Abstract
Background/Objectives: To design, analyze and fabricate aperture coupled waveguide to microstrip transition for Ka-Band where energy is coupled through slot in ground plane and a metal patch placed over the substrate. Methods: Impedance matching approach has been adopted for transition design. Microstrip line is inserted into the waveguide through aperture acting as a probe. Followed by inductive line and transformer line for impedance translation between waveguide and microstrip line. Waveguide transition has been designed using Ansoft High Frequency Structure Simulator (HFSS) full-wave EM simulator. Findings: Designed transition shows return loss performance better than 15 dB and insertion loss better than 0.5 dB for back to back configuration over a frequency band of 34 – 36 GHz. Transition is fabricated on RT5580 Duroid substrate (2r= 2:2) with substrate thickness 0.254 mm. Measured results show return loss better than 25 dB and insertion loss less than 1 dB over a frequency band of 34-36 GHz. Table 2 shows comparison of present design with previously reported designs in terms of performance. Novelty/Applications: Comparison of the presented transition shows superior performance to previously reported transition designs in terms of transition bandwidth and insertion loss. Aperture coupled transitions can be widely used for space applications where hermetic sealing is required and it saves extra effort for sealing. Certain RF circuit applications require narrowband waveguide transitions to attain required performance, in this case aperture coupled transition can be a good option and its integration with RF circuits is also easy. Fabricated transition design results show good agreement with simulated results so it can be concluded that design is tolerant to fabrication errors. Transition has been fabricated using standard PCB process so production of such transition can be done easily without requirement of any special facility for fabrication. Keywords: Aperture coupled transition; waveguide; microstrip; kaBand;hermetically sealed
Highlights
In past few decades, millimeter wave frequencies have been major attraction to lot of researchers due variety of applications in various fields like detection of objects (1), remote sensing (2) and astronomy (3)
At millimeter and sub-millimeter wave frequencies waveguides are often used as interconnect to RF subsystems like Low Noise Amplifiers (LNA), filters, mixers, etc., as it offers low propagation losses and high-power handling capability
Transition design presented in (22) shows comparatively high insertion loss than present design as coupling between waveguide and microstrip line could be maximized if two slots are placed very near to each other but due to fabrication constraint minimum insertion loss achieved was -4.5 dB
Summary
Millimeter wave frequencies have been major attraction to lot of researchers due variety of applications in various fields like detection of objects (1), remote sensing (2) and astronomy (3). Back radiations can be reduced by using slot in ground plane of microstrip in order to couple energy between microstrip line and waveguide as presented in (7) In this design an additional second substrate with certain thickness covers aperture inside the waveguide and it works as quarter wave transformer for matching impedance between waveguide and microstrip line. Simulations have been carried out to optimize the patch element length that controls generation of higher modes Another technique (10) where one side of substrate cover the cross section of waveguide and other side of substrate slot has been defined, coupling between waveguide and microstrip line is employed using quarter wave transformer as a matching element.
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