Frequency mixers are vital to countless RF/microwave circuits and systems, and at the core of superheterodyne receivers. In terms of bringing mixer technology “to the masses,” few companies have succeeded like Mini-Circuits, managing to enhance mixer performance and repeatability over the years while keeping costs low. And just when it looked like the company had done all it could in terms of advancing mixer technology, it does one more thing: offering a hermetic mixer for as little as $5.95 each (for a quantity of 10). These hermetic surface-mount mixers, currently available for use at RF and local oscillator (LO) frequencies to 12 GHz and eventually through 18 GHz, are members of the new MAC family of ceramic-packaged diode mixers. This line brings truly sealed performance to hostile environments at a fraction of the cost of traditional hermetic mixers.

Hermeticity is important in a number of applications, especially in environments associated with high humidity and in situations where failure is not an option. Various studies by NASA’s Jet Propulsion Laboratories (JPL), among others, on the possible degradation faced by nonhermetic mixers used in deep-space applications have shown the merits of using hermetic mixers and other components in hostile environments. Typical degradation exhibited by nonhermetic semiconductor-based mixers in high-humidity environments included oxide growth on ohmic contacts, resulting in degradation of contact resistance and changes in the current-voltage (I-V) characteristics of semiconductor devices (such as mixer diodes) over time.

Double-balanced mixers in the MAC series are based on reliable low-temperature-cofired-ceramic (LTCC) technology with a eutectic gold-tin solder hermetic seal. The ceramic materials used in LTCC circuits are extremely stable with temperature, minimizing performance variations with temperature. Mini-Circuits has produced LTCC components for the better part of the last decade; the company has developed a series of proprietary models for use with three-dimensional (3D) electromagnetic (EM) circuit simulation programs that help speed the development of new products.

The MAC series Ultra-Rel® ceramic mixers have undergone a barrage of package-level tests to ensure reliability, including gross and fine leak testing, thermal (to +150°C) and mechanical shock testing, vibration, and high-temperature operating life (HTOL) testing per MIL-STD-883. They have proven to be so reliable, in fact, that they are available with a three-year guarantee.

The MAC series of hermetically sealed mixers measure just 0.30 x 0.25 x 0.060 in. (7.62 x 6.35 x 1.52 mm) in their ceramic housings (Fig. 1). They can serve a wide range of applications, from commercial communications to military radar systems. In fact, any system in which service and maintenance may be difficult because of lack of accessibility can benefit from a mixer that provides reliable performance in a package that is sealed against outside environments. Models currently range from the MAC- 24+ with an RF and LO frequency range of 300 to 2400 MHz to the MAC-12G+ with an RF/LO range of 3.8 to 12.0 GHz. Variants of each model are available in the basic hermetic ceramic package for different LO drive levels, such as +7, +10, and +13 dBm. All are designed for operating and storage temperatures from -55 to 100°C and all are protected by US Patent No. 7,027,795.

For example, model MAC- 24+ is designed for LO drive level of +7 dBm (often referred to as a “Level 7” mixer). When fed with LO signals from 300 to 2400 MHz, RF input signals over the same range will yield intermediate-frequency (IF) signals from DC to 700 MHz with typical conversion loss of 6.0 dB (Fig. 2). It provides high isolation between its LO and RF ports, with somewhat less isolation between the LO and IF ports: The typical LO-to-RF isolation is 40 dB (minimum of 27 dB) while the typical LO-to-IF isolation is 24 dB (minimum of 17 dB). The mixer reaches its 1-dB compression point at an RF input power level of +1 dBm. As a measure of the mixer’s linearity, its third-order-intercept point (IP3) is typically +10 dBm. As noted above, model MAC-24+ is priced at only $5.95 in quantities of at least 10.

Variants of the model MAC-24+ mixer are models MAC-24LH+ and MAC-24MH+, designed for higher levels of LO drive power, at +10 and +13 dBm, respectively. Both have identical RF, LO, and IF ranges as the +7-dBm LO version, and similar amounts of isolation between ports, but with slightly higher typical conversion loss of 6.1 dB. As might be expected from the higher LO drive levels, models MAC-24LH+ and MAC-24MH+ are designed for somewhat higher linearity than the +7-dBm mixer. Model MAC-24LH+ reaches its 1-dB compression point with an RF input power level of +5 dBm and has an IP3 level of +12 dBm. Model MAC-24MH+ achieves 1-dB compression with an RF input power level of +9 dBm and has an IP3 level of +14 dBm. These higher-power variants of the MAC-24+ are offered at the same $5.95 price per unit in quantities of 10 or more.

Moving higher in frequency, model MAC-42+ is designed for an RF/LO range of 1000 to 4200 MHz and for use with LO signals at +7 dBm. It has a typical IF range of DC to 1500 MHz and exhibits typical conversion loss of 6.1 dB. It has typical LO-to-RF isolation of 35 dB (a minimum of 25 dB) and typical LO-to-IF isolation of 20 dB (a minimum of 12 dB). Model MAC-42+ reaches 1-dB compression at an RF input power level of +1 dBm and has a typical IP3 of +10 dBm. Model MAC-42+ is priced at only $6.95 in quantities of at least 10.

The higher-power variants of the MAC-42+ mixer are model MAC-42LH+, which is designed for LO drive of +10 dBm, and model MAC-42MH+, which has been optimized for LO drive level of +13 dBm. Both have identical RF/LO and IF ranges as the MAC-42+ mixer, as well as the same typical conversion loss of 6.1 dB at 30 MHz (as Fig. 3 shows, the conversion loss rises with increasing IF). The Level 10 model MAC-42LH+ exhibits typical LO-to-RF isolation of 38 dB (a minimum of 24 dB) and typical LO-to-IF isolation of 20 dB (a minimum of 11 dB). It hits its 1-dB compression point with RF input power level of +5 dBm and has a typical IP3 of +12 dBm. The Level 13 model MAC-42MH+ has typical LO-to-RF isolation of 35 dB (a minimum of 22 dB) and typical LO-to-IF isolation of 20 dB (a minimum of 12 dB). It reaches 1-dB compression with an RF input power level of +9 dBm and has a typical IP3 +16 dBm. These two higherpower mixers also sell for $6.95 each in quantities of 10 or more.

For applications to 6 GHz, model MAC-60+ is optimized for LO drive of +7 dBm. It features an RF/LO frequency range of 1600 to 6000 MHz and IF range of DC to 2000 MHz. This mixer has typical conversion loss of 6.4 dB for an IF of 30 MHz (Fig. 4). It has typical LO-to-RF isolation of 35 dB (a minimum of 19 dB) and typical LO-to-IF isolation of 15 dB (a minimum of 9 dB). Its 1-dB compression point occurs with RF input power level of +1 dBm, and it has a typical IP3 of +10 dBm. It is priced at $7.45 each in quantities of 10 or more.

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