CAD models for suspended and inverted microstrip

The accuracies of CAD models for suspended and inverted microstrip are examined, and new models are proposed. The models are compared over the range of 0.1⩽w/h⩽10 and for ϵ_r values of 3.78 and 12.9. Of the three models examined, the Tomar and Bhartia (T&B) model is shown to be the most accurate. For ϵ_r=12.9 (the worst case), the T&B model shows maximum and average errors of 2.94 and 1.28% respectively over its valid range. New CAD models are presented which demonstrate significantly improved accuracy and range of convergence. For suspended and inverted microstrip, the new models demonstrate worst case errors of 0.65 and 1.02%, respectively, and average errors of 0.23 and 0.27%, respectively. Further, the new models are valid for the full 0.1⩽w/h⩽10 range, and unlike the other models, converge for the limiting cases of either complete substrate filling or a zero thickness substrate     

Millimeter-wave Fermi tapered slot antennas on micromachinedsilicon substrates

This paper presents 90 GHz Fermi-type tapered slot antennas (TSA) on a micromachined 100 μm thick silicon substrate (ϵ_r=11.7) and for comparison purposes, 90 GHz Fermi-type TSA on 150 μm thick quartz substrate (ϵ_r=3.78). A 100 μm thick wafer is chosen because it is compatible with 90-100 GHz low-noise amplifier circuits on GaAs-InP substrates. The effective thickness of the substrate was reduced by selectively micromachining holes in the silicon wafer using deep reactive ion etching (deep RIE). The radiation patterns of the micromachined antennas were significantly better than the nonmicromachined version and had similar radiation patterns to the quartz design. The etched hole diameter was changed from 300 to 750 μm with minor effect on the radiation patterns. This shows that the predominant reason for the improved patterns lies in the reduced effective dielectric constant and not in substrate-mode suppression effects. This type of antenna is well suited for millimeter-wave imaging arrays     

Dielectric constant measurements of finite-size sheet at microwavefrequencies by pseudo-Brewster's angle method

Dielectric constant (ϵ_r) measurements for finite-size dielectric sheets (DS's) at centimeter wavelengths are presented using the method-of-measuring pseudo-Brewster's angle. This method is applied to measure ϵ_r of sheets of Plexiglas and window glass. In the experiment, two horn antennas are used to transmit and receive p-polarized waves. A dielectric sheet is located between the two antennas and rotated 180°, which produces two peaks in the transmittance curves. For a more accurate measurement of Brewster's angle, an optical spectrometer with 1-min accuracy is also used. By this method, ϵ_r of Plexiglas and window glass are obtained to be 2.55±0.13 and 5.35±0.1, respectively. This method measures |ϵ_r|, but the measurement is easy and nondestructive for DS's. Finally, an accurate method of error calculation is used to calculate the error in the measured values of ϵ_r     

Pulse dispersion distortion in open and shielded microstrips usingthe spectral-domain method

The spectral-domain method is used to compute the effective dielectric constant [ϵ_r/_eff(f)] of open and shielded microstrip lines to analyze the dispersion distortion of short electrical pulses. Precise expressions for the longitudinal and transverse current distributions allow a high level of accuracy for ϵ_r/_eff(f). It is determined that computation time can be minimized for the open microstrip calculations by using the shielded microstrip formulation provided large dimensions for the conducting walls are assumed     

Neural network-based CAD model for the design of square-patchantennas

An artificial neural network (ANN) has been developed and tested for square-patch antenna design. It transforms the data containing the dielectric constant (ϵ_r), thickness of the substrate (h), and antenna's dominant-mode resonant frequency (f_r) to the patch length (l)     

New empirical unified dispersion model for shielded-, suspended-,and composite-substrate microstrip line for microwave and mm-waveapplications

By introducing the concept of “virtual relative permittivity,” this paper reports several closed-form dispersion models for a multilayered shielded/unshielded microstrip line over 1<ϵ_r⩽20, 0.1⩽(w/h)⩽10, (h₃/h)⩾2 in the frequency range up to 4 GHz.cm. The maximum deviation of the one model against the results of the spectral-domain analysis (SDA) is limited to 3%, while for the other three models, the maximum deviation is <2% and the root-mean-square (rms) deviation is <0.8%. This paper also reports improvement in the closed-form model of March for the determination of ϵ_eff(O) of the shielded microstrip line     

ALPSS: a millimetre-wave aperture-coupled patch antenna on asubstrate lens

The feasibility of millimetre-wave (MM-wave) aperture-coupled patch antennas, printed at the back surface of substrate-lenses is demonstrated and the corresponding radiation characteristics are investigated. A specific realisation of such an air-lens-patch-slot-strip (ALPSS) antenna on a low-permittivity ϵ _r=4.0 extended hemispherical lens substrate is theoretically and experimentally characterised at 70 GHz. It is demonstrated that the ALPSS antenna exhibits clean, axially symmetric patterns of low cross-polarisation (26 dB), a directivity of 30.4 dB and the 3 dB pattern full-beamwidth remains within 6°-5° between 60-80 GHz. In addition, a very-high front-to-back (F/B) ratio, of the order of 50 dB is measured at 70 GHz, despite the absence of a backing ground-plane. The ALPSS antenna is well suited for low-cost broadband point-to-point communications and collision avoidance applications     

