CHAPTER 4 Dual Leaky-wave Antenna Arrays Structure Design
4.4 Integrating the Antenna Arrays and the CMOS Transceiver into a
The mechanical fixture of first version FMCW sensor will be designed for integrating with the antenna arrays and CMOS transceiver. The fixture was used for an experiment of the range measurement. The structure of this fixture includes a hollow box with the CMOS transceiver and accessory circuits are placed into and the antenna arrays are put on, a rotated holder with the hollow box is held and rotated, and the base of a fixture. The mechanical drawing was illustrated in Fig. 4.28 the fixture photograph was demonstrated in Fig. 4.29, and the hardware integration of the FMCW sensor system was also shown in Fig.
4.30.
Feeding Input
Leaky-wave Antenna Array
Fig. 4.29 Photograph of the leaky-wave antenna array system.
Fig. 4.30 Hardware integration of the FMCW sensor system.
Figure 4.30 show that the signal processor was followed the RF transceiver is analog circuits.
The building blocks of the new version FMCW sensor system shown in Fig. 4.31, which has an RF transceiver, a digital signal processing unit and two antenna arrays, were integrated within a metallic enclosure prior to experiments
RF Frond-End
Analog Signal Processing Unit
Antenna Array
were performed. The width, length and height of the enclosure were 20cm, 22cm and 12cm, respectively (Fig. 4.32). Two antenna arrays were installed on top of the enclosure, and covered by a radome, which is 2.0mm-thick a Teflon sheet.
Fig.4.31 Prototype of the leaky-mode antenna arrays.
Fig. 4.32 Mechanical installation of the FMCW sensor for TMS.
CHAPTER 5
Design of the Accessory Circuits: the External IF Circuits and Digital Signal Processing Unit
The major contribution of the paper is to integrate a 0.18µm CMOS transceiver and antenna arrays into a FMCW RF-frond, then adopt a triangle-wave generator, an IF amplifier and a digital signal processor to prove the nearly uniform SNR concept. Hence, the paper focuses on the design and integration of RF system. However, the function blocks and response figures of the external IF and DSP modules are provided an additional remark. The main structure of external IF circuits include a linear modulated circuit and an IF active filter and those circuits were built by the operational amplifiers (OPA).
At FMCW system, the exception of the linearity of the voltage-controlled oscillator (VCO) in chapter 3 is a key point, and then the circuit design of modulation in the chapter is also important. The modulated circuit includes a triangle-wave generator, a telemetric control circuit, and a synchronous signal generator (Fig. 5.1). The most important circuit is the triangle-wave generator that was transferred from the integral squared-wave generator. The operating frequency of the triangle-wave generator was controlled by the capacitor C1, the amplitude was adjusted by the proportion of resistors R1 and R2 (the main adjustment of R2), and the DC bias was varied by resistor R3. By modulating of the VCO, the bias level of the triangle-wave generator set the center frequency of FMCW system, the amplitude of the triangle-wave generator decided the frequency span (bandwidth) of FMCW system, and the period of the triangle-wave generator also control the frequency resolution of FMCW system.
Another important parameter is the slope of the triangular waveform that also determined the linearity of the FMCW system, and next key factors is the good symmetry of this isosceles triangle waveform that avoided the error message of Doppler shift. Hence, a constant slope and a good symmetry of the triangular waveform are the preliminaries of a linear modulation for the FMCW system and then the system can achieve the function of the range measurement.
Fig. 5.1 Frequency modulated circuits includes a triangle-wave generator, a telemetric control circuit, and a synchronous signal generator
Figure 5.2 shown the time-domain response of the triangle-wave generator involve that the triangular waveform and the squared waveform were excited by the frequency modulated circuit in Fig. 5.1. Especially, the telemetric signal was triggered by the digital signal processor or other circuits, and then the action would turn off the triangular and squared signals. In other words, the duration of the telemetric signal was excited and then the frequency modulated continuous wave system was converted into the pure continuous wave system. The primary
Telemetric control
Fig. 5.2 Time-domain response of the triangle-wave generator in frequency modulated system.
The next circuit of the external IF circuit is IF active filter. The filter used to define the scope of the beat frequencies, that is, it also set the measurement range of the radar. The RF circuit simulation was illustrated at chapter 3, the IF output power of the mixer in the transceiver was about −125 dBm. The output impedance of IF port of the mixer is 50 Ω, it bases on this reference impedance to estimate the minimum output voltage is nearly 5 mV. Therefore, the exciting level of the IF active filter input will be set to 1 mV. In the chapter 3 of the thesis, the measured distance of FMCW sensor was defined from 5 meters to 30 meters.
