Zhi Ning Chen

Circularly polarized rectangularly bent slot antennas backed by a rectangular cavity

Rectangularly bent slot antennas backed by a rectangular cavity for circular polarization are proposed. Characteristics of three types of cavity-backed rectangularly bent slot antennas for circular polarization-the single square loop slot, the two-element square loop slot, and the two-arm square spiral slot antenna-are analyzed numerically. The generalized network formulation based on the equivalence principle is given in terms of the method of moments. The magnetic currents on the thin rectangularly bent slots in the presence of the backing cavity are obtained and used to calculate the input impedance, radiation pattern, and axial ratio. Experimental results on the input impedance, radiation pattern, and axial ratio are in good agreement with calculated data.

A new inverted F antenna with a ring dielectric resonator

A new antenna combining the use of a ring dielectric resonator (DR) and an inverted F antenna (IFA) is proposed and investigated experimentally. In this application, the DR not only fills the role of a dielectric coating, but also serves the function of a radiator. The measurements of input impedance, return loss, and radiation pattern for both the IFA with the DR (IFA-DR) and the wire IFA (WIFA) are conducted at the S band. The measured data demonstrate that the IFA-DR operates in multiple resonance modes unlike a WIFA. Compared with the WIFA, the one proposed here incorporating a ring DR and an IFA is more attractive in having a smaller size and a larger impedance bandwidth.

A novel top-sleeve monopole in two parallel plates

A novel top-sleeve monopole antenna in two parallel plates is presented, which is developed to enhance its impedance bandwidth in a significant manner. By the introduction of a sleeve into a common SMA connector with a thin dielectric jacket, a noticeably broad bandwidth on the order of up to 70% is achieved for the proposed antenna. An eigenmode expansion technique is used to simulate the impedance characteristics of the top-sleeve monopole. The effects of geometric parameters of the structure, such as the sleeve length, monopole length, and the plate spacing on its impedance characteristics, are investigated. On the basis of our theoretical studies, an experimental prototype with bandwidth of 50% is designed and its characteristics are confirmed experimentally.

Broadband and Compact Coupled Coplanar Stripline Filters With Impedance Steps

Novel broadband and compact stepped-impedance coupled coplanar stripline bandpass filters are presented, analyzed theoretically, and demonstrated experimentally. These filters are based on impedance step, capacitive gap, broadside coupling, and inductive shorted strip discontinuities, which are modeled in terms of impedance (K-) and admittance (J-) inverters. Broadside coupled coplanar stripline is analyzed for the first time by the even-/odd-mode decomposition technique using the finite-element method. The broadband and compact nature of the filters is explained from the discontinuities and the coupled line structures. Specifically, cross coupling is used to enhance the selectivity of both the low and high cutoffs, leading to triplet and quadruplet cross-coupled broadband filters with finite-frequency transmission zeros. Due to their broad bandwidth, compact size, differential configuration, and low fabrication cost, the proposed filters represent excellent solutions for codesigned RF and microwave systems such as ultra-wideband transceivers.

A broad-band sleeve monopole integrated into parallel-plate waveguide

In this paper, a sleeve monopole is proposed and studied theoretically and experimentally. It consists of a resonant loading and a conventional sleeve monopole vertically integrated in a parallel-plate waveguide. A modal expansion technique is used to model the induced currents over the monopole surface, and fields in the region of interest are characterized by cylindrical harmonic functions. A Fourier least-square integration is applied to find the expansion coefficients by the boundary and continuity conditions. A 5.8-GHz industrial-, scientific-, and medical-band (ISM-band) example is selected for the studies. It is found that the new monopole exhibits a large bandwidth exceeding 37% for -10-dB return loss. Calculated results are validated by the measurements.

