Building a High-Performance S-band Upconverter with Mini-Circuits Components

Aug 18, 2026 | Filters

Introduction

A frequency upconverter is used to shift a signal’s frequency to a higher frequency so that the signal can be efficiently transmitted. Frequency upconverters are often built as complex integrated assemblies that consist of various components, including amplifiers, filters, mixers, etc. In this application note, we show how a high-performance S-band upconverter can be designed exclusively using components from Mini-Circuits. To validate the performance, measured data is shown at the conclusion.

Frequency Plan

The goal here is to design an upconverter that shifts the frequency of a fixed IF input signal to a higher frequency within a specific S-band frequency range. Table 1 shows the frequency plan, which includes an IF input frequency of 1 GHz and a local-oscillator (LO) frequency range of 4.1 to 4.5 GHz. The frequency of the RF output signal is the difference of the IF and LO frequencies (i.e., 3.1 to 3.5 GHz). This S-band frequency range is used for a wide range of military radar operations, including air defense and surveillance.

IF Input FrequencyLO Frequency RangeRF Output Frequency Range
1 GHz4.1 – 4.5 GHz3.1 – 3.5 GHz
Table 1. Frequency plan of the S-band upconverter.

Functional Aspects of the S-band Upconverter

As stated, we want to design an S-band upconverter that consists solely of Mini-Circuits components. The complete upconverter is built by employing the available evaluation board for each model. Before discussing each individual component, let’s describe the general functionality of the overall design. The upconverter’s operation requires a 1 GHz signal to be applied to the IF input port. This 1 GHz signal is amplified, filtered, and then applied to the sum port of a 90-degree hybrid coupler. This 90-degree hybrid coupler splits the signal into two signals 90 degrees apart in phase. These two signals are then applied to the IF I and IF Q ports, respectively, of an in-phase/quadrature (I/Q) mixer.

In addition, an LO signal (ranging from 4.1 to 4.5 GHz) is applied to the LO input port. This signal is amplified and then applied to the LO port of the same I/Q mixer. This mixer then generates an RF signal with a frequency ranging from 3.1 to 3.5 GHz (difference of the IF and LO frequencies). This RF signal then travels through a path that includes an attenuator, filters, and amplifiers before reaching the final output.

Breaking it Down Component by Component

Now that we have discussed the basic functionality of the upconverter, let’s dive into the details. Figure 1 shows the complete block diagram of the S-band upconverter. Note that every component shown includes the corresponding Mini-Circuits model number.

Figure 1. Block diagram of the S-band upconverter.

1. IF Section

Let’s first examine the IF section shown on the upper lefthand portion of the block diagram (Fig. 1, again). As mentioned, a 1 GHz signal is applied to the IF input port. This signal is then amplified by the GALI-49+ MMIC gain block amplifier. At 1 GHz, this amplifier achieves about 14 dB of gain along with output power at 1 dB compression (P1dB) greater than +17.5 dBm.

The signal then passes through the LFCG-1000+, which is a lowpass filter developed using low-temperature co-fired ceramics (LTCC) technology. The LFCG-1000+ has a specified passband of DC to 1 GHz, with an insertion loss of about 0.8 dB at 1 GHz. It also offers more than 35 dB of rejection from 2 to 6 GHz, allowing for adequate suppression of any unwanted harmonic content. Note that the LFCG-1000+ comes in a small 0805-size package.

Following the LFCG-1000+ lowpass filter, we have the BAT-3+ attenuator. The BAT-3+ is a 3 dB attenuator that is placed here for leveling purposes and to minimize any reflections. It has an operating frequency range of DC to 60 GHz and can handle as much as 2 W of input power. A major benefit of the BAT-3+ is its extremely small size, as it comes in a QFN-style package that measures only 1.5 × 1.5 mm.

Next, the signal reaches the sum port of the QCN-13D+, which is a 90-degree hybrid coupler specified for use from 675 to 1300 MHz. The QCN-13D+ splits the signal into two signals 90 degrees apart in phase, which appear at the 0° and 90° ports, respectively. Also developed using LTCC technology, the QCN-13D+ offers low insertion loss (0.4 dB) and high isolation (19 dB). It comes in a package that measures 0.12 × 0.06 × 0.035 inches. Note that the QCN-13D+ also requires an external 50 Ω termination.

The two output signals from the QCN-13D+ are then applied to the IF I and IF Q ports, respectively, of the SMIQ-263H+ I/Q mixer. The SMIQ-263H+ is an I/Q mixer specified for use over an RF/LO frequency range of 2 to 6 GHz and an IF frequency range of DC to 3 GHz. Employing an I/Q mixer enables us to reject one sideband. In this case, the upper sideband (LO + IF) is the one we wish to reject, while the lower sideband (LO – IF) is the desired one. To reject the upper sideband, we must connect the mixer’s IF I port to the 0° port of the QCN-13D+, while the mixer’s IF Q port must be connected to the 90° port of the QCN-13D+ (see the SMIQ-263H+ datasheet).

