International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869 (O) 2454-4698 (P) Volume-8, Issue-4, April 2018 55 www.erpublication.org Abstract— This work reviews literatures concerning major techniques used in the design of cavity and waveguide filters particularly for microwave frequencies. Cavity and waveguide filters are widely used where high Q value and high power handling capability are essential. Advances have been achieved in this area in the last few decades. The design processes for each filter are reviewed and accompanied by the simulated and experimental results. A comparison of these filters in terms of passband and stopband performance is discussed. The SIW resonator is compared with other microwave resonators from the viewpoint of tradeoffs between loss and cost. The Qu of an SIW cavity resonator is found to be in the range of 150~1000. Index Terms— substrate integrated waveguide (SIW), low temperature co-fired ceramic (LTCC), direct-coupled cavity waveguide bandpass filter (C_DWB) I. INTRODUCTION The electromagnetic (EM) spectrum is becoming more crowded, and it is densely populated with various wireless signals and parasitic interferers in connection with communication and sensing services. Increasingly sophisticated radio-frequency (RF), microwave, and millimeter-wave filters are required to enable the selection and/or rejection of specific frequency channels. Compact passband filters with good performance are highly demanded in communication [8]. New techniques and solutions for designing the compact microwave cavity and waveguide filters are discovered and explored to improve the performance and to reduce the filter size [4].The papers are reviewed on the basis of quality defining parameters of filters relative insertion loss, quality factor, size and cost of microwave resonators made by different techniques as shown in figure 1.The choice of dielectric substrate is also critical to quality factor as loss tangent characteristics are different from one material to another [3]. When high selectivity is required dielectric resonator or metallic waveguide is preferred. The recent widely studied SIW technology is able to fill the technological gap between microstrip or stripline (planar type) and dielectric resonator or metallic waveguide (non-planar type), since it combines the best parts of both and offers high-quality factors that are close to those of non-planar structures with the size- and cost related advantages of printed planar circuits [1]-[3]. Asmita Mary Soreng, Department of Electronics and Telecommunication Engineering, M.E. Scholar, Jabalpur Engineering College, Jabalpur, India. Dr. Agya Mishra, Department of Electronics and Telecommunication Engineering, Associate Professor, Jabalpur Engineering College, Jabalpur, India. Figure 1: The relative insertion loss, size, and cost of various RF resonators [2]. II. CONCEPT OF CAVITY FILTERS Cavity filters are the basic circuitry behind a duplexer and are sharply tuned resonant circuit that allow only certain frequencies to pass. Generically, filter of this kind are known as notch filters. Physically a cavity filter is a resonator inside a conducting "box" with coupling loops at the input and output. Still widely used in the 40 MHz to 960 MHz frequency range. Higher Q quality factor, as well as increased performance stability at closely spaced (down to 75 kHz) frequencies, can be achieved by increasing the internal volume of the filter cavities. Physical length of conventional cavity filters can vary from over 82 in the 40 MHz range, down to under 11 in the 900 MHz range. In the microwave range (1000 MHz (or 1 GHz) and higher), cavity filters become more practical in terms of size and a significantly higher quality factor than lumped element resonators and filters [2]. Cavities are often grouped in series with each other to increase filter effectiveness by making the pass band deeper with respect to surrounding frequencies. This can be very useful when ham repeaters are situated very close to other spectrum users such as pager whose unwanted signals can interfere with the ham equipment. Cavity filter are a very effective way to create a notch at the repeater frequencies. Cavity Filters are known for low insertion loss and higher power handling ability. The filters based on cavity resonators have the advantages of low insertion loss and high power handling capability compared to the filters based on lumped-element LC resonators or planar resonators. Cavity resonator filters are widely used in the wireless and satellite applications [1]. There are different technologies for implementing the cavity resonators, including rectangular/circular waveguide resonator, coaxial resonator, and dielectric resonator [3]. Rectangular/circular waveguide resonators are rectangular/circular waveguides with both ends terminated in a short circuit. Similarly, a section of coaxial transmission line can be short circuited at both ends to form a coaxial resonator. Design Techniques of Microwave Cavity and Waveguide Filters: A Literature Review Asmita Mary Soreng, Dr. Agya Mishra