CPW-fed stacked microstrip antennas

This paper presents a systematic parameter study of aperture-coupled stacked patch antennas fed by coplanar waveguide. These antennas are to be used at millimeter-wave frequencies in the 30-GHz range. The influence of the most important design parameters, such as patch dimensions, aperture dimensions, and substrate thicknesses, was studied extensively. It has been found that these antennas can easily be impedance-matched by tuning the dimensions of the excitation slot and adding a small tuning stub. In this way, an antenna element with a -10 dB impedance bandwidth of 36.8% has been designed. Furthermore, the results of this parameter study have allowed to formulate some general guidelines concerning the design of this type of antenna element.     

CPW-fed passive and active microstrip antennas

A numerical modelling based on the solution of coupled integral equations is used for the design ofCPW-fed microstrip antennas. This type of antennas shows properties close to those of aperture-coupled antennas fed by microstrip lines. Oscillating antennas and large bandwidth antennas working in the C-band are realized with the help of the theoretical model. Various shapes of excitation slots are studied and the slot-loop is shown to be a convenient feeding for the insertion of active devices.     

CPW-fed dual-annular-ring slot antennas

A new type of CPW-fed dual-annular-slot antenna operated in the 5.8 GHz band is introduced. Both the inductive and the capacitive configurations are presented. The design considerations of the antennas are discussed. Measurement shows that the antennas have a wide bandwidth of 16% with a peak gain of 5.4 dBi for the inductive configuration and 7.8% with a peak gain of 4 dBi for the capacitive configuration.     

A CPW-fed microstrip patch quasi-optical amplifier array

A quasi-optical power-combining amplifier array based on coplanar waveguide (CPW)-fed microstrip patch antennas is introduced in this paper. Both the transmit and receive antennas employ CPW-fed patches. This amplifier is not only compatible with monolithic-microwave integrated-circuit implementations, but can also provide a greater bandwidth than circuits based on conventional microstrip-fed patch antennas. A 4×4 amplifier array was designed and constructed at X-band. Results for the gain and power compression are also presented     

CPW-fed slot antennas on multilayer dielectric substrates

Coplanar wave (CPW)-fed slot antennas printed on multilayer dielectric substrates are numerically analyzed using a full-wave integral equation technique and the method of moments. The Green's function is derived with an iterative formulation. Results obtained with a simplified and a rigorous model of the feeding CPW lines are compared. The mutual coupling between the slot antennas in an array environment is calculated for a three-layer high-low-high permittivity combination. The theoretical results are verified with measurements     

Conformal microstrip antennas and microstrip phased arrays

A new class of antennas using microstrips to form the feed networks and radiators is presented in this communication. These antennas have four distinct advantages: 1) cost, 2) performance, 3) ease of installation, and 4) the low profile conformal design. The application of these antennas is limited to small bandwidths. Phased arrays using these techniques are also discussed.     

Frequency scanning microstrip antennas

The principles of using radiating microstrip resonators as elements in a frequency scanning antenna array are described. The resonators are cascade-coupled. This gives a scan of the main lobe due to the phase-shift in the resonator in addition to that created by the transmission line phase-shift. Experimental results inX-band, in good agreement with the theory, show that it is possible to scan the main lobe an angle ofpm30degby a variation of the frequencypm300MHz, and where the 3 dB beamwidth is less than10deg. The directivity was 14.7 dB, while the gain was 8.1 dB. The efficiency might be improved by a trade-off between the efficiency and the scanning angle, or by using a better amplitude distribution.     

Circular-waveguide-fed microstrip patch antennas

A microstrip patch antenna fed by a circular waveguide is presented. The microstrip patch built on a foam substrate is laid on the flange of the circular waveguide's open mouth. The waveguide feeds the patch by coupling energy to the patch through a narrow slot underneath the patch. Two operating frequency bands were observed and the characteristics of the antenna were measured.     

Small dual-frequency microstrip antennas

The characteristics of a dual-frequency compact antenna, which uses a rectangular microstrip patch with a shorting pin, are studied. Compared with the conventional rectangular patch antenna, this antenna can achieve both a significant reduction of antenna size and a dual-frequency operation with a single feed. A detailed parameter study is performed. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD codes are developed and validated by measurement results. One antenna has been designed and fabricated, and the comparisons between the measured results and the calculated results are provided. The effects of several antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna have been analyzed and compared. The results of the return loss are also presented. It is shown that various frequency ratios (2.82-4.23) can be obtained by varying the design parameters of this antenna. Several design curves are also presented     

Dual-polarised CPW-fed microstrip antenna for wireless applications at 2.45 GHz

The design and fabrication of a dual-polarised microstrip antenna fed by two coplanar waveguides (CPWs) for operation at 2.45 GHz are presented. Obtained results show an impedance bandwidth of 44.3 MHz using a single layer of substrate. The simulated return loss for both polarisations is less than -35 dB, and the isolation between the ports of the antenna is better than 21 dB.     

