# A Bunch of YBCO Josephson Generators for the Analysis of Resonant Cold-Electron Bolometers
## 3 Experimental Results  
For preliminary measurements of the radiation bandwidths of YBCO oscillators a sample, representing array of broadband dipole antennas with CEBs [23] has been used. In Figure 3, the response versus frequency of the same CEB sample to radiation from different JJ structures is shown by solid curves. For comparison, dashed curves show the results of electromagnetic simulations for these structures. The positions of the main radiation maxima approximately coincide with theoretical expectations, while the widths of the maxima in the experiment are somewhat smaller and are restricted by the CEB antennas, since the bands of the modified dipole antennas, shown in Figure 1, are broader than the previous ones, used in [23]. In addition, half harmonics and doubled harmonics are visible on the measured amplitude-frequency characteristics (AFCs). The narrowing of resonant curves and the appearance of half harmonics can probably be explained by the fact that the modeling has not accounted for the possible back effect of resonant loading on the dynamics of an essentially nonlinear system, which is a long Josephson junction. The doubled harmonics have lower intensity than in the simulations. Perhaps this is due to the fact that at such high frequencies, the Josephson generation becomes weaker due to the effect of surface losses, increasing with frequency. The presence of other harmonics in the AFC of the generators makes it possible to use them more flexibly to analyze the resonant properties of bolometers. A total of 5 JJ structures were studied, only three of which are shown in Figure 3. In accordance with the designations of Figure 1, their main emission maxima are as follows: str#0--222 GHz, str#1--257 GHz, str#2--380 GHz, str#3--180 GHz, str#4--158 GHz. The advantage of using a bunch of JJ oscillators with different dipole antennas for various frequencies (compared to using a single oscillator with a broadband antenna) is due to the low impedance of such generators. It is known [11; 31] that the  
Figure 2: Schematic representation of two setups with closer (**a**) and remote (**b**) placement of YBCO Josephson generators for the study of the amplitude-frequency characteristics of bolometers. impedance of YBCO Josephson junctions is normally not larger than a few Ohms. In this case, unlike a broadband antenna with an impedance close to 50 Ohms, the dipole antenna can be modified to match the impedance of the single JJ. After characterizing the oscillators themselves, they have been used to study resonant systems based on Cold-Electron Bolometers, whose AFCs are narrower than that of the JJ oscillators. In Figure 4, the examples of the characteristics of three different receiving systems designed for different tasks in different frequency ranges are demonstrated. Due to the different response values of resonant bolometers, the figure shows the normalized characteristics for clarity. The black curve corresponds to the frequency response of the seashell 75 GHz antenna with CEBs [30]. This antenna represents one polarization channel of the multichroic seashell antenna system with polarization resolution, proposed in [32]. The internal resonance is organized by a series resonance of the capacitance of the SIN tunnel junctions and \(\lambda/2\) slots for 75 and 105 GHz. For proper RF matching, slots and CEBs are connected by coplanar waveguides near the slot ends. Each CEB includes two SIN junctions with a nano-absorber. Such single element receiving system is intended for powers below 1 pW [4]. Figure 3: Amplitude-frequency response of a broadband bolometer to the radiation of three JJ generators. Solid curves—measurements, dotted curves—electro-magnetic modeling of JJ antennas. Structure notations correspond to Figure 1.  
The blue curve corresponds to the response of the single receiving cell based on a double-folded slot antenna with CEBs for the 220/240 GHz frequency range [24].