Minimum Return Loss Research Articles

Maximum and minimum return losses from a passive two-port network terminated with a mismatched load

An analytical expression is derived for determining load-reflection coefficient phase-angle values that will lead to maximum and minimum return losses from a terminated two-port network. The expression is derived in terms of two-port network S-parameters and a load whose reflection-coefficient magnitude is a constant but can be any value greater than zero and less than or equal to unity. The equation is useful for cases where it is desirable to know how to position a load (1) to obtain maximum return loss for network-matching purposes or (2) to obtain minimum return loss for some types of reflector antenna applications. Two examples are given: One shows that for some types of reflector antennas with a mesh-type surface that is backed by another reflecting surface, a resonance phenomenon can occur and cause unexpectedly large dissipative losses (>30 dB) to occur. The other example shows that when a particular type of reflector antenna with a dielectric layer becomes wet from rain or condensation, large (>10 dB) signal losses can occur. For both examples, equations presented in this article were used to calculate the exact load-reflection coefficient phase values that led to worst-case return loss values. In practical situations, once the phenomenon is understood and predictable, steps can be taken to avoid these resonance regions. >

Comparison of junctions in both dielectric guides and metallic guides above 75 GHz

The paper contains a comparison of the return losses caused by misalignment of the junctions in both metallic and dielectric waveguides. The practical measurements of these return losses for dielectric guides show that they are much smaller than the minimum return losses for metallic guides. The paper concludes with a summary of the features of dielectric guide which make it a viable alternative to metallic guide above 100 GHz.

Degradations in Gbit/s DFB laser transmission systems due to phase-to-intensity noise conversion by multiple reflection points

Severe system degradations and bit error rate floors are observed in Gbit/s fibre transmission systems due to the interferometric conversion of laser phase noise to intensity noise by multiple reflections from connectors and splices. Studies of penalties as a function of both the magnitude and number of reflections indicate that fibre joints with guaranteed minimum return losses of better than 20dB may be required for high-speed direct detection systems as well as future coherent systems, even though optical isolators may be employed in such systems.

Optimum design of waveguide E-plane stub-loaded phase shifters

Broadband low-insertion-loss E-plane stub-loaded rectangular waveguide phase shifters are designed with the method of field expansion into normalized eigenmodes, which includes higher-order mode interaction between the step discontinuities. Computer-optimized three-stub prototypes of 90 degrees differential phase shift with reference to an empty waveguide of appropriate length, designed for R140-band (12.4-18 GHz) and R320-band (26.5-40 GHz) waveguides, achieve typically +or-0.5 degrees phase shift deviation within about 20% bandwidth. For two-stub designs, the corresponding values are about +2.5 degrees /-1 degrees and 17%. Both designs achieve minimum return loss of 30 dB. The theory is verified by measurements of a compact R120-band (10-15 GHz) waveguide phase shifter design example milled from a solid block, showing measured insertion loss of about 0.1 dB and about +2.5 degrees /-0.5 degrees phase error between 10.7 and 12.7 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modal-S-Matrix Design of Optimum Stepped Ridged and Finned Waveguide Transformers

Optimum stepped transformers from rectangular waveguide to ridged and all-metal finned waveguides are designed with the method of field expansion into eigenmodes, which includes higher order mode interaction between the step discontinuities. Computer-optimized design data are given for a Ku-band ridged waveguide prototype with a ridge width of 1 mm, as well as for Ku-band and E-band finned waveguide transformers with commercially available metal fin thicknesses of 0.19 mm and 0.1 mm, respectively, suitable for metal-etching manufacturing technique. The optimum designs achieve a minimum return loss of about 36 dB, or 34 dB for the whole Ku- or E-band, respectively. The theory is verified by comparison with measured results.

A 90-dB Microstrip Switch on a Plastic Substrate (Correspondence)

A single-pole double-throw (SPDT) microstrip switch has been designed on a plastic (polyolefin) substrate to switch two 10-W CW carriers into a common load over the frequency range 1.7 to 2.3 GHz. No tuning adjustments are used over this 30-percent bandwidth to obtain a 90-dB minimum isolation, a 23-dB minimum return loss, and a 1-dB maximum insertion loss. Units now in production typically have a 0.6-dB insertion loss, a 26-dB return loss, and isolation levels of 105/spl plus mn/5 dB.

A Strip-Line Directional Coupler Utilizing a Non-Homogeneous Dielectric Medium

A 3 dB directional coupler which utilizes nonhomogeneous dielectric media to produce different phase velocities for the even and odd modes of propagation is described. The two output ports are conductively connected to each other as are the input and null ports with dc isolation between the input and both output ports. Well known thin-film techniques can be used to realize the coupler. General coupler equations and design parameters are given along with computer solutions and experimental verification. A minimum return loss of 22 dB was experimentally achieved over a 20 percent bandwidth and 27 dB minimum return loss with equal isolation over the same bandwidth is predicted with the application of simple compensation techniques. It is shown that the coupler maybe used to effect an impedance transformation between the input and output ports; however, the isolation is degraded.

Tables of element values for capacitively coupled double-tuned networks

Tables of element values are developed for capacitively coupled double-tuned interstage networks with finite source and load resistances and equiripple insertion-loss characteristics corresponding to minimum passband return losses of 10, 15, 20, 25 and 30dB. In each case the lower edge of the passband is varied from 0.1 to 0.95 by increments of 0.05 with the upper edge normalised to unity. The insertion-loss method of design is used for evaluating the network elements.

Further tables of element values for inductively coupled double-tuned networks

The insertion-loss method of design is used to develop further tables of element values for the double-terminated, inductively coupled, double-tuned interstage network, with equiripple insertion-loss characteristics corresponding to minimum passband return losses of 10, 15, 20, 25 and 30dB. In each case, the lower edge of the passband is varied from 0.1 to 0.95 in increments of 0.05, with the upper edge normalised to unity.