A TM 01 mode transducer based on dipole antenna is proposed to design a broadband and low-loss radial power combiner at . It is an essential component in the radial power combiners to convert the electromagnetic modes between rectangular and circular waveguides. The latter feeds the cylindrical cavity in TM 01 mode of which the fields exhibit a circular symmetry. The proposed TM 01 mode transducer consists of the dipole antenna, microstrip, and probe on a dielectric substrate. It is an in-line mode transducer. In other words, the rectangular and circular waveguides are aligned along the same axis of wave propagation. Therefore, it does not require the waveguide components such as tee junctions, steps, and bends which are normally used in the traditional mode transducers and increase the complexity, size, and loss of entire power combiner. The eight-way radial junction is also designed using a cylindrical cavity, where the rectangular waveguides are placed along the circumference of the cylindrical cavity. The dimensions of each component are determined based on the full-wave electromagnetic simulations. The designed eight-way radial power combiner consisting of the TM 01 mode transducer and radial junction is fabricated in four-split blocks by mechanical machining. In the measurements, the proposed power combiner exhibits a broadband and low-loss performance under a compact size while maintaining the magnitude and phase balances between the eight ports.INDEX TERMS Ka-band, millimeter waveguide power combiner/divider, mode-conversion, radial junction, TM 01 mode transducer.

A tray-type spatial power combiner is proposed at Ka-band using an H-plane expanded waveguide with side-ridges and a dipole transition array. In order to overcome the small size of the Ka-band standard waveguide and accommodate as many as trays (six trays in this work), the H-plane of the waveguide is expanded by three times using two-stepped waveguide transition. A circular post is employed to effectively suppress higher-order modes in the expanded waveguide. In addition, a side-ridged waveguide is proposed to reduce non-uniformity in the field and power distribution along the expanded H-plane which seriously degrades power combining efficiency. It boosts the electric field close to the waveguide sidewalls by adding the metallic ridges which reduces the waveguide height at the sides. It is shown from the simulation that the proposed side-ridged waveguide can evenly distribute the electromagnetic power and reduce the magnitude imbalances between the trays. In addition, a capacitive iris is introduced in the ridges to improve the phase balance as well. The H-plane expanded waveguide with side-ridges was fabricated and the measurement showed an insertion loss as low as 0.2 dB at Ka-band. Then, six trays consisting of dipole transition and microstrip line on the dielectric substrate was accommodated between the H-plane expanded waveguides with side-ridges. The overall power combining system exhibited the measured insertion loss of 1.2 dB (backto-back loss) at Ka-band. This result belongs to the excellent performance in terms of insertion loss and the number of the trays among the tray-type spatial power combiners reported at Ka-band.INDEX TERMS Expanded waveguide, millimeter-wave, spatial power combiner, waveguide transitions.

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