic dielectric regions. In order to demonstrate the possibility of exploiting such 3D-printed ceramics, a singly fed dual-band circularly polarised DRA is presented. To achieve circular polarisation at both bands, the relative permittivity of the dielectric resonator is locally controlled by introducing anisotropic dielectric regions. The 3D-printed DRA is finally measured, and its results agree well with the simulations.

A dual-band liquid cylindrical dielectric resonator antenna with pattern diversity at two different frequency bands is proposed using the lower order and higher order modes of the HEM and TM modes namely HEM_11δ, HEM_12δ+1, HEM_31δ+1, HEM_13δ, TM_01δ, and TM_02δ. The proposed antenna is designed to cover the GPS L2 band and the lower Wi-Fi band at 1.227 and 2.4 GHz frequencies, respectively. The HEM modes which constitute the primary radiating modes achieved around 20.84% and 19.35% impedance bandwidth at lower and higher bands, respectively. In the later stage, beam-steering is performed, whereby the realised broadside HEM modes at both lower and higher bands were passively steered with simple physical re-orientation of the antenna structure. For this, the liquid's natural fluidic property of adhering to gravity is taken as an advantage which makes the proposed antenna adaptively steer its radiation pattern always towards the sky, irrespective of the tilt angle of the antenna. This concept of passively steering two modes at two different frequency bands without the use of any mechanical, electrical, or other associated components is presented for the first time.

In order to employ periodic corrugated microstrip lines for reducing or suppressing electromagnetic interference in high-speed or high-frequency circuits, a precise method is necessary to calculate and measure the characteristic impedance of periodic microstrip lines. The equation for characteristic impedance (depending on frequency) of lossless periodic microstrip lines was obtained based on the transfer matrix method. A time domain pulse was used to measure the instantaneous impedance of conventional microstrip lines, and when the instantaneous impedance does not change with distance, it can be identified as the characteristic impedance of microstrip lines. However, when the time-domain pulses are employed to measure the instantaneous impedance of periodic microstrip lines, rapid oscillations occur with distance. Therefore, a standard for spacing between adjacent grooves in the microstrip line can be suggested by analysing the interaction between the time-domain pulses and the microstrip line grooves. Once such a standard is satisfied, many grooves etched along the microstrip line would no longer be distinguished by the time-domain pulses. Such a principle and method can be used to determine the instantaneous impedance for the microstrip lines that have periodic grooves. On the other hand, when several periodic structures with different lattice constants coexist on a microstrip line, they can also be distinguished via the instantaneous impedance. A time domain reflectometer was used for measuring the instantaneous impedance of periodic microstrip lines, and the measured results are in agreement with the theoretical analysis.

A two-layered wideband single-fed circularly polarised (CP) antenna is presented by the authors. A single-fed corner-truncated square patch with four identical rectangular matching branches acts as a bottom-driven patch to generate CP radiation. To broaden the 3-dB axial ratio (AR) bandwidth, a similar patch with a larger size is loaded atop the driven patch as a parasitic patch. The measured results show that the proposed CP antenna has a 17.9% impedance bandwidth from 2.13 to 2.55 GHz and an 11% 3-dB AR bandwidth from 2.15 to 2.4 GHz, respectively. The measured total gain is 7.1 dBic. The results indicate that the proposed antenna is a good candidate for Wireless Local Area Network band applications.

A new multi-band frequency response controlling method using groove loading technique on the narrow wall of an open-ended waveguide is proposed by the authors. The feature of this scheme is a larger stopband spacing that is independent of the position of the loading structure. A tri-band antenna is designed as an example to verify the effectiveness of the idea. Two notches are introduced, and the bandwidths, as well as stopband spacings, can be adjusted by independent parameters. The tri-band prototype can be fabricated using 3D printing technology or machining technology. Reasonable agreement between the measured and simulated results of impedance and radiation characteristics have been achieved.