If the frequency of triangular wave is set to 1.42 KHz, then the corresponding frequency resolution is 2.84 kHz. The range resolution is 1 meter in accord with the RF bandwidth of 150 MHz. The beat frequency of 5 meters is 2.84 KHz × 5
= 14.2 KHz and of 30 meters is 2.84 KHz × 30 = 85.2 KHz. Hence, the bandwidth of the IF active filter is from 14.2 KHz to 85.2 KHz by initial estimation. If the 3-dB bandwidth is an actual specification and the input level of the analog-to-digital converter is less than 3 V, then the modified bandwidth of the IF active filter is from 12 KHz to 100 KHz and gain is about 68.7 dB.
Ultimately, the schematic of the IF active filter was shown in (a) of Fig. 5.3 and the frequency response was also displayed in (b) of Fig. 5.3.
(a)
(b)
Fig. 5.3(a) schematic of external IF active filter, (b) the frequency response of external IF active filter.
Figure 5.4 displays the architecture of the digital signal processing unit of the proposed FMCW radar. The operational principle of the FMCW radar for detecting the distance from the output signal of the digital signal processor can be mathematically described as in the previous paragraph.
F=12KHz
16-bit
Fig.5.4 Block diagram of the digital signal processing unit.
The flowchart of fast-Fourier transformation and the target discrimination of the digital signal processing were shown in Fig. 5.5.
Fig.5.5 Flowchart of the digital signal processing unit.
Since the IF amplifier and the digital signal processor (TMS320C6701) is accessory circuits in the paper and these circuits assist to prove the performance of CMOS transceiver. The CMOS transceiver also integrates with antenna arrays, an IF circuit, and a DSP circuit to realize the FMCW system. If size and
A/D 256 pts
Range CFAR Target
Dwell
Target Post
FFT Processing Target Processing
cost of the DSP will be miniaturized and cost-down, then can choose the DSP of MicrochipTM or realize an ASIC chip.
CHAPTER 6
Measurement and Verification of the FMCW System
6.1 Measurement of the First-version FMCW Radar
Figure 4.29 shows the fixture for the revolving spindle that facilitates accurate positioning the main beam of an antenna array to a desired target. The leaky-mode antenna arrays were purposely lifted to expose the RF module and analog signal-processing unit installed on the backside of antenna arrays. Figure 3.1 shows the proposed sensor system, which can detect distance and velocity of objects simultaneously. In the following section, experimental results, including those for detecting distance and velocity, demonstrate the capability the FMCW sensor.
6.1.1 Distance Measurement
The initial design employs the triangular waveform as a modulation source, and so has various applications. If the modulation source were a sawtooth waveform, then information about the speed would be lost. In other word, there is no Doppler shift in the range measurement. Since the original paper, the FMCW sensor is also designed for the speed measurement. To simplify the thesis and because of the special purpose to which is applied, the measurement of speed is omitted. In the paper, the sensors were located in the roadside are set up vertically to the multiple-lines, since the vertical direction to the target results in a zero-frequency Doppler shift whether the vehicle is moving or stationary.
The photograph of the field test (Fig. 6.1(a)) presents the setup for detecting distance between an object and sensor. A small moving vehicle carrying an
aluminum plate 80 cm×60 cmin size is applied as a reflective object for static detection of target distance. Given the parameters of ΔF =50 MHz, Fm= 100 KHz, the output spectrum of the IF-ABPF is shifted from 100 KHz to high frequency for each increase in stepping distance of 3 m. During measurements for distance detection, echo signal power spectra were monitored continuously.
Part (b) in Fig. 6.1 presents the measured spectrum at the mixer output for a target 25.8 meter from the sensor. No reflected signals were observed near 200.0–400.0 KHz (Fig. 6.1(b)), indicating that isolation inside the CMOS transceiver chip and isolation between two antenna arrays are attained.
Additionally, the measured distances are calculated by (2-1) with the sensor parameters already mentioned. Figure 6.2 plots the measured and theoretical beat frequency of the sensor, indicating that the error bound is consistently <3.0
% when the D is increased from 10 to 30 meters.
(a) D
(b)
Fig. 6.1 Distance measurement using the FMCW sensor: (a) field test setup, (b) measured spectrum of the mixer output for a distance of 25.8 meters
600 800 1,000 1,200 1,400 1,600 1,800 2,000 Beat frequency (KHz)
8 10 12 14 16 18 20 22 24 26 28 30
Meter
Actual Distance Theoretical Distance
Fig 6.2 Measured and theoretical values of distance vs. beat frequency of the proposed FMCW sensor.
