M.S. Leong

A broad-band dual-polarized microstrip patch antenna with aperture coupling

In this communication, a dual-polarized aperture-coupled microstrip patch antenna with a broad-bandwidth high-isolation low cross-polarization levels, and low-backward radiation levels is designed and its features are presented. For broad bandwidth and easy integration with active circuits, it uses the aperture-coupled stacked patches. The corner feeding of square microstrip patches is applied and the coupling aperture is the H-shaped aperture. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. A dual-polarized antenna is designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of over 24.4% and the isolation is better than 30 dB over the bandwidth. The cross-polarization levels in both E and H planes are better than -23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results for S parameters and radiation patterns are presented and discussed.

A Note on the Mutual-Coupling Problems in Transmitting and Receiving Antenna Arrays

In antenna arrays, mutual coupling between antenna elements is well known as an undesired effect, which degrades the performance of array signal-processing algorithms. The compensation of such an undesired effect has been a popular research topic throughout the years. Various approaches for mutual-coupling compensation have been developed, and they can easily be found in the open literature. In general, the mutual-coupling problems for a transmitting and receiving array are different, even if the physical geometry of the array remains unchanged. However, it seems that antenna engineers are not well aware of such differences in the analysis of receiving antenna arrays. In this note, the mutual-coupling problems in transmitting and receiving antenna arrays are revisited. The differences between the mutual coupling and mutual impedances for transmitting and receiving antenna arrays are explained. It is concluded that the mutual-coupling problems of transmitting and receiving arrays are in general different, and hence different mutual impedances should be used for mutual-coupling analysis and compensation.

A modified microstrip circular patch resonator filter

Circular holes are etched off a microstrip disk resonator. This results in a size reduction of 30%. By offsetting the positions of some of these holes, a degenerate orthogonal mode is excited, resulting in a split-mode bandpass filter. This filter can be considered as a lattice-type structure. A filter with a bandwidth of 8% centered at 2.0 GHz was designed. The measured insertion loss is 0.6 dB.

Decoupled 2D Direction of Arrival Estimation Using Compact Uniform Circular Arrays in the Presence of Elevation-Dependent Mutual Coupling

Based on the rank reduction theory (RARE), a decoupled method for 2D direction of arrival (DOA) estimation in the presence of elevation-dependent mutual coupling is proposed for compact uniform circular arrays (UCAs). Using a new formulation of the beamspace array manifold in the presence of mutual coupling, the azimuth estimates are decoupled from the elevation estimates and obtained with no need for the exact knowledge of mutual coupling. For the elevation estimation, a 1D parameter search in the elevation space for every azimuth estimate is performed with the elevation-dependent mutual coupling effect compensated efficiently. Though the computational load for the elevation estimation is increased compared to that of the original UCA-RARE algorithm, the 1D parameter search in our method overcomes most of the inherent shortcomings of the UCA-RARE algorithm. This enables unambiguous and paired 2D DOA estimation with the elevation-dependent mutual coupling effect being compensated for effectively. Numerical examples are presented to demonstrate the effectiveness of the proposed method.

Integration of Circular Polarized Array and LNA in LTCC as a 60-GHz Active Receiving Antenna

A compact 60-GHz active receiving antenna array is designed and fabricated using low temperature co-fired ceramic (LTCC) technology. It integrates a 4 × 4 circularly polarized (CP) patch array and a 21-dB low noise amplifier (LNA) into the same package substrate. By applying a stripline sequential rotation feeding scheme the CP array exhibits a wide impedance bandwidth (SWR <; 2) and 3-dB axial ratio bandwidth, both over 8 GHz, as well as a beam-shaped pattern with a 3-dB beam width of 20° and a peak gain of 16.8 dBi. By applying a bond wire compensation scheme and low-loss transition optimization, the LNA is successfully integrated into the package. The final fabricated prototype measures only 13 × 20 × 1.4 mm3, demonstrates the good integration performance as well as the CP polarization characteristics in measurement, and is estimated to have a peak overall gain of at least 35 dBi.

On the eigenfunction expansion of dyadic Green's function in planarly stratified media

Using the eigenfunction expansion, a terse expression of the scattering dyadic Greens function is presented for defining electromagnetic fields in a planarly stratified medium with a current source arbitrarily located in one of the layers. The scattering dyadic Greens function for each layer is constructed in terms of the cylindrical vector wave functions by applying the method of scattering superposition. The general but succinct expression of the coefficients of the scattering dyadic Greens function for each layer of the multilayers is derived directly from the boundary conditions of the dyadic Greens function. To demonstrate how to apply this method, the coefficients of the scattering Green dyads for a three-layered medium, as an example, are reduced from the general expression for the cases where the current source is located in the first, the intermediate, and the last layers. The complete agreement of such coefficients derived in this article and obtained in the previous published papers asserts...

On the eigenfunction expansion of electromagnetic dyadic Green's functions in rectangular cavities and waveguides

The electric dyadic Greens functions of both the first and the second kinds due to the presence of electric and equivalent magnetic sources in rectangular cavities are obtained. A method for directly reducing the dyadic Greens functions for a rectangular cavity to those for a semi-infinite and an infinite rectangular waveguides is presented. The Green dyads of the second kind for an infinite and a semi-infinite rectangular waveguides, and a rectangular cavity are obtained. >

A two-year measurement of rainfall attenuation of CW microwaves in Singapore

The authors present two-year statistics on the rainfall attenuation of 21.225 GHz vertically polarized CW microwave signals in Singapore. The CCIR recommendation is found to underestimate the microwave specific attenuation (dB/km) per path average rain rate (mm/h) as well as the accumulated time of attenuation exceeding preset levels. A negative exponential raindrop size distribution based on spherical droplets is constructed from the measured data. >

A dual-mode bandpass filter with enhanced capacitive perturbation

A dual-mode ring bandpass filter with two pairs of capacitors has been designed. The capacitors are used to control the location of the even- and odd-mode frequencies independently, allowing weak coupling for narrow-band filter design with realizable capacitance values. Theoretical expressions have been derived for these frequencies. A 4% bandwidth bandpass filter centered at 1.9 GHz was designed and tested with good agreement between theoretical and measured results.

Electromagnetic dyadic green's functions in spectral domain for multilayered cylinders

Dyadic Greens function (DGF), as an electromagnetic response of dielectric medium or the field contributed due to a delta source, is quite useful to solve electromagnetic boundary-value problems. DGFs for multilayered structures are of particular interest to many engineers and scientists because of its better accuracy in modelling practical problems. Cylindrically multilayered medium is one of the most common structures used in practice, and the DGF for such a medium was recently published by Xiang and Lu [1]. However, it is found that there are some critical mistakes made and certain constraints assumed in the representation of the DGFs and their coefficients. The present paper serves as an amendment of [1] so as to avoid possible misleading of readers.