The Mixer and Multiplier Synthesis Wizard allows you to synthesize several types of mixer and multiplier structures to be implemented in microstrip transmission line structures:
Singly balanced Rat Race Mixer (180 deg.) and Branch Line Mixer (90 deg.) - These components create similar projects, differing primarily in the type of hybrid used in the circuit. The most important subcircuits are called "MxrElement1" and "MxrElement2". These include stubs that have a tuning function as well as bypassing the diode at appropriate frequencies; they can be tweaked to optimize the passband shape and return loss. The hybrid’s center frequency can be adjusted via the Scale variable.
Simple Single Diode Doubler - This component creates a single-diode resistive frequency doubler using a Schottky diode (not a varactor). The doubler usually has approximately 10 dB conversion loss, and output power depends on the capabilities of the diode. A shorted stub on the input side of the diode realizes the second-harmonic current return, and a stub on the output creates a current return for the fundamental frequency. The latter stub is one-quarter wavelength long at the output frequency, making it one-eighth wavelength at the fundamental. As such, it is not a perfect return, and its length can be adjusted to trade off second-harmonic rejection against efficiency. The input stub can also be adjusted to optimize input return loss and to center the passband.
Balanced Rat Race Doubler - This component creates a two-diode, balanced frequency doubler. The circuit is superior to the single-diode circuit in its power handling and even-harmonic rejection, but it is a larger circuit, requiring a rat-race hybrid. The project creates graphs of the hybrid’s performance as well as the complete doubler.
The input stub of the DblElement subcircuit can be used for tuning. The element has no output stub, as the junction between the two diodes is a virtual ground. The lack of an output stub allows greater bandwidth than the single-diode mixer and it allows a lower-impedance return for the fundamental-frequency diode currents.
Z0 - Specify the component's port impedance. 50 ohms is the default.
To access the Mixer and Multiplier Synthesis Wizard, open the Wizards node in the Project Browser and double-click Mixer and Multiplier Synthesis. The Mixer and Multiplier Synthesis dialog box displays.
On the Mixer/Multiplier Setup tab, select a Component Type and then specify the design parameters:
Diode Type - You can specify any of four diode types: GaAs and low- medium- or high-barrier silicon. The synthesis inserts a diode having typical parameters for the diode type and the frequency of operation. You must then select an available diode having similar parameters and substitute the wizard-selected parameters with those of the desired diode. The silicon-diode parameters are based on typical, commercially-available beam-lead devices, and the GaAs diode is based on a MMIC element. The parameters of diodes used in these circuits are usually not critical. In selecting a diode to replace the one inserted by the wizard, you should view the junction capacitance as the most important parameter to be matched.
Mode of Operation - This option allows you to define a wide range of mixer frequency plans: upconverters or downconverters, low- or high-LO mixers, fixed IF or LO frequencies. When the Sweep RF and LO in Sync check box is selected, a project is created in which the RF and LO signals are both swept and have a fixed difference frequency. This is most useful in ordinary downconverters having a fixed IF frequency. When selected, you can specify either a high- or low-side LO and the RF-LO difference frequency.
Frequency Setup - If Sweep RF and LO in Sync is selected, the frequency setup involves specifying only the RF frequency range in RF Min and RF Max and the number of Points in the swept range. If Sweep RF and LO in Sync is cleared, the wizard creates a project in which the RF frequency is swept and the LO frequency is fixed, and values are entered in the boxes for all quantities. You also specify whether the IF is the RF-LO difference (a conventional downconverter) or sum (upconverter). The LO can be either above or below the RF range. If a harmonic mixer is desired, you should enter the fundamental LO frequency. You can then manually modify the measurements in the project to display the desired mixing product. Even for an upconverter, the IF is always the output frequency and the RF is the input. The LO is always the large-signal excitation. Default values of the number of harmonics for the RF and LO, and other harmonic-balance setup parameters, are created by the wizard. You should review these values to ensure they are sensible for the particular design and its application.
Create Graph or Overwrite Existing Documents - Select an option to create a new graph or overwrite an existing graph.
Clickto synthesize the component and send the design to the AWR Microwave Office program. The wizard creates a large number of subcircuits and output graphs. Each mixer or multiplier circuit is hierarchical, having separate subcircuits for the hybrid, diodes and matching circuits, and test circuits for fixed and swept LO power. Several graphs document the performance of each circuit.
On the Microstrip Setup tab you can configure the microstrip technology parameters for the components:
Substrates - Select a substrate type with its editable default parameters, or select Global Definitions MSUB, a substrate that is already defined in the project’s Global Definitions and available from the drop-down list.
Substrate parameters - You can modify the default parameters for the selected Substrate.
Length Units - Select the desired length units. It is always best if the units are the same as the project units, as this is the most precise. In any case, the synthesized component’s dimension are entered in project units when the AWR Microwave Office project is created.
Tee/Step Type - Specify discontinuity elements that use either the Closed Form or electromagnetic (EM) models.
The synthesized project includes the AWR Microwave Office schematic, necessary subcircuits, and graphs, but not finished layouts; you need to manipulate the layout to finalize the component design. Appropriate quantities in the subcircuit are entered as tunable variables. Line lengths in the synthesized circuit are modified to compensate for the size of interconnects and bends. That compensation may not be exact in all cases, causing the center frequency to differ from the value entered. To compensate, the synthesized circuit includes a “scale” variable, which proportionately scales the lengths of all relevant microstrip elements, allowing adjustment of the center frequency.