Multi-band RF data conversion is an essential part of radar and satellite sensing applications. Teledyne e2V showcased several new products at Electronica 2022. In this article we will highlight their new RF Analog to Digital (ADC) and Digital to Analog (DAC) converters that can operate from the L to Ka/Ku RF bands. These RF devices enable simultaneous multi-band operation in some key applications areas, as explained in the next section.
Multi-band RF Operation Advantages
Systems architectures capable of operating in multiple frequency bands have the following advantages:
- Reconfigurability of the same hardware for different frequency plans from one program to another
- Change of frequencies of operation in a sequential manner, one band at a time. This can be useful in some datalink systems to mitigate atmospheric signal degradation effects by changing bands of operation depending on weather conditions
- Leverage the benefits of phase coherent multi-band radar sensing, either for SAR radar imaging applications such as earth observation from space or airborne platforms. And also, in new emerging medical imaging areas based on micro-doppler radar sensing
- Leverage the possibility for secure communications systems to extend frequency hopping encryption across multiple frequency bands compared to most current systems operating in one single frequency bands.
The EV10AS940S ADC
The EV10AS940 (Figure 1) offers broadband sampler capability with direct microwave conversion.
Figure 1: The EVP10AS940S RF ADC
Advantages of Direct RF sampling
Conventional radio systems are typically based on heterodyne principles in which the incoming RF signal to the receiver is mixed in a non-linear mixer, creating a baseband, low frequency reception signal. This baseband reception range is usually defined by the input bandwidth of the ADC. Increasing the sampling frequency capability of ADC’s allow conception of simplified, software defined receivers with frequency agility. Beam-steered applications require parallelism and this software defined approach can simplify the receiver topology. External mixers and Numerically Controlled Oscillators (NCO’s) can be avoided and frequency planning, signal demodulation, and the entire front-end design can be simplified. This can enable digital beam forming in phased arrays.
Key features of the EV10AS940
- Ultra wide input bandwidth of 33 GHz (-3 dB)
- Samples up to 13 GSPS
- Low power consumption of 2.5 W at a sampling rate of 1.8 GSPS (195 mW/GSPS)
- In-orbit payload reconfiguration in multiple bands, with the ability to digitize signals from the L-Band to the Ka-Band
- Programmable Digital Down Convert (DDC) with I/Q decimation (x2 to x1024)
- Four independent NCO’s enable agile frequency hopping
- A multi-channel synchronization facility guarantees synchronous sampling across a plurality of devices, which is ideal for phased sensitive, beam steered applications
- A single ended analog input for the clock and signal allow for the elimination of frequency dependent baluns, which save on cost, space and weight. Eliminating baluns also potentially improves the dynamic performance allows multi-band RF operation.
Figure 2 shows the performance of this ADC when sampling a 25.1 GHz signal. Excellent spurious free dynamic range (SFDR) and signal to noise (SNR) numbers have been demonstrated in this laboratory trial.
Figure 2: The EVP10AS940S RF ADC
First customer samples of the EV10AS940 are scheduled for Q3 2023.
The EV12DD700 DAC
Synthetic Aperture Radars (SARs) are used for remote sensing to provide wide area images using antennas mounted on a moving platform. Optimal processing of received echoes can provide a large synthetic aperture with good resolution across a range of weather conditions. The frequency of operation creates tradeoffs. A higher frequency for example (e.g., in the Ku, Ka bands) can provide better accuracy as they have a broader bandwidth and narrower beam antennas, but with lower penetration depths. Lower frequencies (e.g., in the P, L bands) can improve target detection. Hence a multi-band SAR can provide operational flexibility for different applications. The new EV12DD700 DAC (Figure 3) is capable of direct signal generation to the Ka band with a large output analog bandwidth.
Figure 3: The EV12DD700 DAC
Key features of the EV12DD700
- Direct conversion up to Ka band
- 8-bit or 12-bit, up to 12 GSPS sampling rate, dual channel
- Instantaneous bandwidth of 6 GHz, with a up to a 3 dB analog bandwidth of 25 GHz
- Programmable output mode (Non-Return-Zero NRZ, RF, 2RF)
- Multi-device synchronization
- Adjustable gain
The EV12DD700 can operate simultaneously in multiple Nyquist Zone’s (NZ). For examples, L-band waveforms between 1 – 1.5 GHz simultaneously with C-band signals in the 4.75 – 5.5 GHz can be directly synthesized without overlap in the NRZ mode. X-band waveforms can be generated in the 2nd NZ simultaneously with the Ku-band pattern in the 3rd NZ. The 2RF mode allows for an up-conversion free direct synthesis at 21 GHz and beyond, as shown in Figure 4. This enables very broadband Software Defined Radios (SDR).
Figure 4: The EV12DD700 Output mode example
Multi-band RF SAR system used the EV10AS940 ADC and the EV12DD700 DAC
A use case example showing the operation of these devices in a SAR application is shown in Figure 5.
Figure 5: A Multi-band SAR use-case example for the EV10AS940 ADC and EV12DD700 DAC
Advantages of above SAR system
Radar sensing at specific frequencies have different and specific capabilities, characteristics and applications. RF signal penetration across vegetation and other material vary depending on microwave frequencies [1].
Typically, penetration distance is inversely proportional to microwave frequency. The higher the frequency, the lower the penetration depth. And terrain characteristics affect penetration capabilities and humidity acts as a shield to microwave penetration [2]. Emerging military and civilian applications of P- and L-band radar systems include the detection of targets concealed by foliage and/or camouflage, detection of buried objects, forestry applications, biomass measuring, archaeological and geological exploration.
L-band radar sensing allow for the detection of buried objects, detection of targets concealed by foliage and/or camouflage, forestry applications, biomass measuring, archaeological and geological exploration.
On the other hand, it is easier to obtain accurate range and position measurements at the higher radar frequencies, e.g., X-, Ku- and Ka-bands, since they have broader bandwidth (which determines range accuracy and range resolution) and narrower beam antennas for a given physical size antenna (which determines angle accuracy and angle resolution) [3].
Phase coherent multi-band SAR imaging provides the ability of fusing the detections made at different depths at each frequency band. And benefit from high accuracy of surface sensing and angular measurements of high frequency sensing. And correlate all those detections thanks to the phase coherency that direct conversion provides across multiple bands.
This allows the determination of the height and health of trees in a forest, volcano monitoring, draught and humidity sensing and other earth health indicators on the entire planet.
Conclusion
In conclusion, Nicolas Chantier, Strategic Marketing Director at Teledyne e2v Semiconductors explained “We are going to live an exciting decade of innovation in RF digitization across multiple bands. Now in 2023 we already see the emergence of several building blocks that are necessary to design disruptive architectures. And the choice of technology blocks across the entire signal chain will continue to expand in the coming years, and the maturity of multi-band RF systems architecture will also grow. By 2030 this will likely lead us all to see a broad expansion of multi-band approaches in an array of different applications that we do not yet foresee. And market leaderships are likely to move in various industry segments depending on who will master these architectures faster than others.”
References
[1] Flores, Africa & Herndon, K. & Thapa, Rajesh & Cherrington, Emil.; “The SAR Handbook: Comprehensive Methodologies for Forest Monitoring and Biomass Estimation”, 2019.
[2] Davis, Mark Edward; “Foliage penetration radar”; SciTech Pub., 2011.
[3] Skolnik, M. I. “Radar Handbook 3Rd Edition/Merill I. Skolnik“, 2008.