Substrate-integrated waveguide (SIW) technology has recently drawn attention to its benefits in the microwave field, such as integration in planar microwave circuits, low manufacturing cost, and high-quality factor compared to other technologies. In this paper, a broadband and high gain SIW cavity-backed L-shaped slot antenna structure has been designed and made for X-band applications. Three pairs of L-shaped half-wave resonators are placed on the lower wall of the cavity (backed-slots) to further expand bandwidth and improve gain. The final antenna designed operates on a band ranging from 9.4 to 10.5 GHz with a bandwidth of 11%. Moreover, the gain reaches a value of 9.5 dBi. The final antenna is realized on a Rogers RT/Duroid 5870 substrate. The gain, the reflection coefficient, and the radiation patterns are measured and compared to the EM simulation results and a very good agreement is obtained. The proposed cavity-backed L-shaped slot antenna gives a good compromise between a high gain and a large bandwidth.

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The present paper sheds light on designing a new and high performance microstrip diplexer. The latter is based on new octagonal meandrous resonators combined with the connected common port, without adding any transmission line junction, in order to get a miniaturized structure. The suggested compact resonator is formed through combining the octagonal meandrous lines and coupled lines, which create a bandpass filter. These filters operate at 3.5 GHz and 5 GHz which make them suitable for 5G and Wi-Fi applications. Accordingly, an approximated equivalent LC model of the presented octagonal meandrous resonator is suggested and analyzed so as to validate the simulation results. On top of that, the suggested diplexer is compact, as it occupies only 0.0768 λ g × 0.024 λ g. Thus, it attained excellent performance in terms of S-Parameters as the transmission coefficients are about -1 dB and the reflection coefficient is about -20 dB at both channels, whereas the isolation is about -25 dB. Hence, the validation of theoretical and simulated results is carried out through measurements of the manufactured prototype.