A Novel Metamaterial-Based Orthomode Transducer With Symmetric Port Parameters

This article presents a novel metamaterial-based orthomode transducer (Meta-OMT) with symmetric port parameters, surpassing those of conventional OMTs. Using the polarization modulation properties of metamaterials, this design achieves complete port symmetry, enabling all three ports to serve as input terminals for the OMT. By harnessing the high polarization selectivity of metamaterials, the isolation of cross-polarized signals is significantly enhanced. Within the operating frequency range of 9.4–10.6 GHz, this Meta-OMT achieves low insertion loss ranging from 0.1 to 0.5 dB and facilitates efficient signal transmission. Moreover, it exhibits exceptional isolation capabilities, with isolation levels exceeding 40 dB for both co-polarization and cross-polarization signals and reaching 50 dB in 80% of the operating frequency band

Passive Intermodulation Due to Conductor Surface Roughness

The physical mechanism of the experimentally observed dependence of passive intermodulation (PIM) in printed circuits on conductor surface roughness is studied. It is shown that electrothermal (ET) nonlinearity, arising due to heating of imperfect conductors by high-power carriers in a multicarrier system, is correlated with conductor surface roughness and has a unique signature. Carriers modulate the conductor resistivity, skin depth, and surface impedance which generate PIM products. The detailed analysis demonstrates that ET-PIM depends on the conductor resistivity, shape, and roughness profile and also on the electric and thermal properties of the substrate. Their effects on PIM are illustrated by examples of uniform microstrip lines with different conductor and substrate materials, and periodically perturbed and meandered microstrip lines

Passive Intermodulation in Metal-to-Metal Contacts Caused by Tunneling Current

Passive intermodulation (PIM) by metal contacts limits the bandwidth and capacity of radio links used in mobile and satellite communications. In this work, we investigate the effect of nonlinearities in metal-insulator-metal (MIM) contacts and their effects on PIM generation. An analytical expression is obtained for the tunneling current density which has an error of $\sim$ 1.6% in the case of a very thin insulator and low voltages in MIM junctions. The presented analytical model of the contact surfaces with the fractal geometry is used to simulate PIM products of third-order (PIM3) and fifth-order (PIM5) versus the contact resistance and applied pressure. The simulation results are validated experimentally by an open-ended rectangular coaxial structure with a slotted enclosure. The measurement results demonstrate that the presented model predicts the PIM with a mean error of about 4.8 dB when the contact pressure varies from 0.5 to 1.7 MPa