A miniaturised integrated passive device (IPD) balun design with low insertion loss and balanced amplitude and phase is proposed for Wi-Fi/Bluetooth applications. In this design, a novel topology based on the modified T-type filter structure is introduced to offset the parasitic and coupling effects that cause poor balance in IPD design. The proposed balun design is fabricated on a GaAs substrate. The measured insertion loss is lower than 0.9 dB and the measured return loss is >16 dB in the frequency range of 2.2–2.9 GHz. The measured results of amplitude and phase show rather minor imbalances, which are lower than ±0.67 dB and ±1.8° respectively. The fabricated device size is 0.9 mm × 0.6 mm only.

In the design of antenna arrays which require fast and robust flat-top beam synthesis, computationally efficient methods are preferred. This feature is usually met by analytical techniques or simple optimisation procedures. On the other hand, in the flat-top beam synthesis, a common requirement is the ability to control beamwidth or sidelobe level. However, this can result in a high dynamic range ratio (DRR) of array's excitation coefficients. In this paper, a straightforward method for the design of symmetrical flat-top arrays with controllable sidelobe level or DRR is proposed. The method is based on quadratic and cubic transforms of Gaussian excitations. In addition, the method utilises zero coefficients whose positions are used to control the DRR, including the ability to achieve its minimum. Compared to other flat-top arrays with analytically shaped beams, the proposed arrays have lower DRRs for the same sidelobe level.

A 0.45-V low-power wideband image-rejection low-noise amplifier (LNA) using Taiwan Semiconductor Manufacturing Company (TSMC) 0.18-μm CMOS process has been proposed. The supply voltage, power consumption and chip area of the proposed LNA can be reduced using forward body biasing, folded cascode topology and a feedback capacitor. Moreover, a wideband gain-enhancement-and-image-rejection (WGEIR) circuit including a variable resonant LC tank and a common-gate amplifier has been developed. The inductance of the variable resonant LC tank can enlarge the gain of the proposed LNA. The capacitance of the variable resonant LC tank can achieve the image rejection. Using the WGEIR circuit, gain enhancement and wideband image rejection can be achieved simultaneously. The variable inductors and capacitors are developed for suppressing wideband image signals and good image rejection ratio (IRR). The combination of the variable inductors and capacitors can achieve eight image-reject frequencies under three control voltages. The proposed LNA shows the measured results including a 10-dB power gain, a 3-dB noise figure (NF) and a −11-dBm input third-order intercept point (IIP₃) at 2.4 GHz, respectively. The measured IRR ranges from 18 to 23 dBc around 3.6–4.5 GHz, which is 900-MHz image-reject bandwidth. The measured proposed LNA using the mentioned techniques consumes 0.8-mW power.

A 3D metal-only waveguide-based phoenix cell for reflectarray is presented. The proposed cell consists of two concentric square waveguides and a metallic block in the centre, which offers two operation modes. The first mode uses its cross section to tune reflection phase while the second mode varies the heights of two waveguides to manipulate reflection phase. The principle of the two different modes is analysed in detail. A metal-only reflectarray antenna at 20 GHz is designed based on the first mode of the phoenix cell. It is fabricated using selective laser melting 3D printing technology. A good agreement between simulations and measurements is achieved. The measured gain at 19.75 GHz is 30.25 dBi with an aperture efficiency of 51.17% respectively. Also, the measured 1-dB gain bandwidth is 15% (19–22 GHz). A dual band metal-only reflectarray operating at 20 and 25 GHz is designed based on the second mode of the phoenix cell. The two metal-only reflectarray antennas fully demonstrate the capabilities of the proposed 3D metal-only phoenix cell.

The inconsistent polarised directions and the radiation pattern transformation of the elements need to be considered in the analysis and simulation of large circularly polarised conformal arrays. Without relying on full-wave simulations of the full array, a polarisation phase compensation and a pattern transformation method are proposed to solve these problems. When the position and orientation of the conformal array elements are known, the polarisation phase compensation method can provide a solution to keep the initial phase direction of each circularly polarised antenna element consistent in the global coordinate system. Then, a pattern transformation method is proposed to obtain the radiation pattern of each antenna in the global coordinate system. In this method, the local antenna polarised radiation patterns with amplitude and phase information are expressed in the global coordinate system through the mutual conversion relationship between the local and global coordinate systems. These methods can provide a guidance for array design and performance simulation, especially theoretically applicable to the arbitrary conformal arrays.