High Performance, Low Cost, Surface-mount Microwave Mixers

High Performance, Low Cost, Surface-mount Microwave Mixers

Blue Cell Technology, a family member of Mini-Circuits
Brooklyn, NY

As communication bandwidth requirements increase, industry is demanding higher performance in passive devices as well as smaller footprints. Although attempts are being made to utilize semiconductor technologies, they are capital intensive and, hence, the selection is limited. Blue Cell™ technology lends itself to low cost mixer designs for moderate to high volume markets and utilizes standard thick-film technology. A series of high performance passive mixers has been developed that uses patented Blue Cell technology. Each mixer exhibits good conversion loss from 2.5 to 6.7 GHz with excellent LO-to-RF and LO-to-IF isolation. The finished part has an ultra-low height of 0.07" and its footprint measures 0.25" x 0.30".

The Mixer Design
The design for the mixer series was accomplished using the HP Momentum 2.5D electromagnetic simulator; the nonlinear analysis was performed with HP Microwave Design System software. Because the grounding is through inductive leads, the actual high end performance of the mixer was slightly lower than the computer predicted. However, excellent performance was achieved with just one design iteration.

Assembly Details
The mixer is fabricated in multilayer thick film using materials and processes chosen to optimize their high electrical performance. Strict controls are placed on both the materials and the processes to ensure repeatable performance from part to part. The diodes are attached using automatic die attach and assembled using automatic wire bonders. The package consists of 10 leads attached to the substrate with high temperature melting point solder. The leads are solder plated, have good solderability and are shaped to provide strain relief to account for variations in the temperature coefficient between the host PCB and the mixer. A proprietary epoxy cure process has been used to protect the diodes and traces, ensuring a part rugged enough to withstand repeated high temperature reflows while maintaining good moisture resistance.

Performance
The model MBA-671 mixer operates from 2400 to 6700 MHz. Typical conversion loss is less than 6.5 dB from 2600 to 5000 MHz and increases to 8.2 dB at 6700 MHz. LO-to-RF isolation is typically greater than 30 dB across the entire range, while LO-to-IF isolation is typically greater than 22 dB. Figure 1 shows the mixer’s conversion loss with a 4, 7 and 10 dBm LO drive. Figure 2 shows the port-to-port isolations at a 7 dBm LO drive. Figure 3 shows the RF, LO and IF port SWRs. Performance is dependent on the quality of the printed ceramic substrate. High performance materials with ground vias placed less than an eighth-wavelength apart are employed. A recommended footprint is provided in the mixer data sheet and can be downloaded from the company’s Web site at www.minicircuits.com in the online catalog. Table 1 shows the mixer’s specifications.

Applications
The mixer is a standard double-balanced design and can be used both as an upconvertor and a downconvertor. The IF is DC coupled so the mixer can be utilized for balanced modulator applications. The broad IF range allows the mixer to be used in satellite applications for multichannel communications. The low conversion loss results in lower noise figure. For applications requiring higher dynamic range, higher level mixers that improve IP3 performance are offered.

Conclusion
A new series of microwave high performance surface-mount mixers has been presented. These mixers are very low height and are suitable for Personal Computer Memory Card International Association computer card applications. The MBA-series products are designed for demanding low cost, high quality, high volume applications.

Blue Cell Technology, a family member of Mini-Circuits, Brooklyn, NY (718) 934-4500.