A.B. Smolders

A Shared Aperture Dual-Frequency Circularly Polarized Microstrip Array Antenna

A novel 2 2 array of microstrip antennas was developed that generates orthogonal circularly polarized waves at two frequencies simultaneously. This true shared aperture can be used as a building block in full-duplex wireless communication applications such as focal-plane arrays for satellite internet (VSAT) and wireless connectors. An alternative implementation of the sequential rotation technique was applied to create dual-frequency operation using only a single aperture. The concept was verified with experimental results from a prototype consisting of a 2 2 array of aperture coupled microstrip antennas (ACMAs) with corresponding feed network operating at 4 and 6 GHz. Measurements show that the axial ratio (AR) is below 1.2 dB for both the low-band as well as the high-band mode of operation. The isolation between both modes is larger than 26 dB, eliminating the need of high-performance duplexers.

An efficient computation scheme for the free space Green's function of a two-dimensional semiinfinite phased array

A simple scheme is developed to compute the Greens function of a periodic semiinfinite array in free space. It is based on the spectral representation of the fields radiated by an infinite linear array of dipoles. Results related to successive linear arrays are added in the space domain. This summation can be accelerated tremendously by using an elementary extrapolation technique. The resulting formulation converges everywhere in the plane containing the array, and the number of terms required to achieve a given precision increases slowly away from this plane.

Axial Ratio Enhancement for Circularly-Polarized Millimeter-Wave Phased-Arrays Using a Sequential Rotation Technique

Circular polarization is indispensable for robust wireless communication between mobile devices that operate at mm-wave frequencies. Additionally, phased-array solutions are required to cope with the associated free space path loss. In view of the size constraints for antennas integrated on (Bi)CMOS chips, an array of linearly polarized dipoles using a sequential rotation scheme is an attractive approach to comply with all mentioned requirements. When steering such an array off broadside, however, the axial ratio will severely degrade. It is the purpose of this communication to demonstrate how the axial ratio can be retained by compensating the amplitudes and phases of the individual antenna elements. Measured results on a 6 GHz test-bed show that the axial ratio with the proposed calibration scheme remains below 3 dB within the 3 dB beamwidth of the scanned beam. Results from a 60 GHz test-bed confirm the effectiveness of the method.

Substrate loss reduction in antenna-on-chip design

We have explained the effect of the silicon substrate on the off-chip radiation of an integrated antenna on chip. From this consideration a low-cost approach for an enhanced antenna-on-chip design has been derived and its improved radiation effciency has been confirmed by measurements.

RF SiP: the next wave for wireless system integration

This paper discusses the opportunities of the system-in-package (SiP) concept for integrating complete wireless systems into a single package, providing the smallest size and lowest cost in the end application. SiPs offer the flexibility to use the optimal technology mixture for a particular wireless system. Two SiP approaches are introduced. The first approach is based on a low-cost laminate platform (LAMP) and the second approach uses a thin-film passive integration IC technology. In both approaches, multiple active dies (CMOS, BiCMOS, GaAs, etc.) can be placed on the passive substrate using either conventional wire-bonding technology or more advanced flip-chip technology. Two examples are described in the wireless connectivity area, i.e. a Bluetooth radio SiP and a complete WLAN 802.11b system SiP.

Analysis of wide-band infinite phased arrays of printed folded dipoles embedded in metallic boxes

A theoretical method is presented to analyze the scan performance of infinite phased arrays of printed folded dipoles embedded in metallic boxes. By using the equivalence principle, each unit-cell is divided into an inhomogeneous interior region and a homogeneous exterior region. The exact dyadic Greens function for both regions is derived. The current distribution on the antenna elements and the corresponding active impedance are found by solving the pertaining integral equations with the method of moments. Numerical results show that the E-plane scan performance is improved significantly by placing the folded dipoles inside metallic boxes. Without the use of additional matching circuits a bandwidth of more than 16% was obtained over a wide scan range. A disadvantage of the use of metallic boxes is the strong appearance of a blind scan angle at the higher frequencies. Measurements of the element pattern of an 1152-element prototype show a very close agreement with the presented theoretical computations.

High-Q BAW Resonator on Pt/Ta2O5/SiO2-based Reflector Stack

This paper discusses the design and optimization of high-Q Bulk-Acoustic-Wave resonators using a Pt/Ta2O5/SiO2 reflector stack. It can be shown that by properly designing the reflector stack and boundary conditions, large performance improvements can be realized. In this paper the characterization and design of the reflector stack is described and its results are presented.

Wide-band antenna element with integrated balun

A wide-band antenna element with an integrated balun has been successfully developed. This element will be used in the OSMA demonstrator array. The measured and predicted bandwidth of an isolated balun is 4:1 for a return loss lower than -18 dB (VSWR 1.3:1). For an antenna element with integrated balun a VSWR of 2:1 is achieved over an octave bandwidth. A VSWR< 2.7:1 was measured over a frequency band of 4:1.

THousand Element Array (THEA)

As part of the development path towards a new radio telescope, the Square Kilometre Array, a demonstrator phased-array system (THEA) is currently being build in the Netherlands. THEA consists of 1024 receiving elements connected to a novel mixed RF/digital beamforming architecture that produces 32 beams simultaneously. Adaptive digital nulling techniques are applied to reduce the effect of interfering signals. A system overview is presented as well as some preliminary results.

Design and construction of a broadband wide-scan angle phased-array antenna with 4096 radiating elements

Phased-array radar must provide a multifunction capability and offer a high degree of flexibility to the users. A broadband wide-scan phased array antenna with 4096 elements was designed and constructed. The array can be used over a wide frequency band of 0.3f/sub 0/. The agreement between the measured and the predicted data is very good. In addition, the position errors of the array elements were measured. The additional RMS sidelobe level due to these errors is negligible.