Terahertz Antenna Design Based On High Temperature Superconducting Josephson Junction

Benefiting from the considerable absolute bandwidth,terahertz(THz)communication is convinced to have the advantages on high transmission rate,large capacity,strong directivity,high security and good penetration.THz application has made great progress in THz generation,detection,mixer,imaging and so on.However,an ultrasensitive THz receiver is highly demanded for effective detection due to the severe atmospheric attenuation at THz bands.High temperature superconducting(HTS)Josephson junction(JJ)detectors and mixers are attractive candidates for receiver frontends due to their superior sensitivity,wide bandwidth,low noise,low power consumption,etc.HTS bicrystal YBa2Cu3O7-?(YBCO)JJ has a high critical temperature and a large energy gap,resulting in a high cutoff frequency.Therefore,it has a good high-frequency response and becomes an ideal detector at THz bands.However,the normal state resistance(NSR)of bicrystal YBCO JJ is very small because of the limitation of its own structure,resulting in poor coupling efficiency between THz signal and the detector,thus producing low sensitivity and other issues.In this paper,some kinds of terahertz antennas are designed from the perspective of impedance match and applied to the JJ.Meanwhile,a method of JJs in series(JJS)is proposed.Thus,the sensitivities have been improved and new contributions have been made to THz detection and receivers.The main research results are as follows:1.Based on our terahertz quasi-optical system,a novel bowtie loaded meander antenna(BLMA)is proposed at 210 GHz as one of the atmospheric windows for THz wave propagation.And high-quality superconducting detectors are fabricated.A bowtie is loaded on a meander antenna,integrated with a silicon super-hemispheric lens,to achieve a good impedance match with the HTS bicrystal YBCO JJ at 210 GHz.HTS bicrystal YBCO JJs coupled with the novel antennas are designed and fabricated with good performances.The related characteristics of the JJ are measured by three methods,which are the first order Shapiro step responsivity,the coupling efficiency between JJ and the antenna,and the voltage responsivity.These three measured results indicate the designed antenna works and contributes to a better performance of the detector.2.Up to 146th harmonic mixing has been achieved with the conversion efficiency of-63.6 dB when a HTS bicrystal YBCO JJ mixer coupled with the novel BLMA under the 210 GHz radiation,while the mixer coupled with a LPA has less than 46 order harmonic number with the conversion efficiency of-71.6 dB in harmonic mixing.The mixer coupled with the BLMA has a higher-order harmonic mixing with a lower LO power,which further illustrates its superiority to that coupled with a LPA.The mixer coupled with the novel antenna has made the performance of HTS JJ mixers to a higher level.3.A bowtie antenna with a meander adjustor is proposed.The input reactance of this antenna can be adjusted by adjusting the meander properly with the input resistance nearly unchanged.Parameters of the meander unit are studied to establish a theoretical basis on conjugative impedance match in antenna design.In the experiment,two bowtie antennas with different meander adjustors are designed to estimate the imaginary part of the AC impedance of a HTS JJ by measuring the voltage responsivity.4.A HTS YBCO JJS mixer is proposed.Benefiting from operating synchronously,3JJS as a mixer with the harmonic number up to 154 is studied with 210 GHz radiation at zero bias.The maximal harmonic number is much higher than that of 46 obtained by a JJ coupled with a LPA.And the signal-to-noise ratio(SNR)of IF output increases by 3 dB,which indicates the sensitivity and the conversion efficiency of the mixer have been improved with this JJS structure.Besides,zero-bias operation is feasible for HTS JJ mixer and has a great advantage of reducing the thermal noise caused by DC bias.Therefore,the mixer with JJS array has a great prospect in terahertz application.5.Planar THz antennas in broad bands and narrow bands are designed and fabricated in arrays to be measured by a THz time-domain spectroscopy(TDS)system.Broadband antennas of LPA and log-periodic sinus antenna are designed and studied in self-complementary structures.On the other hand,narrowband antennas of double-U antenna and bowtie antenna with a quarter of wavelength impedance matcher are proposed with low input impedances to improve the coupling efficiency between low-impedance devices and antennas,so as to improve the sensitivities of devices.The TDS analysis also provides a new and effective way for the characterization of THz antenna.