The wideband echo signals of the imaging radar can be processed by pulse compression to obtain high-resolution range profile (HRRP). The resolution of HRRP is proportional to the signal bandwidth. The pursuit of high resolution makes the bandwidth of radar transmitting signal larger and larger. And the corresponding sampling rate of receiver becomes so high that analog-to-digital conversion cannot be realized by a single chip correctly. Time-interleaved analog-to-digital converter (TIADC) technique increases sampling rate of radar receiver, but channel mismatches are brought in. Channel mismatches significantly deteriorate the dynamic performance of radar receiver. Effects of channel mismatch on SNR, SNDR and SFDR are studied in previous literatures. Derivation and simulation of TIADC channel mismatch effecting on HRRP are performed in this letter. Simulation results show that without considering the amplitude-frequency distortion and phase-frequency distortions of the radar system, when the gain mismatch is less than 0.7 times and the clock mismatch is less than 0.25 rad, the influence of the channel mismatch on the HRRP can be neglected. The results provide a reference for system design and compensation method, which are useful for the designer to determine whether complex channel mismatch calibration is necessary under specific application background.
We present a numerical optimization approach to simulate the output characteristics of a mid-infrared quantum cascade laser, taking into account the effect of subband electron temperature (Tei). The shooting method is used to simplify the calculation. The results give accurate subband electron temperatures when the external electric field is above the threshold. The results of the calculations are consistent with experimental results, thereby confirming that consideration of the subband electron temperature can improve our understanding of quantum cascade lasers and help guide future experimental work.
In this paper, a concurrent dual-band hybrid down conversion architecture based on continuous-wave (CW) Doppler radar is demonstrated. The proposed system operates at 2.05-/1.64-GHz simultaneously. The dual-band can solve the null detection point problem generated at quarter-wavelength distance between the target and antenna. The detection results from different channels can be mutually verified to improve the system accuracy. The vital sign can be detected by the radar through the wooden board at higher transmit power. For satisfying the requirements of dual-band RF transmitters, and a two-stage dual-band power amplifier is designed. Experimental results have demonstrated the feasibility of the system.
A triple-layer wideband transmitarray (TA) which works at 18.5 GHz with reduced profile is presented in this paper. The unit cell composed of three metal layers, each layer is etched on the corresponding dielectric substrate. The top layer consists of double square rings, the same as the bottom layer. The intermediate layer consists of a Jerusalem cross slot. The thickness of designed unit cell is 0.15λ, where λ is the wavelength in free-space. A large frequency range is implemented by parallel sets of phase curves generated by proposed unit cell. The magnitude of transmission coefficient is less than 1 dB and the phase shift range exceeds 360 degree across the entire frequency range. We design, fabricate and measure a TA operating at 18.5 GHz to show the validation of this paper. Through the measurement, we can obtain that the 1-dB gain bandwidth is 14.8% (17.5–20.3 GHz), and maximum gain is 22.5 dB at 18.5 GHz. The proposed transmitarray’s maximum aperture efficiency is 46%.
A highly-selective tunable balanced bandpass filter (BPF) with wide tuning range of center frequency is presented. The balanced BPF is designed by using compact varactor-tuned parallel coupled-line resonators with the direct-feed structure. It can realize a wide tuning range with an almost constant fractional bandwidth (CFBW). Three differential-mode (DM) transmission zeros (TZs) close to the tunable passband are obtained by mixed electromagnetic coupling and frequency-variant source-load (S-L) coupling. Meanwhile, the three TZs can almost keep the same relative location of passband to achieve continuous high selectivity and good out-of-band rejection over the whole frequency-tuning range. For verification, a tunable 1.02–3.25 GHz balanced BPF with three self-adaptive TZs is designed, fabricated and measured. And experimental and simulated results are in good agreement.
A circularly polarized radial line slot array with enhanced bandwidth is presented in this letter. The proposed antenna consists of two parallel plates, a monopole probe and a spiral slot array. The parallel plates form a radial cavity and is fed by the probe. Then, the spiral slot array etched on the upper substrate can be excited by the radially outward wave to provide broadside radiation. In this design, the side wall of the cavity is left open, which helps to obtain wideband operation and has little effect on radiation patterns. To enhance the bandwidth further, a square cavity is used here to substitute for an initial circular one. With such a structure, the antenna is wide in bandwidth and compact in size. The proposed antenna is designed and fabricated. Measured results reveal that the antenna can provide an impedance bandwidth of 37.2% (15.1–22.0 GHz) and an axial ratio bandwidth of 31.0% (15.0–20.5 GHz), respectively. Additionally, the measured maximum gain is 26.7 dBic at 17.5 GHz.
This paper proposes a dual-receiver wireless power transfer system that uses bipolar coils as a transmitter and receivers. Compared with a traditional dual-receiver system with unipolar coils, the proposed system can effectively and conveniently eliminate cross-coupling between the receivers, and another significant feature of the system is the ease of changing the received power of the two receiver loads by changing the relative angle of the bipolar coils. The mutual inductance of the bipolar coils is modelled by Newman’s formula. Then a system design method to eliminate the influence of cross-coupling and realize controllable power allocation is proposed.