LAUSR

In this article, the design, construction and characterization of band‐pass filters (BPF), based on the classic single‐structure, square‐loop, dual‐mode resonator rings (SL‐DMRR) is revisited. A specific requirement is proposed for using such a basic topology: the design and fabrication of L‐band SL‐DMRR filters to be part of the intermediate frequency (IF) section of a heterodyne K‐band microwave transceiver. The heterodyne K‐band transceiver has been designed and implemented to measure atmospheric attenuation at 22.4 GHz, in the vicinity of the strong absorption peak by water vapor molecules in the atmosphere. The BPFs are designed to operate at a center frequency of 1.1 GHz and a minimum bandwidth of 200 MHz. SL‐DMRR filters in the L‐band microwave range are more compact when compared to other microstrip structures such as parallel coupled lines, tapped input digital filters, hairpin filters, and so on. Filter realizations on FR4 and RT/Duroid 6010 substrates are optimized by resolving narrow coupling gap (0.07‐0.1 mm), between the input/output stubs and the resonator ring. Narrow gaps (less than 0.1 mm) are an original achievement in our work to ensure insertion losses of 1 dB for FR4, 0.5 dB for RT/Duroid, return losses better than 20 dB and a minimum bandwidth of 200 MHz. These figures represent an appreciable advancement of the state‐of‐the‐art for these classic structures for filters. The simulated and measured electrical responses of the filters show an excellent agreement. The IF filter has been incorporated to the K‐band receiver and the system's performance is also reported in this article.