Improved coupling for aperture coupled microstrip antennas

Aperture shape and size are the crucial parameters for the aperture coupled microstrip antennas (ACMSA). A systematic comparision of various aperture shapes for the aperture coupled rectangular microstrip antenna has been carried out. An optimum “hour glass”-shaped aperture configuration has been proposed for maximum coupling     

Improved coupling for aperture coupled microstrip antennas

An aperture shape that gives significantly improved coupling for an aperture coupled microstrip antenna is described. This 'dogbone' aperture consists of the usual rectangular slot augmented with loading slots at each end. Measured data show an increase of more than three for the resonant input impedance of an antenna using the dogbone-shaped aperture, as compared with the input impedance of the same antenna with a rectangular slot of the same overall length. The field distributions of both slots are also measured, and compared.<>     

Improved analysis method for broadband rectangular microstrip antenna geometry using E-plane gap coupling

An analysis method for the broadband rectangular microstrip antenna geometry using E-plane gap coupling is considered. The return loss of the designed broadband antenna is computed theoretically and compared with experimental results for illustrating the usefulness of this method.<>     

Characteristics of aperture coupled microstrip antennas withvarious radiating patches and coupling apertures

A full wave moment method is applied to the analysis of aperture coupled microstrip antennas, in which all components of the electric and equivalent magnetic surface currents are considered. The electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. The effects of the coupling aperture shape and size on the input impedance and radiation performance are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation     

Flat lens antenna concept using aperture coupled microstrip patches

A planar lens antenna based on aperture coupled microstrip patch elements with stripline delay lines is described. Features of this design are discussed, and results for transmission coefficient magnitude against frequency are presented. The background for the development of this lens configuration is discussed in terms of a natural progression from frequency selective surfaces, and the inadequacies of simpler geometries are explained     

Improved theory for microstrip antennas

An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory that is simple and inexpensive to apply. This is achieved by lumping all antenna losses into an effective dielectric loss tangent and then analysing the microstrip antenna as a lossy cavity. It is found that the resulting expression for impedance of the microstrip antenna is in good agreement with measured results for all modes and feed locations.     

Compact gap coupled resonator using negative refractive index microstrip line

A compact gap coupled resonator implemented with a negative refractive index microstrip line section is presented. The resonator offers harmonic suppression and an 86% size reduction compared to a conventional gap coupled resonator operating at 1.2 GHz. The resonator should have many applications in the design of filters and oscillators.     

CPW feed circularly polarised microstrip antenna using asymmetric coupling slot

Design of a coplanar waveguide (CPW) feed square microstrip antenna with circular polarisation (CP) radiation is described. This CP design is achieved by using an asymmetric inductively coupling slot in the ground plane of the CPW feed line. Results show that the proposed antenna can have a CP bandwidth of 2.4%, whereas a simple inclined coupling slot case has 1.6% CP bandwidth at a fixed square patch size. Typical experimental results are presented and discussed     

Tri-band microstrip bandpass filter using input/output cross coupling

A compact tri-band bandpass filter using input/output cross coupling is proposed. Three passbands can be adjusted by changing the characteristic impedance of the T-shaped structure with a shorted stub. The three passbands are designed to operate at 1.85, 3.5 and 5.2 GHz based on the T-shaped structure. Four transmission zeros are used to realise high selectivity for the passbands. Good agreement can be observed between the measured and simulated results.     

Planar microstrip UWB bandpass filter using U-shaped slot coupling structure

A compact planar microstrip UWB bandpass filter is proposed. It is realised by cascading a lowpass filter and a highpass filter. A transmission line with U-shaped slots coupled with two DGS units on the back of the circuit board has the characteristic of highpass, while a periodic uniform DGS array has the characteristic of lowpass. Combining these two structures, a new UWB bandpass filter (BPF) is fabricated and measured. Measured results show that the proposed BPF has wide bandwidth from 3.0 to 10.9 GHz, all the measured return loss less than 13 dB in the passband. The BPF achieves a wide stopband with 18 dB attenuation up to 18.0 GHz     

Series expansions for the mutual coupling in microstrip patcharrays

A dominant-mode mutual coupling theory is developed for an array of microstrip patches. One of the key features of the formulation is that only values for isolated self- and mutual impedance are needed in the formulation, making the method suitable for either a cavity model or spectral-domain analysis, or compatible with experimental measurements. The formulation is equivalent with D.M. Pozar's (1982) moment-method formulation. A series expansion of the solution is derived, allowing for approximate formulas accurate to any specified order. These formulas do not require matrix inversion. Formulas up to third order require less computation time that the exact solution, for single elements of the impedance, admittance, and scattering matrices. These expansions are computationally efficient for large sparse arrays     

Backward directional coupler for weak coupling of double-sided microstrip lines using longitudinal double-slots

A backward directional coupler for double-sided microstrip lines is presented. Aligned microstrip lines are coupled via two parallel slots in the common ground plane. This design works well for weak coupling smaller than 20 dB and has some advantages over the single-slot coupler. Geometrical dimensions of the proposed coupler design are presented for coupling values of 20, 25 and 30 dB, together with measurements for a 30 dB coupler.     

