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CSDBQ structure

A Marchand balun is often part of the design of balanced multipliers, mixers, and amplifiers. The balaun can be designed in a number of different ways, with multiple planar balun structures proposed in ref. 9. The balaun shown in Fig. 2 offers a similar design. From a study of Fig. 3, it is possible to learn that (a) the phase difference (P2 minus P3) is 185 to 190 deg. between 80 to 100 GHz, and (b) the insertion loss (from P2 to P1 and from P3 to P1) is less than 3.6 dB from 80 to 100 GHz.

Phase and insertion loss

The input-power network and the input/output reflector networks can be optimized with the assistance of computer analysis using the Advanced Design System (ADS) software from Agilent Technologies and load-pull technology for analysis. It is well known that the output port of a balanced frequency multiplier will only contain even-harmonic signals and, according to the nonlinear characteristics of the multiplier, the impact of CL is weak on the higher multiplied harmonic signals. Consequently, analysis at the input port of the multiplier can focus on the input power, the fundamental-frequency signals, and the second- and fourth-harmonic signal impedance at the multiplier’s input port.

Table 1

In addition, the second-, fourth-, and sixth-harmonic impedances at the output port of the multiplier should also be studied. The input and output reflector networks for the multiplier include SCs, OCs, and matching circuits (MCs).

Table 1 provides data for analysis of CL performance for different networks, making it possible to draw a number of conclusions. For one thing, a change of CL impacted by the second- or fourth-harmonic reflector networks at the input port is about 0.1 dB, and this can be ignored. The appropriate input fundamental-frequency power reduces the VCL by about 1 dB, so the level of the fundamental input power should be a concern in the design of a frequency multiplier. When the second-harmonic reflector network is an open circuit at the output port, the CL is reduced by about 1 dB, which is an important consideration.

Balanced quadrupler

Also, when the six-harmonic reflector network is an open circuit at the output port, the CL is reduced by about 0.2 to 0.4 dB—not a small amount of loss. According to these data, it is possible to optimize a Schottky diode multiplier for certain operating conditions. The specific structure is shown in Fig. 4.

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