A Low-Loss Impedance Transformer-Less Fish-Tail-Shaped MS-to-WG Transition for K-/Ka-/Q-/U-Band Applications

This paper presents a low-loss, high-transmission, broadside-coupled, transverse, reciprocal, two-port, and nature-inspired Ka-band transition design to move the electromagnetic energy of a rectangular waveguide (RWG) to the microstrip (MS) line. The proposed transition is simple in structure, with an excellent insertion loss, S-12/S-21, (IL) near -0.40 dB and return loss, S-11/S-22, of <-21 dB, while the VSWR value is very close to one. Thus, this transition is an outstanding candidate for MIC/MMIC-based millimeter wave, military, and RADAR applications, as well as in wireless and satellite communications as a compatible connector. This transition also provides a bandwidth of 21.50 GHz (23.52-45.0 GHz) for the abovementioned microwave applications, at a <-10 dB return loss (RL). The proposed transition model also exhibits a -15 dB absolute bandwidth of 27.06-23.44 GHz, with an insertion loss < -0.60 dB. Due to a return loss of <-15 dB over an ultra-wide bandwidth, the proposed transition is not only a good candidate for full Ka-band (26-40 GHz) applications but also covers applications for K-band from 23.74 GHz to 26.0 GHz, Q-band applications from 33.0 to 45.0 GHz, and U-band applications from 40.0 GHz to 45 GHz, with approximately 97% power transmission between the transmission lines and only 3% power reflections. The impedance matching at the designed frequency between the RWG and MS line is achieved by flaring one end of the MS line inside the RWG in a fishtail shape, without the need for a quarter-wave/tapered/exponential/Binomial, or multi-section Chebyshev transformer. The main goal of this research was to design a multi-section impedance-transformer-free, simple, and easy-to-fabricate MS line, to share electromagnetic (EM) energy between an MS line and RWG in 30 GHz satellite applications and 30 GHz high-frequency applications, for interconnects screen printed on an organic substrate for flexible, wearable, textile conformal antennas. This work also presents an exact RLC electrical equivalence model of the MS line (fishtail) to RWG transition at 30 GHz. The novelty of this work is that the proposed transition can be used for four microwave bands of electromagnetic energy transmission, with extremely low reflection, and with a compact, simple-design MS line, and simple RWG.