COM DEV International

This chapter presents five different techniques for computer‐aided tuning of microwave filters. The five different techniques are: sequential tuning of coupled resonator filters, computer‐aided tuning based on circuit model parameter extraction, computer‐aided tuning using poles and zeros of the input reflection coefficient, time‐domain tuning, and Fuzzy logic (FL) tuning. The sequential and the time‐domain tuning techniques are useful in guiding the technologists to tune the resonators and coupling elements, one by one. The FL technique is investigated to deal with both the science and the art parts of the tuning process. The chapter outlines two automated filter tuning setups. The first setup has a built‐in mechanism, making it possible to lock the screws once the filter is tuned. The second setup is built with flexible arms, which make it possible to tune microwave filters and multiplexers with tuning screws scattered over the three‐dimensional filter body.

This chapter describes the circuit synthesis approach, based on the [ABCD] transfer matrix, or the “chain” matrix, as it is sometimes known. The network synthesis procedure is demonstrated by first building the A(s), B(s), C(s), and D(s) polynomials, corresponding to a third‐degree lowpass prototype ladder network with the elements C 1 ,1 1 , and C 2 . Such prototype networks require the hypothetical frequency‐invariant reactance elements (FIR). Another element that is required in the synthesis of filters at microwave frequencies is the frequency‐invariant impedance or admittance inverter, commonly referred to as the immittance inverter. The chapter describes the evaluation of the overall [ABCD] and the equivalent admittance [y] matrix from the characteristic polynomials of the desired filter function. From this matrix, it synthesizes the network given its topology. The chapter concentrates on the synthesis of parallel‐connected components in an open‐wire transmission environment, because many waveguide and coaxial elements are modeled directly as shunt‐connected elements.

This paper proposes a novel and unified synthesis approach and design procedure for microwave filters with extracted pole and nonresonating node (NRN) technique. By introducing a general circuit topology, the traditional extracted pole and NRN filters can be unified to a general prototype. With the new design process, the exact mapping relationship between the electromagnetic (EM) model of the pole producing element and the circuit model can be achieved. All the physical dimensions of the filter structure can be obtained by a fully analytical approach. No full EM optimization or adjustment is needed in the filter design. A three pole TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm { {101}}}$ </tex-math></inline-formula> mode waveguide filter with one finite transmission zero is designed to illustrate the new procedure. In addition, a seven-pole TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm { {011}}}$ </tex-math></inline-formula> mode filter with four finite transmission zeros covering all three possible types of arrangements is designed and fabricated to demonstrate the versatility of the proposed method. The simulated and measured results verified the efficiency and the accuracy of the proposed design method.

This paper proposes a new synthesis technique for extracted pole and non-resonating nodes (NRN) filter. The circuit elements can be set to the values extracted from the simulation of its electromagnetic (EM) model during the synthesis procedure. Accurate mapping relationship between the physical dimensions and prototype circuit can be achieved with the fully analytical approach. A three pole waveguide filter with one finite transmission zero is designed to illustrate the new procedure. A four pole waveguide filter with two finite transmission zeroes from literature is re-designed and analyzed to show the validity of the proposed approach, accuracy and key differences.

This paper outlines a new class of diplexers realized using a combination of dual-band cavities and single-band cavities. The proposed diplexer does not require junctions and can achieve similar performance with fewer cavities, thus significantly reducing the size of the diplexer when compared to traditional approaches. The concept is potentially applicable to most dual-band cavities as demonstrated in this paper using rectangular waveguide cavities. A unique layout is proposed that combines the use of dual-band cavities operating in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> modes as well as single-band cavities operating in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> or TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> mode. The result is a diplexer that is very compact in size while offering increased Q and an improved spurious free window. To verify the concept a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order Ku-band diplexer is designed, manufactured, and tested to allow comparison to a traditional design.

The development and optimization of a circularly polarized (CP) antenna using an array of four folded-shorted patch elements is investigated. The realized antenna is compact ( 0.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> by 0.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ), highly integrated, and offers good radiation performance at 400 MHz. A compact coupler-based feeding network for the four elements within the array, integrated into the antenna ground plane, provides a sequential 90° phase difference between the radiating folded-shorted patches. This very compact CP antenna design may be useful for microsatellite and other miniaturized phased array systems for communications.

In this paper, a novel dielectric-resonator filter configuration is presented. The new filter offers superior Q and wider spurious-mode free range at Ku-Band. Moreover, it offers 70% mass savings over the TE114 dual mode designs and over 50% footprint reduction compared with the TE113 dual-mode implementations. These characteristics make this technology well suited for the output multiplexer used in Ku-Band satellite applications. A five pole filter has been implemented to prove the superior performance of this new technology. Test data over temperature and high power test results are also presented, including a 3-Channel output multiplexer.

Presents the guest editorial for this issue of the publication.

This article outlined several optimization techniques applied in different steps of the synthesis of filters and multiplexers. The importance of the subject has been appreciated by more and more researchers and engineers in this community. As it is impossible to cover all technologies available, the objective here is to provoke a broader thinking beyond basic filter synthesis. Established computer-aided design methodology is a true blend of both synthesis and optimization. In most cases, to meet a set of well thought-out specifications, the science of filter synthesis and trade-off applies. In other cases, the optimization of design is an art which creates opportunities and new possibilities.

In this paper, the performance improvements and limitations of the enhanced microwave multiplexer are thoroughly studied for applications in communications satellites considering in-band flatness of gain and group delay, out-of-band rejection, temperature stability and insertion loss. The overall performance of the enhanced multiplexer with M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order channel filters is similar to conventional design with M+1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order channel filters. It is shown that the difference in the coefficients of thermal expansion of the materials for the channel filters and the manifold has an effect on the multiplexer temperature stability. Impact of channel filter resonator Q factor and fractional bandwidth on the passband insertion loss is also demonstrated using different designs.