6.1.2 Velocity Measurement
The results of equation fd = fb-− fb+ indicate that the speed is a down-converted after two beat frequencies are mixed. A traditional FM system accepts demodulated signals using an envelope-detected circuit containing diodes and a low-pass filter. In the work, the analog signal processing circuit also has an envelope-detected circuit that is substituted for a digital signal processing (DSP) unit to measure target speed. The moving target was detected by aiming the antenna at a vehicle traveling at 60 km/hr at an angle (θ) of 30° from the forward direction (Fig. 6.3). Actual speed was read from the automobile speedometer. The beat frequency (fb) was increased from 100.0 KHz to 1.0 MHz.
Such an increase reduces response time of the FMCW radar when detecting moving targets.
Fig.6.3 The outdoor test area for distance and velocity detection
Figures 6.4 (a) and (b) were present measurement results at the output of the envelope detector in frequency and time domains, respectively. When the
),
Therefore, v=16.66(m/sec) = 59.976(km/hr), validating the receiver chain when processing to echo signals from the target, and yields the performance of the velocity measurement using the proposed FMCW sensor.
(a)
(b)
Fig. 6.4 Velocity detection using the proposed FMCW sensor: (a) input spectrum of the envelope detector; (b) time-domain waveform at the output of the envelope detector
6.1.3 Field Test of the Azimuth Resolution of Antenna Arrays
Since the azimuth resolution (E-plane) haven’t discussed in the dissertation.
Nevertheless, the experiment is applied the leaky-wave antenna arrays of the paper integrate with the RF transceiver using by Institute of Traffic and Transportation of National Chiao-Tung University to do field test.
Main purpose of the experiment is that estimated the performance of the E-Plane radiation pattern application of leaky-wave antenna arrays for the vehicle classification of the transportation management system. Hence, the comparison of the E-Plane radiation pattern in the actual measurement was made, such as the leaky-wave antenna arrays and the original dual-horn antennas.
The experiment is carried out and tested dynamically in the balcony of second floor of Center of Transportation Studies of National Chiao-Tung University; the product’s idea of its experiment is as follows. In antenna parts:
First, the dual leaky-wave planar antennas were designed by the Graduate Institute of Communication Engineering of NTU. Second, the pairs of horn antennas were designed by UUEI Engineering INC. In transceiver parts: the design of microwave circuits is only UUEI Engineering INC. In the digital circuit: First, the computer base development of the NI LabviewTM signal processing system is designed by Institute of Traffic and Transportation of National Chiao Tung University, second, the development of the DSP Chipset signal processing circuit is developed by UUEI Engineering INC.
arrays.
1) The range measurement was made. If the development of the digital signal processing circuit (TI DSP Chipset) is designed by the UUEI Engineering INC., two types of antennas can be satisfied with the high-quantity signal analysis of the beat frequencies, but the computer base development of NI LabviewTM signal processing system is designed by Institute of Traffic and Transportation of National Chiao-Tung University, the lack of signal quantity was occurred in both antennas system. The reason may be due to operating speed of NI DSP or the impact of the time-division multiplexing (TDM) with the computer system.
2) For the azimuth resolutions (E-plane) measurement: the balcony of ground height is ranging over 4.7M and the measured instruments located in the edge of the balcony near the first lane. Then the nearest measuring distance from the body of the car at the first lane to the measured instruments was 6.7M and the body of the car at the second lane to the measured instruments was about 9－ 10M. The effectively azimuth angles in the scope of two types of antennas such as Fig. 6.5 were detected. The detection range of the leaky-wave antenna arrays is a parallel region in the experiment and the width of the region less than the length of a car, rather than is along the direction of the fan-shaped extension of the dual horn antennas.
Fig. 6.5 The region was enclosed by the red dotted line is a detected range by the leaky-wave antenna arrays. On the one hand, the region was enclosed by the blue dotted line is by the dual horn antennas.
6.2Measurement of the New-version FMCW Radar
6.2.1 Signal-to-Noise Ratio of CMOS-Based FMCW Sensor System
The SNR of the proposed FMCW sensor system was characterized theoretically before performing additional measurements. Additionally, the calculated data were confirmed by the experimental results of a field test. Figure 6.6 presents the setup for vehicle detection using the proposed sensor system.
