Sanghoon Shin

Bandstop filters with extended upper passbands

Previous microwave distributed bandstop filters have had their second harmonic response centered at no more than three times the fundamental bandstop mid-band frequency, due to the use of quarter-wave resonators. This limitation has now been removed by the use of compound resonators having shorter electrical length. Some configurations incorporate lumped capacitors, resulting in additional design degrees of freedom and wider passbands. The new theory has been developed to apply to both wide and narrow stopbands. Example filters having upper passband widths of up to six times the fundamental bandstop center frequency are presented

At least N+1 finite transmission zeros using frequency-variant negative source-load coupling

A second-order cross-coupled combline filter which has three finite transmission zeros is presented. The problem of the frequency-invariant coupling in a real circuit is introduced. To make extra transmission zeros, a top metalized dielectric block is used.

Magnetic and structural properties of sintered bulk pucks and aerosol deposited films of Ti-doped barium hexaferrite for microwave absorption applications

We report structural, compositional, and magnetic properties for a commercially available doped barium hexaferrite material produced by Temex Ceramics. The material is designed to absorb electromagnetic radiation near the upper edge of the Ku frequency band ( ∼18 GHz) and may serve as an important component to microwave circuitry. To aid in the development of such circuits that may utilize this or similar materials, we present results of the material properties of the raw starting powder, sintered pucks, and in the form of a film deposited by aerosol deposition. We find that the structural and magnetic properties are consistent with the parent compound, barium hexaferrite. Samples sintered at 1250 °C show some degree of preferred magnetic and structural orientation. Chemical analysis indicates that a titanium dopant has been added and that the material demonstrates broad absorption above 13 GHz that improves with sintering temperature. To our knowledge, this is the first report on the properties of this c...

Microwave bandstop filters with minimum through-line length

The theory of bandstop filters with minimum through-line length is developed in this paper. In contrast to conventional similar-resonator bandstop filters that employ odd multiples of 90-degree impedance inverters between resonators, the proposed design technique enables filters with through-line length restricted to only that which is required to obtain a desired coupling coefficient magnitude between a resonator and the through-line. Both even- and odd-order designs are shown to verify the concept. A 4th-order microstrip prototype with 45 degrees of through-line length per resonator was fabricated, measured, and compared to two conventional designs. It has half the through-line length of conventional designs.

Switched Allpass-to-Bandstop Absorptive Filters With Constant Group Delay

A new reconfigurable bandstop filter class is proposed, which has the unique property of possessing multiple insertion loss states with a common group delay state. These filters switch between a low-insertion-loss allpass state and a high-rejection bandstop state. The theory, synthesis, and design of these filters are presented. As a demonstration of the concept, a fourth-order constant-group-delay switched bandstop filter microstrip prototype was designed, built, and tested. The prototype has a measured bandstop-state center frequency of 1000 MHz, a 3-dB bandwidth of 119.15 MHz, a stopband rejection of 32.52 dB, a maximum allpass-state insertion loss of 4.08 dB, and a negligible group delay variation between the two states.

RF-Power-Activated and Signal-Tracking Tunable Bandstop Filters

Two new classes of RF-power-dependent tunable bandstop filters that share a common filter topology are presented in this paper. RF-power-activated tunable bandstop filters transition from a resonant-allpass response to a bandstop response in the presence of a high-power RF signal, allowing for optimum use of the spectrum when used to solve interference issues in a receiver. Signal-tracking tunable bandstop filters automatically tune their center frequencies to that of a high-power RF signal, eliminating the need for complex sensing and control systems. The theory and design as well as laboratory prototypes are presented for both. The RF-power-activated tunable bandstop filter prototype achieves a minimum allpass-state insertion loss of 2.5 dB and a bandstop-state attenuation of greater than 50 dB. The signal-tracking tunable bandstop filter prototype attenuates a high-power signal by greater than 33 dB over a frequency range of 251–304 MHz.