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This paper presents a 60-GHz $4 \times 4$ differential -fed patch antenna array using low-temperature cofired ceramic (LTCC) process. Wideband patch with L-shaped feeding scheme is adopted as antenna element, while differential substrate integrated waveguide feeding network with low insertion loss is applied for the integration of antenna array. The differential-fed structure improves the symmetry of radiation patterns and reduces the cross-polarization level significantly. To further suppress the surface wave and improve the gain of the antenna array, one kind of soft surface structure is proposed. The equivalent circuit model of the soft surface is developed for calculating its dispersion diagram and analyzing stopband characteristics. The simulated results indicate that the antenna gain enhancement can be up to 2 dB because of the proposed soft surface. For demonstration, one prototype using LTCC process is fabricated and measured. The measured 10-dB impedance bandwidth of the antenna array is 11.7%. The measured antenna peak gain of 18.62 dBi at 61.5 GHz and symmetrical radiation patterns with a low cross polarization of −25 dB across the whole operating frequency are achieved. [ABSTRACT FROM AUTHOR]

This study designed a compact Ka-band open-circuited stub bandpass filter by using the low-temperature cofired ceramic technology. A novel inverted-L stub resonator was developed in the design of 37-GHz third-order bandpass filters. When the operating frequency is high, the proposed structure is highly useful for maintaining extremely low impedance levels in stubs to prevent distorting the filter performance. The design concept was validated by measuring a fabricated filter; the filter demonstrated an insertion loss of 1.9 dB, return loss of 18 dB, and bandwidth of 23.5%. [ABSTRACT FROM AUTHOR]

In this paper, compact multilayered helical resonators and various coupled resonator pairs with a mixed electric and magnetic coupling structure were developed. A multilayer structure is suitable for miniaturization and enhances mutual coupling. A pair of transmission zeros (TZs) can be created using mixed coupling between two coupled helical resonators, achieving superior frequency selectivity. An equivalent circuit model was proposed to analyze the creation of TZs. The planar helical structure provides design flexibility in control of TZs. Eight coupled resonator pairs were proposed for synthesizing various filter responses. An experimental second-order helical filter was fabricated using low-temperature cofired ceramic technology. The measurement results of this second-order filter showed the center frequency to be 0.976 GHz, with two TZs located at 0.8 and 1.4 GHz. The insertion loss was lower than 1.96 dB, and the return loss was 25 dB at f0 . The size of this filter was only 5.7~\textrm mm \times 3.4 mm ( 0.051~\lambda g\times 0.031~\lambda g ), which is highly compact compared with filters from other published studies. In addition, the proposed coupled pairs have potential in the construction of high-order filters with superior frequency selectivity by cascading multiple coupled helical pairs. [ABSTRACT FROM AUTHOR]

This paper presents a cross-coupled bandpass filter with stacked substrate-integrated waveguide cavities on low-temperature cofired ceramic substrates. The proposed filter has a local multipoint distribution service band with a novel same-side-feed input/output structure. Conventionally, a cross-coupled structure generates only a single pair of transmission zeros. The proposed filter can generate two pairs of transmission zeros beside the passband, thereby providing an excellent cutoff rate in the stopband and improved frequency selectivity. The additional pair of transmission zeros is created by the same-side-feed structure, which constructs an additional source–load coupling path without increasing the circuit size. A multipath coupling diagram is used to illustrate the conformation of the second pair of transmission zeros and predict its behavior. The experimental filter exhibits responses centered at 27.95 GHz with an insertion loss of -2.8~dB, and a bandwidth of 9%. Two pairs of transmission zeros (at 26.3 and 29.6 GHz, and at 23.2 and 37 GHz) around the passband were obtained, achieving excellent selectivity and a wide stopband. [ABSTRACT FROM AUTHOR]

This work designs miniaturized stub-type microstrip bandpass filters and develops a novel vertical interconnection scheme in a multilayer structure to design vertically folded filters for size reduction. The current study exploits the fabrication process of low-temperature cofired ceramic (LTCC) for filter realization and fabricates two LTCC Chebyshev stub-type filters at 28 GHz and 5.8 GHz to verify effectiveness of the proposed structure with a maximum size reduction of 50%. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1389-1394, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26024 [ABSTRACT FROM AUTHOR]