It is a MODIFIED proportional representation system. But, then again, if you can only think in absolute, then I guess that you think that it would be appropriate for any state with a population of less than 3,343,053 (100th of the population of the US) NOT to have any Senate seats at all. You might want to try telling that to the folks from Utah, Iowa, Nevada, Arkansas, Mississippi, Kansas, New Mexico, Nebraska, Idaho, West Virginia, Hawaii, New Hampshire, Maine, Rhode Island, Montana, Delaware, South Dakota, North Dakota, Alaska, Vermont, and Wyoming. I suspect that you would have some "slight" difficulty in getting a constitutional amendment passed when 22 states are automatically going to vote against it.
The Senate was never intended to be a "rep by pop" chamber.
What you appear to be talking about is
§10101. Voting rights
(a) Race, color, or previous condition not to affect right to vote; uniform standards for voting qualifications; errors or omissions from papers; literacy tests; agreements between Attorney General and State or local authorities; definitions
(1) All citizens of the United States who are otherwise qualified by law to vote at any election by the people in any State, Territory, district, county, city, parish, township, school district, municipality, or other territorial subdivision, shall be entitled and allowed to vote at all such elections, without distinction of race, color, or previous condition of servitude; any constitution, law, custom, usage, or regulation of any State or Territory, or by or under its authority, to the contrary notwithstanding.
(2) No person acting under color of law shall—
(A) in determining whether any individual is qualified under State law or laws to vote in any election, apply any standard, practice, or procedure different from the standards, practices, or procedures applied under such law or laws to other individuals within the same county, parish, or similar political subdivision who have been found by State officials to be qualified to vote;
(B) deny the right of any individual to vote in any election because of an error or omission on any record or paper relating to any application, registration, or other act requisite to voting, if such error or omission is not material in determining whether such individual is qualified under State law to vote in such election; or
(C) employ any literacy test as a qualification for voting in any election unless (i) such test is administered to each individual and is conducted wholly in writing, and (ii) a certified copy of the test and of the answers given by the individual is furnished to him within twenty-five days of the submission of his request made within the period of time during which records and papers are required to be retained and preserved pursuant to title III of the Civil Rights Act of 1960 [52 U.S.C. 20701 et seq.]: Provided, however, That the Attorney General may enter into agreements with appropriate State or local authorities that preparation, conduct, and maintenance of such tests in accordance with the provisions of applicable State or local law, including such special provisions as are necessary in the preparation, conduct, and maintenance of such tests for persons who are blind or otherwise physically handicapped, meet the purposes of this subparagraph and constitute compliance therewith.
Yes, "poll taxes" have been ruled to be unconstitutional, but "Property Qualifications" have NOT been ruled to be unconstitutional (and, since the Founding Fathers actually approved of them when drafting the constitution AND since they have NOT been explicitly ruled out by subsequent legislation, they are still "constitutional".