Experience in developing Ka-band waveguide filter with HTS E-plane insert

Abstract

To improve the performance of receivers of both satellite microwave links and radio telescopes, developing the bandpass filter (BPF) with low insertion loss is the actual task. The filter is installed at LNA input and jointly cooled to cryogenic temperatures. Every 0.1 dB insertion loss in BPF increases the receiving system noise temperature for 7-7.5 K at 300 K, which should be considered as notable addition, if we consider that noise temperature of the modern transistor amplifiers in the Ka range is about 60 K when cooled to the liquid nitrogen temperature. The mentioned noise addition depends on operating temperature and level of insertion loss. For a correctly designed multy-pole BPF, level of insertion loss in the passband is ultimately determined by the unloaded Q-factor of individual resonators. The introduction of HTS elements in the filter resonators increases the unloaded Q, therefore, should reduce insertion loss. The idea of the application of HTS materials in the waveguide E-plane BPF was expressed earlier, e.g., in [1], where the authors proposed to cover the waveguide internal walls with the bulk HTS material or to replace the normal metal E-plane insert by HTS one. This idea was advanced in [2] while creating two-pole X-band filter with HTS E-insert. However, the promising directions of developing HTS E-plane filters remained unclear.This paper presents the results of the design and testing of seven-pole BPF Ka band with bilateral HTS insert in the E-plane rectangular waveguide. Study of the possibility of reducing the insertion loss in the E-plane filters with HTS inserts compared with losses in the filters with normal metal inserts is a purpose of the work. Fig. 1 shows CST project of BPF, and Fig.2 displays photos of BPF prototype and HTS insert. HTS insert is a single crystal MgO substrate of 0.5 mm thickness, of which the two surfaces are coated with superconducting YBCO films. By photolithography method, identical insert portions of the superconducting layers were removed on both sides of a substrate and thereby "window" chains were formed with a height equal to the height of the standard rectangular waveguide of 7.2x3.4 mm 2 section. The lengths of all "windows" and the distance between them along the axis 0Z were calculated as a result of designing the filter. Therefore, individual resonators of seven-pole BPF are rectangular waveguide sections with dielectric MgO plates in the E-plane. The mutual coupling between the resonators and the coupling of the first and the last resonators with matched waveguide are carried out by means of pairs of the below-cutoff waveguide sections formed by the original walls of the waveguide and the conducting YBCO layers. It is clear that the principle of operation of the filter with HTS insert analogous to the principle of BPF widely used in practice with normal metal E-plane inserts [3]. Figure 1. CST project of seven-pole BPF Figure 2. Photos of BPF and HTS insertMethods of designing E-plane filters with a dielectric insert and bilaterally deposited metal ...

Compact and Wide Stopband E-Plane Waveguide Diplexer Design

“…These rectangular apertures have comb-like periodic ridges on upper and lower edges. The configuration of the septum insert creates necessary periodic boundary conditions required for slow wave propagation within the resonators [7][8][9][10], which results in a physically smaller waveguide but with improved stopband and rejection characteristics.…”