To Design in Software

Maker Code 128B in Software To Design

1 A = 90 long at LO frequency or at (fRF + fLO)/2, using 50- microstrip 2 B = 90 long at LO frequency or at (fRF + fLO)/2, using 355- microstrip 3 C = 90 long at RF frequency, using 50- microstrip (C shorts RF to ground Bends do not affect actual length, but are used for compactness) 4 D = 90 long at LO frequency, using 50- microstrip (D shorts LO to ground Bends do not affect actual length, but are used for compactness) 5 E = 50- microstrip, with the two traces before the D1 and D2 diodes being of equal length 6 RFC = 90 long at LO frequency, using 100- microstrip 7 D1 and D2 = select the appropriate Schottky diodes for the frequency of operation and the application

NOTE : The B section is extremely sensitive to exact dimensions for LO suppression at RF port The LPF is used to attenuate all frequencies above the IF

A Quick Example Design a Passive Single-Balanced RF Diode Mixer (Fig 78) Goal: Create a single-balanced diode RF mixer The specifications and parameters for the circuit are: fRF = 58 GHz fIF = 40 MHz fLO = 576 GHz PLO = +5 dBm POUT = 5 dBm Conversion loss = 6 dB

10 11 32

53 74 95 116 137 158 179 200 001

IF OUTPUTPORT (dBm)

RF INPUTPORT (dBm)

10 11 32 53 74 95 116 137 158 179

01 1 10

200 001

Frequency (GHz)

Frequency (GHz)

FIGURE 78 The example single-balanced diode mixer circuit with calculated part s values, along with harmonic balance frequency sweep results (log scale): (a) All the signals present at the RF input port; (b) All the signals present at the IF output port

Diodes = Avago HSMS-2820 (Schottky type, appropriate for frequency of interest) Substrate = Roger s RO-4003, 20-mils thick Solution: 1 A = 45-mils wide by 314-mils long 2 B = 76-mils wide by 306-mils long (to decrease LO feedthrough to RF port, B section optimized in simulator slightly to 70-mils wide by 307-mils long) 3 C = 45-mils wide by 312-mils long 4 D = 45-mils wide by 314-mils long 5 E = 45-mils wide by variable length 6 RFC = 10-mils wide by 330-mils long 7 LPF = C1, C2 = 63 pF; L1 = 204 nH (cutoff frequency = 42 MHz) 8 C3 = 4 nF (coupling capacitor for 40 MHz IF)

Microwave Circular Rat Race Single-Balanced Diode Mixer (Fig 79)

Very similar to the above mixer, this low-cost, distributed microwave diode mixer, when used with Schottky diodes, is an excellent choice for very high frequencies It requires an 8-dBm LO drive level, has decent intermodulation performance, good RF/ LO-to-IF and LO-to-RF port isolation and, as with all diode mixers, will have a conversion loss (in this case, 6 dB) The IF must be no higher in frequency than 50 MHz or so, since the difference between the LO and RF frequencies must be relatively small due to the mixer s resonant distributed design; which has to be able to effectively react to both the RF and the LO frequencies

fRF + fLO (for midway between the RF and LO frequencies) 2 2 A = 90 long at fm, using 707- microstrip 1 fm = 3 B = 270 long at fm, using 707- microstrip 4 C = 10 long at fm, using 50- microstrip 5 D1 and D2 = select the appropriate Schottky diodes for the frequency of operation and the application

E 50

6 LPF = in the included AADE Filter Designer software, design a 50- lumped lowpass filter with 15 IF frequency cutoff (a shunt capacitor must begin the filter for the LO and RF currents) The LPF may also be designed as a distributed network, or by using a small multilayer ceramic filter 7 E = short 50- microstrip