The sensor, which is a road-side unit, was installed above the ground at the height h. The vehicle occupancy in multiple lanes was detected by performing a range measurement with the FMCW sensor system. The total width of the multiple-lanes is denoted by D in Fig. 6.6, and represents the maximum coverage of the FMCW sensor. The values of h and D were set to 3.0m and 30m, respectively, in the field test. The building blocks of the FMCW sensor system, which had a CMOS transceiver, a digital signal processing unit and two antenna arrays, were integrated within a metallic enclosure before experiments. The width, length and height of the enclosure were 20cm, 22cm and 12cm, respectively, according to Fig. 4.31. Two antenna arrays were installed on top of the enclosure, and covered by a radome, which is a Teflon sheet with a thickness of 2.0mm. The H-plane of the antenna array was orthogonal to the traffic lane, and slanted at an angle of 35° by mechanical rotation, as indicated in Fig. 6.6.
The configuration helped the FMCW sensor to suppress the Doppler effect of the moving vehicle.
The csc2θ type radar was constructed from the present antenna array with the H-plane pattern, and the appropriate sensor height and mechanical rotated.
The major capability of a csc2θ type antenna pattern is performing the multiple-lanes measurement. The antenna pattern thus has a similar function to
the sensitivity time control (STC) of the IF filter, of providing a spatially uniform SNR within the range measurement. The proposed antenna arrays not only realized the nearly spatially uniform SNR to compensate the power level at farther section, but also achieved high isolation, thus suppressing heavy interference in the near field.
Fig. 6.6 The FMCW sensor adopted the multiple-lane vehicle detection of TMS. The H-plane antenna radiation is orthogonal to the moving vehicle
The power of the electromagnetic waves that propagate between the sensor and the single vehicle was estimated from the range measurement presented in Fig. 6.6 by the following well-documented equation: [49]
4
where S denotes the receiving power at the output of the receiving antenna;
PTX represents the transmitting power at the input of the transmitting antenna; GT
Elevation angle θ= 0°
θ is measured from broadside
cross section (RCS) of the vehicle at the operating frequency, and R represents the effective distance between the sensor and the vehicle [49].
According to stated electrical characteristics of the proposed CMOS transceiver and antenna arrays in chapter 3 and 4, the operating frequency was 10.5 GHz, and the corresponding wavelength in the air was 2.86cm. Since the H-plane main-beam of an antenna array was aimed at the vehicle by making mechanical adjustments, the antenna gains for both transmitting and receiving paths were calculated from the curves plotted in Fig. 4.25. Additionally, an irregular metallic body was applied as the reflected target with an effective RCS (σ) of about 0dBsm at 10.5 GHz by the user manual and the RCS of the irregular metallic body be equivalent to a spherical object with a radius of 1.0m [49]. The output power of the CMOS FMCW transceiver in Fig. 3.6 was
−18.2dBm at 10.5GHz, rising to 0dBm at the input of the transmitting antenna through an external PA. Therefore, the reflecting power of single target at the input of the CMOS transceiver was about −87dBm at D=30m. The conversion gain from LNA input to the mixer output at the IF output port in the receiver path was 0.2dB. The 49dB IF amplifier was found to be adequate for enabling the DSP unit to carry on signal processing in the presented sensor system.
Significantly, the leaky-mode antenna array eliminates the R4 equalizer, thus compensating for the R4-dependence of returned signal power. The property is similar to the csc2 type antenna of the surveillance radar by military application.
The most important contribution of this study is to present a sensor system that supports the almost equal to echo power for range measurement of multiple lanes, using the H-plane antenna pattern in Fig. 4.25. The gain factors GT and GR
in (6-1) can be extended to a cross-section of the H-plane pattern in Fig. 4.25 as
GT(θ) and GR(θ).The gain of GIF is sum of a mixer and an amplifier was added to radar equation in order to compare the measured data directly. A new radar equation was derived from (6-1) with reference to Fig. 6.6, which shows the antenna arrays.
where θ denotes the elevation angle that measured from the broadside; β represents the elevation angle set by mechanical rotation, and GT(θ+β) and GT(θ+β)indicate the transmitting and receiving antenna patterns, and are functions of θ and β. Restated, the antenna pattern functions are shifted through an angle of β. The parameter h is the height of the sensor box containing the antenna arrays, the radio frequency module and other circuits. The function h⋅cscθ was substituted for R in (6-1) using the trigonometric relationship in Fig.
6.6. The term R is a function of h and β, and is given by
Equation (6-3) and new parameters in (6-1) yield the modified radar equation, (6-2). The receiving power S is a function of θ, β and h. Equation (6-2)
Since the angle of maximum gain of the H-Plane in Fig. 6.6 is 56°, and the
Since the angle of maximum gain of the H-Plane in Fig. 6.6 is 56°, and the