A printed antenna array with conical beam is presented. Coplanar waveguide (CPW) is used to feed the antenna. Loop slots with finite width of ground plane, which play the role of radiating elements are arranged collinearly to form a traveling wave antenna array. The widths of the loop slots are adjusted to achieve low sidelobe performance. The design procedures are proposed and a 16-element array with beam-pointing angle of 77° is fabricated and measured to verify the design. The measured 15-dB return loss bandwidth is 11.4% at central frequency of 10.5 GHz. The measured gain and the sidelobe level are 10.3 dBi and $-20\;\text{dB}$, respectively. The agreement between the measured and the simulated results is acceptable.

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.

This paper presents a novel wideband aperture-coupled circularly polarized stacked patch antenna. With the combination usage of the aperture-coupled feed, one stacked parasitic patch and one three-stub hybrid coupler, both the impedance bandwidth and the 3 dB axial ratio (AR) bandwidth have been improved considerably. The proposed antenna operating in the X band exhibits a simulated -10 dB return loss bandwidth of 37% and an AR<3 dB bandwidth of 40.3%. The maximum gain is 8.4 dBi

In modern communication and radar applications, large-scale sensor arrays have increasingly been used to improve the performance of a system. However, the hardware cost and circuit power consumption scale linearly with the number of sensors, which makes the whole system expensive and power-hungry. This paper presents a low-cost nested multiple-input multiple-output (MIMO) array, which is capable of providing $O\left(2N^2\right)$ degrees of freedom (DOF) with $O\left(N\right)$ physical sensors. The sensor locations of the proposed array have closed-form expressions. Thus, the aperture size and number of DOF can be predicted as a function of the total number of sensors. Additionally, with the help of time-sequence-phase-weighting (TSPW) technology, only one receiver channel is required for sampling the signals received by all of the sensors, which is conducive to reducing the hardware cost and power consumption. Numerical simulation results demonstrate the effectiveness and superiority of the proposed array.

This paper gives an overview of the microstrip antenna research carried out at Millimeter Wave Technique Laboratory (MWTL) of Nanjing University of Science and Technology (NJUST). It describes the development on both the antenna elements and the arrays for different requirements such as high gain, low side lobe level, wide frequency bandwidth, equal beamwidth in both principal planes, wide angle coverage pattern, low cross polarization, pattern diversity array, circular polarization array and specific function array needed in monopulse radar. In addition to the structure, the design approaches and tools are briefly introduced. The performance of adaptive nulling under the presence of mutual coupling in digital beamforming microstrip antenna array is discussed as well