IEEE Microwave Magazine - October 2016 - 65

Original Coffee Can Radar

Mini-Circuits
ZX95-2536C+

5.9 dBm

Cantenna

Mini-Circuits
VAT-3+

Mini-Circuits Mini-Circuits
ZX60-272LN+ ZX10-2-42+

Mini-Circuits
ZX60-272LN+
Baseband
Signal
Cantenna
Mini-Circuits
ZX05-43MH+

Figure 5. The OCW system diagram implemented with behavioral models.
System Simulator (VSS) system-design software from
National Instruments (NI).
System-simulation blocks are essentially mathematical models representing the performance of RF
components and are configured using information
supplied in the vendor data sheets such as gain, 1-dB
compression point (P1dB), and noise figure. The simulator used for this project, VSS, has a built-in radar
component library that contains more complex models such as targets and baseband processing blocks,
which were pulled directly onto the system diagram,
as shown in Figure 5, representing the OCW transmit/
receive chain. The system block values for the behavioral models were populated in the system simulation
diagram according to each individual Mini-Circuit
component's data sheet.
Figure 5 shows that, in addition to the transmit/receive chain, a target model including distance, velocity,
and radar cross-section parameters is inserted between
the transmit and receive antennas. The system model
in Figure 5 supports both RF link budget analysis and
time-domain envelope simulations, which enable baseband processing algorithms to be applied to the simulated signals. Therefore, the hardware and baseband
processing software can be developed jointly by RF
and system engineering, providing immediate and direct feedback to both engineering groups when design
changes are made.
The original RF chain in Figure 5 provided the
performance baseline for the entire system. The "recaffeinated" system shown in Figure 6 replicates the

October 2016

exact original system topology but replaces the connectorized components' behavioral model parameters with performance metrics of comparable SMT
parts, mostly in the US$2.00-3.00 price range. The
exact part numbers and performance values are
shown in Figure 6.
RF system designers have many choices for amplifiers, mixers, and VCOs in the ISM Wi-Fi bands, available through distributors with convenient online
ordering and quick shipping. For example, Table 1
shows a small sample compilation of parts that were
considered for the PA slot in this redesign project.
The decision for each of the active RF functions in the
redesigned radar was researched in this way before
the final parts were chosen based on price, size, PCB
implementation complexity, and, ultimately, performance. Being able to compare the parts' performance
in the system simulator was very valuable to this redesign effort because different parts could be evaluated
for system metrics such as total system noise figure,
transmit power, and margin-to-power compression at
different points in the system diagram.
The PCB implementations for the pad attenuator
and low-pass filter (LPF) were chosen to be simple SMT
capacitors and resistors using the circuit simulator to synthesize and design their exact values. Both the LPF and
attenuator were designed as π-network circuit topologies so that they could be easily shorted out with a series
zero-Ω resistor if deemed unnecessary later. Based on
the system simulations, the attenuation was chosen to be
2 dB, and the LPF bandwidth was set to 10 MHz.

Table of Contents for the Digital Edition of IEEE Microwave Magazine - October 2016