2. LO Section

Let’s now turn our attention to the LO section seen on the bottom lefthand portion of the block diagram (Fig. 1, again). Here, we have the LO signal, which ranges in frequency from 4.1 to 4.5 GHz. This signal is then amplified by the LVA-273PN+, which is an extremely wideband MMIC amplifier (10 MHz to 26.5 GHz). From 4.1 to 4.5 GHz, the LVA-273PN+ offers about 17 dB of gain along with P1dB greater than +17.5 dBm. An important aspect of this model is its ultra-low phase noise (−172 dBc/Hz at 10 kHz offset), which enables it to be ideal for use as an LO amplifier.

Note that the evaluation board for the LVA-273PN+ (TB-LVA-273PNC+) requires both a DC block and a bias tee to be connected to the input and output, respectively. The DC block used here is the BLK-89-S+ coaxial model, which has a specified frequency range of 0.1 to 8000 MHz. The bias tee used is the MBT-283+ MMIC wideband bias tee, which covers a frequency range of 1.5 to 28 GHz. Finally, the amplified LO signal is then applied to the LO port of the I/Q mixer.

3. RF Section

The I/Q mixer then generates the RF signal, which has a frequency equal to the difference of the IF and LO frequencies. Again, the I/Q mixer is configured to reject the upper sideband (LO + IF). The generated RF signal first passes through BAT-2+ 2 dB attenuator before reaching the ABF-3R3G+ thin-film bandpass filter. This filter has a specified passband of 3.1 to 3.5 GHz, with a typical passband insertion loss of 1.6 dB. The ABF-3R3G+ achieves more than 40 dB of rejection over the LO frequency range of 4.1 to 4.5 GHz. It also achieves more than 50 dB of rejection over the frequency range of 5.1 to 5.5 GHz, which corresponds to the upper-sideband frequency range (LO + IF). Hence, the ABF-3R3G+ provides additional rejection of the upper sideband on top of the rejection provided by the SMIQ-263H+ I/Q mixer.

At this point, the RF signal must be amplified. Hence, after the ABF-3R3G+ bandpass filter, the signal reaches the PMA3-14LN+ MMIC wideband amplifier. Over the frequency range of 3.1 to 3.5 GHz, the PMA3-14LN+ achieves about 22.5 dB of gain along with P1dB greater than +21 dBm. The next component is the BFCV-2895+, which is an LTCC bandpass filter used here for additional suppression of out-of-band signals.

The next stop in the signal chain is the PMA3-83MP+ MMIC medium power amplifier, which is used here as a driver for the final power amplifier. Over the targeted frequency range of 3.1 to 3.5 GHz, the PMA3-83MP+ offers more than 19 dB of gain and achieves P1dB greater than +26 dBm. The signal then passes through the LFCG-3500+ lowpass filter for rejection of unwanted harmonics.

The next and final component is the GNA-63-5W+ MMIC power amplifier (PA). Based on gallium-nitride (GaN) technology, the GNA-63-5W+ can achieve over 6 W of saturated output power over a frequency range of 10 MHz to 6 GHz. Over the frequency range of 3.1 to 3.5 GHz, it achieves about 17 dB of gain. The GNA-63-5W+ comes in a 5 × 5 mm, QFN-style package.

Measured Performance

Figure 2 shows the complete S-band upconverter built into a test box. Figure 3 shows the upconverter’s output power versus frequency. For this measurement, the IF input power was set to a fixed level of −5 dBm while the LO frequency ranged from 4.1 to 4.5 GHz. The RF output power level was then measured across the entire RF output frequency range of 3.1 to 3.5 GHz. Across this frequency range, the upconverter achieves an output power level greater than +36.4 dBm.

Figure 2. This is the S-band upconverter built into a test box.
Figure 3. Shown is the upconverter’s output power versus frequency. For this measurement, the IF input power was set to a fixed level of −5 dBm while the LO frequency ranged from 4.1 to 4.5 GHz.

Conclusion

In conclusion, we demonstrated how an S-band upconverter can be built entirely with Mini-Circuits components. By employing evaluation boards for each component, a complete upconverter was built into a test box. Included are some of the latest innovations from Mini-Circuits, including a MMIC PA based on GaN technology, attenuators that measure only 1.5 × 1.5 mm, various MMIC amplifiers, a MMIC I/Q mixer, and more. In the end, the S-band upconverter achieves an output power level greater than +36.4 dBm across the entire output frequency range.