Analysis and design of periodic structures for microstrip lines by using the coupled mode theory

In this work, the coupled mode theory is formulated to analyze distributed periodic structures for microstrip lines. After it, several reasonable approximations are introduced giving rise to analytical solutions for the problem. The obtained results, both numerical and analytical, are checked against measurements showing very good agreement. The proposed method is very attractive for the study of these devices since it avoids the time-consuming full-wave electromagnetic simulations customarily employed and provides analytical solutions that are very useful for analysis and synthesis purposes.     

A distributed millimeter-wave isolator using nonreciprocal coupling structure

A new distributed millimeter-wave isolator is proposed. This device employs a nonreciprocal coupling mechanism between a dielectric slab and a conductor-backed ferrite slab. Transverse resonance and mode matching techniques are used for analysis. A numerically optimized structure at 200 GHz will be discussed and experimental results at 35 GHz will be presented.     

High mutual coupling reduction between microstrip patch antennas using novel structure

In this paper, a novel parasitic configuration to reduce the mutual coupling between two adjacent microstrip patch antennas is presented. It is shown that mutual coupling between the antenna elements can be reduced significantly by two simple slots structure on the ground plane and several shorted simple conducting strips between patch antennas. The structure has been constructed and tested. Both simulated and measured results are presented. The results are shown that more than 7 dB reduction within operational frequency bandwidth with the maximum 41 dB mutual coupling at center frequency can be achieved. The measurement results prove the high efficiency of this configuration in multi antenna systems.     

A planar-lumped model for coupled microstrip lines anddiscontinuities

A convenient model for analyzing coupled microstrip line discontinuities is presented. A planar-lumped model similar to the planar waveguide model for single microstrip lines is developed for coupled microstrip lines. Fields underneath the two strips and those fringing at the outer edge are modeled by two equivalent planar waveguides. Electric and magnetic field coupling in the gap region is modeled by a lumped network. The lumped network parameters are evaluated such that [C] and [L] matrices for the model are identical with those for coupled lines. The model is verified by comparing coupler characteristics with those obtained by the conventional coupled line analysis. Just as the planar model of a single microstrip has been used for characterizing microstrip discontinuities, the planar-lumped model developed is used for coupled line discontinuities. Examples given include coupled microstrip sections with chamfered bends located at right angles to single microstrip lines, for which the results are in good agreement with experimental values     

耦合微带线设计的一种实用方法

本文根据耦合微带线的某些特性,提出了耦合微带线设计的一种实用方法.     

Improved analysis method for multiport microstrip annular-ringpower-dividers

An improved analysis method for multiport microstrip annular-ring power-dividers is presented which is essentially based on the planar circuit theory assuming magnetic walls at conductor edges. The generalized impedance matrix of the power-dividers is evaluated using two approaches, the Green's function approach and the circular harmonic function approach. The concept of effective dimensions is adopted for taking into account fringing fields to compensate the planar circuit theory. The properties of the power-dividers can be controlled by varying the width of the conductor ring in contrast to those of disk structures. Characteristics of a four-port power-divider in the form of microstrip lines calculated with the present approach are in good agreement with experimental data     

Nonuniformly coupled microstrip transversal filters for analog signal processing

The Fourier transform relationship between frequency response and impedance profile for single nonuniform transmission lines is used to derive the time-domain step response of single and coupled nonuniform lines. The expression for the step response of a characteristically terminated nonuniformly coupled transmission line structure is shown to correspond to the characteristic impedance profile. By using this relationship, any arbitrary step response can be realizing by utilizing nonuniformly coupled strip or microstrip lines for possible applications as waveform-shaping networks and chirp filters. A numerical procedure to compute the step response of the nonuniform coupled line four-port is also formulated in terms of frequency-domain parameters of an equivalent cascaded uniform coupled line model with a large number of sections. Sinusoidal and chirp responses are presented as examples that are readily implemented using coupling microstrip structures. The step response of an experimental nonuniformly coupled microstrip structure is presented to validate the theoretical results.<>     

Transmission line model for mutual coupling between microstrip antennas

Although more rigorous treatments have been developed for mutual coupling between microstrip antennas, the purpose of this transmission line model is to provide a numerically efficient substitute for them. Therefore, two approximations have been introduced: first, the surface waves have been neglected and second, each rectangular resonator is replaced by two equivalent radiating slots. In most practical cases the approximations are acceptable; this has been proved while comparing the transmission line model with other published results. It is obvious that the efficieney of the transmission model and can be used to include mutual coupling in practical analysis or synthesis routines for arrays of rectangular microstrip antennas.