Tan-Huat Chio

Parameter study and design of wide-band widescan dual-polarized tapered slot antenna arrays

A parameter study of dual-polarized tapered slot antenna (TSA) arrays shows the key features that affect the wide-band and widescan performance of these arrays. The overall performance can be optimized by judiciously choosing a combination of parameters. In particular, it is found that smaller circular slot cavities terminating the bilateral slotline improve the performance near the low end of the operating band, especially when scanning in the H-plane. The opening rate of the tapered slotline mainly determines the mid-band performance and it is possible to choose an opening rate to obtain balanced overall performance in the mid-band. A longer tapered slotline is shown to increase the bandwidth, especially in the lower end of the operating band. Finally, it is shown that the H-plane anomalies are affected by the array element spacing. A design example demonstrates that the results from the parameter study can be used to design a dual-polarized TSA array with about 4.5:1 bandwidth for a scan volume of not less than /spl theta/=45/spl deg/ from broadside in all planes.

Experimental results of 144-element dual-polarized endfire tapered-slot phased arrays

Two 9/spl times/8/spl times/2 (144 element) dual-polarized endfire tapered-slot phased arrays have been built. Measured data for mutual coupling coefficients and scan-element patterns are presented. Also, element resonances, predicted by numerical infinite-array analysis are examined. The dimensions of the two arrays are identical. They differ in that plated-through vias have been repositioned to eliminate element resonances. One array was expected to operate from 1.0 to 4.6 GHz and the other from 1.0 to 5.9 GHz. It was found that, at low frequencies, the central elements are heavily affected by the finiteness of the arrays due to strong mutual coupling between array elements. Extrapolation of the observations indicates that a tapered-slot phased array, designed for wide-angle scanning, should be comprised of at least 30-40 rows and columns of elements to obtain low-frequency performance that is comparable to infinite-array predictions. In spite of the smallness of the array, predicted-element resonances could be identified by examination of the phase of the mutual coupling coefficients. Based on these observations, the plated-through vias are adequate to remove element resonances.

Elimination of impedance anomalies in single- and dual-polarized endfire tapered slot phased arrays

A method to eliminate bandwidth-limiting impedance anomalies or resonances in stripline-fed single- and dual-polarized tapered slot phased arrays is presented. For dual-polarized arrays, others have shown that the resonance with the lowest frequency is related to a cavity constituted by the dielectric region of the tapered slot element. Simulations have been performed to test if this cavity model also predicts the remaining resonances. It was found that the cavity model predicts some but not all of the resonances. However, it was found that all resonances in both single- and dual-polarized arrays have some dependence on the dielectric region. The resonances are effectively suppressed by introducing plated through vias in the element. The vias are positioned along the edges of the slotline, slotline cavity, stripline, and stripline stub. The analysis is performed with the finite-difference time-domain method by considering a unit cell in an infinite array.

A Low Profile and Low Sidelobe Wideband Slot Antenna Array Feb by an Amplitude-Tapering Waveguide Feed-Network

A low profile slot antenna array is designed to operate over a wide bandwidth with low sidelobe levels. Taylor synthesis is used to taper the power distribution among array aperture. An efficient approach to design an equal-phase but unequal-power symmetric waveguide divider is proposed for constructing an amplitude-tapering feed-network for the array. Phase differences are balanced by adjusting the waveguide phase velocities. The basic radiator is a 2 × 2 slot subarray, uniformly fed by such a waveguide divider. A 16 × 16 array is then constructed by 8 × 8 of such subarrays. A 1-to-64 way corporate-feed waveguide network is designed to excite all subarrays instead of individual slots, and the required power distribution is obtained by adopting a 30 dB Taylor N̅ = 4 synthesis. Measured results indicate that the array can achieve a 13.8% bandwidth and a gain of more than 29.5 dBi. The first sidelobe level is -26.5 dB in the E-plane and -30.4 dB in the H-plane. The holistic sidelobe levels in both planes are better than -25 dB with a better than -40 dB cross-polarization.

Low-Profile, Wideband Dual-Polarized Antenna With High Isolation and Low Cross Polarization

A wideband dual-polarized antenna with high isolation and low cross polarization is presented. A pair of orthogonal planar printed dipoles, with a reflector ground plane, are used to obtain the two linear polarizations. Slots cut at the dipoles corners and shorted connections between the orthogonal dipoles are used to improve the isolation and cross polarization. Measured results show that the antenna achieves a VSWR <; 1.5 from 575-722 MHz (22.7% bandwidth). The isolation between the two polarizations is better than 35 dB, and the cross-pol level is 30 dB below the co-pol level over the entire band. The overall height of the antenna is 80 mm, which is about 0.15λ at 575 MHz.

