Da-Gang Fang

Dielectric Loaded Substrate Integrated Waveguide (SIW)

A dielectric loaded substrate integrated waveguide (SIW) H-plane sectoral horn antenna has been proposed in this paper. The horn and the loaded dielectric are integrated by using the same single substrate resulting in easy fabrication and low cost. Two antennas with rectangular and elliptical shaped loaded dielectrics were designed and fabricated. These antennas have high gain and narrow beamwidths both in the E-plane and in the H-plane. The results from the simulation and those from the measurement are in good agreement. To demonstrate applications of the array, the small aperture elliptical dielectric loaded antenna has been used to form an array to obtain higher gain and to form a one-dimensional monopulse antenna array.

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A compact single layer monopulse microstrip patch antenna array for the application of monopulse radar has been designed, manufactured and tested. The array, the monopulse comparator and the feed network are placed on the same layer, resulting in a very compact structure. The limitation of this structure is discussed. The effects of spurious radiation and blockage caused by the comparator on the sidelobe level are estimated. A space mapping (SM) technique is applied to design microstrip subarray. The bandwidth (VSWR<2) of the antenna is 5.6%, the operating frequency is between 13.85-15.1 GHz and the designed central frequency is 14.25 GHz. Our measurements show that, both for the E plane and for the H plane, the sidelobe levels of the sum pattern are less than -17 dB, and the null depths of the difference pattern are less than -30 dB. The maximum gain at the operating frequencies is 24.5 dBi.

-Plane Horn Antennas

Amplitude and phase weighting at the subarray outputs alone causes grating lobes (GLs) in the array factor. A combined approach to disrupt the periodicity in the array is proposed to reduce the GLs. In this approach, three measures are simultaneously used. They are: (1) the optimized amplitude weighting at the subarray ports; (2) using the random subarray; and (3) the random staggering of the rows. The optimization was carried out by using genetic algorithms (GAs). The 24 (along X) times 32 (along Y) phased array was designed to verify the proposed approach. Along Y, the scan range is (-10deg, +10deg) and the subarrays are used. Along X, the scan range is (-45deg, +45deg) without using the subarrays. The comparison was done through array factor. In the whole two dimensional scan space, the simulated results show that the GL is -3.77 dB when using the conventional array, -4.28 dB when using (1) alone, -11 dB when using (2) alone, -14 dB when using (3) alone, -20 dB when using the combined approach proposed in this paper. This approach can be used for a phased array with limited scanning and for the digital beamforming antenna array with adaptive nulling.

A compact single layer monopulse microstrip antenna array

Mutual coupling between radiation frequency (RF) components, antenna elements in a microstrip antenna array or between two microstrip antenna arrays is a potential source of the performance degradation. The degradation includes the impedance mismatching, the increased side-lobe level, the deviation of the radiation pattern from the desired one, and the decrease of gain due to the excitation of the surface wave. In the application of continuous wave radar, when the transmitting antenna and the receiving antenna are placed closely side by side, the transmitting energy may even blockade the receiver. In the application of adaptive nulling arrays, the mutual coupling will result in the serious degradation of the adaptive nulling performance. The mutual coupling is also important to the issues of electromagnetic compatibility (EMC) when a lot of RF systems work simultaneously in a limited space, especially to the signal integrality (SI) design. The mechanism of the mutual coupling is quite complicated which involves both the near field and the far field couplings. In dealing with these problems, the full wave analysis is indispensable. In the meantime, in the analysis or optimization design, the frequency response should be taken into account as well. In this paper, the effective frequency dependent full wave analysis will be introduced. Examples of mutual coupling reduction are given that involve the mutual coupling reduction between two microstrip antenna arrays and the mutual coupling reduction between microstrip antenna elements,. In addition, the mutual coupling effect on the performances of some antenna arrays will be briefly addressed.

Grating Lobe Reduction in a Phased Array of Limited Scanning

A single-layer single-patch four-band U-slot patch antenna, with linear polarization, is proposed for WiMax and WLAN systems. Using this antenna, impedance bandwidths (|S11|<;-10 dB) of 2.1%, 3.3%, 7.1% and 5.0% were achieved at central frequencies 3.35 GHz, 3.70 GHz, 5.20 GHz and 5.80 GHz, with gains of 7.6 dBi, 8.6 dBi, 8.5 dBi and 9.0 dBi, respectively. This antenna was made by cutting four asymmetrical U-slots in the patch. This structure has the following advantages: (1) the feed is simple, (2) the antenna has single-layer, (3) the structure of the antenna is simple, (4) the asymmetry of the U-slot arm provides one more degree of freedom in the design, (5) the antenna is inexpensive. The design guideline for the proposed antenna is given and the acceptability of the design is verified by other scenarios. The simulated and measured results are in good agreement.

On the Mutual Coupling of the Finite Microstrip Antenna Arrays

A new correction method is proposed for the single RF channel digital beamforming (DBF) antenna array. In this array, each array element is followed by a

Single-Layer Single-Patch Four-Band Asymmetrical U-Slot Patch Antenna

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Comparison of Correction Techniques and Analysis of Errors for Digital Beamforming Antenna Array With Single RF Receiver

phase shifter, and the element outputs can be recovered by the single channel through the time sequence phase weighting (TSPW) technique. The outputs can be used to form desired beams through DBF. The performance of the DBF is influenced by the imperfection of the phase shifters. To obtain the errors in each phase shifter, the online test method based on a single known plane wave is introduced. The online test results are used to correct the element outputs using the relationship between the actual and the incorrect outputs. Compared with another previously proposed correction method, the new method is simpler and more suitable for real time correction. The factors that may influence the capability of the correction are analyzed. To validate the proposed method, an eight-element prototype is measured, and the data are used to synthesize low sidelobe patterns. Results show that the sidelobe level and gain improvements after correction are 11.1 and 2.6 dB, respectively.

Rectangular waveguide Green's function involving complex images

Waveguide Greens function is a powerful tool for analyzing discontinuity problems in a waveguide. The rectangular waveguide Greens function has been extensively investigated previously. Recently the Greens function for a partially filled rectangular waveguide has been presented. In the derivation of the Greens function, to match the boundary conditions both on the conducting walls and the dielectric interfaces, the real images are used. In this paper, all the images are replaced by the full wave discrete images which are complex. Compared to the existing rectangular waveguide Greens function, the Greens function proposed in this paper possesses some advantages of being efficient and fast convergent. The numerical results confirm the validity of this Greens function.

A low loss frequency scanning planar array using hybrid coupling

An X-band frequency scanning microstrip array is proposed in this paper. In the structure, an E-plane bent rectangular waveguide is used as slow-wave structure to achieve the low loss. The array is fed by using a combination of aperture coupling from the slotted waveguide and microstrip line feeding. The simulated results show that the range of the scanning angles is (−48°, 45°), the gain is above 21.6dBi at the working bandwidth and the peak gain is 23.2dBi. In addition to low feed loss and wide angle scanning capability in one dimension under limited bandwidth, this proposed design is with compact structure.