Millimeter-wave tapered-slot antennas on synthesized lowpermittivity substrates

This paper presents 30-GHz linear-tapered slot antennas (LTSA) and 94-GHz constant-width slot antennas (CSWA) on synthesized low dielectric constant substrates (ϵ_r=2.2). The performance of tapered-slot antennas (TSA) is sensitive to the effective thickness of the substrate. We have reduced the effective thickness by selectively machining holes in the dielectric substrate. The machined substrate antenna radiation patterns were significantly improved independent of the machined hole size or lattice as long as the quasi-static effective thickness remained the same, even if the hole/lattice geometry is comparable to a wavelength. The method was applied at 94 GHz on a CSWA with excellent radiation pattern improvement, making it suitable for f/1.6 imaging array applications     

S-parameter broad-band measurements on-microstrip and fastextraction of the substrate intrinsic properties

A broad-band technique for determining the electromagnetic properties of isotropic film-shaped materials, which uses a microstrip line, is presented. Complex permittivity and permeability are computed from analytical equations and S-parameter measurements of microstrip cells propagating the dominant mode. Measured ϵ_r and μ_r data for several materials are presented between 0.05 GHz and 40 GHz. This technique shows a good agreement between measured and predicted data     

Analysis of dispersion and series gap discontinuity in shieldedsuspended striplines with substrate mounting grooves

Dispersion and series gap discontinuity of shielded suspended striplines (SSLs) on Duroid substrate (ϵ_r=2.22) are analyzed using the finite-difference time-domain method (FD-TD). Numerical accuracy of better than 0.15% is achieved when the FD-TD is used to calculate the effective dielectric constant (ϵ_reff ) of an air-filled rectangular coaxial transmission line. Data obtained for the frequency-dependent ϵ_reff of uniform SSLs and both scattering and equivalent circuit parameters of various series gap discontinuities are presented. In general, the presence of sidewall mounting grooves causes a nearly frequency-independent small reduction in ϵ_reff. On the other hand, proximity effects of the housing are found to be more important. For the gap discontinuity, coupling across the gap is stronger for wider strips and/or narrower gap width. Irregular transmission behavior is also found when the strip is wide enough to interact strongly with the sidewalls     

Low profile equilateral-triangular dielectric resonator antenna ofvery high permittivity

An aperture-coupled equilateral-triangular dielectric resonator antenna (DRA) of very high permittivity (ϵ_r=82) is investigated experimentally. The triangular DRA is more compact in size than rectangular and circular disk DRAs operating at the same frequency. The impedance matching, radiation patterns and antenna gain of the triangular DRA are presented     

Slot excitation of the dielectric disk radiator

Dielectric disk radiators which are excited by a narrow slot in the ground plane of a microstrip line are investigated. The resonance frequencies of the dielectric disk for the HEM₁₁ mode are computed numerically in the complex frequency plane. From the later results, the actual resonance frequency and the Q-factor are obtained. The dielectric disk is made of a high dielectric constant ceramic material with ϵ_r=22. The radiation patterns and reflection coefficients are measured and presented for several slot lengths and dielectric disk dimensions. The radiation patterns are also computed assuming a magnetic current element, which models the slot and excites the HEM₁₁ mode. Good agreement is obtained between the computed and measured results. The results presented here also demonstrate the viability of this type of antenna, which has high dielectric constants an efficient radiator provided the proper mode is excited     

Theoretical and experimental studies of the resonant frequencies ofthe equilateral triangular microstrip antenna

A critical study of the resonant frequency of the equilateral triangular patch antenna is presented. The contributions include: (1) comparison of the previous experimental data of J. S. Dahele and K. F. Lee (see ibid., vol.AP-35, no.1, p.100-1, 1987) with moment method results; (2) new measurements and moment method results for ϵ_r=10.5 and comparison with Gang's hypothesis; (3) verification of the relationship among the various modes by measurements and by the moment method; and (4) a curve fitting formula yielding the resonant frequency of the lowest mode, which is within 1% of the value obtained from moment method analysis     

Uniaxially anisotropic substrate effects on resonance ofrectangular microstrip patch antenna

The influence of uniaxial anisotropy in the substrate on the resonant frequency of a rectangular microstrip patch is investigated. Computations shown that changes in ϵ_z can drastically shift the resonant frequency; moreover, a small shift is observed when ϵ_x changes. Other result also indicate that the effect of ϵ_x tends to be insignificant for low substrate thicknesses     

