Microwave Circuits

Linear Transistor Modeling Using Equivalent Circuits

This note shows accurate transistor characterization for amplifier design using WIPL-D Microwave, providing a complete environment for implementing lumped circuit equivalent transistor models that deliver reliable S-parameter data. A low-power packaged GaAs HEMT is modeled, with intrinsic and extrinsic elements partitioned and their physical basis briefly explained. The calculated S-parameters are highly accurate, enabling designers to overcome limitations of sparsely tabulated transistor data and determine optimal biasing points for specific applications. WIPL-D Microwave ensures the flexibility to implement schematics of any commonly used linear transistor model, supporting efficient and precise amplifier design workflows.

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Rectangular Waveguide Interdigital Filter

This application note describes the detailed simulation of a band-pass interdigital filter in rectangular waveguide technology, modeled in WIPL-D Pro CAD using the native editor and built-in primitives. A symmetry plane was carefully utilized to reduce structural complexity, and two waveguide ports served as feeders. The model was simulated from 5 GHz to 14 GHz at 26 frequency points, with convergence checks performed to ensure high accuracy. After the convergence study, filter dimensions were finely tuned to achieve S11 values below –20 dB in the passband (8.30–10.86 GHz). Simulations can be efficiently performed on any desktop or laptop, preferably with multiple CPU cores, with per-frequency simulation times measured in seconds overall.

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Matching Network Design for Power Amplifiers

This application highlights the design and simulation of power amplifier matching networks using WIPL-D Microwave Pro, providing a complete environment for accurate, efficient, and fully integrated modeling and analysis. A commercially available power transistor is used to illustrate typical matching network topologies and the full design flow, emphasizing the importance of including electromagnetic analysis to capture coupled discontinuity effects that can significantly impact performance. Designs are demonstrated on a microstrip substrate recommended by the manufacturer, with easy adaptation to alternative substrates, showcasing WIPL-D Microwave’s versatility, precision, and efficiency for advanced microwave amplifier engineering.

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Power Detector with Zero-Bias Schottky Diode

This application note presents the design of power detectors using WIPL-D Microwave, a complete one-stop environment for microwave circuit designers. Analytical-element-based modeling can be seamlessly expanded to full 3D EM analysis, automatically transferring any schematic with proper layout into an EM component when higher accuracy is needed. Detector choices, including non-matched or matched configurations, depend on the specific application. For matched detectors, simple networks optimize sensitivity, while more complex networks may need to improve return loss. Electromagnetic modeling ensures all effects are accurately captured, highlighting WIPL-D Microwave’s efficiency, precision, and versatility for advanced power detector design.

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Multi-hole Waveguide Coupler

The multi-hole waveguide coupler, basically an extension of the single-hole coupler, is specifically designed to increase operational bandwidth. Its overall performance mainly depends on the size of the coupling holes and the distances between them, ensuring wave amplification in the through-direction and cancellation in the opposite direction. Standard X-band WR-90 waveguides (22.86 mm × 10.16 mm) are coupled through a series of rectangular holes arranged in a zig-zag pattern. Simulations use a relatively low number of frequency points thanks to powerful built-in interpolation, and hardware requirements are minimal—any standard desktop or laptop can typically perform the simulation in seconds due to the rather small number of unknowns.

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7-Port Divider

In this application note, a 7-port divider is simulated from 1.4 GHz to 1.6 GHz in microstrip technology, with a probe-fed SMA Tx port and six Rx microstrip ports. The model is created in WIPL-D Pro using parametrized geometry, defining symbols, nodes, and plates, which, while slightly slower than importing DXF or other files, produces an optimal mesh minimizing simulation time. Efficiency is further improved with Copy/Layer manipulation. Thanks to built-in interpolation, only a few frequency points are required. WIPL-D Pro treats the 7-port divider as electrically small, resulting in minimal unknowns and very fast simulation. Simulation is completed on a standard desktop in few seconds, demonstrating accuracy and computational efficiency.

