Abstract-In this paper, a compact waveguide bandpass filter is proposed. The proposed structure consists of some inductive diaphragms in a rectangular waveguide and the regions between them have been filled fully by dielectrics. The relations between the physical and electrical parameters of the existed asymmetrical impedance invertors are obtained. The usefulness of the proposed structure and its performance are verified by designing and simulating an equal-ripple X-band bandpass filter.

A new waveguide slot antenna using radiating surface as the superstrate has been proposed. A simple metal sheet as the ultimate radiating surface due to its larger size leads to higher gain compared with a standalone slot. The proposed configuration is composed of an extended wall on a waveguide, incorporating a slot together with a metal sheet as superstrate. The proposed antenna, which can be classified as a resonance cavity antenna, compared with the conventional one, has improved antenna gain and bandwidth simultaneously. Based on cavity model, the distribution of currents on the radiating surface has been explained. It has been shown that the proposed configuration enhances the antenna peak gain from 6.7 to 12 dBi and in the same time, antenna bandwidth from 5.8% to around 23% compared with the conventional one. The design method is straight forward and based on optimisation using simulation software. In addition to gain and bandwidth enhancement, the proposed configuration has some advantages in terms of simple design method and fabrication cost. To validate the simulation results, the proposed antenna is designed, fabricated and measured. Measured and simulated results are in good agreement that confirms the performance of the proposed structure.

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In this article, a way based on using miniature patch cells has been proposed to increase gain and bandwidth of the waveguide slot antenna. In the presented approach, an array of 3 × 3 metal patches has been used as superstrate to create Fabry Perot theorem resonance cavity. The proposed high‐gain and simple antenna is composed of a conventional waveguide slot antenna with an extended broad wall, and an array of parasitic patches which are symmetrically placed over slot at a distance of about free‐space half wavelength. The slot has been created on a rectangular waveguide WR90 with 22.86 mm × 10.16 mm × 52.5 mm dimension, also extended wall dimension is 2λ0 (67.5 mm) × 3λ0 (107 mm). It has been shown that the proposed structure compared with the conventional waveguide slot antenna improves antenna peak gain from 6.5 to 16.5 dBi and, in the same time, antenna bandwidth from 11% to around 16.2%. More important advantage of the proposed antenna is that unlike to other Fabry Perot antenna with the same gain, there is not any dielectric material in the proposed structure. A prototype antenna was simulated, fabricated, and measured for verification.