Performance of an anisotropic artificial absorber for truncatingfinite-element meshes

A new artificial material absorber for truncating finite element meshes is investigated. The interface of the absorber is made reflectionless by choosing ϵ_r and μ₄ to be complex diagonal tensors. With some loss, a metal backed thin absorber layer is then sufficient for terminating the mesh. This scheme is simpler to implement than conventional absorbing boundary conditions and offers the potential for higher accuracy. We investigate the effectiveness of this anisotropic absorber on the basis of results obtained for problems in propagation (waveguide and microstrip line) and scattering     

Single-feed circularly polarized microstrip ring antenna and arrays

An analysis is presented for a microstrip-feed proximity-coupled ring antenna and a four-element array. Interactions between the embedded microstrip feed and the radiating element(s) are rigorously included. Results demonstrate that circular polarization of both senses can be achieved with a ring antenna with proper design of two inner stubs located at angles of ±45° with respect to the feedline. Theory and experiment demonstrate an axial ratio 3-dB bandwidth of 1% and the voltage standing wave ratio (VSWR) <2 bandwidth of 6.1%. The axial ratio bandwidth is typical for a microstrip antenna with perturbations, while the VSWR bandwidth is larger than for the circular or rectangular patch with perturbations. A mutual coupling study between two elements shows that the axial ratio is less than 2 dB for interelement spacing greater than 0.55λ_eff, while the VSWR <2 for all spacings considered. A comparison between theory and experiment is provided for a 2×2 element array. The benefits of sequentially rotating the antenna elements in an array environment are presented. The axial ratio and VSWR bandwidths are both increased to 6.1% and 18% for a four-element array. A single-element antenna with two orthogonal feeds to provide both senses of polarization is demonstrated. The ring antenna is small (D/λ₀=0.325), the substrate thickness is thin (H/λ₀~0.035), and the microstrip feed produces a completely planar antenna system, which is compatible with microwave and millimeter integrated circuits (MICs), and monolithic microwave integrated circuits (MMICs)     

Theoretical and experimental investigations on rectangulardielectric resonator antennas

Theoretical and experimental investigations on rectangular dielectric resonator antennas having a value of ϵ_r, in the range of 10 to 100 are reported. The resonant frequencies and radiation Q-factors of the lowest order “magnetic-dipole” modes are derived on the basis of a first-order theory. The accuracy of the model in predicting the resonant frequency and radiation Q-factor is verified by comparison with results of a rigorous theory and experiments. Various feeds for the antennas such as probe, microstrip slot, and microstrip line are described. Measured radiation patterns are shown and the effect of feed and mode degeneracy on the cross-polarisation levels is discussed     

Bow-tie antennas on high dielectric substrates for MMIC and OEICapplications at millimetre-wave frequencies

A two-element bow-tie dipole antenna and a single-element bow-tie slot antenna fabricated on a high dielectric constant (ε_r=10.2) substrate are introduced for applications at millimetre-wave frequencies. The former antenna provides 2 GHz bandwidth at 35 GHz and the latter 1.3 GHz at 32.7 GHz. With a broadband match, these antennas would yield significantly higher bandwidths     

A study on wideband gap-coupled microstrip antenna arrays

A method for increasing the bandwidth of microstrip antenna arrays by using gap-coupled patches is described. The input impedance properties of gap-coupled patches are analyzed by the use of the spectral dyadic Green's function for a grounded dielectric slab and the moment method. The dependence of different parameters such as s, L and ϵr on the impedance characteristics is investigated. In considering the effect of feed network, the impedance bandwidth for a VSWR<2 of two-element gap-coupled patch array is as large as 2.5 times that of an ordinary array. The radiation patterns over this bandwidth are measured and discussed. All the microstrip antenna arrays are fabricated on a substrate with ϵr=2.86, h=1.5 mm. A comparison of theoretical and experimental results for both input impedance and radiation patterns are given     

Analysis and measurements for improved crank-line antennas

This paper describes the radiation characteristics of crank-line antennas radiating a circularly polarized wave. First, the radiation efficiency versus substrate permittivity is evaluated. Second, a 12-cell crank-line antenna of substrate permittivity ε_r=1 and antenna height B=λ_11.85 is investigated as a reference antenna, where λ_11.85 is the wavelength at a frequency of 11.85 GHz. It is found that the main beam direction of the reference antenna varies 7° over a frequency range of approximately 6%, with an axial ratio of less than 3 dB and a gain of approximately 21 dB. Third, attention is paid to the gain behavior versus the antenna height. A way to increase the gain by modifying the antenna height is proposed. An increase of 1.5 dB from the gain of the reference antenna is demonstrated. Finally, the axial ratio, gain, and decoupling factor for crank-line antenna arrays are presented and discussed