Very Compact Waveguide Orthomode Transducer in the K-Band for Broadband Communication Satellite Array Antennas

Abstract

A very compact waveguide orthomode transducer (OMT) is described in this paper. The design is characterized with a twofold rotationally symmetric cross-section in the probing area, adapted from a side-coupling OMT design, simultaneously enabling low port-to-port coupling and high cross-polarization discrimination (XPD) over a fractional bandwidth of about 15–20%. Compared to previously reported compact waveguide OMTs, the proposed design is simpler, thus facilitating its manufacture at millimeter-wave frequencies. The concept is demonstrated with a design in the K-band for a broadband communication satellite downlink over the frequency band of 17.3–20.2 GHz. For test purposes, transitions to standard waveguide WR42 are included, and the OMT is assembled with a conical horn antenna. The measured reflection and coupling coefficients are below −19.5 dB and −22.9 dB, respectively, over the nominal bandwidth, and they are in good agreement with the simulation’s results. The on-axis XPD, measured in an anechoic chamber, is better than 30 dB over the nominal bandwidth, which is also in line with simulations. The proposed waveguide OMT may be designed to fit in a lattice below one wavelength at the highest operating frequency, which is desirable for dual-polarized closely spaced array antennas in low and medium Earth orbit communication satellite systems. The simple mechanical design of the proposed OMT makes it particularly appealing for additive manufacturing techniques, as demonstrated with a variant of the design having folded single-mode waveguides, which preserves the RF properties of the original design.

Design and fabrication of waveguide‐based graded refractive index Rotman lens with an improved insertion loss at Ka‐band

“…Furthermore, it is noteworthy that the dual‐ridged waveguide Rotman lens [32], similar to our own work, does not suffer from dielectric losses. However, it does experience power spillover losses, resulting in reduced energy directed towards the array elements.…”

“…Conventional Rotman lenses also face challenges due to inherent power losses, where a considerable amount of power is dissipated in non‐radiating ports, especially dummy ports when input ports are excited. To address these issues, various techniques [22–32] have been utilised to suppress these losses. Tekkouk et al [29] have proposed stacking two layers to create a compact lens with suitable insertion loss but limited to a narrow frequency band.…”

“…To eliminate dielectric losses, Fonseca et al [32] have proposed a Monolithic Double‐rigged waveguide‐based Rotman lens with high power handling capability at K a ‐band frequencies. However, due to power dissipation in non‐radiating ports, there is a significant insertion loss.…”