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Use of Agilent Advanced Design System

Wide-Locking Range Oscillator Design using ADS Optimization Routine:
The optimization routine in ADS was used to design an oscillator and minimize the phase slope of the loop gain, so as to maximize the locking range of the oscillator. The oscillators are designed using the open loop gain, and here you see two stages of the optimization process.

First, the oscillator was designed using lumped components. The transistor, a NE38018 from NEC, is represented by its 2-port S parameters. The optimization routine used 4 "Goals": one for magnitude of loop gain, and three for minimizing the slope of the loop gain phase. The inductor, capacitor, and load impedance were all optimization variables.

The first graph shows the results before optimization, and the second graph, after optimization. Initially, the loop gain was 4dBm with a phase slope of 40°/GHz; after optimization, 1.46dBm with a phase slope of 22°/GHz. This corresponds to an improvement in locking range from about 65MHz to 135MHz at -25dBm injection power.

The circuit was then analyzed using microstrip transmission lines in place of the lumped components. The same four "Goals" were used, but here the transmission line lengths and width were the optimization variables.

Again, notice the results before optimization and then after optimization. Initially, the loop gain was 3.36dBm with a phase slope of 55°/GHz; after optimization the loop gain was 1.23dBm with a phase slope of 32°/GHz. This corresponds to an improvement in locking range from 60MHz to 85MHz at -25dBm.

Measured results have not yet been obtained for these oscillators. Previously, with this same procedure, it was shown that progressively decreasing the phase slope, through the optimization routine in ADS, the measured locking range of the oscillators did improve (taken from the Ph.D. dissertation of Xing Wang).


Case 1

Case 2

Case 3

Phase slope (°/GHz)




Injection locking range at -30dBm (MHz)





Microwave Transversal Band Pass Filter Design using ADS:
Transversal microwave band pass filter was designed using ADS- Schematic. The filter was designed at a center frequency of 6.85 GHz. The heart of the filter is a parallel combination of two 100 ohm transmission lines designed at the center frequency. The filter is based on an elliptic prototype. The schematic of the filter is as shown,

The of the raw filter is periodic and has to be shaped to get the desired band pass filter.

of the Raw Filter

The first cycle of the filter is alone utilized. The filter has a stop band attenuation of around -13 dB. The desired filter was designed for a pass band attenuation of 2dB and a stop band attenuation of 20dB. of the desired filter is shown below. The ripple in the pass band is due to the elliptic function . The stop band attenuation is exactly 20 dB.

of the filter





CAD Applications

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