Dual-band radiator interactions in rectangular and triangular grids are analysed. The frequency ratio between the individual sub-bands of operation is 1.86:1. Performance comparison is essentially based on the coupling between adjacent elements and detuning levels of the radiators in array configuration. Results provide essential insights to understand the radiator's coupling behaviour, especially when the bands of operation are separated by a substantial frequency gap. The analysis is also important for providing wide scan performance at both bands of operation, as there is a direct correlation between the coupling and the scan behaviour of the array.

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In this paper a novel differentially fed Ultra-Wide Band (UWB) antenna in low-temperature co-fired ceramics (LTCC) technology to be used in the 60 GHz band for integrated RF front-ends is presented. The antenna is based on the aperture stacked patch fed via H-shaped aperture to achieve more than 10 GHz operational bandwidth. The antenna is fed by a parallel-wire transmission line which enables the antenna to be directly integrated with differential Monolithic Microwave Integrated Circuits (MMICs). To alleviate influence of the surface waves (efficiently excited in LTCC material due to its high dielectric constant) on the antenna radiation and realize uni-directional radiation patterns, a dedicated shield is added to the antenna. The measured results of the shielded antenna showed that the antenna has an operational bandwidth from 51 GHz to over 65 GHz, the gain is about 3.5-8 dBi, and 25 dB beamwidth is about +308. The measurement results also demonstrated that the shield indeed improves the antenna impedance bandwidth, gain, and radiation patterns substantially. I . I N T R O D U C T I O NThe demand for using the unlicensed 60 GHz band for communication and radar applications is growing rapidly. The large available bandwidth in the 60 GHz band is appealing to high data rate multimedia communications. Furthermore, the 60 GHz band is very suitable for ultra-high-resolution imaging with short-range radar, thus it is attractive for such application as concealed weapon detection (CWD) [1]. These demands have motivated many developments in the 60 GHz systems, especially in the integrated 60 GHz front-end. The low-temperature co-fired ceramics (LTCC) technology provides an effective solution enabling integration of passive components including antennas and filters with MMICs in a single, cost-effective package. In addition, the multilayer nature of LTCC technology gives the possibility to realize three-dimensional structures such as cavities and vias. The passive components can then be placed at different layers, which enable miniaturization of modules. Therefore, the research of integrated LTCC antennas is very popular, such as in [2][3][4]. Challenges of realizing antennas with the LTCC material in the mm-wave region are related to fabrication accuracy and limitations on structures such as lines, metal plates, or vias. In addition, high relative permittivity of the LTCC material may limit the bandwidth of the antenna and supports excitation of the surface waves in the substrate. As a result, several attempts have been used to lower the effective dielectric constant such as using an air cavity [5,6] or punching holes [7]. However, these approaches will complicate the manufacturing of the antenna, lower the yield rate, and increase cost. The operational bandwidth of LTCC antennas reported in literature is typically below 18% [6,8].This paper presents a novel differentially fed UWB antenna for CWD imaging radar. The antenna should be manufactured using the LTCC technology to be ready for integration with 60 GHz MMICs ...

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