Fabrication of a High-Efficiency Waveguide Antenna Array via Direct Metal Laser Sintering

The direct metal laser sintering (DMLS) technique, using aluminum alloy, is adopted to fabricate a relatively large 8 ×8 wideband multilayer waveguide array with an integrated corporate-fed network in the Ku-band. This DMLS technique offers the flexibility to fabricate waveguide structures with complicated embedded structures with good reliability and high precision. It is favorably compared to the time-consuming machining technique when the array must be built in separate pieces and secured together. Experimental results show there is 1.0 ~ 1.5 dB gain improvement compared to one that is fabricated by machining technique. Antenna aperture efficiency is higher than 80% over a wide operational bandwidth and even exceeding 90% at most frequencies. This work shows that the metal-direct-printing technique is a promising manufacturing method for the fabrication of complicated waveguide antenna arrays.

Wide-band photonically phased array antenna using vector sum phase shifting approach

In this paper, a wide-band photonically phased array antenna is demonstrated. The array configuration consists of a 4 /spl times/ 1 Vivaldi single-polarization antenna array and an independent photonic phasing system for each element. The phasing network of this array is implemented using two novel photonic phase shifters based on the vector summation approach. A vector sum phase shifter (VSPS), which exhibits a frequency-linear characteristic from dc to 15 GHz and can be continuously tuned from 0 to 100/spl deg/, is presented. A second-order VSPS (SO-VSPS), a modification of the VSPS that is capable of 0-430/spl deg/ phasing range, is also demonstrated. This paper presents the operation and characterization of each component of the array, including the radiating elements and the various photonic phase shifters and, finally, a demonstration of the combined system. A discussion on the practicality of this system for airborne applications is presented, along with suggestions for simplification and improvement.

Wideband Dual-Polarized and Dual-Monopulse Compact Array for SAR System Integration Applications

A wideband dual-polarized and dual-monopulse array with highly self-compact configuration is proposed for synthetic aperture radar (SAR) applications. To investigate the monopulse performances, a monopulse comparator network integrated with a 16 × 32 antenna array is designed to form a complete monopulse array. In order to realize the complicated monopulse array and avoid the disadvantages from conventional machining methods in manufacturing waveguide structures, a 3-D metal-direct-printing technique is adopted in this work to obtain better mechanical and electrical performances. Experimental results show that the monopulse array can operate in a wide bandwidth of 12.5% in the Ku-band. Port isolation and polarization isolation better than 30 and 45 dB are achieved, respectively. Furthermore, satisfactory monopulse performances in sumand difference-patterns are also obtained in the wideband. In particular, a high efficiency of 95% is achieved at the center frequency of the sum-patterns, validating the design feasibility and merit of the 3-D printing technique in SAR applications.

Design of a Wideband Dual-Polarization Full-Corporate Waveguide Feed Antenna Array

A wideband and dual-polarization antenna array with high efficiency and high isolation is proposed. In order to achieve the desired performance, a wideband radiating element and a full-corporate waveguide feed network are employed in the design. In particular, E-plane waveguides are utilized for the feed-network configuration so as to suppress wave leakage between adjacent layers when the antenna is fabricated via conventional machining techniques. The operational mechanism is presented and a 16 × 16 antenna array is tested for verification. Experimental results show that the bandwidths of VSWR <; 2.0 for both of the polarizations are about 17.1% (12.45-14.78 GHz) and the isolation between the two polarization ports is better than 39.5 dB. In addition, more than 70% antenna efficiency with higher than 29.4 dBi gain is achieved over the operational bandwidth.

Highly-Efficient Self-Compact Monopulse Antenna System With Integrated Comparator Network for RF Industrial Applications

A highly-efficient monopulse antenna system is proposed for radar tracking system application. In this study, a novel integrated front-end and back-end complicated three-dimensional (3-D) system is realized practically to achieve high-level of self-compactness. A wideband and compact monopulse comparator network is developed and integrated as the back-end circuit in the system. Performance of the complete monopulse system is verified together with the front-end antenna array. To ensure the systems electrical efficiency and mechanical strength, a 3-D metal-direct-printing technique is utilized to fabricate the complicated structure, avoiding drawbacks from conventional machining methods and assembly processes. Experimental results show the monopulse system can achieve a bandwidth of 12.9% with VSWR less than 1.5 in the Ku-band, and isolation is better than 30 dB. More than 31.5 dBi gain can be maintained in the sum-patterns of wide bandwidth. The amplitude imbalance is less than 0.2 dB and null-depths are lower than -30 dB in the difference-patterns. In particular, with the help of the metal-printing technique, more than 90% efficiency can be retained in the monopulse system. It is a great improvement compared with that obtained from traditional machining approaches, indicating that this technique is promising for realizing high-performance RF intricate systems electrically and mechanically.