Travelling wave microstrip dipole antennas

While it is a common antenna, the unloaded conducting microstrip dipole suffers from a very limited bandwidth because it is a resonant structure supporting a standing wave of current. The authors present the characteristics of a microstrip dipole modified to behave like a travelling wave structure     

FDTD analysis of CPW-fed folded-slot and multiple-slot antennas onthin substrates

Folded slot antennas are attractive for active arrays due to relatively large bandwidth, fabrication simplicity, and ease of integration with devices. Currently, there is little design information for these antennas, especially on thin substrates. The finite-difference time-domain (FDTD) method is applied to the analysis of CPW-fed folded-slot antennas. The paper describes the problems encountered in the analysis, compares the theoretical results and measured data, and provides some design information for folded slots. In addition, it explores the manipulation of input impedance through the use of additional slots, yielding antennas with a broadband 50 Ω input impedance     

Size reduction of microstrip antennas

A scheme to reduce the size of a microstrip antenna is investigated both theoretically and experimentally. For a given operating frequency the patch length is significantly reduced when microstrip width discontinuities are introduced in the middle of the antenna patch     

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.     

Near fields of microstrip antennas

The paper presents an iterative method for the computation of the near fields of single layer microstrip patch antennas. A judicious combination of the advantages of the MPIE (mixed potential integral equation) method, the FFT algorithm and the biconjugate gradient leads to an efficient numerical solution. The scheme can deal with patches of arbitrary shapes and is capable of dealing with a very large number of unknowns. Near field computation is done in a straightforward manner by computing the weighted near fields. For illustration, three patches belonging to the family of generalized annular sector have been chosen. Computed results of input impedances with a coaxial probe excitation have been compared with measurements. Computed near field amplitudes have also been compared with measured results where possible. Computed far field characteristics have been correlated with the near field information     

Vertical currents in microstrip antennas

An analysis of the radiation characteristics of a vertical current inside a dielectric-layer over ground is carried out. The general solution for the fields is given for the case of a vertical current which is independent of the vertical (z) coordinate. An "equivalence-principle" for the replacement of the vertical current by an appropriate surface current is presented. Expressions for the complex input power and for the power which goes into the lowest order transverse magnetic (TM)-type surface-wave mode are derived. In addition, graphs for the case of a short vertical dipole inside a dielectric-layer over ground for the radiation pattern, radiation resistance, and surface-wave resistance are presented. The calculations described above can be applied to the analysis of vertical feeds and short circuits in microstrip antennas.     

Compact broadband S-shaped microstrip antennas

A compact and broadband stacked S-shaped microstrip antenna with corner shorted square microstrip antenna is proposed. A broadband slotted S-shaped microstrip antenna is also proposed which does not require any parasitic patches.     

Compact broadband E-shaped microstrip antennas

A broadband E-shaped microstrip antenna is discussed. Its bandwidth is further increased by cutting a pair of tapered slots. Using the even-mode symmetry of an E-shaped microstrip antenna, a compact single slot loaded rectangular microstrip antenna is proposed, which reduces the antenna size by half.     

Mutual coupling between microstrip antennas

A theoretical study of mutual coupling between microstrip antennas is presented. The cavity method is used, and from the equivalence theorem application the problem is reduced to interaction of two magnetic loops. The mutual impedance is then calculated from the reaction theorem. Theoretical results and measurements are in good agreement.     

Hybrid-coupled broadband triangular microstrip antennas

Two broadband configurations consisting of three hybrid-coupled equilateral and isosceles triangular microstrip antennas have been proposed. Both configurations yield more than four times the bandwidth as compared with the corresponding single triangular microstrip antenna. The radiation pattern of a hybrid-coupled isosceles triangular microstrip antenna is in the broadside direction with very small variation over the entire bandwidth. In addition, this antenna has wide half power beamwidth, making it suitable as an element for the large scan broadband antenna array.