Bandwidth Extension of Planar Microstrip-to-Waveguide Transition by Controlling Transmission Modes Through Via-Hole Positioning in Millimeter-Wave Band

Abstract

This paper presents a design technique to achieve a broadband planar microstrip-to-waveguide transition in a millimeter-wave (mmWave) band. In the conventional planar microstrip-to-waveguide transition, via holes are located around the rectangular waveguide and microstrip line to prevent power leakage due to the generation of a multi-transmission mode. Therefore, a single-transmission mode is dominant at the input port of the transition, with a narrow bandwidth of the single resonance. In the broadband planar microstrip-to-waveguide transition, via-hole positioning is utilized to add inductance to constrain the predominance of the single-transmission mode at the input port of the transition. The double-resonant frequency yielded by excitation of the grounded coplanar waveguide transmission mode and parallel plate transmission mode is obtained by controlling the positions of holes adjacent to the microstrip line. Moreover, to simplify the structure and meet the requirement of high assembly accuracy in fabrication, two holes adjacent to the microstrip line are maintained, but the remaining holes are replaced by a choke structure that performs the equivalent function to the via-hole arrangement. The influences of the multi-transmission mode and choke structure on the characteristics are investigated by electromagnetic analysis, and the feasibility is confirmed by experiments in this work. A double-resonant frequency and a broad bandwidth of 10.6 GHz (13.8%) are obtained. The measured results of the broadband planar microstrip-to-waveguide transition using via-hole positioning show an insertion loss of 0.41 dB at the center frequency of 76.5 GHz. INDEX TERMS Microwave and millimeter-wave circuits, broadband, microstrip transition, waveguide transition, multi-transmission mode.

Broadband Waveguide-to-Differential-Line Transition in Multi-Layer Substrates With Triple Stacked Patch in 300 GHz Band

“…The design methodology for a waveguide to two microstrip lines transition using a rectangular patch was proposed in reference [22]. Recently, the types of transitions that have gained recognition are the E-shaped patch element [23], slot coupling technique in multi-layer substrates [24], V-shaped patch element [25], via-less with choke structure transitions [26], [27], rectangular patch with the positioning of the via-hole to control the transmission mode [28], and via fence and air hole matching structures [29], [30]. CPW to airfilled rectangular waveguide transition using a rectangular radiator etched with a semi-elliptic slot [31].…”

Broadband Partially Covered Microstrip-to-Waveguide Transition With Enhanced Radiation Suppression for Millimeter-Wave Transmission

“…A broadband planar microstrip-to-waveguide transition has been proposed as an alternative solution, involving the excitation of multiple transmission modes to form a double-resonant structure [7]. However, this approach offers a limited bandwidth of only 13.8% within the mm-wave band.…”

A Broadband Inline Transition From On-PCB Microstrip to Hybrid Stack-Up Integrated Additively Fabricated Air-Filled Waveguide

“…In the literature, different metallic waveguides to PCB transitions can be found e.g., inline ridge stepped transformer [17], [18], quasi-Yagi [19], probe-feeding [20], slot coupling [21], patch-coupling type [22], inline guide stepped transformer [23], [24]. The realizations presented in [17]- [19] require the insertion of PCB into the waveguide, however, offer in-line transition with multi-step impedance transformation.…”

“…The transitions shown in [21]- [22] require vertical orientation of waveguide which is not suited for highly integrated circuits such as additively fabricated air-filled waveguide integrated with a printed circuit board hosting a strip transmission line. The transitions shown in [23], [24] require down and up impedance transformation due to the intermediate guide.…”