A new kind of contactless electromagnetic bandgap (EBG) structure in the form of interdigital-pin bed of nails is introduced for the first time in this paper. It consists of two metal plates with interdigital-pin bed of nails face to face with each other, where each pin is surrounded by four pins on the other plate. The working mechanism of the interdigital-pin contactless EBG structure is suppressing the modes supported by the parallel plate waveguide (PPW) by loading interdigital pins inside the PPW. The advantage of the interdigital-pin lattice is there is a significant pin gap increase. This lattice makes the minimum pin gap that could be processed by the machining center, after assembling, reduced from the diameter of the milling clutter to its radius. It provides a way to process EBG structures at higher frequency band with the same milling cutter. The cases the pins allocated between the two plates in a random manner are also studied. Compared to its traditional counterpart, the stopband is stable with a small variation. A W-band groove gap waveguide (GGW) prototype with interdigital-pins and a Ka-band GGW with randomly allocated pins are designed, manufactured, and tested. The measured results agree well with the simulation.

A compact asymmetric waveguide orthomode transducer (OMT) with broad bandwidth and high isolation is presented in this letter. A novel combined transition-bending structure is proposed within the common arm in the design of the OMT branching T-junction. It implements the E-/H-plane 90° waveguide bends and the square-to-rectangular waveguide transition for both polarization sidearms. Its multiple roles help to reduce the geometry discontinuities and improve the matching bandwidth. The measurements demonstrate that the OMT achieves higher than 50 dB isolation level between the two modes and better than 18 dB return loss from 30.3 to 36.3 GHz (18%). Furthermore, the isolation level is typically 60 dB over 50% of the operation bandwidth. The insertion loss of each polarization is below 0.23 dB for a single OMT. The overall size of the OMT functional section is reduced to $1.55\,\,\lambda _{0}\times 1.45\,\,\lambda _{0}\times 0.78\,\,\lambda _{0}$ .

A 220-GHz balanced frequency tripler with independently biased diodes is presented. By introducing parallel coupled suspended lines in the circuit, an even mode signal is supported to propagate and excite the diode pair involved in the tripler in antiphase, thus the even harmonics are suppressed. By using two physically separated suspended lines, the diodes can be biased with different voltages and the circuit imbalance can be compensated. The presented tripler does not require any on-chip capacitor or discrete bias-tee, thus the circuit size and requirements on the circuit fabrication technology are greatly reduced. A prototype using a discrete diode and quartz substrate is fabricated, assembled, and measured. Measurement shows with 160–220-mW input power, a typical efficiency of 8% can be achieved, the average output power is 17 mW, and the 3-dB bandwidth covers the 212–228-GHz band. The output power can be improved by about 6.5% with an independent bias for each diode chip.

An E-band antenna module and corresponding beam sharpening method is proposed to achieve high azimuth resolution for front-looking real aperture radar application. To achieve high angular resolution with a small antenna aperture size, a solution involving real beam and super-resolution is investigated. A monopulse antenna is developed to produce two coprime channels, which are essential for the subsequent beam sharpening in digital domain. A dual-aperture horn antenna and a monopulse comparator that make up the monopulse antenna are designed respectively, and the experimental prototypes are fabricated and tested. Experimental results show the antenna module can operate in the 75 to 80 GHz band, more than 20 dBi gain and 12° half power azimuth beamwidth can be maintained in the sum-patterns, and the null-depths are lower than −20 dB in the difference-patterns. Based on the measured sum and difference patterns, an azimuth super-resolution processing based on two-channel deconvolution is implemented. The simulation results show the sharpening ratio can achieve 12 dB with 0 dB signal-noise-ratio and truncated half power beamwidth. Theoretically, the azimuth super-resolution of 0.8° can be achieved with 20 mm aperture size. The corresponding achievements are valuable in the follow-up E-band civil front-looking imaging system.