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In this paper, the design of a three-layer linear polarization converter based on substrate-integrated waveguide (SIW) technology is demonstrated. The transmission-type polarization converter with dual frequency polarization conversion characteristics is realized by a square-slot sandwiched by two layers of off-center dipole-slot resonator, and its asymmetric transmission (AT) property can be obtained by rotating the upper and the lower dipole-slot resonator to form an interlaced layout. An excellent polarization conversion ratio (PCR) can be realized by integrating the traditional transmission-type polarization converter with an SIW, and its physical mechanism can be explicated by guided wave field theory. Experimental results are presented and compared with the simulation results, and they demonstrated that ultra-high PCRs of the presented polarization converter are 0.87 and 0.99 for the measurement at the working frequency of 7.34 GHz and the simulation at the working frequency of 7.6 GHz, respectively. The designed polarization converter has greatly expanded the application field of SIW technology.

In this paper, two closely spaced dual-frequency antennas are developed using the combined electromagnetic soft surfaces loading techniques for reducing their mutual coupling. The dual-frequencies antenna is designed and its return loss is less than − 10 dB at 4.1 GHz and 5.65 GHz. The electromagnetic soft surfaces are realized by metal strips with C-shaped slots, which have variable working frequency with unit size changing. The dual-band electromagnetic bandgap can be obtained by combined with two electromagnetic soft surfaces with various cell sizes. Experimental results are presented and compared to numerical simulations, and they demonstrated that the proposed electromagnetic soft surfaces loading advance excellent suppression of electromagnetic coupling and the coupling decrease about 16 dB and 19 dB near the working frequencies, respectively. Furthermore, the return loss of the dual-frequencies antennas with this technique is further reduced at its working frequency bands. Measured data show a reasonably good agreement between the simulation and experimental results.