A Waveguide Embedded 250 GHz Frequency-Tripler 2D Array
Paper in proceedings, 2014
This work reports on a 248 GHz HBV (Heterostructure Barrier Varactors)-varactor quasi-optical multiplier array with a maximum output power of 18 mW and a corresponding conversion efficiency of 2 %. The module utilizes a mechanically compact and simple shim system, combining the large array power handling capability with the convenience of waveguide interfaced circuits. At the same time this approach offers excellent power and frequency scalability.
The multiplier is based on a 12 by 6 element, 72 in total, planar 2D HBV varactor array. The diodes are fabricated on a three barrier InGaAs/InAlAs material system on InP as carrier substrate. Easch diode consist of two 20um^2 serially connected mesas, yielding a total of six barrier per diode. The HBV diodes are coupled to a uniform dipole array through which the power is coupled in and out. One HBV diode and the corresponding dipole make up a square unit cell with a side of 211 um. The chip measures 2,54 x 1,27 mm^2, fitting inside a standard WR10 waveguide.
The complete module consists of three parts, the 2D HBV array, a combined output filter and output matching slab and an input matching slab. A rhombic aperture frequency selective surface is used as the uutput bandpass filter and the quartz filter substrate also serves as a matching slab for the output tone. On the input a piece of InP substrate is used to match the incoming pump signal to the diodes. The components are mounted inside two WR-10 waveguide shims, providing an easy assembly and a modular system.
The current version of the multiplier module produces 18 mW at 248 GHz but a significant increase in output power and efficiency is expected with a new output matching network and more pump power.
Recent measurement results will be presented together with a detailed discussion regarding the design, pointing out advantages and challenges compared to more traditional approaches to frequency multiplier design in the frequency range. Future improvements and challenges will also be covered.