Compact Coaxial Filters for BTS Applications
A new class of coaxial cavity filters with low-profile suitable for base transceiver station applications is proposed. The benefits of the technology are volume reduction, high performance, and superior spurious-free response. An equivalent lumped element circuit allows for a fast and efficient initial design of the resonators. Full-wave optimization is required to produce the final configuration of the filters. Experimental results demonstrate the high performance of the proposed filters. The electrical length of the experimental resonators is as low as  $\lambda _{0}/16$ . The measured insertion loss of the five-pole filter is 0.92 dB at 722 MHz. Experimental results show a spurious-free response of the order of 7.6 times.
Bandpass filter with an ultra-wide stopband designed on miniaturized coaxial resonators
Characteristics of a new miniaturized coaxial resonator are theoretically investigated. It is shown that the first resonant frequency of the resonator can be significantly lowered relative to the second one and the resonator dimensions can be considerably decreased as compared to those of a traditional dielectric-filled quarter-wavelength coaxial resonator. Based on the investigated resonator, a fourth-order bandpass filter has been designed and fabricated. The filter stopband at a level of no worse than −90 dB extends to the frequency that exceeds the passband center frequency by a factor of 47. Calculated frequency responses are in good agreement with those measured on the fabricated filter prototypes.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.