Articles written in Sadhana

    • Analysis and design of broadband U-slot cut rectangular microstrip antennas


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      Broadband microstrip antenna using variations of U-slot has been widely reported. However, in most of the reported work, an in-depth explanation about the mode introduced by U-slot and procedure to design U-slot cut antennas at any given frequency is not explained. In this paper, first an extensive analysis to study thebroadband response in symmetrical and a new configuration of asymmetrical U-slot cut rectangular microstrip antennas is presented. The U-slot tunes higher-order orthogonal mode resonance frequency of the patch with respect to fundamental mode to realise wider bandwidth. Further formulation in resonant length at modified patch modes in symmetrical U-slot cut antenna is proposed. Frequencies calculated using these formulations show closer agreement with simulated and measured results. Using proposed formulations, a procedure to design U-slot cut antenna at different frequencies over 800–4000 MHz range which shows broadband response is explained. Thus, the proposed work gives an insight into the functioning of widely used U-slot cut antennas and the formulations will be helpful for designing at any given frequency

    • Modified designs of broadband E-shape microstrip antennas


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      Wideband designs of rectangular microstrip antennas embedded with three rectangular slots are proposed. These slots modify resonance frequencies of patch’s TM₁₀, TM₀₂ and TM₁₁ mode, to give bandwidth of more than 500 MHz (>50%). Further, pair of slots cut variations of rectangular patch with three slots is proposed. Additional pair of slots tune the next higher order TM₁₂ mode frequency with respect to modified lower order resonant modes, resulting in further increase in bandwidth of more than 600 MHz ([55%). Increased bandwidth obtained in the proposed designs is more than that obtained from equivalent E-shape and U-slot cut patches. As compared with Ψ-shape patch antenna, the proposed configurations yield wider bandwidth with 38% reduction in patch size.

    • Miniaturized composite band pass filter using folded transmission lines for wideband radar


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      A composite design of Band Pass Filter (BPF) is developed with 3-dB fractional bandwidth (FBW) of more than 140%. This BPF is suitable for the development of wideband radar, communication and EW system in 1 to 6 GHz. Composite BPF design utilizes stepped impedance Low Pass Filter (LPF) along with thequarter wavelength (λg/4) short circuited stub. λg/4 short circuited stubs incorporated High Pass Filter (HPF) response which transforms overall design into BPF. Four cases of filter have been discussed. In case-I, the proposed BPF is developed with a size of 32.6 mm X 7.0 mm. Further in case-II, design has been realized with improved roll-off at the lower edge of the bandwidth (i.e., 1GHz). In case-III, developed design is 75% lengthwise miniaturized that of case-I. Further in case-IV, about 55% length-wise miniaturization is done. Case-III andIV have their response similar to that of the case-I with miniaturized design. All designs are simulated, optimized and fabricated over RT-Duroid 5880 substrate. For case-I, III and IV fabrication has been done on 20 mil thick substrate, whereas for case-II 31 mil thick substrate is used. Comparisons between all the cases havebeen presented in tables and S-parameter plots.

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