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SPDT Shunt PIN Diode Switch

This application demonstrates the design and simulation of a single pole double throw (SPDT) switch using PIN diodes in WIPL-D Microwave Pro. The diodes are modeled with equivalent circuits for ON and OFF states, while other schematic elements, including microstrip and coaxial components. Simulations show accurate performance analysis of semiconductor-based switches over relevant frequency ranges.
WIPL-D Microwave integrates full-wave 3D EM solver, circuit modeling, and built-in optimization, enabling efficient evaluation of complex microwave designs. This approach reduces simulation time, minimizes unknowns, and allows execution on standard desktop or laptop PCs, making WIPL-D a versatile solution for advanced microwave engineering.

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Lowpass Filter Design

In this application note, three filter models are designed and analyzed using WIPL-D’s Filter Designer, a wizard-like GUI for automated design of lowpass, highpass, bandpass, and bandstop filters of Chebyshev or Butterworth type. A lowpass Chebyshev approximation is considered: first model is an LC ladder, second a transmission line, and third a microstrip filter. The microstrip model is also simulated in WIPL-D’s 3D EM solver using full-wave EM analysis. The operating band is 0.014–2.8 GHz, and due to efficient interpolation, only 11 frequency points suffice for EM simulation on a standard desktop or laptop. Simulation time for circuit models is negligible, while full-wave EM simulation takes only a few seconds per frequency point.

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Metallic Cover over Wilkinson Power Divider

The Wilkinson power divider is a compact microwave circuit designed to split input power evenly between two output ports. In this note, the divider is simulated in WIPL-D Pro at 25 GHz on an ultra-thin 0.005 mm substrate (εr = 3), yet model remains stable. Microstrip ports are implemented using two trapezoidal plates connected by a short wire with triple junctions, ensuring excellent matching, minimal reflections, and accurate excitation. Output isolation is provided through a lumped resistor. A metallic enclosure is added to evaluate realistic packaging effects, and its influence is compared to the open version. Simulated results show clean −3 dB splitting, strong isolation, low return loss, and only slight impact from the added cover, overall simulation accuracy.

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Design Flow for Microstrip Bandpass Filter

The accurate and efficient design of a microstrip bandpass filter can be achieved using the WIPL-D design suite, which integrates microwave circuit, EM, radiation, and near-field analysis within a single environment. The built-in Filter Designer enables direct synthesis of a microstrip filter based on user specifications through wizard-like interface. Analytic microstrip elements can be optimized to meet specifications and then seamlessly transferred to the EM model. A metallic enclosure can be added to study shielding effects, which may impact fundamental and parasitic bandwidths. Techniques for suppressing box modes can be tested immediately using full-wave EM simulation, avoiding costly and time-consuming rework after filter fabrication.

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Microstrip Combline Bandpass Filter

Simulation of a microstrip combline bandpass filter is performed using WIPL-D Pro, full-wave 3D MoM solver. The filter operates from 4 to 5.5 GHz and is modeled on a cost-effective desktop using a common microstrip substrate. With only 37 simulated frequency points, the WIPL-D Fitter accurately reconstructs the wideband response, revealing clean
S-parameters and a useful transmission zero above the passband for improved selectivity. Optimized resonator lengths, line widths, and gaps are easily realizable in standard technology, enabling easy prototype fabrication. The workflow highlights WIPL-D’s efficiency and reliability for both commercial and academic filter design while offering practical guidance for further development and research.

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Microwave Circuits Design in WIPL-D Microwave

Simulation of complex microwave circuits is demanding, so circuit-level analysis is typically the best starting point since it delivers quick, reliable results by using predefined library components that compute far faster than full-wave EM analysis, even across wide bands. WIPL-D Microwave provides a fast, accurate, and user-oriented environment, compatible with other tools through Touchstone import and seamlessly connected with the WIPL-D EM solver, Optimizer, and Time Domain Solver. Demonstrated designs include a single-stub tuner in rectangular waveguide matched at 10 GHz, a diplexer operating at 2 GHz and 2.2 GHz, and a Chebyshev coaxial impedance transformer spanning 2 to 8.5 GHz, all simulated on any standard desktop or laptop.

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