Broadband and Compact Double Stepped-Impedance CPS Filters with Coupled-Resonance Enhanced Selectivity

Three broadband and compact double stepped-impedance coplanar stripline (CPS) filters are proposed and studied. These filters are based on cross-coupled resonances within a high-impedance transmission line section sandwiched between two lower-impedance sections. The initial filter is composed of two high-impedance resonators coupled by a capacitor. In a second design, the upper cutoff selectivity of this filter is improved by an additional attenuation pole (triplet cross-coupled system), which is provided by strips coupled to the high-impedance line. Finally, in the third design the selectivity of both the upper and lower cutoffs is enhanced by the introduction of a shorting strip inductance (quadruplet cross-coupled system). The proposed filters are significantly more compact than typical conventional bandpass filters. The designed filters exhibit a fractional bandwidth of 63%, 70% and 83%, respectively, and a pass-band insertion loss of less than 1 dB.

A broadband monopole in a parallel plate waveguide

A new kind of top-sleeve is designed to greatly enhance the bandwidth of a monopole operating in a parallel plate waveguide. A modal expansion technique is extended to numerically evaluate the characteristics of the monopole with a top-sleeve. Based on the numerical simulations, a prototype of a monopole with a top-sleeve is made for 5.8 GHz applications. The relevant measurements validate the numerical simulations and engineering design. Compared to traditional structures, this modified monopole has a merit of a very broad impedance bandwidth with a good match and still maintains the feature of simple structure, low cost, and pure polarization.

A novel sleeve monopole with broad bandwidth

Owing to simplicity, polarization purity, power capacity, good match, and low cost, the use of a coaxially fed monopole in a parallel plate waveguide is an attractive option as an adapter or a feed and has been extensively investigated for years. However, a simple coaxially fed linear monopole particularly offers a narrow impedance bandwidth. So some modified monopoles have been often applied to wireless communication antennas in the past decades. The input impedance performance has been significantly improved by means of the various loading techniques, such as dielectric coatings, attached dielectric resonator structures, and disc-ended or top-hat structures. Previously, an alternative is a leaky-mode aperture-coupled dielectric resonator, which has been successfully used as a feed of a class of omnidirectional antennas suitable for wireless communication systems. In this article, a novel sleeve monopole type is proposed to further improve the impedance performance of a monopole. This structure simply consists of a second sleeve and a sleeve monopole vertically put between a parallel plate waveguide. Compared to traditional structures used in a parallel plate waveguide, this modified sleeve monopole has the merit of noticeably broad impedance bandwidth and still maintains the feature of simple structure, low cost, and pure polarization. Because of simple manufacture, broad bandwidth, and good match, this novel structure has shown a promising potential application in various microwave applications and wireless/satellite communications.

Characterisation of probe-fed dielectric resonator between parallel grounded plates

Many kinds of dielectric resonator (DR) antennas have been investigated theoretically and experimentally in the literature. Also, as a resonator, a cylindrical homogeneous dielectric short-circuited at both ends by parallel grounded planes has been well-discussed. However, the consideration that a probe-fed dielectric resonator is short-circuited at its both ends by two parallel conducting plates, has not been conducted. The characterisation of this structure is investigated experimentally and theoretically. The cylindrical mode matching method (MMM) is applied to find the input impedance of this structure. The trapped and leaky modes of the resonator are considered. The study shows that as expected, the consideration of the effect of a probe length on the characteristics of a resonator is very important and necessary. The effect of DR dielectric constant and DR radius/height ratio on the input impedance are studied as well.

Electromagnetic scattering from the probe-fed hemispherical dielectric resonator antenna

In this paper, we study the scattering problem of the probe-fed hemispherical dielectric resonator (DR) antenna. The mode matching method (MMM) as well as the method of moments (MoM) are used in this paper. The former is used to calculate the DR antennas scattered field whereas the latter is used to determine the induced current flowing on the probes surface, The field radiated by the current in presence of the grounded DR is found using the Greens function technique. Finally, the fields obtained above are added together to give the total scattered field from the DR antenna. The radar cross section (RCS) calculated using this method converges to the Mie results as the probe length L/spl rarr/0. Moreover, when the dielectric constant of the DR approaches unity, the calculated radar cross-sections (RCSs) agree very well with that of a wire scatterer available in the literature. In this paper, the effects of the probes length and the probes impedance loading on the RCS are studied.